Simultaneous Measurement of Nonlinearity and ...Measured Biological Data before...

Simultaneous Measurement of Simultaneous Measurement of Nonlinearity and ElectrochemicalNonlinearity and Electrochemical

Impedance for Protein Sensing Using Impedance for Protein Sensing Using TwoTwo--Tone ExcitationTone Excitation

Jon Daniels, Ph.D. [email protected]

IEEE EMBC08 24-Aug-08 SuBT2.5

Stanford Department of Electrical EngineeringStanford Genome Technology Center (SGTC)

Co-authors:

Erik P. Anderson – Stanford EE, SGTC

Prof. Thomas H. Lee – Stanford EE

Prof. Nader Pourmand – SGTC, UC Santa Cruz

Affinity Affinity BiosensorsBiosensors

• Immobilized probe selectively captures target

• Target capture changes surface propertiesIncubation,

probe

target

[email protected] 2IEEE EMBC08 24-Aug-08 SuBT2.5

properties

• Detecting change in surface properties = detecting target

Incubation,washing

Probe Layer

Solution

Impedance for Affinity Impedance for Affinity BiosensorsBiosensors


• Binding changes electrical properties of surface

• Selectivity determined by probe layer => platform amenable to various applications by changing probe

Electrode

Probe Layer

(Insulator)( )

Measuring ImpedanceMeasuring Impedance

I

−

+

Vout

Vin

Zf

ZDUT

Vout = -Vin (Zf /ZDUT)


V


Electrode “Electrode “ImpedanceImpedance” is Nonlinear” is Nonlinear

• Electrode-electrolyte impedance depends (quite strongly) on DC bias => nonlinear

• ionic double layer capacitance:

Cdl(φ) =(

228 µF/cm2)

√

C0

mol/L

(

1 +1

8

(

φ

VT

)2)

I


( )

√

mol/L

(

8

(

VT

)

)

I

V

Question #1Question #1

Can changes in nonlinearity be used to discriminate target binding?


vs. ?

Question #2Question #2

Can nonlinearity be quantified without extra measurement time?

I


I

V

Measuring Nonlinearity w/ 2 tonesMeasuring Nonlinearity w/ 2 tones

Vin = A cos(ωAt) + B cos(ωBt)

ZDUT (ω) = Z0(ω)(

1 + α1Vin + α2V2in

)

Vout = −Vin

Zf(ω)

Z0(ω)

1

1 + α1Vin + α2V2in

−Z (ω )

−

+

Vout

Vin

Zf

ZDUT


Conventional Low frequency

Small-signal impedance


Vout =−Zf (ωA)

Z0(ωA)A cos(ωAt)

+ 12α1AB

Zf (ωA−ωB)

Z0(ωA−ωB)cos((ωA − ωB)t)

+ 12α1AB

Zf (ωA+ωB)

Z0(ωA+ωB)cos((ωA + ωB)t)

+ 14α2AB

2 Zf (ωA−2ωB)

Z0(ωA−2ωB)cos((ωA − 2ωB)t)

+ 14α2AB

2 Zf (ωA+2ωB)

Z0(ωA+2ωB)cos((ωA + 2ωB)t)

+ other terms far removed from ωA

Small-signal impedance

IM2

IM3

ADCFFT

Select DUT

Tone Outputs

0.1-100 kHz

PC with LabViewand ADC/DAC card

chip with 36electrodes

ωΑ

System DiagramSystem Diagram


−

+

ZDUT,1 16:1

ZDUT,16

Σ

17 Hz

Zf

PCB

electrodes

Vout

Vin

ωΒ

PCB ImplementationPCB Implementation


12.35

12.4

12.45

12.5

Cap

acit

ance

[n

F]

10 nF

1 kΩ

Validating Measurement ApproachValidating Measurement Approach


−100 −75 −50 −25 0 25 50 75 100

12.2

12.25

12.3

12.35

Bias [mV]

Cap

acit

ance

[n

F]

o = measured manually with custom setup

= measured manually with commercial LCR meter

– = extrapolated from nonlinearity tones at 0 mV

Making “Biology” Happen is HardMaking “Biology” Happen is Hard

fluorescently-labeledstreptavidin BSA BSA-biotin

polymer multilayer


300µm electrodes

Contact pads

O-ring (holds solution)

