Integrated CMOS microsystems for electrochemical sensing

Abstract This work presents a novel integrated CMOS microsystem for electrochemical sensing and biopotential recording applications. The system provides a platform to enable concurrent monitoring of chemical and electrical signals in vitro. The microsystem consists of microelectrode arrays (MEAs), a potentiostat, a biopotential amplifier and an analog-to-digital converter, featuring portability, sample volume reduction, high spatial resolution, low power consumption and compatibility with mass manufacturing.;Microelectrode arrays offer numerous benefits over macroelectrodes due to their smaller sample size requirement, small form factor, low power consumption, and higher sensitivity due to increased rates of mass transport. These features make MEAs well suited for lab-on-a-chip applications. MEAs are implemented with an individually addressable 32 x 32 array of 7 um square microelectrodes with 37 um center to center spacing on a CMOS chip with a built-in VLSI potentiostat for electrochemical analysis. The potentiostat features a low input impedance, high sensitivity, high gain and low power trans-impedance amplifier front end, with programmable control of electrode potential, thus facilitating continuous bi-directional measurement of reduction-oxidation (redox) current in a potentiostat for cyclic voltammetry (CV) experiment. The integrated CMOS MEAs is post-processed at the die level to coat the exposed Al layers with Au. To verify microelectrode array behavior with individual addressability, cyclic voltammetry was performed using a potassium ferricyanide (K3Fe(CN) 6)) solution. Such microelectrode arrays with built-in potentiostat can be used in variety of applications, ranging from water quality monitoring for detection toxic chemicals, to bioanalysis in cellular microenvironment.;For biopotential recoding applications, we present a low noise, low power, bandwidth tunable amplifier. By employing depletion-mode pMOS transistor in diode configuration as a tunable sub pA current source to adjust the resistivity of a MOS-Bipolar pseudo-resistor, the bandwidth is adjusted without any need for a separate band-pass filter stage. Electrocardiogram (ECG) measurement and direct electrophysiological measurements on electrogenic cardiac cells are performed using the proposed amplifier to show its feasibility for low power biopotential monitoring applications.;We have combined both of our platforms, namely electrochemical sensing and biopotential recording into a single low-power integrated sensing system on chip with added functionality. Such a platform facilitates concurrent measurement of electrochemical and biopotential measurements in cellular microenvironments. The integrated CMOS microsystem is designed in a 0.5mum CMOS technology and consumes a total of 36muW and features a novel dynamic-gain delta sigma converter for direct digital readout.