Inkjet Printing as a Tool for the Inkjet Printing as a Tool for the Fabrication of Conducting PolymerFabrication of Conducting Polymer--
Based Sensors & BiosensorsBased Sensors & Biosensors
Dr. Aoife Morrin
The National Centre for Sensor ResearchThe National Centre for Sensor Research1
National Centre for Sensor Research
School of Chemical Sciences
Dublin City University
Ireland
OverviewOverview
1. Introduction
2. Inkjet printing of conducting polymer
3. High specification, flexible, inkjet printed gas sensor platform
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3.gas sensor platform
4. Biosensor fabrication & application
OverviewOverview
1. Introduction
2. Inkjet printing of conducting polymer
3. High specification, flexible, inkjet printed gas sensor platform
The National Centre for Sensor ResearchThe National Centre for Sensor Research3
3.gas sensor platform
4. Biosensor fabrication & application
IntroductionIntroduction
• Advances in materials and engineering are paving the way for new and more capable sensors
• Most recent advances are not originating from new transduction materials, but more from materials and innovations that reduce overall cost and improve quality
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• ‘Enabling technologies’ are principle drivers in sensor fabrication development
Printed SensorsPrinted Sensors• Mass market application areas
• High demand for low-cost, mass-producible sensor products in specific key markets such as point-of-care medical diagnostics and smart packaging, remote environmental sensing, etc….
• Early 1980s saw the enormous commercial success of the screen-printed glucose biosensor
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• 9 billion glucose tests performed annually
• Inkjet printing – set to surpass screen-printing???
• Today we have more sophisticated materials available…
Enabling Technology: Inkjet Enabling Technology: Inkjet Printing….Printing….• Rapid, reproducible, cheap way to manufacture sensors• Easily scaled up, suited to large and small production volumes• Quality control in real time• High precision, claiming a resolution of ~ 25 µm• Thin film deposition (nm). Thinner films can yield faster response times• Amenable to simultaneous deposition of more than one material – multi-component layers, microarrays•
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• Sensor optimisation through combinatorial printing• Non-contact printing (substrate and print head don’t touch), suitable for fragile substrate e.g., membranes• Aqueous solution are printable – important for biological species• Low wastage, important for precious materials• Flexible design process• ………..
…..Combined With Processable, …..Combined With Processable, High Quality Sensing Materials….High Quality Sensing Materials….
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Interesting Functional Materials for Sensing Include:Electroactive/Optically active materials
Conducting PolymersMetallic Inks
Biomolecules for BiosensingMembranes
….
OverviewOverview
1. Introduction
2. Inkjet printing of polyaniline
3. High specification, flexible, inkjet printed gas sensor platform
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3.gas sensor platform
4. Biosensor fabrication & application
• Suitable for chemical sensing
of acids and bases through its
excellent doping/dedoping
capabilites
• Desirable material for
Sensor Platforms Based on Sensor Platforms Based on PolyanilinePolyaniline
NH2
Aniline Monomer
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• Desirable material for
biosensing because of its good
redox properties and hence can
act as a diffusionless mediator
for electron transfer between
enzyme centres and the
electrode transducer
Doped Polyaniline (conductive state)
• Developing various electrochemical sensor/biosensor
platforms using polyaniline-based polymers
• Examining various sensor fabrication approaches such as
• electrochemical deposition
• nano-templating
• printing approaches
PANIPANI--based Sensor Researchbased Sensor Research
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• printing approaches
• Printing methods permit processability, low cost and
disposability
• Aiming to demonstrate that inkjet printing, combined with the
right materials is a feasible, valid approach to sensor fabrication
Back In The Old Days….Back In The Old Days….
• Glassy Carbon Electrode Platform
• Traditional 3-electrode cell setup to electropolymerise PANI films to electrode surface
Auxiliary Electrode
Working Electrode
Reference Electrode
N2 in
Supporting electrolyte
(with analyte)
Potentiostat (for control and analysis of response)
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• Works really well, but laborious fabrication procedure
• How to translate into a commercially relevant product??
