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U10EC055, ODD SEMESTER 2013-2014 Page1
SEMINAR REPORT
Entitled
“OPTICAL FIBER BIO SENSORS APPLICATIONS”
Submitted in partial fulfilment of the requirement
For the Degree of
: Presented & Submitted By:
Mr. BHEEMSAIN
(Roll No.U10EC055)
B. TECH. IV (Electronics & Communication) 7th Semester
: Guided By:
Prof. Dr.V. MISHRA
Associate Professor, ECED.
DEPARTMENT OF ELECTRONICS ENGINEERING
Sardar Vallabhbhai National Institute of Technology
Surat-395 007, Gujarat, INDIA.
(DECEMBER – 2013
((EELLEECCTTRROONNIICCSS &&
CCOOMMMMUUNNIICCAATTIIOONN))
BBaacchheelloorr ooff
TTeecchhnnoollooggyy
U10EC055, ODD SEMESTER 2013-2014 Page2
Acknowledgement
It gives me great pleasure to present my seminar report on ―Optical fiber biosensors
applications‖ No work, big or small, has ever been done without the contributions of
others.
I would like to express deep gratitude towards Prof. Dr. V. Mishra (Associate Professor
at Electronics & Communication Engineering Department, SVNIT) who gave me
their valuable suggestions, motivation and the direction to proceed at every stage. He
extended towards a kind and valuable guidance, indispensible help and inspiration at
times in appreciation I offer them my sincere gratitude.
In addition, I would like to thanks Dept. of Electronics and Communication
Engineering, SVNIT finally, yet importantly, I would like to express my heartfelt thanks
to my beloved parents and my brother for their blessings, my friends/classmates for their
help and wishes for the successful completion of this seminar.
Bheemsain
U10EC055, ODD SEMESTER 2013-2014 Page3
Sardar Vallabhbhai National Institute of Technology
Surat-395 007, Gujarat, INDIA.
DEPARTMENT OF ELECTRONICS AND COMMUNICATION
This is to certify that the B.Tech. IV (7th
Semester) SEMINAR REPORT
entitled “OPTICAL BIO SENSORS APPLICATION” is presented & submitted by
Candidate Mr. BHEEMSAIN bearing Roll No. U10EC055,in the partial fulfilment of
the requirement for the award of B. Tech. degree in Electronics & Communication
Engineering.
He/She has successfully and satisfactorily completed his/her Seminar Exam in all
respect. We, certify that the work is comprehensive, complete and fit for evaluation.
Prof. Dr. V.MISHRA Prof . P.K.Shah
Seminar Guide Head of the Deptt. ECED
Associate Professor Associate Professor
SEMINAR EXAMINERS:
Name Signature with date
1.Prof.____________________ __________________
2.Prof.____________________ __________________
3.Prof.____________________ __________________
EPARTMENT SEAL
December-2013
CCEERRTTIIFFIICCAATTEE
U10EC055, ODD SEMESTER 2013-2014 Page4
ABSTRACT:-
Currently, cancer detection is a difficult, long and invasive process. Many times the
symptoms are unclear or tumors are detected far into the stages of cancer. Clinical
diagnostics aim to recognize abnormal characteristics as efficiently and quickly as
possible. The optical biosensor is a faster, cheaper alternative for cancer cell detection.
With this new machine for cancer screening integrated into the clinic, a more
comprehensive healthcare tool would be more widely available to health care
professionals.
In other applications HIV, Hepatitis, other viral disease, drug testing, environmental
monitoring, genetic monitoring, disease, functional sensors, drug testing, blood, urine,
electrolytes, gases, steroids, drugs, hormones, proteins, food industry, medicine,
environmental, diabetics, drug testing, detection of environmental pollution and toxicity,
agricultural monitoring, ground water screening and Ocean monitoring.
So at present the optical bio sensors are play very important role in the biological and
Environmental application point of view.
U10EC055, ODD SEMESTER 2013-2014 Page5
TABLE OF CONTENTS:-
TITLE……………………..................................................1
ACKNOWLEDGEMENT…………………………….......2
ABSTRACT………………............................……………4
1. Bio-Optical gas-sensor (sniffer device)
With a fiber optic oxygen sensor...............................................................6
1.1 Abstract..............................................................................................................6
1.2 Introduction........................................................................................................6
1.3 Experimental section..........................................................................................8
1.4 Results and discussion........................................................................................9
2. Optical Bio-sniffer (Biochemical gas sensor)
For dimethyl sulphide vapour...................................................................11
2.1 Abstract……………………………………………………………………….11 2.2 Introduction......................................................................................................11
2.3 Experimental section........................................................................................12
2.4 Results and discussion......................................................................................13
2.5 Conclusions......................................................................................................14
3. Fiber Optic Bio-sniffer (Biochemical gas sensor) using UV-LED light for
monitoring ethanol vapour with high sensitivity & selectivity.....................15 3.1Abstract……………………………………….................................................15
3.2 Introduction……………………………………..............................................15
3.3 Experimental………………………………………........................................16
3.4 Results and discussion………………………………......................................18
4. Optical sensor in the application bio-detection………………................20 4.1 Abstract………………………………………………………........................20
4.2 Introduction………………………………………………..............................20
4.3 Experiments and results……………………………......................................20
4.4 Conclusion……………………………………………...................................23
5. Optical Bio-Sensor from DNA and Nano Structures …………….……25 5.1Abstract……………………………………………………………………….25
5.2 Introduction………………………………......................................................25
5.3 Discussion…....................................................................................................28
6. A hemispherical Omni-directional bio inspired
Optical sensor…….................................................................................29 6.1Abstract………………….………....................................................................29
6.2 Introduction …..…...........................................................................................29
6.3 Conclusion…...................................................................................................35
U10EC055, ODD SEMESTER 2013-2014 Page6
7. Mechanical characterization of totally optical tactile sensor oriented on
bio applications..............................................................................................36
7.1Abstract………………………………………………………………………...36
7.2 Introduction…....................................................................................................36
7.3 Tactile sensor description...................................................................................38
7.4 Conclusion…......................................................................................................40
8. Optical Bio-Chemical Sensors on Snow Ring Resonators........................41
8.1 Abstract…………………………………………………..................................41
8.2 Introduction…....................................................................................................41
8.3 Sensor structure…………………………………..............................................44
8.4 Conclusion……………………………………..................................................49
REFERENCES…................................................50-53
U10EC055, ODD SEMESTER 2013-2014 Page7
CHAPTER-1 BIO-OPTICAL GAS-SENSOR (SNIFFER DEVICE) WITH A FIBER OPTIC OXYGEN SENSOR
1.1 Abstract:-
This bio-optical gas-sensor (sniffer device) was constructed by immobilizing flavin-
containing mono-oxygenase 3 (FM03, one of xenobiotic metabolizing enzymes for
catalyzing the oxidation of odorous. Substances such as tri methylamine: TMA onto a tip
of a fiber optic oxygen sensor with oxygen sensitive ruthenium organic complex,
excitation: 470 nm, fluorescent: 600 nm, with a tube-ring.
A reaction unit for circulating buffer solution was applied to the tip of the sniffer device.
A substrate regeneration cycle was applied to the FM03 immobilized sensor in order to
amplify the output signal by coupling the mono oxygenase with a reducing reagent
system of ascorbic acid in phosphate buffer.
The bio-optical sniffer was possible to detect the oxygen consumption induced by FOM3
enzymatic reaction with TMA application. The sniffer device with 10.0 mmol/l As A
could be used to measure TMA Vapor from 0.31 to 125 ppm, this covers the maximum
permissible concentration in tube work place 5ppm, and the sensing level-5 of smell in
humans, 3.0 ppm. The sniffer device possessed high selectivity for TMA being
attributable to the FM03 substrate specificity, continuous measurability.
1.2 Introduction:-
The sensing and measurement of chemical substances in the gas phase, such as malodor,
flammable and harmful gases with higher sensitivity and selectivity than the sense of
smell in humans are required in many fields. Tri methylamine is one of volatile nitric
compound. The maximum permissible concentration of TMA vapors in the work place
are 5.0 ppm (12 mg/m3, TWA Time Weighted Average Concentration) and 15 ppm.
Flavin-containing monooxygenase as one of xenobiotic metabolizing enzymes has been
reported to catalyze the oxidation of sulfuric and nitric compounds. FM03 is possible to
be expressed from human FM03 cDNA using a baculovims expression system and
commercialized. Oxygen consumption accompanied the enzyme reaction has been used
U10EC055, ODD SEMESTER 2013-2014 Page8
for analyzing the enzyme activity or the substrate concentration. Then we have also
developed and reported a bio electronic nose for TMA using FMO. On the other hand,
some optical fibers with chemical sensitivity were commercialized, and have been
expected to be newly sensing device for biological analysis. The optical fiber is
considered to be adaptable device for constructing the arrayed intelligent nose system for
multi-analfle in the gas-phase. In this work, we have constructed a bio-optical sniffer
using FMO enzyme for measurement of gaseous TMA. The performance of the sensor is
evaluated, such as sensitivity, calibration behavior and selectivity.
1.3 Experimental Section:-
The bio-optical sniffer consisted of a reaction unit and an oxygen-sensitive optical fiber
(FOXY-"-Flat (silicone overcoat), 1/16" outer diameter with an enzyme membrane
immobilized with flavin-containing monooxygenase. The optical fiber was coated by sol-
gel process with Ruthenium-organic complex which indicates an optical quenching
(excitation wavelength: 470 nm, fluorescent wavelength: 600 nm) to the existence of
oxygen molecule in both the liquid and gas phases.
