By Valentin KulikovRegensburg 08.06.2004 Automated System for Combinatorial Synthesis and...

by Valentin KulikovRegensburg 08.06.2004

Automated System for Combinatorial Synthesisand High-throughput Characterization of

Polymeric Sensor Materials

Application in development and optimizing of sensors for gaseous hydrogen chloride (cable fire alarms)

Valentin Kulikov

Munich 2004


• Introduction to conducting polymers• Electropolymerization concept and its realization• Measurement concept and its realization• Data analysis of experiment • Influence of temperature to experiments• Optimal thickness of polymer layer • Representative results on HCl sensor based on aniline derivates• Conclusion• Outlook, application range of conducting polymers

Outlook of the presentation


One has been taught that plastics, do not conduct electricity. Usually plastics are used as insulation around the copper wires in ordinary electrical cables.

* Nobel Prize in Chemistry 2000 being awarded to Profs. A. J. Heeger, A. G. MacDiarmid and H. Shirakawa (MacDiarmid A.G., "Synthetic metals: A novel role for organic polymers (Nobel Lecture)", Angewandte Chemie, International Edition 40, 2581-2590, 2001)

In 1977 three scientistsProf. A. J. Heeger, Prof. A. G. MacDiarmid andProf. H. Shirakawacointidentaly discowered and report conductive properties of the alternating-bond conjugated polymers (Polyacetylene). They found that the polymer could be (n- or p-) doped to the metallic state and thereby transformed into a good electrical conductor.

Photo acknowledged from report of Nobel Prize in Chemistry 2000

History of conducting polymers


Conducting polymers

Polymers are molecules formed of many identical units (monomers) bound to each other. For a polymer to be electrically conductive it must "imitate" a metal – the electrons in the bonds must be freely mobile and not bound fast to the atoms. One condition for this is that the polymer consists of alternate single and double bonds, termed conjugated double bonds:

Example: Oxidation of Polyacetylene with iodine causes the electrons to be jerked out of the polymer, leaving "holes" in the form of positive charges that can move along the chain, thus leading to opening of an band gap and causes (semi)conductivity. (Nobel Prize in Chemistry 2000 )

- low weight- conductivity can be varied over a very broad area, from poor semi-conductors to metallic-level conductivity - Excellent tolerance to corrosion- large, flexible surfaces can be made relatively easily and cheaply


- electrochemical devices (ion exchangers, catalysts, batteries ...) - semiconductor electronics (wires, diodes, transistors, LEDs, displays, solar cells, ...)- supercapacitors, whole integrated circuits ...)- functional coatings (antistatic coating, electrochromic windows ...)

Wide application range of polymers

Analytical devices:

- chemical and biological sensors (immobilization of sensor components, electrical contact between electrode and enzyme or intermediator)- formation of molecularly imprinted polymers- gas sensors (HCl, NH3, O3, artificial nose ...)- many others

Target applications summary:

- Flat displays for TVs, monitors, mobile phones, terminals, etc.- Cheap solar cells for energy conversion- Sensors (artificial nose - gas, chemo-, bio-)- Cheap semiconductors for general use- Corrosion protection and electrochromic windows- many others


Electropolymerization concept

Serial synthesis

EP sequence can be randomized to form a polymer layer or ,multilayer structure. The electrodes are polymerized consequently.

Electrochemical cell

Electrode array

What can be varied?

- chemical parameters (reagents, reagents ratio, additives, ...)- physical parameters (temperature, EP potential, deposition time and charge ....)- structural parameters (thickness, number of layers, sequence, ...)

What concept should cover?

- Control of preparation and transport of target reagents- Control of addressation of electrodes- Control and synchronization of electropolymerization- Screening of EP kinetics

Polymerization

- Polymerization is process of building of blocks from monomers (mer - basic building block) - Depending on what element is added to the carbon backbone, different materials can be produced.