10

11

12

13

14

15

CPE Magnitude ["nF"]

0.9

0.905

0.91

0.915

0.92

0.925

CPE phase parameter

24

25

26

27

28

29

30

|Zdut

| @ 1 kHz [kΩ]

Measured Biological DataMeasured Biological Data

before


0 50 100 150Electrode Bias [mV]



0 50 100 150

10

11

12

13

14

15

Electrode Bias [mV]

CPE Magnitude ["nF"]

0 50 100 150

0.9

0.905

0.91

0.915

0.92

0.925

Electrode Bias [mV]

CPE phase parameter

0 50 100 150

24

25

26

27

28

29

30

Electrode Bias [mV]

|Zdut

| @ 1 kHz [kΩ]

after addition of1 µg/mL avidin

−0.02

0

0.02

0.04

0.06

α1 [

V−

1]

Nonlinearity Nonlinearity Indicates BindingIndicates Binding

change after addition of250 ng/mL avidin


BSA−biotin (positive) BSA (negative)

−0.08

−0.06

−0.04

−0.02

∆ α

1

n=4 n=8

ConclusionsConclusions

• Two-tone approach allows simultaneous measurement of small-signal impedance and nonlinearity– No extra measurement time

– Cost is redesigning measurement apparatus

• Nonlinearity can indicate target binding


• Nonlinearity can indicate target binding

• Nonlinearity appears to be influenced by surface charge– Surrogate for field-effect sensor?

Questions?Questions?

Suggestions?Suggestions?


Suggestions?Suggestions?

[email protected]@stanford.edu

Backup SlidesBackup Slides


Backup SlidesBackup Slides

What is Impedance?What is Impedance?

• impedance = measure of opposition to a sinusoidal alternating electric current, generalizing Ohm's law to AC circuit analysis

• impedance = ∆voltage / ∆current

Z = 1000 + 15915 j Ω10 nF


15915 j Ω

1000 Ω

10 nF

|Z| = 15947 Ω

θZ = -86.4°

Impedance SpectroscopyImpedance Spectroscopy


Source: http://www.gamry.com/App_Notes/EIS_Primer/EIS_Primer.htm

Affinity DetectionAffinity Detection

Kd =koff

kon, probe coverage

Readout/transducer type

Transducer

Selective Probe

Electrical

Chemical

Target concentration

Target surface coverage

Surface property change

affinity

readout


Post-processing

Amplifier

Data Acquisition

Transducer

Acquired

Electrical

(a) (b) (c)

Measured change

Instrumentation

Surface property change readout

Daniels/Pourmand, Electroanalysis 19:1239-1257 (2007)

Typical Measurement ApproachTypical Measurement Approach

$10-30k


• Single electrode measurement

Custom Measurement ApparatusCustom Measurement Apparatus

300µm electrodes

Contact pads

O-ring (holds solution)Rknown

Vin

DUT

Computerwith LabView


Socket

PCB with circuitry

Chip

Vout

DUT

ZDUT = -(Vin/Vout)*Rknown

Double Layer CapacitanceDouble Layer Capacitance

• α2 ~ 188 V-2 for double layer capacitance according to Gouy-Chapman model

• Predict α ~ 14 V-2 in our measurement based

Cdl(φ) =(

228 µF/cm2)

√

C0

mol/L

(

1 +1

8

(

φ

VT

)2)


• Predict α2 ~ 14 V-2 in our measurement based on voltage across ionic layer (vs. interface)– expect less due to Stern modification

• We observe |α1| ~ 0.1-1 V-1 and |α2| ~ 1-10 V-2

in all our measurements

Next StepsNext Steps

• Custom measurement IC design (in progress) and testing

• Explore nonlinear effects with constant phase element?

• Try “real biology”?


• Graduate and get a “real job”!

AcknowledgementsAcknowledgements

• Nader Pourmand, Prof. Ron Davis (Biochem)

• Erik Anderson, Prof. Tom Lee (ElecEng)

• Heng Yu (surface chemistry)

• Other SGTC personel

• NIH and NSF for direct and indirect funding


• NIH and NSF for direct and indirect funding

Simultaneous Measurement of Nonlinearity and ...Measured Biological Data before...

Documents

Transcript of Simultaneous Measurement of Nonlinearity and ...Measured Biological Data before...