For enzyme immobilization, FMO3 was mixed with PVA-SbQ monomer solution in a
weight ratio of 1: 2, to the surface of a dialysis membrane (thickness: 15 pm), spread on a
glass plate, and then irradiated with a fluorescent lamp for 30
A bio-optical sniffer Min in order to photo crosslink the monomer solution and immobilize the enzyme to the
dialysis membrane. The reaction unit was constructed by connecting two T-tubes to both
U10EC055, ODD SEMESTER 2013-2014 Page9
sides of a stainless steel pipe and the inner side edges of the two T-tubes were closed by a
sealing tape. The enzyme membrane was used to close one of the open edges of the
reaction unit and secured with a rubber O-ring. The fiber tip of the optical biosensor was
inserted from another open edge to the reaction unit and adjusted so as to directly touch
the surface of the enzyme membrane. Then the edge was also closed by the sealing tape.
Buffer solution in the obtained reaction unit was flowed into the stainless tube from the
middle edge of the root-side T-tube to that of the tip-side one, thus rinsing and cleaning
the fiber tip and enzyme membrane. The sensor tip was connected to the side hole of a
PTFE tube supplied the gaseous substances.
The bio-optical sniffer was used in a batch flow measurement system. In the system, gas
and phosphate buffer solution could be flowed individually through the reaction cell,
respectively. A standard substance in the gas phase was supplied from a gas generator
.Phosphate buffer solution in a carrier reservoir was flowed and circulated to the fiber tip
and the enzyme membrane of the optical-sniffer with a flow rate of 0.69mllmin using a
peristaltic pump.
A computer controlled spectrophotometer with analog-digital converter DAQ700,
PCMCIA A/D card with 100 kHz sampling frequency, was optically connected to the bio-
optical sniffer and monitored the optical quenching by oxygen consumption caused by
FMO catalytic reaction with TMA The gas-selectivity of the bio-optical sniffer was
evaluated using various odorous substances.
1.4 Results and Discussion:-
The calibration curve of the bio-optical sniffer for TMA in the gas-phase. The bio-optical
sniffer was calibrated against gaseous TMA from 0.31 to 125, deduced from exponential
regression analysis of the log-log plot by a method of least squares according to the
following equations:
Sensor output (counts) = 89.39 x [gaseous TMA (ppm)] 0.45
U10EC055, ODD SEMESTER 2013-2014 Page10
Calibration curve of the bio-optical sniffer with 10.0 mm o vlAsA for
TMA in the gas phase his calibration range of the sniffer with FM03 covers the maximum
permissible concentration of TMA 215 vapor in the work place, thus allowing to
determine the level of intoxication and also encountered the TMA sensing level-S (3.0
ppm) for the human smell as described above. Figure 3 shows the gas selectivity of the
bio-optical sniffer for various substances (50 ppm) in the gas-phase. As figure indicates,
the sniffer device with FM03 gave negligible to most of gaseous substances, whereas
application of dimethyl sulfide (DMS) and methyl mercaptan (MM) induced an increase
in the sensor output. The response to DMS and MM was consistently lower than that to
TMA because the FM03 from human liver is one of a polymorphic family of FMOs
catalyzed in the oxidation of heteroatom-containing compounds for a xenobiotic
metabolism.
As the previous results, the bioelectronics nose arrayed with 3 kinds (FMO1, 3 and 5) of
FMO electrodes was possible to distinguish gaseous substance by applying the patted
recognition approach, thus improving gas-selectivity of the nose system. From that point
of view, the optical sensor will be suitable for constructing the arrayed intelligent nose
system for assaying multi-analyte vapor.
U10EC055, ODD SEMESTER 2013-2014 Page11
CHAPTER-2 OPTICAL BIO-SNIFFER (BIOCHEMICAL
GASSENSOR) FOR DIMETHYL SULFIDE VAPOR
2.1 Abstract:-
An optical gas-sensor (bio-sniffer) for dimethyl sulfide (seaweed-odor substance) was
constructed by immobilizing flavin-containing mono oxygenase (FMO) to an oxygen-
sensitive optical fiber. The sniffer was calibrated against gaseous DMS over the range of
10 - 100 ppm.
Keywords: flavin-containing mono oxygenase, bio sniffer, dimethyl sulfide.
2.2 Introduction:-
Dimethyl sulfide is the colorless solution in the liquid phase and one of volatile sulfur
compounds with characteristic malodor in the gas phase as defined by the International
Occupational Safety and Health Information Center, The substance decomposes on
burning producing toxic and corrosive fumes, and reacts violently with oxidants causing
fire and explosion hazard. Flash point, auto-ignition temperature and explosive limits of
DMS are -49"C, 205°C: 2.2 - 19.7 vol% in air, respectively. A harmful contamination of
the air can be reached rather quickly on evaporation of DMS at 20°C. The substance
irritates the eyes and the skin. In humans, flavin-containing mono oxygenase as one of
xenobiotic metabolizing enzymes has been reported to catalyze the oxidation of sulfuric
and nitric compounds including DMS. FM03 is possible to be expressed from human
FM03 cDNA using a baculovirus expression system, and commercialized. Oxygen
consumption accompanied the enzyme reaction has been used for analyzing the enzyme
activity or the substrate concentration including DMS. On the other hand, some optical
fibers with chemical sensitivity were commercialized. An oxygen-sensitive optical fiber
coated with ruthenium-organic complex reacts to the existence of oxygen molecule in
both the liquid and gas phases. The optical fiber with biocatalyst has been expected to be
newly sensing device for biological analysis including gas analysis for volatile organic
compounds (VOC). In this work, we developed an optical bio-sniffer using FMO enzyme
U10EC055, ODD SEMESTER 2013-2014 Page12
for measurement of gaseous DMS .The performance of the sensor is evaluated with a gas
flow measurement system for gas-phase detection.
2.3 Experimental Section:-
Construction of optical bio-sniffer for DMS The optical bio-sniffer consisted of a reaction
unit and an oxygen-sensitive optical fiber ([FOXY-WRTV-Flat (silicone overcoat), 1/16’’
outer diameter, Ocean Optics, Inc., FL, USA) with a dialysis membrane immobilized with
flavin-containing mono oxygenase type FM03, EC 1.14.13.8, P233, 30200 pmolimg-
amin, from Adult human liver. The optical fiber was coated by sol-gel process with
Ruthenium-organic complex which indicates an optical quenching excitation wavelength:
470 nm, fluorescent wavelength: 600 nm to oxygen molecule in both the liquid and gas
phases .For enzyme immobilization, FM03 was mixed with PVA-SbQ monomer solution
in a weight ratio of 1 : 2, to the surface of the dialysis membrane (thickness: 15pm)
spread on a glass plate, and then irradiated with a fluorescent lamp for 30 min in order to
photo crosslink the monomer solution and immobilize the enzyme to the dialysis
membrane. The reaction unit was constructed by connecting two T-tubes to both sides of
a stainless steel pipe and the inner side edges of the two T-tubes were closed by a sealing
tape. The enzyme membrane was used to close one of the open edges of the reaction unit
and fixed with a rubber O-ring. The fiber tip of the optical biosensor was inserted from
another open edge to the reaction unit and adjusted so as to directly touch the surface of
the enzyme membrane. Then the edge was also closed by the sealing tape. Buffer solution
in the reaction unit was flowed into the stainless tube from the middle edge of the root-
side T-tube to that of the tip-side one, thus rinsing and cleaning the fiber tip and enzyme
membrane. The sensor tip was connected to the side hole of a PTFE supplied the gaseous
substances.
U10EC055, ODD SEMESTER 2013-2014 Page13
Principle of a chemical measurement of DMS using FMO enzyme reaction and substrate
regeneration cycle. A substrate regeneration cycle was applied to the FM03 immobilized
sensor in order to amplify the output signal by coupling the mono oxygenase with a
reducing reagent system of ascorbic acid (AsA) in phosphate buffer. The optical bio-
sniffer was possible to detect the oxygen consumption induced by FOM3 enzymatic
reaction with DMS application. Evalmfion of optical bio-sniffer for DMS The optical bio-
sniffer was used in a batch flow measurement system. In the system, gas and phosphate
buffer solution could be flowed individually through the reaction cell, respectively. A
standard substance in the gas phase was supplied from a gas generate. Phosphate buffer
solution (pH8.0,100mm oil) in a carrier reservoir was flowed and circulated to the fiber
tip and the enzyme membrane of the optical sniffer with a flow rate of 0.69mlimin using a
peristaltic pump. Schematic diagram of gas flow measurement system for gas-phase
detection.
A computer controlled spectro photo met with analog-digital converter was optically
connected to the bio-sniffer and monitored the optical quenching (fluorescent: 600 nm) by
oxygen consumption caused by FMO catalytic reaction with DMS. The gas-selectivity of
the optical bio-sniffer was evaluated using various odorous substances.
2.4 Results and Discussion:-
Evaluation of optical bio-sniffer for DMS the optical sniffer was calibrated against
gaseous DMS over the range of 10 to 100 ppm, deduced from exponential regression
analysis. The calibration range of the optical bio-sniffer for DMS vapor is lower than
explosive h I t s of DMS vapor (~01%in air: 2.2 - 19.7) as described above. As the food
application, the optical bio-sniffer was used to a gas assessment for seaweed sample. The
sample was prepared by immersing Ig of the dried seaweed with 5 ml of the distilled
water in 790 ml of the container. The optical sniffer successfully detected gaseous DMS
in the sample container. The concentration of DMS in the gas-phase was calculated as 7.0
ppm in the container, which consistent with the result value obtained with a commercial
available detection tube. As the previous results, the bioelectronics sniffer devices arrayed
with 3 kinds of FMO electrodes was possible to distinguish gaseous substance by
applying the 'pattern recognition approach, thus improving gas-selectivity of the sniffer
U10EC055, ODD SEMESTER 2013-2014 Page14
array. From that point of view, the optical-fiber sensor will be slit able for constructing
the arrayed intelligent nose system for the assessment of multi- analytevapor.