Potential (V)
-0.4-0.20.00.20.40.60.81.0
Cu
rre
nt (µ
A)
-100
-50
0
50
ScreenScreen--Printing for Electrode Printing for Electrode FabricationFabrication
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l Low start up and manufacturing cost
l Mass production
l Disposability
l Platform for glucose biosensor industry
3 cm
1 cm
Inkjet Printing of Silver for Inkjet Printing of Silver for Electrode FabricationElectrode Fabrication
Silver Inter-Digitated Array (IDA) Single Electrode
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• Commercial Ag product
• ~ 1 Ω cm-1 (1 layer)
• Challenge will be to print inert carbon electrode layers comparable to screen-printed carbon
• Can print gold or platinum as alternatives
Modifcation of Electrode: Modifcation of Electrode: Processable PANIProcessable PANI
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• New, processible materials
• Water-soluble, or stable nanodispersions
• High processibility
• Aqueous-based
• Good redox activity and conductivity
PANI Nanodispersion PANI Nanodispersion CharacterisationCharacterisation
0
10
20
30
1 10 100 1000 10000
Diameter (nm)
Volu
me (%
)
< 100 nm diameter
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No Stabiliser Present* DBSA Stabiliser Present
*Jiaxing Huang, Richard B. Kaner, Angew. Chem. Int. Ed. 2004, 43, 5817-
5821
Inkjet Printing of PANIInkjet Printing of PANIMulti-Head Desktop Epson Inkjet Printer
Commercial Research Fuji Dimatix Printer
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Inkjet Printed PANI ElectrodesInkjet Printed PANI Electrodes
•• PANI nanodispersions inkjet printed onto IDAs for gas
sensor platform
• Also printed to carbon paste working electrodes
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Resulting ‘Smooth’ MorphologyResulting ‘Smooth’ Morphology
(a) Bare SPE (b) 10 Prints
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(c) 20 Prints (d) 30 Prints
MorphologyMorphology
1 print
1 cm1 cm
40 prints
1 cm
10 prints
1 cm1 cm
4000
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Elimination of classic drop-coated ‘coffee-ring effect’
No. of Prints of PANI
1 5 10 20 30 40
Film
Th
ickn
ess (
nm
)0
1000
2000
3000
OverviewOverview
1. Introduction
2. Inkjet printing of conducting polymer-based sensor
3. High specification, flexible, inkjet printed
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3. High specification, flexible, inkjet printed gas sensor platform
4. Biosensor Fabrication & application
Ammonia SensingAmmonia Sensing• Ammonia is a highly toxic chemical species
• Classified as a major pollutant
• The ammonia sensing industry spans a wide range of markets
• Mature market, lacking in innovation
• Niche for low-cost portable sensors e.g., for health & safety
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Detection Mechanism Detection Mechanism –– Gas SensingGas Sensing• Conductimetric mode
– 2 electrode cell
• Ammonia deprotonates PANI backbone
– Emeraldine salt (ES) to emeraldine base (EB) form
– Decrease in
N
H
N N
H
N
Hn
N
H
N N N
H
Emeraldine Salt
Deprotonatedby NH3
+ (NH3)n
- (H+)n
+•
•• ••
••
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– Decrease in conductivity
• Apply potential to IDA
– current flows through PANI film
– Vapp : step or ramp
• Measure change in current on NH3 exposure
H Hn
Emeraldine Base
Vapp
Imeas
Vapp
Imeas
PANI (ES) PANI (EB)
+ NH3
- NH3
Increasing Print Layers Increasing Print Layers –– Increasing Increasing Current Current
• Sequential inkjet printed layers– Quasi-linear
increase from 1 – 10 layers
– Begins to plateau
µA
400
500
600
µA
400
500
600
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– Begins to plateau above 10 layers (inset)
– Thicker layers do not seriously effect response/recovery times – porous film
No. of PANI layers
0 2 4 6 8 10
Sa
mple
d c
urre
nt /
0
100
200
300
y = 60.4 x - 67.2r ² = 0.9939200x1500 IDAn = 3
No. of Layers
0 5 10 15 20 25
No. of PANI layers
0 2 4 6 8 10
Sa
mple
d c
urre
nt /
0
100
200
300
y = 60.4 x - 67.2r ² = 0.9939200x1500 IDAn = 3
No. of Layers
0 5 10 15 20 25
No
rmalis
ed s
am
ple
d c
urr
en
t
0.6
0.8
1.0 T50
T90
Sensor Response TimesSensor Response Times
• Response times for PANI IDA (n=4)– t50 ~ 15 s
– t100 < 60 s
• ~ 60 ppm NH3
Exposed to
NH3 vapour
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Time / s
0 15 30 45 60 75 90 105 120 135 150 165 180
No
rmalis
ed s
am
ple
d c
urr
en
t
0.0
0.2
0.4
• 3
• Response times currently within those specified by ISA (Instrument Society of America)– t50 < 90s
Flexible Heater SubstrateFlexible Heater Substrate
• MincoTM thermofoil heaters
• Thin and flexible– fast temperature equilibration
• up to 200°C– sub 100°C used for PANI