Addressation of electropolymerization

Electrical addressation

+ Simplest addressation technique+ No moving parts involved+ High reliability+ Electropolymerization is performed in single electrochemical cell- Constant relatively large volume of reagents required (given by size of electrochemical cell)

Mechanical addressation

- Required expensive robotic systems- Required continuous user inspection- Low reliability- High instrumentation requirements (multi-channel systems)+ Low volume of reagents involved+ Not limited amount of electrodes

Counter

Work

Multiplexer

Pot

enti

osta

t

Reference

EC

Aux

Wo

rk

Ref

EA

CounterWork

Potentiostat

Robot

Ref

Movement

Droplet of reagent

Reagent transport(e.g. syringe)

Polymer. electrode

Electrode array (EA)

Aux

Ref


Control of analytes additions

Control of meas. Electronics & Multiplexer 96 Writing of data onanalytes influence into database Measurement ofI-V characteristics or / and optical spectra

Electrical or / andoptical investigation of gases influence on combinatorial libraries

Measurement program

Measurement Combinatorial libraries of polymers(electrode array)

Design of combinatorial libraryElectropolymerization (EP)

Writing of EP data into database Measurement of cyclovoltammetry or current - time dependence

Electropolymerization

Feedback

Control of Multiplexer 96

Control of dosing station

Control of electronics for EP

Dataanalysis

polymerized electrode

Concept of combinatorial electrochemical synthesis and high-throughput investigation of their electrical properties


Electropolymerization set-up


Dosing station

A B C DCL1 CL2

2W 2W

TR

PP

3W

EA

DP DP DP DP1

2

MC

EC

MM




Electrochemical cell

Source Lo

Source Hi

Sense Hi

K24

00

Sense Lo

V

Cou

nter

Wor

k

FB

Ref

eren

ce

EC

A

General

- Three electrode system- Sat. Ag/AgCl KCL ref. electrode- central Aux and Ref. electrode- limit applications to high conduct. electrolytes

In

TrashF

E

UP

EA activeareaP

3W

reaction cell

Fluidic system- One input, two outputs- Sensors of liquid level not required- Only single, one directional peristaltic pump required- driven by underpressure


Electrochemical cell and its practical realization


Electrode Array

dimensions:60,8 x 60,8 mm

384 Contact pins

96 interdigital electrodes IDT4for four-point conductancemeasurement

Single IDT4electrode

Electrode detail

SiO2 layers: ~1 umPt layer: ~0,5 um

Pitch 0,5 mm

PtSi support

SiO2

SiO2

Pt


Reproducibility of electropolymerization(possible effects of cell geometry and polymerization order)

50 60 70 80

1.0

2.0

3.0

4.0

5.0

EP time cut 250s Mean value (average) Standard deviation

Mean=3.55616E-6SD=3.95799E-7SE=6.4207E-8numPts=38

(C)

elec

trop

olym

eriz

atio

n cu

rren

t (

A )

electropolymerization order

2) Influence of electropolymerizationorder

- observed no effect of the electropolymerization order

4 6 8 10 12

1.0

2.0

3.0

4.0

5.0

EP time cut 250s Mean value (average) Standard deviation

Mean=3.55616E-6SD=3.95799E-7SE=6.4207E-8numPts=38

(D)

elec

trop

olym

eriz

atio

n cu

rren

t (

A )

distance Work from Ref. electrode ( mm )

d

Electrode array

Reference electrode

Single electrode (IDT)

1) Influence of distance among work electrodes and reference electrode

- observed no effect of the cell geometry on polymerization rate

Experiment: Aniline 0,1 M in 1M H2SO4Conditions: 40°C, Vp = 0,9V vs. sat. Ag/AgClEP time app. 100 sec.




Electrical addressation, Multiplexer 96

- High impedance (due to reed relays)

- Multifunctional computer controlled device

- Addressation of 96 work el.