2.5Conclusions:-
The optical bio-sniffer for DMS was constructed by immobilizing FMO onto a tip of a
fiber optic oxygen sensor coated with an oxygen sensitive ruthenium organic complex,
together with the reaction unit. The sniffer was used to measure DMS vapor from 2.1 to
126 ppm with gas-selectivity based on the FMO substrate specificity. And the sniffer was
also applied to detect gaseous DMS from the seaweed sample as the food application,
Potential application of the fiber sensor includes a smart nose system for continuous
monitoring of the odorous multi analyte by arraying the optical fiber. We will report
about other optical bio-sniffer and the smart nose in the near future.
U10EC055, ODD SEMESTER 2013-2014 Page15
CHAPTER-3 USING UV-LED LIGHT FOR MONITORING
ETHANOL VAPOR WITH HIGH SENSITIVITY & SELECTIVITY
3.1 Abstract:-
A fiber optic bio-sniffer (biochemical gas sensor) for alcohol gas monitoring with high
sensitivity and high selectivity was fabricated and tested. The bio-sniffer is a gas sensor
that uses molecular recognition of enzyme to improve selectivity. Usually, enzyme loses
activity in the gas phase. Applying a flow cell with a gas-intake window to the sensing
probe, enzyme immobilized at the sensing region was kept in the sufficient wet condition
to maintain activity. The bio-sniffer measures ethanol (EtOH) vapor by measuring
fluorescence of nicotine amide adenine dinucleotide (NADH), which is produced by
enzymatic reaction at the flow-cell. In order to construct a simplified system suitable for
on-site applications, a high-intensity ultraviolet light emitting diode (UV-LED) was
utilized as an excitation light. Owing to low power consumption comparing with previous
light sources, the bio-sniffer was considered to be suitable for laptop applications such as
on-site monitoring. According to the characterization, the bio-sniffer for was useful for
continuous alcohol monitoring and showed high selectivity. The calibration range was
0.30-300 ppm which is suitable for evaluation of capacity to metabolize alcohol.
3.2 Introduction:-
Volatile components transpired from patients, which can be associated with disease, is
expected as a marker for noninvasive and convenient screening in modern medicine.
Since many kinds of chemical components are transpired from human bodies, a high-
selective and high-sensitive gas sensor is strongly requested for this purpose. Utilization
of substrate specificities of biocatalysts such as enzymes is one of the promising
approaches to improve selectivity of chemical sensors. In the previous study, we reported
a NADH dependent biochemical gas sensor (bio-sniffer) for breath analysis using
electrochemical method. Although the electrochemical method is relatively simple and
high-selective method, there are several struggle points to be cleared for clinical
U10EC055, ODD SEMESTER 2013-2014 Page16
applications. Particularly, simplified and miniaturized sensing system for portable
application is expected. Alcohol dehydrogenase (ADH) based biosensors measures
alcohol as production of NADH, which yields fluorescence for 340nm excitation light.
Recently, high intensity GaN and AlGaN based LEDs with peak emissions in mid- to
near-UV (265-360nm) was developed. For its low power consumption, UV-LEDs are
suitable for laptop applications such as on-site monitoring. Therefore, we applied a UV-
LED (λ=340nm) as an excitation source of NADH fluoro metric biosensor in the previous
study [9]. Continuous alcohol gas monitoring with simplified measurement system can be
expected by applying such a fluoro-metric bio sensing system to the gas phase. Enzyme
based biosensors are usually used in the liquid phase because enzyme, which function is
determined by its cubic structure, loses activity in the dry circumstance. For this reason,
an interface of the gas component and the enzyme in a wet condition with adequate pH
and temperature is requested to realize continuous gas monitoring by bio-sniffers. In this
study, a fiber optic bio-sniffer for high-selective and continuous alcohol vapor monitoring
was developed using the UV-LED excitation system and a flow-cell with a gas-intake
window. This paper reports the optical setup, working principle and the characteristics of
the bio-sniffer for alcohol gas monitoring in detail.
3.3 Experimental:-
A. Optical system The UV-LED based portable excitation system was constructed with a
UV-LED and a custom-fabricated UV-LED power supply system produced by KLV CO.,
LTD. A fiber optic spectrometer and the UV-LED excitation system were connected to a
Y-shaped optical fiber assembly with optical filters.
Band-pass filter with transparent wavelength of 330~350nm was placed in the excitation
line. In the detection line, a long- 978 pass filter with cut-on wavelength of 400nm was
placed to cut the excitation light coupled into the spectrometer. B. Fiber Optic Biosensor
with UV-LED Prior to construct the bio-sniffer, a fiber optic biosensor for ethanol
U10EC055, ODD SEMESTER 2013-2014 Page17
measurement in the liquid phase was constructed and tested. At first, an enzyme
immobilized membrane was prepared by the previously reported method. A mixture of
PMEH solution (1μl cm-2) and ADH (50 unit’s cm- 2) was first spread on the H-PTFE
membrane filter and cured in a refrigerator (4 °C, 180min). Afterward, the redundant
ADH was rinsed using PB. An ADH immobilized, membrane was thus obtained. The
enzyme membrane was cut into 1cm 1 cm and tightly fixed on the optical fiber probe
using a silicone O-ring. The biosensor measures the fluorescence of NADH (491nm),
which is produced by the enzymatic reaction as follows:
EtOH+ NAD+ ⎯A⎯D⎯⎯H→ acet aldehyde + NADH+H+ (1)
The fluorescence of NADH was guided into the fiber optic
Spectrometer via LPF and recorded using a laptop PC C. Fiber Optic Bio-sniffer after
that, a high-selective bio-sniffer for alcohol gas monitoring was constructed. As
mentioned above, wet atmosphere with adequate pH and temperature is requested for gas
sensing probe to prevent enzyme from deactivation. A flow cell with a gas-intake window
was attached on the probe of the fiber-optic biosensor. The flow cell is also used for
supplying NAD+ and removing the reaction products from the sensing region. Alcohol
gas monitoring with the bio sniffer was then carried out. A PB containing NAD+ (20
moll/l) was circulated in the flow cell with a flow rate of 1.0ml/min. After the
fluorescence signal became steady state, ethanol gas (200 ml/min) was exposed to the
window of the flow cell using a standard gas generator for 8 minutes. The change of
fluorescence intensity (λ=491nm) was recorded for exposure of various concentrations of
alcohol gas (0.30 to 300 ppm). Also, the gas selectivity of the bio-sniffer was evaluated.
U10EC055, ODD SEMESTER 2013-2014 Page18
A 50.0 ppm of ethanol, methyl ethyl ketone (MEK), acetone and n-pentane was exposed
to the bio-sniffer. These gases were also exposed to a commercially available solid-state
gas sensor as a comparative experiment.
3.4 Results and Discussion:-
Characteristics of the Biosensor for Ethanol Solution typical spectral change of the fiber
optic biosensor for ethanol solution (1000 moll/l). The background noise was relatively
well reduced by the effect of LPF. When ethanol solution was added into the measuring
cell, an emission with the peak wavelength of 491nm was generated immediately. This
signal is the fluorescence of NADH, produced by the enzymatic reaction as shown in. The
value of the fluorescence intensity was related to ethanol concentrations. The biosensor
was useful for the ethanol solution with the concentration from 0.10 – 100 mmol/l. The
fluorescent intensity reflects the concentration of NADH proximity to the sensor probe.
This indicates that the output signal of the biosensor is influenced by the enzyme activity.
The activity of ADH used for this biosensor is most active with ethanol and the activity
decreases as the size of the alcohol increases. Thus, the biosensor s showed 30 times
higher output for ethanol than that of methanol. According to the result, the fiber-optic
biosensor for ethanol solution was considered to be useful for gas monitoring use.
B. Characteristics of the Bio-sniffer for Alcohol Vapor
Change of fluorescent intensity when the standard ethanol gas was exposed to the fiber-
optic bio-sniffer. As the figure indicates, the output signal was sufficiently stable before
alcohol gas exposure.
U10EC055, ODD SEMESTER 2013-2014 Page19
7yr4\] [` during gas exposure, significant increases of fluorescent intensity and the steady-
state values depend on ethanol gas concentrations were obtained. Periodical fluctuation of
the fluorescent signal indicates the pulsation flow of the buffer flow. This can be
eliminated by use of non-pulsation pump or damper device to absorb the pulsation.
Reductions of the fluorescence output due to buffer flow were also confirmed when
alcohol gas was eliminated from the sensing region (after 10 min). This suggests that the
bio-sniffer is useful for continuous monitoring. The output fluorescence was, confirmed
from 0.32 - 1000.0 ppm. However, the fluorescent signal was saturated for higher
concentration than 300 ppm. The calibration range was suitable for evaluation of human
capacity to metabolize alcohol. Also, the calibration range included both the lower limit
of the human sense of smell level-1 (0.36 ppm) and the standard for driving under the
influence of alcohol (78 ppm). Gas selectivity for various chemical substances of the bio
sniffer was also investigated. As a result, the bio-sniffer showed excellent selectivity in
compare with a commercially available semiconductor gas sensor. No output signal was
confirmed when MEK, acetone and n-pentane were exposed to the bio-sniffer. On the
other hand, solid state sensors showed, 102%, 119%, 113% of the output signal for MEK,
acetone and n-pentane, respectively. Such a high-selectivity of the bio sniffers due to the
specificity of ADH. According to the result, the bio-sniffer is considered to be useful for
metabolic capacity for alcohol from expired breath. It is also possible to measure other
volatile chemical substances with high selectivity by changing enzyme with similar
system.
U10EC055, ODD SEMESTER 2013-2014 Page20
CHAPTER-4 OPTICAL SENSOR IN THE APPLICATION OF BIO-
DETECTION
4.1 Abstract:-
This optical sensor was designed and developed for the application in bio-detection. It
consists of excitation module, optical detection module and signal processing module.
