A multichannel femtoampere-sensitivity potentiostat array for biosensing applications

Rapid and accurate detection of pathogens using conductometric biosensors requires potentiostats that can measure small variations in conductance. In this paper, we present an architecture and implementation of a multichannel potentiostat array based on a novel semi-synchronous (ΣΔ) analog-to-digital conversion algorithm. The algorithm combines continuous time ΣΔ with time-encoding machines, and enables measurement of currents down to femtoampere range. A 3-mm × 3-mm chip implementing a 42-channel potentiostat array has been prototyped in a 0.5-μm CMOS technology. Measured results demonstrate that the prototype can achieve 10 bits of resolution, with a sensitivity down to 50-fA current. The power consumption of the potentiostat has been measured to be 11 μW per channel for a sampling rate of 250 kHz. Experiments with a conductometric biosensor specific to Bacillus Cereus bacterium, demonstrate the ability of the potentiostat in identifying different concentration levels of the pathogen in a biological sample.