Array12 x 8

MC

U A

TM

EL

AV

R

2 x

AM

P97

car

d e

dg

e c

on

ne

cto

r3

84

co

nta

cti

ng

pin

s

CH1

CH96

Sel

ect

or

bo

ard

Vx

Power module8 outputs

open collector

Powersource

+12V

+5V+5

V

2 HzclockTr

igg

ersi

gna

lTo

inte

rfac

e b

oard

+12V +12V

To p

aral

lel p

ort 8

b+A

CK

RS

T

Power

To dosing station

display

Au

x

Ref Vx

Analog Digital

Multiplexer 96

1 2 3 4

S1

- special 4A + 2B switch configuration

o f f

ID

T

el

ec

tr

od

e

Vx Vp

o f f

ID

T

el

ec

tr

od

e

Vx Vppolymerized el.

protected el.

- Time synchronization


V

A

Potentiostat

FB

IA

I W1 I W2

I WXVp

Auxiliary electrode

Vx

Iw

Reference el.

Buff

W2W1 W Wx

C1 C C2 Cx

Semiconducting support

SiO2 layer (EA)

SUP

+

+

0 V

+ 0

.2

V~

0.7

+0,9 VWork

Ref

Au

x

EP

of A

nili

ne V

p=+

0.9

V V

x no

t app

lied

0 V

~ +0.7 V

+0,4 VWork

Ref

Aux

EP

of

Pru

ssia

n b

lue

Vp=

+0.4

V V

x no

t app

lied

Electrode potentials

0

96 electrodes involved during experiment in one electrochemical cell

How to prevent undesirable electropolymerization on neighboring electrodes?

Possible protection techniques:

1) application of Vx potential close to the reference level (not working)2) application of Vx close to the auxiliary electrode potential level (working)3) application of the potential of Aux. electrode to the semiconducting array support (working)4) combination 2 and 3

Electrical addressationvisual test of protected electrodes

Protected electrodes


Electropolymerization set-upelectropolymerization circuit


Electropolymerization circuit

- protected electrodes connected to Aux. potential- two diodes limits the potential difference between Ref. and Aux. level to prevent undesirable electrochemical processes- Dosing station controlled by Multiplexer 96 device- Electropolymerization synchronized by clock generator 2Hz

MX

96IB +T

H

Power output module Clock generator

Buffer

Dosing station

EC

PC

AuxAux

Work

Ref

EA

180

k

1N4007

100

Vx

Source Lo

Source Hi

trigger in

Sense Hi

K2400

Sense Lo





Measurement program





Feedback




Dataanalysis

Measurement concept

polymerized electrode


Measurement set-upDC conductance

- The same instrumentation as in EP set-up involved- Additionally high impedance voltmeter K2000 for simultaneous 4p and 2p measurements


Simultaneous two- and four-point measurementDC conductance

Sour

ce H

i

Senc

e Hi

Senc

e Lo

Sour

ce L

o

VI

1 2 3 41 2 3 4

1

2 3 4

VI

Polymer layer

Electrodes

four long strip electrodesthe most effective using of the surface area

folding

four point technique involved

- eliminates contact effects - measurement of bulk conductance - required special topology of electrodes - improvement for simultaneous four - and two- point measurement


Simultaneous two- and four-point measurementDC conductance

- possible to separate bulk and contact resistance- according to the designed geometry of the electrode, the ideally R2/R4 ratio is approximately 3


Measurement set-up


Multiplexer 96, addressation during measurement

Array12 x 8

MC

U A

TM

EL

AV

R

2 x

AM

P97

car

d e

dg

e c

on

ne

cto

r3

84

co

nta

cti

ng

pin

s

CH1

CH96

Sel

ect

or

bo

ard

(me

asu

rem

ent)

Vx

Powersource

+12V

+5V

To in

terf

ace

boa

rd

+12V

To p

aral

lel p

ort 8

b+A

CK

RS

T

Po

wer

display

Au

x

Ref

Analog Digital

Multip

lexer

96

1 2 3 4

S1

S3S2

- Addressation of 96 electrodes- four-pint configuration- auto zero offsetting mode- auto calibration mode


