Rapid detection of pathogens using field deployable biosensors requires integrated sensing and data processing. Detection of low concentration of biological agents is possible using accurate and real-time signal characterization devices. This paper presents a multi-channel conductometric array that can detect and measure current up to femtoampere range. The architecture uses a novel semi-synchronous SigmaDelta modulation that allows measurement of ultra-small currents by using a hysteretic comparison technique. The architecture achieves higher energy efficiency over a conventional SigmaDelta by reducing the total switching cycles of the comparator. A 3 mm x 3 mm chip implementing a 42 channel potentiostat array has been prototyped in a 0.5 microm CMOS technology. Measured results show 10 bits of resolution, with a sensitivity of upto 50 fA of current. The power consumption of the potentiostat is 11 microW per channel at a sampling rate of 250 kHz. The multi-channel potentiostat has been integrated with a conductometric biosensor for field deployable applications. Results with a Bacillus Cereus based biosensor demonstrate the effectiveness of the potentiostat in characterizing different concentration levels of pathogens in realtime.