The sensor has highly sensitive and applied to detect protein concentration in urine
arranging from 0.01mg/ml to 0.3 mg/ml. The results show the feasibility of such optical
sensor as biomarkers detection in home healthcare
4.2 Introduction:-
Biomarkers have been of vital importance in diseases diagnosis and monitoring. If
patients suffer certain disease, i.e. kidney problem, they can excrete some special
biomarkers, albumin, and creatinine, in their urine. By identifying these special
biomarkers, the biomarker-related diseases can be diagnosed. The paper is focused to
explore the potential of optical sensor for detecting biomarkers in body fluids, i.e. urine.
We have designed and developed an optical sensor which consists of excitation module,
optical detection module and signal processing module. If there is biomarker in test
sample, the sample will emit certain wavelength fluorescence when the sample is mixed
with selected dye. The emitted fluorescence intensity is proportional to the biomarker
concentration in sample. The detection module will detect the emitting fluorescence from
the sample while the excitation module excites the sample. The detected fluorescence
intensity will be changed into electrical signal and processed. We did a series of
experiments with artificial urine of different protein concentrations using both our optical
sensor and a commercial spectrofluorophoto meter by Shimadzu. The experiment results
show that our optical sensor fit in with the commercial spectrofluorophoto meter and can
be used to quantify biomarkers, i.e. protein in urine effectively.
4.3 Experiments and Results:-
A System design our optical sensor has three main functions, excitation, detection and
signal processing. If there is the disease related biomarker in the sample, the biomarker
U10EC055, ODD SEMESTER 2013-2014 Page21
will be addressed by the dye added in. Under the expose of UV light, the addressed
biomarker will emit certain wavelength fluorescence. The intensity of fluorescence is
proportional to the biomarker concentration. To make the test sample to be exposed
uniformly under UV light and emit constant fluorescence, an excitation module was
designed and developed. By controlling the bias voltage, the UV light intensity can be
adjustable to meet requirement. The UV light will be cast on the sample under test once
the sample, i.e. urine, is mixed with dye and is put between excitation module and
detection module. Next, the optical detection module will be activated to detect the
fluorescence emitted from the sample under test. Following that the detected fluorescence
will be converted into electrical signal and be processed. After calculation, the biomarker
concentration is displayed. In our design, an excitation light of 390nm was used in the
excitation module. In order to block background light, a bandwidth 10nm filter was
placed in front of the UV light source. For the same reason, another filter was used in
detection module. A photodiode was used to collect the fluorescence signal from sample
and converted it into equivalent current. The photodiode was configured in photovoltaic
(PV) mode so as not to introduce additional noise current into the system. The detection
module deployed a Tran’s impedance amplifier (TIA), an 8th order elliptic low-pass filter
and a 16-bit delta-sigma ADC to convert the current from the photodiode into a digitized
voltage level with ample amplification to make the result stable and meaningful while
providing a high signal-to-noise ratio. The MCU was in charge of all signal controlling
and processing. The final result was displayed onto the LCD and saved for future
reference.
Experimental Procedure:-In experiments, we used artificial urine as test sample. In order
to test our optical sensor, we took protein as the biomarker to be detected and added the
protein with different concentrations in different samples. According to a standard
laboratory procedure, we prepared a batch of thirty samples consisting of artificial urine
with difference .Protein concentrations ranging from 0.01mg/ml to 0.3mg/ml in steps of
0.01 we pipette 500ul of artificial urine containing specific protein concentration, borate
buffer and dye into a test tube let. The test tube let with sample was excited by UV light
and the corresponding fluorescence emitted from the sample were collected by detection
module. The detection module was programmed to read in one hundred readings at an
interval of 20ms between readings for a single detection from the test tube let and the
U10EC055, ODD SEMESTER 2013-2014 Page22
final result was the averaged value of the particular one hundred readings. The
experiment was repeated four times for each of the prepared samples.
The fluorescence intensity was determined by protein concentration in artificial urine
samples. Over the range from 0.01mg/ml to 0.30mg/ml, the measured fluorescence
intensity linearly increased with the increasing of protein concentration. The R2 was
equal to 0.9906. The minimum detectable protein concentration was 0.01mg/ml. With the
linearity between the fluorescence intensity and protein concentration, our optical sensor
0.001 demonstrated the capability to quantify biomarker, protein, another experiment, we
used Nano-fluorescent CdSe/ZnS quantum dots (QDs), Carboxy-EviTag as a dye.. They
are approximately 10 to 35 nanometers in size. 2 to 20 biotin molecules are covalently
bonded to the surface of the modified QDs. While preserving the fluorescent properties,
the CdSe/ZnS QD keeps the attached bio markers active and is able to recognize specific
biomarkers. The QD Carboxy- EviTag with Em 630nm was activated with DEC (1-Ethyl-
3- [3-dimethylaminopropyl] carbodiimide hydrochloride) and sulfo-NHS (N-
hydroxysulfosuccinimide), then conjugated to affinity purified goat anti human-alpha-
TSH antibody at 1:10 ratio of EviTag mg to antibody mg. Conjugated antibody was
separated by a spinning filter. As a result, alpha-TSH antibody biomolecules were
immobilized on the surface of the QD Carboxy-EviTag, forming alpha-TSH antibody-QD
conjugate the alpha -TSH antibody has a function of recognizing TSH protein captured by
anti-alpha-TSH antibody which is pre-immobilized on the solid surface of the test
biochip. In order to capture the biomarker, TSH, mouse anti alpha-TSH Ab was coated
onto 96 biochip plate and non-specific binding sites were blocked prior to assay. Biochip
coated with non-related mouse Ab serves as system control (Control wells). TSH
specimen and conjugates at desirable concentrations were simultaneously added into the
coated biochip. During the test, if TSH exists in the specimen, a sandwich complex
composed of anti-alpha-TSH Ab-TSH – EviTag conjugate would form in the coated
biochip. All the testing materials and reagents were warmed up to room temperature prior
to testing. The QD conjugate were diluted to 1:100. 50 microl of TSH at concentration
from 2.5 microIU/ml, 10microIU/ml, 20 microIU/ml, and 40 microIU/ml was added into
anti alpha-TSH antibody coated biochips, respectively. Next, 50 micro l of diluted QD
conjugate were then added into the biochips, respectively. The biochips were sealed to
avoid solution evaporation. The samples were incubated at 25°C for two hours. The
solution was then removed and unbound reagents were washed away with 4 rinses of DI
U10EC055, ODD SEMESTER 2013-2014 Page23
water. The biochips were drained completely by tapping on an absorbent paper. 100
microl of BS buffer was added into each biochip. The amount of the QD conjugated
alpha-TSH antibody retained on the biochip was proportional to the amount of the TSH in
the specimen. As a control, above process was repeated on the biochips coated with
control antibodies. The emission fluorescent signals from each biochip were detected and
recorded by our optical sensor. All measurements were made in triplicates. Exhibited the
variation of fluorescence intensity of the QD conjugates as a function of TSH
concentrations. One can see that the fluorescence intensity of the QD marked TSH was
enhanced with increasing TSH concentration. This suggested that the detected QD
fluorescence signal was a result of the specific interaction of QD-antibody conjugates and
TSH protein. Low levels of target concentration reached to 2.5 microIU/ml which was
good enough for normal clinical screening test. In fact, a high signal to noise ratio, or
high sensitivity, was crucial for us to discern smaller changes in the fluorescence of the
samples with high accuracy. Optical purity was achieved with the selection of excitation
and emission wavelengths which led to a very low.
4.4 Discussions:-
In order to make sensor simple and compact, we used solid state devices for both the
excitation source and detector. UV LEDs are available in many different grades and sizes,
but none of them gives a clean narrow excitation spectral. When the UV LED is turned
on, the detector detects some level of light when there is no sample or the sample contains
no biomarker. Therefore we used a narrow band pass filter (D365/10X, Chroma
Technology Corp) that allowed light within 365+/-5nm to pass through while blocking
the rest. Another filter was used at the detector side which corresponded to the emission
maximum of fluorescence from sample. We had successfully eliminates both, the light of
other wavelength from the UV LED, the excitation lights itself and the ambient light from
entering the detector with the combination of these two filters. Hence, we were able to
obtain a high signal-to-noise ratio for the sensor with the used of low cost solid state
excitation source and detector simple filters. Our sensor used a low cost PD with gain less
than one as the detector, thus a very high gain was required from the TIA circuit in order
to output useful readings. One main drawback of operating any op amp with very high
gain was its frequency response being greatly reduced as gain and bandwidth of an op
amp were inversely proportional to each other (limits by its GBW) Though the overall
U10EC055, ODD SEMESTER 2013-2014 Page24
system response was much slower as compared to high cost detection systems, it did not
pose a problem in our protein quantification application as our sensor did not require high
speed response e.g. in the range of KHz or MHz Additionally, the op amp would go into
oscillation due to internal capacitance of the photodiode together with feedback resistor
forms a low-pass filter and contributes a negative phase to the feedback loop which
caused instability and hence oscillation occurred. The problem was solved by adding a
small capacitance to the feedback loop to form a high-pass filter with the feedback
resistor. In this way, a positive phase would be introduced to the feedback loop to push to
the circuit toward stability but at the same time sacrificing bandwidth. We had shown that
high sensitivity was achievable and thus a low cost, compact and portable detection
system can be used as effectively and accurately as compared to large, costly detection
system. The significant difference between the excitation and emission wavelengths
provided high resolution and signal-to-noise ratio, thus making the fluorescence signals
easily detectable with simple low-cost photo detector. As a result, the complexity and cost
of the entire detection system can be significantly reduced. The application of our optical
sensor is not only limited to disease related biomarkers detection. With the use of
different fluorescence dye that can react with specific targets of interest, the sensor can be
extended to areas like food and beverage industry to test for food safety or the
environmental monitoring field for pollution level monitoring. The rapid detection of the
sensor can also be used to speed up the process of blood test or urine test done in the
police station for drunk-driving as traditional methods usually takes up to a day which is
time consuming (samples to be sent to lab for testing) or other drug testing process.