Measurement protocolMulti-parameter High-Throughput Characterization of HCl-sensitive Materials

- The minimal amount of most informative measurements is required to provide the most comprehensive characterization of polymer libraries within reasonable time

1 0 - - - ~122 2,5 2 times 2 times - ~2303 3,5 - - - 44 5 - - - 45 7 - - - 46 10 - - - 47 14 - - - 48 20 - - - 49 28 - - - 410 40 2 times 2 times - ~23011 40 - - - ~12

~12:15

Measurement time (min)

Total procedure time Note: presented, - not presented

Procedure step

HCl conc. (ppm)

Conductance measurement

Slow kinetics

Fast kinetics

I-V sweep

Measurement procedure and protocol

V-s

we

ep

V-s

we

ep

SK1 SK3SK2 SK4FK1 FK3FK2 FK43,5 ppm

40 ppm

- comprehensive meas. + reversibility + reproducibility + response + drifts + concentration depend. + fitting models

- reasonable invest. time (12:15 for one library)

time

S

enso

rre

spon

se

t0 t2 t3 t5 t6 t8 t1 2 t1 3t4t1

t1 = 2 min

t2 = 33 m in

FA1

FD1

FA2

D32

FD2

0

C

FK1 FK2

response on analyte concentration

Ana

lyte

con

cent

ratio

n

time

Gas adsorption

Gas desorption

t5 - t t t4 1 3 1 2 - = ... = = 2 m inutes

Fast kinetic ( two consequent cycles ) + analyte concentration sweep

Parameter extraction: reversibility and reproducibility of gas effect, fitting to Langmuir or Henry model

time

Sen

sor

resp

onse

t0 t2 t3

t4 - t t t t t3 5 4 6 5 - - = = = ~ 33 m inutes

t4 t5 t6t1

A11

A21

D11 D21 D31

A31

G0

0

C

G0

A12

A22

D12 D 22 D32

A32A32

1-st adsorption / desorption cycle 2-nd adsorption / desorption cycle

Ana

lyte

con

cen

trat

ion

time

t0 = 0 min

t1 = 2 min

t2 = 12 m in

t3 = 22 m in

Gas adsorption

Gas desorption

Slow kinetic ( two consequent cycles )

Parameter extraction: reversibility and reproducibility of gas effect


Measurement protocol, definition of parametersMulti-parameter High-Throughput Characterization of HCl-sensitive Materials

Characteristics Calculations (measurements) Ideal presentation

Drift during gas exposure: KA1=A2c/A1c; KA2=A3c/A2c KA1, KA2 vs. xDrift trend during gas exposure: KA3=KA2/KA1 KA3 vs. xDrift without gas: KD1=D2c/D1c; KD2=D3c/D2c KD1, KD2 vs. xDrift trend without gas: KD3=KD2/KD1 KD3 vs. x

RVS1 = (D31-G0)/G0; RVS1 vs. xRVS2 = (D32-D31)/D31 RVS2 vs. xRVF1 = (FD1-D32)/ D32 RVF1 vs. xRVF2 = (FD2-FD1)FD1 RVF2 vs. x

Reproducibility in slow kinetics (RPS) RPS = (A32-D31)/(A31-G0) RPS vs. xReproducibility in fast kinetics (RPF) RPF = (FA2-FD1)/(FA1-D32) RPF vs. x

G-G0 vs. x(G-G0)/Go vs. x

k vs. xGood vs. x

Slope ralated to absolute sensitivity dG/dc max dG/dc vs. xSlope ralated to relative sensitivity d(G/Go)/dc max d(G/Go)/dc vs. xCorrelation coefficient Good 1 Good vs. x

Analysis of the concentration dependence in Linear model (Linear fitting of conductance changes on the analyte concentration.)

max Gmax

Langmuir Fitting: G=*C/(C+C1/2), k=1/

Fitting of concentration dependence of the analyte effect by Langmuir isotherm and determination of isotherm parameters.

