Design of a CMOS Potentiostat Circuit for Electrochemical Detector Arrays

Abstract

High-throughput electrode arrays are required for advancing devices for testing the effect of drugs on cellular function. In this paper, we present design criteria for a potentiostat circuit that is capable of measuring transient amperometric oxidation currents at the surface of an electrode with submillisecond time resolution and picoampere current resolution. The potentiostat is a regulated cascode stage in which a high-gain amplifier maintains the electrode voltage through a negative feedback loop. The potentiostat uses a new shared amplifier structure in which all of the amplifiers in a given row of detectors share a common half circuit permitting us to use fewer transistors per detector. We also present measurements from a test chip that was fabricated in a 0.5-μm, 5-V CMOS process through MOSIS. Each detector occupied a layout area of 35μm × 15μm and contained eight transistors and a 50-fF integrating capacitor. The rms current noise at 2kHz bandwidth is ≈ 110fA. The maximum charge storage capacity at 2kHz is 1.26 × 10 6 electrons.

Recent Trends for (Bio)Chemical Impedance Sensor Electronic Interfaces

“…Stanacevic et al [25] propose a 16-channel potentiostat based on a low power current-mode deltasigma (DS) modulator that reaches 100 fA resolution with a conversion time as long as 8 s. A 50 fA sensitivity is obtained by Gore et al with a semi-synchronous sigmadelta converter implemented in 42 channels for biowire molecular sensing [27]. Similar sensitivity is achieved by Ayers et al [26] integrating the input current on a 50 fF capacitor for 400 ms that gives a current noise of 110 fA r.m.s. in 1 kHz.…”

“…Low-noise current amplifiers can be grouped in two main categories: continuous-time [21]- [24] and discrete-time circuits [3,[25][26][27], where the best current resolution is achieved by continuous-time circuits though the discrete-time ones offer maximum flexibility for direct A/D conversion and with respect to the technology scaling. Stanacevic et al [25] propose a 16-channel potentiostat based on a low power current-mode deltasigma (DS) modulator that reaches 100 fA resolution with a conversion time as long as 8 s. A 50 fA sensitivity is obtained by Gore et al with a semi-synchronous sigmadelta converter implemented in 42 channels for biowire molecular sensing [27].…”

“…Although the concept behind all these reading approaches is the same, as stated before, a specific electronic implementation can avoid some of these techniques. As an example, [26] uses a sampled-system with 2.5 kHz of sampling frequency, confining this scheme to DC or quasi-DC acquisitions like voltammetry or amperometry; [3,21,24,27,29,34] have the same limitation as well.…”

A Unified Potentiostat for Electrochemical Glucose Sensors

“…This circuit is simple and can measure low currents by increasing the feedback impedance. On the other hand, this technique requires the positive and negative input voltage to generate the current of both O 2 -based and H 2 O 2 -based sensor, because the direction of the current generated in the O 2 -based sensor is opposite to that of the current generated in the H 2 O 2 -based sensor Other configurations to implement the potentiostat use a current conveyor [4][5][6][7]. This involves the insertion of a resistor in the current path at WE, where the voltage drop is measured.…”

Integrated Biosensor and Interfacing Circuits

“…Specifications of a typical DNA IBS A desirable acquisition circuit should usually accommodate both schemes of biosensing, however, as summarized in Table 3, the fastidious requirements, such as sensitivity, bandwidth, input range, etc., for the following circuits make great challenges to analog integrated circuit designers. There are various methods and circuits dealing with the ultralow current in biosensing applications, e.g., current integrator (sometimes it is called as potentiostat) (Ayers et al, 2007;Narula & Harris, 2006), transimpedance amplifiers (Rodriguez-Villegas, 2007;Basu et al, 2007), and ultralow current-mode amplifiers (ULCA) (Zhang et al, 2007;Ramirez-Angulo et al, 2004;Steadman et al, 2006;. The current integrator is capable of providing sub-picoampere sensitivity, however, the circuit bandwidth is typically below 1 kHz, which cannot fully accommodate the bandwidth of AC sensing.…”