4.5 Conclusion:-
An optical sensor was designed and developed. The sensor consists of excitation module,
optical detection module and signal processing module. The fluorescence properties of
biomarkers conjugated with dye had been studied in a systematic way. The fluorescence
intensity from sample was a near linear function with the biomarkers concentration. Our
sensor can quantify biomarker, protein, in artificial urine and TSH successfully. The
sensor was low cost, rapid, compact and highly sensitive.
U10EC055, ODD SEMESTER 2013-2014 Page25
CHAPTER-5 OPTICAL BIO-SENSOR FROM DNA AND NANO
STRUCTURES
5.1 Abstract:-
This type of optical device can be placed inside living cells and detect trace amounts of
harmful contaminants by means of near infrared light. In this report, we investigate the
working principle, design schemes and the role of surrounding environment of this new
class of optical biosensor from DNA and carbon Nano structures, such as carbon
nanotubes, grapheme ribbons, etc. We also propose some new design models by replacing
carbon nanotubes with grapheme ribbon semiconductors. Index Terms—simplicity,
beauty, elegance.
5.2 Introduction:-
New quantum optic method to research the bio-systems was carried out by using physical
Nano-systems that have clearly and strongly intensity optical properties such as quantum
wire, quantum dot, or Nano particles. By combine bio-systems with Nano physical
systems (bio-Nano systems), then analyze the changes of optical properties of new bio
physical systems through their optical spectra, we can obtain useful information about the
studying bio-systems. At present, the state-of the-art achievements have been made at the
frontier of nanotechnology and biotechnology by employing modern nanomaterial’s to
manufacture biosensors The paramount role of biosensors has covered a board range of
clinical diagnosis, treatment method, and bio- medical studies. Improving qualification of
biosensors gives great challenges in terms of technology and requires the increase of
understanding of biological world as well as new-found nanomaterial’s.DNA molecule is
a very special type of Nano-wires with diameter approximately about 2nm. Not only the
separation of double helix structure of DNA into two single strands is an important
beginning point in informatics replication process of DNA to reproduce living matter but
also its physical properties such as strength, structural phase transition, could be useful in
design new type of Nano bio sensorsand robots. Carbon nanotubes (CNs) are a new class
U10EC055, ODD SEMESTER 2013-2014 Page26
of quantum wires or quasi 1D system. During the last several years, because of their
carbon based native material having useful and promising physical properties, carbon
nanotubes have many important application in bio Nano technology in generally and in
making biosensor and robots in particularly. Having the same scale, DNA and SWNT can
be easily combined together to make a new type of bio-Nano instrument, robot and
machine, such as DNA–CN optical biosensor, one can be placed inside living cells and
detect trace amounts of harmful contaminants using near infrared light. To make this
sensor, the researchers begin by wrapping a piece of double – stranded DNA around the
surface of SWNT, in much the same fashion as a telephone cord wraps around a pencil.
This discovery could lead to new types of optical sensors and biomarkers at the sub
cellular level that exploit the unique properties of nanoparticles in living systems. This
combination is due to the Carbon-structure of SWNTs and net negative charge of DNA
molecule. And DNA-wrapped carbon nanotubes serve as sensors in living cells. This is
the first nanotube-based sensor that can detect analyses at the subcellular level. When the
DNA is exposed to ions of certain atoms (e.g., calcium, mercury and sodium) the DNA
changes shape, perturbing the electronic structure of single-walled nanotube(SWNT) and
shifting the nanotube’s fluorescence to lower energy.II.
THEORETICAL MODELS OF THE DNA OPTICAL BIOSENSOR
The double stranded DNA coil has a helical configuration. Our optical biosensor models
are based on DNA’s ability to wrap around other nanostructures. In this report, this Nano
objects are the carbon Nano structures, such carbon nanotube, Nano grapheme ribbon,
etc. A. CN-DNA optical biosensor According to the experimental model of the CNNTs
wrapped with DNA which serve as bio-sensor in living cell, a simple. In this model, the
exciting theory of CNNTs was used to explain the fluorescence of the bio sensor. Here, to
approximate the dielectric constant of the B- or Z-DNA wrapped CNNT, the effective
medium and effective dielectric constant was introduced. The dielectric constant in the
expression of exaction binding energy. The DNA ribbon regularly wraps around surface
of cylinder radius of R (nm) with period along the axis of cylinder.
U10EC055, ODD SEMESTER 2013-2014 Page27
The effective dielectric constant of medium surrounding SWNT can be written as
" =f’eDNA + (1 - f ) "eS where "DNA and "S are dielectric constants of DNA and
solution, respectively; f is the ratio of surface area covered by DNA per total cylindrical
surface area. When the bio-sensor is in the certain medium where the ionic concentration
exceed a critical value, the structure of DNA will be changed over from B to Z form, and
the emission energy of SWNT was shifted. The calculated ratio of surface area covered
by DNA per total area for two kinds of DNA form vs. radius of SWNT. We see that the
ratio covered by DNA in B-form is larger than one in Z-form It well known that the
dielectric constant of DNA is much smaller than dielectric constant of water, i.e., the
effective dielectric constant in B form must be smaller than that in Form, so the exaction
binding energy of SWNT in B-form is larger than Z-form. We note that the bio-sensors is
only workable in range of small radius In the case of low concentration, there is no phase
transition of DNA and DNA exists in the B-form only. The exaction energy as a function
of ionic concentration is presented in
.
U10EC055, ODD SEMESTER 2013-2014 Page28
The pH of certain solution drastically impacts the biomolecules such as DNA, RNA,
proteins etc. Without doubt, this optical bio-sensor based from DNA and CNNTs is
effected by pH of solution in some way. When the pH of solution varies, the dielectric
constants of DNA and solution around the CNNTs change, it brings about the variation of
effective dielectric constant. Therefore, the optical signals of optical biosensor change.
We have demonstrated that the sensor is influenced drastically by the protons (H+) in
solution, and the pH is strongly dependence. We found that, the workable solution for
sensor should has pH range from 6 to 9 where its parameters are nearly constant.
5.3 Discussion:-
This new combining structure of DNA and CNNTs or AGNR are really interesting and
useful for design a new kind of optical sensors, which can be placed inside living cells to
detect amounts of harmful contaminants. In the future, this design could be improved by
comparing with the new experiment data. Therefore, we can choose the better parameter
set for the model. The working condition and properties of this new optical sensors also
could be investigation with taking in to account the influence of the surrounding living
environmental such as temperature, pKa, pressure, and ionic strength etc. . .CNNTs and
are only carbon base type of Nano wires and tubes. At present there are several new quasi
one dimensional Nano structures are founded such as Si Nano wire, Al Nano pipe, we
will study and develop new design schema of optical bio sensors using them in the future
works.
U10EC055, ODD SEMESTER 2013-2014 Page29
CHAPTER-6 A HEMISPHERICAL OMNI-DIRECTIONAL BIO
INSPIRED OPTICAL SENSOR
6.1 Abstract-
Flying insects possess a surprisingly competent vision and navigation system, which
enables them to control various man oeuvres in their flight. The hemispherical Omni-
directional optical sensor inspired by the compound eye of flying insects. Here, we show
the feasibility of a system based on a low complexity optoelectronic system that estimates
the optic flow, essentially based on biological findings on the fly Elementary Motion
Detectors (EMDs). The valuable properties of our hemispherical compound eye include
being lightweight, low power consumption, panoramic field of view and multi resolution.
The developed modular system with 128 photoreceptors (up-gradable to 256), with a
payload of some hundred grams and power consumption less than 300 mW is light
enough to make it suitable to be mounted on VA Vs, MA Vs and mobile robot
applications. Keywords-Compound eye; elementary motion detection; moving obstacle
detection; Omni-directional camera.
6.2 Introduction:-
Although modern Unmanned Aerial Vehicles (UAVs) control their position and
orientation using systems such as the Global Positioning System (GPS) and the Attitude
and Heading Reference System (AHRS), but they are not sufficient to perform vital
navigation tasks such as terrain-following, smooth landing, and obstacle avoidance in a
complex environment. What's the most important in such tasks is continuously
monitoring the surroundings. Active sensing, using laser range finders or Radar, suffer
from stealth compromising. Hence, passive sensing such as vision would be of more
benefit for UA V s Studies on visual behaviors of flying insects over the decades, has
revealed many cues which are used in flight guidance and environment perception.
Equipped with neither Radar nor GPS, insects, with their small brains, fly autonomously
in unknown environments. Insects like fly, with surprising agility, sense the patterns of
image motions to detect their ego-motions and maintain appropriate actions. A recent
U10EC055, ODD SEMESTER 2013-2014 Page30
trend in biologically inspired vision systems has been to made use of optical flow
information for flight tasks. Numerous designs of self-guided vehicles utilized the
knowledge achieved on insects' abilities in various systems such as Micro-Air-Vehicles,
and UAVs. Conventional cameras lack wide field of view. This raises the question that is
it possible to construct a camera that can simultaneously capture images from all
directions. Such an Omni-directional camera would have improved variety of
applications, including autonomous navigation, video surveillance, and flight control. For
development of a practical Omni-directional camera first of all, its implementation,
calibration and maintenance should be easy; secondly, the mapping from actual world
coordinates to image coordinates should be simple enough to permit fast computation.
Our approach to Omni-directional image sensing includes these properties. We have
distributed photo sensors (photo transistors) in a hemispherical surface to construct an
imaging system. The distribution of phototransistors in the surface is in a way that, in the
main axis the sensor density is more than other directions. In other words, the distances
between sensors in that direction are less than other directions. This causes the system to
have better resolution in its main direction. This is what we refer to as hemispherical
Omni-directional optical sensor. In this paper, we will discuss design and implementation
of a wide-angle vision system that has been tailored for the specific needs of model
aircraft guidance. The rest of the paper is organized as follows. In section2, we will
discuss the flying insects' visual system, Omni-directional vision, and the elementary
motion detector (EMD).II. FLYING INSECTS VISUAL SYSTEM There are some
differences in vertebrate and insect vision. Simple and complex eyes are two types of
insect eyes. The one which is capable of distinguishing lightness from darkness is called
simple. Compound eyes compared to simple eyes are larger and more complex, while
simple eyes are small and round. Compound eyes are made up of thousands of six-sided
compartment, called ommatidia..