Analysis of the concentration dependence in Langmuir model

Parameters related to slow kinetics (c=1 for minimal and c=3 for maximal analyte concentration)

Reversibility of gas effects

Reproducibility of gas effects

Reversibility in fast kinetics (RVS)0

1

1

Reversibility in slow kinetics (RVS)





Measurement program





Feedback




Dataanalysis

Data analysis

one of 96 IDT4 electrodes


Analysis of sensors


Reproducibility of electropolymerization(current kinetic)

Current kinetics for subsequent electropolymerization of aniline at 96 electrode groups: the first experiments

0 20 40 60 80 100 120 1400

2

4

6

8

10

12

14

16

18

elec

trop

olym

eriz

atio

n cu

rren

t (

A )

electropolymerization time ( s )

0 100 200 300 400

2

4

6

8

10

Library: 01-10-03-DQ3Accepted electrodes: 72EP potential: 0.9VEP charge: variousTemperature: 40°C

elec

trop

olym

eriz

atio

n cu

rren

t (

A )

electropolymerization time ( s )

The similar experiment with several Improvements:

- equilibrium of the EP system- application of protection potential- thermo-stabilization- nitrogen atmosphere


Thermo-stabilizationof electropolymerization and measurement

295 300 305 310 315 320 3250

2

4

6

8

10

12 Aniline (HClO4) Vp = 0.9V

EP

cha

rge

(m

C)

Temperature (K)


- influence of temperature on polymerization ratio- thermo-stabilization required- thermostat with proportional (P) and continual current output- temperature range from room temperature up to 80°C

0 5 10 15 20 25 30

-1.0

-0.8

-0.6

-0.4

-0.2

0 Measured by four-point techniqueMode: thermal desorption

180°C 150°C 120°C 100°C 60°C

(G-G

o) /

Go

time (min)

Measurement

- observed influence of temperature on during adsorption and desorption- temperature range from room temperature up to 125°C- Thermo-desorption, improvement of sensors reversibility


Application in conductometric polymer gas sensors(Sensors for gaseous hydrogen chloride)

Why the sensor for gaseous HCl is needed?

polyvinylchloride (PVC) + O2 -> HCl + ...

Application in fire alarmsystems for cable burning

- PVC cables- PVC interior details in cars, planes, trains, etc.

Prevention of fire disasterscaused by burning of cable isolation, PVC (in buildings,transport, and others)


Optimization of HCl gas sensors,Influence of chemical content, representative results

PANI 4ABA 3ABSA 3ABA AA0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6 (A) 5%

7%3%

10%

d((G-Go)Go)/dC=f(reagent C1+C2) four-point two-point

(%) molar part C2C1-Anilin

Re

lativ

e s

en

sitiv

ity (

1/p

pm

)

The best relative sensitivity The best desorption rate

PANI 4ABA 3ABSA 3ABA AA0.75

0.80

0.85

0.90

0.95

(D) ideal=1

C1-Anilin(%) molar part C2

four-point two-point

30%

30%

40%

30%

De

sorp

tion

coe

ffic

ien

t K

D2

The best absolute sensitivity

PANI 4ABA 3ABSA 3ABA AA0

1

2

3

4

5

6 (G)dG/dC=f(reagent C1+C2)


C1-Anilin(%) molar part C2

7%

30%

7%

5%

Ab

so

lute

se

nsitiv

ity (S

/pp

m)

The best reversibility*

PANI 4ABA 3ABSA 3ABA AA

0.2

0.4

0.6

0.8

1.0

1.2

1.4 (E) C1 Anilin(%) molar part C2


30%

30%

40%

30%

Re

vers

ibili

ty R

VS

2 (

fro

m s

low

kin

etic

)

The best response linearity


0.96

0.97

0.98

0.99

1.00

(B) C1-Anilin, (%) molar part C2

fo

ur-

po

int

tw

o-p

oin

t

5%

7%

3%

10%

Re

lativ

e r

esp

on

se li

ne

ari

ty (

R-c

oe

f.)

