ACTIVE CMOS SENSORARRAY FOR ELECTROCHEMICAL BIOMOLECULAR DETECTION

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* INTRODUCTION* ELECTROCHEMICAL SENSING* ACTIVE CMOS SENSOR DESIGN* LIMITATION OF CMOS* CONCLUSION

A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an

instrument.

Cmos array miniaturizes the sensing platform, enhance

portability,enabling high throughput ,highly

parallel analysis.

Electro chemical sensing approaches to DNA detection , rely on detecting changes occurring with hybridization at interface.

CMOS sensor include :•A sensor chip interfaced to a single on-chip WE.•Potentiostat.

Electrochemical sensing

1. POTENTIOSTAT OPERATION

2. CYCLIC VOLTAMMETRY

Feedback control system.

Apply desired potential to elctrochemical cell.

Measure the movement of charge.

Low speed , large signal tech.

Detect redox species.

Determine probe concentration , measure DNA probe target hybridization.

Description of potentiostat operation. (a) Conceptual diagram. (b) Implementation using electronic components.

Active cmos sensor array design :

Each array consist of square gold (WE)having side length 100 µm. Variation allows effect of electrode area on the cell current for different redox and biomolecular reaction.

Dual slope ADC.

Active COS sensor array architecture.

1. Electrochemical cell model Small signal model simulate system behavior and test potentiostat stability when chip is operated in electrolyte. 2. Potentiostat circuits To provide good noise performance stability across wide range of operating condition.3. Chip post processing & Experimental setup Used to create an array of Au elect. on the surface. packaged chip in PCB socket with top plate layer.

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Small-signal circuit models of (a) the electrode–electrolyte interfaces present in an electrochemical cell and (b) the WE–electrolyte interface augmented with noise sources.

Transduction Detection Method Integrated Transducers Sensor Challenge Limitations in CMOS

Electrochemical

Optical

Amperometry Electrode/Electrolyte*

LF pA-nA range currentmeasurement

Proper electrode fabricationCapturing probe immobilization

Potentiometry Electrode/Electrolyte LF 1-100µV range voltagemeasurement

Proper electrode fabricationCapturing probe immobilization

Cyclic Voltammetry Electrode/Electrolyte LF I-V curve measurement Proper electrode fabricationCapturing probe immobilization

ImpedanceSpectroscopy

Electrode/Electrolyte LF impedance measurements Proper electrode fabricationCapturing probe immobilization

Bioluminescence Photodiode LF 1fA-10pA range photocurrentMeasurement

None

FluorescenceSpectroscopy Photodiode LF 1fA-10pA photocurrent

measurement in presence of100pA range background

Excitation sourceEmission filter

Infra-RedSpectroscopy NA LF 1fA-10pA current

measurement in presence of100pA range background

Transducer

MagneticMagnetic Particle

LabelsSpiral Inductors

Hall- Effect Devices10nA-10µA current measurement

1-100pH range inductance measurement

None

Limitation of electrochemical cmos sensors : Lack of proper electrode. Voltage limitation of cmos ic. Require 100-1000 V for proper operation.

CONCLUSION :

1. Eliminate the need for bulky and

expensive optical equipment used in florescent based

microarray.

2. Reduction in size & complexity.

THANKS