An ommatidia cell contains light sensitive cells, a lens, and nerves to brain and able to
detect a tiny portion of visual field, combining these tiny portions, makes a complete
image. So, the final image is made number of cells are, the better image with higher
resolution will be achieved. The eyes of insects are much closer together in comparison
with that of vertebrates. The focus of their motionless eyes is fixed. They cannot guess
the distances to objects neither from the extent to which the directions of gaze must
U10EC055, ODD SEMESTER 2013-2014 Page31
converge; nor from the amount of reflective power needed to focus on the objects. They
possess poorer eyesight, with low special precision, and can only estimate very small
distances.
In spite of these weaknesses, they have an impressive visual system. With limited number
of pixels in each compound eye, large field of view and ultra-light processing system,
flying insects maintain fast responsibility in tasks such as dynamic speed stabilization,
collision avoidance, tracking smooth landing, etc. To deal with visual guidance problems,
insects use alternative solutions. They use image motion caused by their own motion and
estimate the distances to obstacles and control their flight
Compound eye of a fly (Top), beside the built Omni-directional
Optical sensor (Bottom) Omni-directional vision Omni-directional sensors for computer
vision should have wide field of vision, by definition. For flight, wide field of view
sensors are appropriate, and in general useful for mobile robots. Varieties of Omni-
directional sensors include wide FOV dioptric cameras (e.g. fisheye), cat dioptric cameras
(e.g. cameras and mirror systems), and poly dioptric cameras. Poly dioptric cameras have
high resolution per viewing angle but, bandwidth is a problem for them. They also utilize
several cameras instead of several sensors. In comparison with commercial ones,
homemade poly dioptric cameras are cheaper, but require calibrating and synchronization.
Cata dioptric solutions usually incorporate special shaped mirrors into conventional
cameras. This method uses one camera, and therefore produces one image, but low
resolution and blind spot are of its weak points. There are a few existing implementations
that are based on this approach to image sensing. B. Elementary Motion Detector (EMD)
having smart and distributed neural processing, the insects can sense the visual motion of
light contrasted obstacles, and generate a safe trajectory. According to the electro physical
U10EC055, ODD SEMESTER 2013-2014 Page32
response of the fly's compound eyes, Reinhardt made the Elementary-Motion-Detector
(EMD) .This method finds the correlation between two adjacent photo detectors, with
their visual axes diverge by an angle called the inter-receptor angle. According to the
block diagram shown in fig .
Varieties of Omni-directional camera
Magnitude and direction of the velocity is calculated by multiplying the signals output
from the adjacent detectors by a time delay constant T. The greatest correlation is found
when the spatial intensity delay between the photo detectors is equal to the time delay.
Differencing the two correlations yields a direction-sensitive representation of the image
motion. Using a planar field of EMDs can then create an image motion field. III.
OPTICAL SENSOR DESIGN A. Hardware The final system consists of a circular board
with a radius of 60mm which is called central board and 32 modular sensor boards with
the same radius (900 arches) The central board contains thirty two 10-pin female header
connectors and each of the sensor boards has a 10-pin male header connector, connecting
them mechanically and electrically to the central board. These connectors are placed on
the central board separated by 12S around the axe. On the other hand, the sensor board
consists of 8 phototransistors similarly located on 12S arches around a quadrant circle of
radius 60mm. This gives a total inter-receptor angle of 12S in both axes, between the two
U10EC055, ODD SEMESTER 2013-2014 Page33
photoreceptors. A total of 256 sensors could be used in this configuration, In order to use
sensors with different field of view, the sensor boards could be placed on the central
board using one of the available connectors. For example, using 30 degrees of sensitivity
sensors, the sensor boards could be placed in every other position. This kind of
configuration enables us to change the place of sensor boards on the central board easily
and reduce the maintenance and assembly time of the whole system structure. Fig. 6
shows the block diagram of the implemented optoelectronic system. Based on the light
intensity, the phototransistor produces a signal in one form of voltage or current. Due to
limitation in the number of ADC channels, the output of different phototransistors has
been multiplexed. Every multiplexer chip has three control signals to determine which of
its 8 inputs is to be appeared at output pin. These control signals are produced by the
processor located on the central board
Central Board (left) with a radius of 60 mm equal size with a
Compact Disc. And Sensor Board (right) with eight phototransistors
The phototransistor chosen for this application is the L14Nl phototransistor, almost a non-
expensive sensor, available for less than 2$ in quantity. This sensor provides a wide
spectral response of 500 to 1000nm as well as 40 degrees of sensitivity. The L14Nl in
particular has a saturation current of less than 2mA, allowing low power consumption
when used in large numbers. The phototransistors are wired in a common-collector
configuration, with a 10 KO resistor between the emitter and ground. Actually this
biasing resistor defines the strength of the analogue signal. Each phototransistor is
connected via a series of analogue multiplexers to the ADC channels of micro controller.
The micro controller used is ATmega64, one of the 8-bit Atmel AVR microcontrollers.
Clocked at 16 MHz, it can roughly execute 16 million instructions per second. This
U10EC055, ODD SEMESTER 2013-2014 Page34
microcontroller has 8 embedded ADC input channels and samples the signals on each
ADC with 10-bit resolution. The
Complete optical sensor structure, including one main board
With 16 sensor boards (Top View).
System Block Diagram including both the sensor board and the central board
6.3 Conclusion:-
A number of 128 phototransistors (upgradable to 256) are distributed in modular sensor
cards to cover a hemispherical surface. The density of the sensors around the main axis of
the system is more than other. Direction improving its resolution in that direction. The
vision system can produce frame rates of up to 90 fps, a low resolution, but wide angle
image. Its low cost, lightweight and low power consumption make it suitable for mobile
and UA V applications such as corridor navigation, altitude control, and Terrain
Following and auto landing systems. The system can be used as a platform to implement
various visual based navigation and flight control algorithms such as optical flow. In
conclusion, this sensor can be considered as an alternative for CCD-camera based visual
U10EC055, ODD SEMESTER 2013-2014 Page35
systems covering 360 degrees field of view. B. Future work to decrease the dependency
of the response to the tolerances and mechanical assembly of the system, we will
implement a calibration procedure to have a uniform response of the sensors. This can be
done by changing the bias resistors and compensate the tolerances in the software. It
seems that, we should improve the implemented AGC, in order to be fast enough in
various intensity change of the environment. This can be done by implementing a fuzzy
logic in the AGC algorithm. Improvement in Optical Flow calculation is one of the other
aspects that we are going to work on. Finally, in order to improve the field of view, we
should join two such systems as the left and right eyes of the system. The second system
can also be seen as the redundancy system.
U10EC055, ODD SEMESTER 2013-2014 Page36
CHAPTER-7 OPTICAL TACTILE SENSOR ORIENTED ON BIO-
APPLICATION
7.1 Abstract:-
A new class of optical pressure sensors in a robot tactile sensing system based on PDMS
(Poly-dimethyl-siloxane) is presented. The sensor consists of a tapered optical fiber,
where optical signal goes across, embedded into a PDMS-gold Nano composite material.
By applying different pressure forces onto the PDMS-based Nano composite, changes of
the optical transitivity of the fiber can be detected in real time due to the coupling
between the gold Nano composite material and the tapered fiber region. The intensity
reduction of the transmitted light is correlated to the pressure force magnitude. A
sensitivity in the order of 5 grams is checked. As preliminary results, the sensor is
efficiently used for detecting small notches on a beam. The experimental results are very
encouraging for foreseeing successful use of this new sensor in medical robotic
applications especially for sensing system to measure tactile information such as softness
and smoothness of biological tissues.
7.2 Introduction:-
ENSORY information of human skin for feeling materials and determining their physical
properties is
Provided by sensors on the skin. Presently, many researchers are attempting to apply the
five senses to intelligent robot systems. In particular, many kinds of tactile sensors,
combining small force sensors, have been introduced into intelligent robots. These tactile
U10EC055, ODD SEMESTER 2013-2014 Page37
sensors, which are capable of detecting contact force, vibration, texture, and temperature,
can be recognized as the next generation of information collection system. Future
applications of implemented tactile sensors include robotics in medicine for minimally
invasive microsurgeries, military uses for dangerous and delicate tasks, and automation in
industries. Some tactile sensors and small force sensors using micro electromechanical
systems (MEMS) technology have sensors have been realized with bulk and surface
micromachining methods. Polymer-based devices that use piezoelectric polymer films
such as poly vinylidene fluoride (PVDF) for sensing have also been constructed; but,
polymeric piezoelectric materials are not the only ones used for sensing applications.
There are a lot of different polymers investigated for this kind of application and oriented
on MEMS technology. Although these sensors offer good spatial resolution due to the use
of MEMS techniques, they still pick out problems in applications for practical systems. In
particular, devices, that incorporate brittle sensing elements such as silicone based
diaphragms or piezo resistors, are not reliable for robotic manipulation .Previous efforts
have been hindered by rigid substrates, fragile sensing elements, and complex wiring.
Moreover, the polymeric solutions found in literature for fabrication of pressure sensor
systems. Require complex fabrication processes and post processing analysis.
All these drawbacks can be compensated by utilizing flexible optical fiber sensors and
transducers. In addition, optical fiber sensors are immune from electromagnetic fields,
can be easily multiplexed and integrated with small led sources, thus, providing a good
alternative for the implementation of robotic tactile sensors . Moreover, the proposed
optical fiber sensor is obtained by means of a simple fabrication process: the used Nano
composite material which the fiber is embedded in is achieved simply by chemical
reduction that allows to obtain Nano/micro gold particles in the polymeric material (gold
Nano composite material, GNM).