The best reproducibility*


0

1.0

1.5

2.0

(F)C1-Anilin(%) molar part C2


7%

30%

7%

5%

Rep

rodu

cibi

lity

(fro

m s

low

kin

etic

)The best response time


0

1.1

1.2

1.3

1.4

1.5(C)C1-Anilin(%) molar part C2


7%

30%

7%

30%

Res

pons

e co

effic

ient

KA

2

The best contact with electrodes


3.0

3.5

4.0(H)

Gmax (4-point) / Gmax (2-point)C1-Anilin(%) molar part C2

7%

15%

40%

25%

Ra

tio

Gm

ax 4

p /

Gm

ax 2

p

* of gas effect


Conclusion

- Developed and realized:

- concept for combinatorial electropolymerization(including hardware, fluidic system and control software)

- concept for high-throughput screening(including hardware and control software)

- Developed comprehensive measurement protocol for characterization of gas sensors

- Developed analysis software, which simplifies work with results, calculates, visualizes and exports all defined parameters such reversibility, reproducibility, response, desorption ratio, allows fitting to Langmuir and Henry model, etc...

- This combinatorial set-up was used for optimization of sensors for gaseous hydrogen chloride based on aniline derivates

- The representative results illustrates the wide range of application of the developed tool


Outlook - Application in chemo-sensors

Equipment for combinatorial polymer synthesis

electr

ode

Substrate

ProductConductingPolymer

Polymer filter

Enzyme

Conduc

ting po

lymer

(media

tor) Conducting polymer (mediator)

ox

rede

Enzymatic biosensors

Amperometrictransducing methodcollaboration with ...

S e n s o r a rr a y

Electrically addressable immo-bilization of thiolated receptors

Throughput: currently 96 electrodes, but only up to 4 different thiols can be immobilized. A coupling with automated dispenser is possible

MIP through electro-polymerization: The 1-st works havebeen done by our co-workers (V, T), now3 works more are publishedthe main problem ofMIP - optimization

96 experiments per chipThroughput:

Moleculary imprinted polymers Polymer filters for bio- andchemosensors

for any sensor withconductive polymers,as additional polymerlayer

96 experiments per chipThroughput:

DNA Arrays Technology:

Hybridization detection:

entrapping into polymer matrix during EP

fluorescence [Livache] development of electro-

chemical methods [Zhi]

Throughput: currently 96 electrodes, can be simply increased up to 384

Variations of Olygos: currently 4, can be increased.A coupling with automated dispenser is possible

Cell volume: currently > 1.5 ml. Can be decreased, but it demands a new design


Outlook - Application in organic electronics

BA

GG

S SD D

Electrode ElectrodePolymer Polymer

Oxide layer Oxide layer

Substrate Substrate

electrolyte solution

n++

Organic field-effect transistors (OFETs)

Contacts

Mask layer

Substrate Polymer

MSM sructure

=

- Schottky diodes- MSM detectors

A

Contacts

Mask layer

ITO

Substrate

B

ITO1 ITO2

Polymer 2Polymer 1

ITO Polymer 2

Polymer 1 Metal layer

organic light-emitting diodesand displays (OLEDs)Philips announced luminiscent flat TV based on organic polymers available on the market in 2006

organic coatings (corrosion protectors, electrochromic windows), solar cells and many others


Prof. Alexander KochProf. Otto. S. Wolfbeis

PD. Dr. Vladimir M. MirskyProf. Daniel Donoval

Dr. Qingli Haoand others

Acknowledgment

This work was supported by the project "KOMBISENS" from German Ministry for Science and Technology.


Thank youfor your attention

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