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Alan Schilowitz, Andy Riley, Dalia Yablon, Mark DiskoExxonMobil Research and Engineering Co.
Corporate Strategic Research Laboratory
Annandale, New Jersey
Ultra-Sensitive Microsensors for Chemical Analysis
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Why Microsensors ?
• High sensitivity
• Low power consumption– Enables wireless– Improved safety
• Redundancy– Potential for large number of parallel sensors
• Portability– Personal monitoring (e.g. badges)
• Small sample size
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How Many Cantilevers Can Fit on the Head of a Pin ?
2 mm
• Two Modes of Operation
– Dynamic
– Static
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Micro-Cantilevers Background
• Extension of Atomic Force Microscopy- Some experiments carried out in Atomic Force Microscope head- Ultrahigh sensitivity to mass change
• Use for chemical measurement pioneered by Thundat (ORNL) and Gerber (IBM Zurich)
• Applied to analysis of gas and aqueous solutions
• Cantilevers commercially available in variety of shapes and materials- Range of resonant frequencies, spring constants, shapes
Focusing Lens
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• Dynamic Mode – Increasing viscosity changes resonance spectrum– Ultra sensitive to mass changes
• Cantilevers can be driven with piezo-electric crystal
• Mass build-up changes resonant frequency − Viscosity change alters resonant frequency and width of spectrum
0 2000 4000 6000 8000 10000 12000Frequency (Hz)
Am
pli
tud
e
Air
Increasing Viscosity
Analysis in Dynamic Mode
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Cantilevers Respond to Viscous Damping
Viscosity = 5.238 Q-1.88
R2 = 0.9971
0
1
2
3
4
0 1 2 3 4 5
Q
Vis
co
sit
y (
cP
)Frequency
Am
pli
tud
e
Frequency
Am
pli
tud
e
High Q Low Q
Increasing Viscosity
• Viscosity can also be measured by frequency change– Less sensitive than Q
• Measurements can be made on micro liter samples
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Chemical Analysis in Static Mode
• Detection limit is in sub picogram range
Selective adsorbant on one side only
-50
0
50
100
150
200
250
200 300 400
Time (minutes)C
anti
leve
r D
efle
ctio
n (
nm
)
UntreatedCantilever
Gold Coated Cantilever Detects Mercaptans
Mercaptan Injection
• Static Mode - coated cantilevers respond to adsorption- Detect deflection of cantilevers coated on one side
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Functionalized Cantilever Arrays for Aromatics Detection
Self-Assembled Monolayer
Candidates:
SH
Benzyl Mercaptan
SH
Naphthalenethiol
SH
OH
Mercaptohexanol
SH
( )6
Octadecanethiol
Self-Assembled Monolayers Impart Chemical Selectivity to Highly Sensitive Cantilever Transducers
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S
OH
S
S
( )6
S
Cantilever Response To Aromatic Vapor
• Cantilevers exposed to aromatic vapor (parts per thousand) in laboratory air
• Treated cantilevers have unique response to aromatics
-35
-25
-15
-5
5
15
0 200 400 600 800 1000 1200Time (s)
Def
lect
ion
(nm
)
-35
-30
-25
-20
-15
-10
-5
0
5
10
15
0 200 400 600 800 1000 1200 1400 1600
Time (s)
Def
lect
ion
(nm
)
-35
-25
-15
-5
5
15
450 950 1450 1950
Time
Def
lect
ion
(nm
)
-35
-25
-15
-5
5
15
0 500 1000 1500Time (s)
Def
lect
ion
(nm
) toluene xylene
toluene xylene
d. ODT - octadecanethiol
c. MH - mercaptohexanol
b. NT - naphthalenethiola. BM – benzyl mercaptan
toluene xylenetoluene xylene
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Summary
• Micro-Cantilever sensor applications
– Viscosity on micro-liter samples– Potential for sub picogram chemical sensitivity
• Chemical specificity with Self Assembled Monolayers (SAM)
• Potential for applications where:– Sample size is limited– Large scale redundancy is desirable– Low power consumption is necessary
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Medical Applications
Light traces are before exposure to e-coliDark traces are after exposure
mk /
B. Illic et.al., Appl. Phys. Lett. 77(3), 450 (2000)
W. Guanghua et.al., Nature Biotechnology 19, 856 (2001)
Prostate Specific Antigen (PSA) Sensor
E-Coli Sensor
• Vibrational frequency reduced as cells bind to cantilever
– Frequency =
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References - Medical Applications
Rapid and label-free nanomechanical detection of biomarker transcripts in human RNA Zhang, J.; Lang, HP.; Huber, F.; Bietsch, A.; Grange, W.; Certa, U.; McKendry, R.; Guntherodt, HJ.; Hegner, M. & Gerber, Ch. Nature Nanotechnology, 1, 214-220 (2006).
Novel electrical detection of label-free disease marker proteins using piezoresistive self-sensing micro-cantileversWee KW, Kang GY, Park J, Kang JY, Yoon DS, Park JH, Kim TSBiosens Bioelectron 2005 Apr 15;20(10):1932-8
Array of Nano Cantilevers as a Bio Assay for Cancer DiagnosisKlein, K.M.; Jiantao Zheng; Gewirtz, A.; Sarma, D.S.; Rajalakshmi, S.; Sitaraman, K.Electronic Components and Technology Conference, 2005. Proceedings. 55thVolume , Issue , 31 May-3 June 2005 Page(s): 583 - 587
A Review of Microcantilevers for Sensing ApplicationsVashist, S.K., June 2007www.azonano.com/details.asp?ArticleID=1927