The use of elastomer such as poly dimethyl-siloxane has many advantages over silicon or
glass. PDMS is cheaper than silicon, it is more flexible and it bonds easier to other
material than silicon or glass do. PDMS conforms to the surface of the substrate over a
large area and can adjust to surfaces that are non-planar. PDMS is a homogenous and
optical transparent material down to about 300 nm. PDMS is waterproof and permeable to
U10EC055, ODD SEMESTER 2013-2014 Page38
gases. The surface properties of PDMS can easily be changed by exposure of the surface
in oxygen plasma. This way PDMS can bond to other materials that have a wide range of
free energies. Despite all the advantages the use of PDMS provides, there are some
problems with PDMS. Gravity, adhesion and capillary forces stress the features of PDMS
leading to collapse which defects the created pattern. The adhesion between the stamp
and the substrate can also cause sagging of the structures. PDMS is a shrinking material
which can defect the structure of the pattern. It can also swell due to chemical reaction
with some kind of nonpolar solvents such as toluene. PDMS polymer film was chosen for
the proposed sensor due to its ability to generate gold nanoparticles starting from gold
precurson. Additionally, PDMS presents good elastomeric properties which permit to
obtain a real time pressure sensor response of 0.6 sec. The use of GNM for the detection
process is simpler compared to the approaches presented in literature. The GNM supports
the light coupling with a tapered multimodal optical fiber and does not require complex
layouts, such as membrane type devices obtained by photolithography processes. The
information of the pressure detection is included in the optical transitivity response which
decreases by applying pressure forces.
The transitivity intensity can be detected and directly converted in an electrical signal by
a photodiode, and processed by a proper electronic circuit suitable for robotic
implementation. Therefore, we present a newly designed optical fiber, high responsive
force sensor based on electromagnetic (EM) coupling effect.
Tactile Sensor Description:-
The sensors is illustrated in, and it is schematized a possible medical implementation
including endoscopic approach. An optical ray coming from a broad lamp source is
dispersed inside the gold Nano composite material when the sensor is pressed on a
surface: this effect is due to the electromagnetic coupling of the tapered fiber with the
PDMS-Au material which provides reduction of the transmitted signal. The gold
nanoparticles formed in the PDMS material are expected to increase the effective
refractive index of the PDMS and support the electromagnetic coupling with the tapered
region of the fiber since the transmitted light tends to preferentially propagate into the
U10EC055, ODD SEMESTER 2013-2014 Page39
high refractive index regions. The pressure applied on the GNM introduces a
displacement of the nanoparticles along its interface with the tapered fiber increasing the
light scattering: the nanoparticles thus increase the coupling of light with the GNM,
reducing the transmitted light intensity of the optical fiber. Regarding the modifications
of the optical properties of the GNM, the effect of the nanoparticle displacements due to
the applied pressure is to change the effective refractive index of GNM as a function of
gold concentration. In particular the gradual variation of the GNM effective refractive
index is higher near the contact interface of the tapered fiber, and, lower towards the
pressure contact surface. A sensitivity of few grams is checked.
.
Biological application
The Proposed sensor should be used developed as a robotic indenter to measure soft
tissue during surgery (as for abdominal region in laparoscopic). Moreover tactile sensing
techniques may distinguish tumor from healthy tissue and have potential for
intraoperative tumor diagnosis. The aim of the study is to develop a biocompatible real-
time sensing system to measure tactile information such as softness and smoothness of
biological tissues. Moreover, by reducing the dimensions, the proposed sensor should be
used for minimal access surgery (MAS). Important properties such as tissue compliance,
viscosity and surface texture, which give indications regarding the health of the tissue,
cannot easily be assessed. The proposed technology can be addressed from different
U10EC055, ODD SEMESTER 2013-2014 Page40
viewpoints including those of the basic transduction of tactile data (tactile sensing), the
computer processing of the transduced data to obtain useful information (tactile data
processing) and the display to the surgeon of this information (tactile display).
Applications of tactile sensing in MAS, both to mediate the manipulation of organs and to
assess the condition of tissue, are under investigation.
7.3 Conclusion:-
A PDMS-Au Nano composite optical sensor is analyzed. The high sensitivity of the
tactile sensor allows to detect roughness and could be used to detect different tissue
anomalies such lesions or tumors. Mechanical improvement and medical implementation
are under investigation.
U10EC055, ODD SEMESTER 2013-2014 Page41
CHAPTER :-8 OPTICAL BIO-CHEMICAL SENSORS ON SNOW
RING RESONATORS
8.1 Abstract: -
The novel ring resonator based bio-chemical sensors on silicon nanowire optical
waveguide (SNOW) and show that the sensitivity of the sensors can be increased by an
order of magnitude as compared to silicon-on-insulator based ring resonators while
maintaining high index contrast and compact devices. The core of the waveguide is
hollow and allows for introduction of biomaterial in the center of the mode, thereby
increasing the sensitivity of detection. A sensitivity of 243 nm/refractive index unit (RIU)
is achieved for a change in bulk refractive index. For surface attachment, the sensor is
able to detect monolayer attachments as small as 1 °A on the surface of the silicon
nanowires.
8.2 Introduction:-
Optical biosensors have attracted considerable attention in the last decade because of their
promise to contribute to major advances in medical diagnosis, environmental monitoring,
drug development, quality control, and homeland security. Compared to electrical
transducers, optical sensors provide significant advantages because of their small size,
immunity to electromagnetic interference, ease of multiplexing using wavelength
encoding, and capability of remote sensing. Optical sensors can be broadly characterized
in two categories: fluorescence based detectors and label-free detectors. In fluorescence
based detectors, the target molecules are labeled with fluorescent tags such as dyes and
the fluorescence is detected in presence of the targeted molecule. This allows for
extremely sensitive detection down to a single molecule. However, the process is
laborious and may also affect the function of the biomolecules. Further, precise
quantitative measurements are difficult as the number of flourophores attached to the
U10EC055, ODD SEMESTER 2013-2014 Page42
targeted molecules cannot be controlled. In contrast, in label-free detection the targeted
molecules are detected in their natural form. The targeted molecules are surface attached
to the optical sensor using probe molecules and the attachment is detected by measuring
the change in optical properties for the sensor. Sensors based on silicon-on-insulator
(SOI) photonic wire waveguides have attracted considerable attention because of
compatibility with CMOS fabrication and possibility of integrating detection and decision
on the same chip leading to ‖laboratories on a chip‖. Further, guided-wave sensors allow
for integration of multiple sensors on a single chip. As such, different sensors based on
directional couplers, Mach-Zehnder interferometers, Bragg grating based Fabry-Perot
resonators, micro disks, microtoroids, photonics crystal cavities, micro ring resonators,
and slot waveguides have been demonstrated. In these sensors, the targeted molecule is
probed by light guided through a solid medium using the evanescent field. The lower
refractive index surrounding medium (typically water with refractive index ∼ 1.3253) is
displaced by higher refractive index organic molecules (n ∼ 1.45−1.6) changing the
effective index of the propagating mode resulting in a spectral shift of the resonant cavity
which can be measured directly. Mach-Zehnder interferometers,
Fabry-Perot resonators, micro disks, photonic crystal cavities, and ring resonators have
Been demonstrated using silicon photonics .Fabricated SNOW consists of 9 rows of
800nm-long SiNWs with diameter of 40 nm. And the requirement of large interaction
length to increase the sensitivity. Bragg-reflectors for Fabry-Perot resonators are difficult
to fabricate in high-index contrast materials resulting in high insertion losses. Photonics
crystal cavities are also difficult to produce with low propagation losses and it is difficult
to couple light in and out of these waveguides reproducibly. Micro disks have higher
whispering gallery modes which can overlay on the fundamental characteristics making
detection difficult. As such, ring resonators offer most attractive solution as they provide
low insertion loss, single mode cavities, and small form factors. Ring resonators offer a
compelling solution as multiplexing different sensors on a single chip using wavelength is
U10EC055, ODD SEMESTER 2013-2014 Page43
possible by simply changing the diameter of the ring in the resonator. Biochemical
sensors based on SOI photonic waveguides have been studied extensively. In, a 70
nm/RIU sensitivity was achieved for bulk changes of refractive index and a 625 pm shift
of wavelength was achieved for label-free sensing of proteins. The sensitivity can be
further increased by using a slot-waveguide which an optical waveguide is guiding light
in a sub wavelength-scale low refractive index region sandwiched between two ridges of
high index. This enhances the transverse electric field in the slot thereby increasing the
interaction of the optical field with the targeted molecules. An increased sensitivity of 298
nm/RIU was achieved with a foot-print of 13 μm×10 μm. However, the problem with slot
waveguides is the difficulty with introduction of fluids within the slot region. Further
since the slot waveguide works in the quasi-TE mode, it is lower modal index waveguide
compared to SOI waveguides. The proposed and analyzed a new kind of optical
waveguide consisting of arrays of silicon nanowires (SiNWs) where the diameter of the
SiNW is smaller than 75 nm for 1550 nm wavelength. A fabricated waveguide is shown.
For this sample, it consists of 9 rows of 40 nm diameter nanowires with a pitch of 100
nm. The length of the nanowires is 800 nm. If the diameter is less than 75 nm, the
diffraction of light through the SiNWs is limited (provided the electric field is polarized
along the length of the nanowires) and the medium starts to behave like an effective index
medium, thereby guiding light through the structure with very low propagation losses (<
0.2 cm−1). Vertical confinement is provided by the refractive index contrast between the
silicon and the insulator. Unlike, photonic band gap structures, the nanowires do not need
to be aligned in a crystal and can be randomly arranged with minimal excess losses.