sensors
• Compatible with inkjet printing
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• Compatible with inkjet printing
• Possibility of printing directly to heater substrate
Inkjet printed PANI
Silver IDA on PET substrate
Flexible heating foil
No
rmalis
ed c
urr
ent
0.6
0.8
1.0Non-heated
50 C
60 C
70 C
80 C
Response Behaviour Using Response Behaviour Using Flexible Heater SystemFlexible Heater System
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Time / s
0 500 1000 1500 2000 2500 3000 3500
No
rmalis
ed c
urr
ent
0.0
0.2
0.4
0.6
Increasing temperature reduces sensitivity to increase linearity over relevant range
Sensor Recovery Using Flexible Sensor Recovery Using Flexible Heater SystemHeater System
No
rma
lis
ed
cu
rre
nt
0.6
0.8
1.0
Time / s
0 500 1000 1500
1.0
• Room Temp recovery > hours
• 80°C recovery < seconds
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Time / s
-100 0 100 200 300 400
No
rma
lis
ed
cu
rre
nt
0.0
0.2
0.4
No
rma
lis
ed
cu
rre
nt
-2.0
-1.5
-1.0
-0.5
0.0
0.5
log (
ln(I
0 -
I))
0.35
0.40
0.45
0.50
[NH3] / ppm
0 20 40 60 80 100
Cu
rrent /
µA
0.00.20.40.60.81.01.21.41.61.8
r ² = 0.9971
Quantitative AnalysisQuantitative Analysis
PANI IDA sensor is far
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[NH3] / ppm
2 4 6 8 20 40 60 801 10 100
0.20
0.25
0.30 PANI IDA sensor is far
superior when compared
with a commercial sensor
– Honeywell NH3 sensor
– Zellweger Impulse XP
– 1 - 100 ppm range
Extension to Inkjet Printed Extension to Inkjet Printed Gas Sensor ArrayGas Sensor Array
• Recently received ‘Proof of Concept’ Funding to
build an inkjet printed gas sensor array
• Gases including H2S, CO, Cl2 and NO2
• Exploit inkjet printing to fabricate arrays of
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• Exploit inkjet printing to fabricate arrays of
polymer (polyaniline?) layers modified to be
selective towards specific gases
OverviewOverview
1. Introduction
2. Inkjet printing of conducting polymer-based sensor
3. High specification, flexible, inkjet printed gas
The National Centre for Sensor ResearchThe National Centre for Sensor Research30
3. High specification, flexible, inkjet printed gas sensor platform
4. Biosensor fabrication & application
BiosensorBiosensor
Signal Processor
Target Analyte
Induces
Physical
or Chemical
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Transducer
Biomolecule
Signal Processor
Digital
Signal
Matrix
or Chemical
Change
Inkjet Printed Biosensor PublicationsInkjet Printed Biosensor Publications
> 13,000 hits for ‘biosensor’ on Web of Science
> 500 Peer-Reviewed Publications on ‘screen-printed and biosensor’
Just 10 Peer-Reviewed Publications on ‘inkjet and biosensor’!!!
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Field: Publication
Year
RecordCount
% of 10
Bar Chart
2002 1 10.0000 %
2004 4 40.0000 %
2005 3 30.0000 %
2006 1 10.0000 %
2006 1 10.0000 %
biosensor’!!!
Thermally Printed BiosensorThermally Printed Biosensor
• Horseradish Peroxidase (HRP) and Glucose Oxidase (GOD)-based biosensors• Thermal printing does not affect the activity of the enzymes• PEDOT/PSS electronic communication with enzyme (but employed a soluble mediator to enhance this)
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Setti et al. (2007). Sens. Actuat. (126) 252
Inkjet Printed Inkjet Printed Cantilever Array Cantilever Array
ChipsChips
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• Highly controlled deposition of inkjet printed functional layers •Demonstrated prototype as a DNA biosensor and a gas sensor array• Inkjet printing can, uniquely functionalise cantilevers individually very easily• Fast, easy to assemble, scalable
Bietsch et al. (2004). Nanotechnology (15) 873
Characterisation of hydrophilic and hydrophobic inkjet printed SAMs
8 inkjet printed polymers on individual cantilevers
ScreenScreen--Printed Carbon Paste Printed Carbon Paste ElectrodeElectrode
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Scan Rate Study
Cu
rren
t (m
A)
0.0
0.5
1.0
1.5
Electrochemistry of Inkjet Printed Electrochemistry of Inkjet Printed PolyanilinePolyaniline
Relationship of peak current with scan rate
R2 = 0.9679
-1.00E-03
0.00E+00
1.00E-03
2.00E-03
0 100 200 300 400 500
pe
ak
Cu
rre
nt
(A)
peak anodic currents
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Potential (V)
0.20.40.60.81.0
Cu
rren
t (m
A)
-1.5
-1.0
-0.5
0.0
500 mV
300 mV
200 mV
50 mV
25 mV
R2 = 0.9584
-2.00E-03scan rate (mV.s
-1)
peak anodic currents
peak cathodic currents
Relationship of peak current with (scan rate)1/2
-2.00E-03
-1.00E-03
0.00E+00
1.00E-03
2.00E-03
0 5 10 15 20 25
(scan rate)1/2
\ (mV.s-1
)1/2
pe
ak
cu
rre
nt
\A peak anodic currents
peak cathodic currents