Further, the scattering due to side wall roughness results in minimal excess losses. We
have also shown that waveguides with bends of radii smaller than 5 μm can be designed
on the SNOW structure with low loss (less than 0.06 dB per 360◦ turn). Such geometries
have been achieved using electron-beam lithography and BOSCH etching of silicon
mainly for solar cells. Further, we have been able to fabricate SNOW structures with
nanowire diameters and pitch as small as 15 nm and 75 nm respectively. While we are
still in process of measuring optical properties of these waveguides, previous
experimental works show that it should be feasible to guide light through these structures.
Optical loss as low as 0.023 dB/crossing was achieved with a waveguide which worked
as an effective index medium, similar to SNOW .Gain and stimulated emission was
observed in Nano patterned silicon. The device consisted of 100 nm thick arrayed sub
wavelength structures on a SOI wafer cleaved into 1 mm long devices, again working like
U10EC055, ODD SEMESTER 2013-2014 Page44
an effective index waveguide. Fabry-Perot characteristics in the emission demonstrated
guidance of light in the 100 nm patterned silicon layer of the device and corresponded
well with the effective index calculations. These experiments along with experimental
fabrication of SNOW strongly suggest that guidance of light should be possible with the
structures. Even over a bend, the effective index approximation works well. This allows
for designing and building of ring resonators on the SNOW especially for biochemical
sensors. The advantage of SNOW is apparent from the fact that it is a hollow core
waveguide and thus it is possible to introduce the bio-chemical agents in the region of
highest optical field intensity. In this paper, we propose a ring resonator structure with
SNOW in the ring excited by a SOI bus waveguide. We show that the sensitivity is
increased by an order of magnitude compared to the SOI waveguides while achieving a
compact structure.
8.3 Sensor Structure:-
In order to be able to fabricate ring resonators, it is important for the SNOW region to
support waveguide bends. This shows the radiation loss through a 360◦ turn in the SNOW
region as the radius of the bend is changed. For this simulation, the polarization is along
the length of SiNWs and the wavelength of operation is 1550 nm. The diameter of the
silicon nanowires is 50 nm and the pitch between them is 75 nm, similar to what we had
previously proposed. The height of the nanowires is 700 nm. He SNOW region has an
effective index of 2.2 when air is surrounding the medium. The width of the SNOW
region is 650 nm. At this width, the second order mode in the ring is supported but does
not get excited because of the symmetry rules. Further, the radiation loss for the second
order
U10EC055, ODD SEMESTER 2013-2014 Page45
Mode over the bend is appreciably higher compared to the fundamental mode. Also
plotted in the figure, is the radiation loss when the effective-index approximation shown
in is used and SNOW is approximated by a rib waveguide. All the simulations are done
using the finite-difference time domain (FDTD) method with a grid size of 2 nm for
SNOW and a grid size of 10 nm for the effective-index approximation. The simulations
were done in 2-dimensions by using effective index method in the vertical direction to
decompose a 3-D structure into planar waveguides. The method was tested by comparing
results using 3-D simulations with 2-D for few samples. For all the simulations, the
electric field was polarized along the length of the nanowires which corresponds to quasi-
TM polarization for conventional waveguides. At 700 nm waveguide height, the optical
mode is highly confined in the vertical direction and the effective index approximation
works well. It is clear that the loss through the bend is mainly dominated by the caustic
radiation and not by the radiation due to scattering from the individual nanowires. For a
radius of 5 μm, the radiation loss over a 360◦ turn is 4.6×10−4dB.
These simulations show the appropriateness of using SNOW for bends and allow for
fabricating ring resonators on the structure. The proposed structure is shown in. A SOI
waveguide is used as a bus waveguide feeding into a ring consisting of SNOW with
parameters described above. Use of SOI waveguides allows for conventional input and
output optical coupling into the structure resulting in low insertion losses.
The bus waveguide has a width of 100 nm and has the same height (700 nm) as the
SNOW ring. At this width, the bus waveguide is purely single mode. Separation between
the waveguides is adjusted to 100 nm between the end of the bus waveguide and the first
nanowire in the SNOW and achieves critical coupling condition for the ring resonator.
Figure shows the lateral cut of the FDTD propagation of the electric field through the ring
resonator at a wavelength of 1550 nm (not the resonance wavelength) over a few cycles
within the ring. One can clearly see that the SNOW ring is guiding the electric field with
very little radiation happening in the structure. Figure 5 shows the lateral cut of the
electric field through the SNOW structure for the parameters defined above. The lateral
cuts for a straight SNOW and over a bend are shown. Lateral cut for the 200 nm wide
straight SOI waveguides is also shown. Within the effective-index waveguide, the
U10EC055, ODD SEMESTER 2013-2014 Page46
confinement factor for the SNOW is 94 % resulting in the low bend losses as shown in.
The confinement factor for the optical mode within silicon in the SNOW region is only
32 % whereas for a 200 nm SOI waveguide, it is 76 %. The optical mode is better guided
in the SNOW region as compared to the 200 nm SOI waveguide, and the modal power in
the
Color online) Lateral cut of the FDTD propagation of electric field through the
SNOW ring resonator. Surrounding region is larger in the SNOW as compared to the 200
nm SOI. Thus, it should be possible to increase the sensitivity while still achieving
compact devices.
Sensor characteristics for bulk refractive index change
We first calculated the response of sensor for bulk change in the refractive index of the
surrounding medium. The SNOW structure is compared with a SOI waveguide ring
resonator where the width of the SOI waveguide is 200 nm, similar to. The geometric
parameters for the two compared devices are shown in Table I. For the first set of
simulations, the refractive index of the surrounding medium was changed and the
effective index of the guided optical mode through SNOW was calculated. Figure 6
shows the change of effective index of the optical mode as a percentage with respect to
the value of effective index as the surrounding refractive index is changed from 1.0 to 1.6
for the SNOWand the 200 nm SOI waveguide at a wavelength of 1550 nm. For the
SNOW, the effective index changes by a factor of approximately 4 large as compared to a
U10EC055, ODD SEMESTER 2013-2014 Page47
200 nm SOI waveguide for the same change in surrounding refractive index. In a ring
resonator the change of the resonance wavelength is approximately given by
Δλ =Δne f fλng(1)
Where Δne f f is the change of the effective index due to the change of the refractive
index of the surrounding medium, λ is the initial resonance wavelength and ng is the
group index. This suggests that an improvement in sensitivity of 4 is expected if one uses
a SNOW ring resonator as compared to a 200 nm wide SOI waveguide resonator.
A wavelength shift of 12.2 nm is achieved for the SNOW ring resonator resulting in a
sensitivity of 243 nm/RIU. For the 200 nm SOI waveguide, the wavelength shift for the
same refractive index change is 3.14 nm resulting in a sensitivity of 63 nm/RIU.
This compares well with the experimental value of 70 nm/RIU for a slightly higher bulk
refractive index. An improvement by a factor of 3.9 is seen in the sensitivity for the
SNOW ring resonator compared to the 200 nm wide SOI waveguide for bulk change of
refractive index. We also studied the effect on sensitivity as the width of the SNOW
region is changed. The ring resonator coupling was adjusted individually to achieve
critical coupling. The diameter and pitch for the SiNWs are kept the same. An increase of
sensitivity is observed when the waveguide width is decreased, reaching a value of 335
nm/RIU for a width of 300 nm.
The surrounding index is again changed from 1 to 1.05. An improvement by a factor of
5.3 is observed as compared to the SOI waveguide. The behavior exhibited by the SNOW
ring resonator is similar to that of the SOI ring resonators as the width is decreased. This
is because of the increased evanescent field as the width is decreased.
In optical sensors, surface sensing plays an important role for a wide range of
biochemical applications including DNA hybridization, antigen-antibody reactions,
protein attachments etc. A layer of receptor molecules is surface attached to optical sensor
and selective attachment is done for the targeted molecule. Since the refractive index of
the molecules is different from the surrounding medium which is typically water based, a
change of index happens at the surface of the sensor which is measured for detecting the
presence of the molecule.
U10EC055, ODD SEMESTER 2013-2014 Page48
The SNOW ring resonator was simulated for surface attachment of the molecules. A
molecule layer with the test thickness was assumed to be attached the surface of the
SiNWs. Water was considered as the surrounding medium with a refractive index of
1.325 at a wavelength of 1550 nm. The refractive index of the molecule attached is
considered to be 1.6, similar to 3-aminopropyltriethoxysilane (APTES) which we have
measured previously and controllably attached different thickness on the surface.
Structures summarized in Table I were compared. Wavelength shift of 0.35 nm and 3.1
nm and is achieved with a 0.1 nm and 1 nm attachment of the molecule. For these thin
layers, the surface attachment increases linearly with the thickness of the molecule layer.
For the SOI waveguides, surface attachment was assumed over all the exposed surfaces of
silicon including the sides and the top of the waveguide. Only a 1 nm layer attachment
was considered. A wavelength shift of 0.15 nm is achieved for the attachment of 1 nm
layer thickness. This shows an improvement by a factor of 20.5 with the SNOW ring
resonator. The dependence of the width for the SNOW was also considered. Figure 10
shows the percentage change in the effective index of the SNOW structure as the
waveguide width is changed from 300 nm to 1000 nm for a 1 nm thickness of the
attached molecule layer. As opposed to the change in bulk refractive index, the behavior
is different and the sensitivity increases as the width is increased. This is because the
sensor is not working in the evanescent field but within the core of the optical mode. As
the width is increased, the optical mode gets more confined within the SNOW region
resulting in higher interaction with the surface attached material.
5.
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8.4 Conclusion:-
The SNOW ring resonator consists of a SOI bus waveguide coupled into a ring
waveguide consisting of closely etched silicon nanowires acting as an effective index
waveguide. We have compared the proposed sensor to the SOI photonic wire based
sensors. For bulk refractive index changes, an improvement by a factor of 5.3 is achieved
with the SNOW sensor compared to that of the SOI. For surface attachment, an
improvement by a factor of 20.5 is achieved for the SNOW sensor.
U10EC055, ODD SEMESTER 2013-2014 Page50
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