Lab-on-CMOS capacitance sensor array for real-time cell viability measurements with I2C readout
Capacitance sensing is an emerging technology for monitoring cell viability. This work extends a previously developed sensor that measured capacitive loading by cells on the oscillation frequency of a current-starved ring oscillator and converted the frequency to a digital value by counting oscillation cycles. The new sensor array has been developed into a one-chip lab-on-CMOS system with integrated temperature sensors, serial readout to an external microcontroller using an Inter-Integrated Circuit (I2C) bus, and automatic scanning to allow for autonomous data collection. To allow sensing at the required aF levels, the system was realized on single chip to reduce the baseline capacitance, and long counting times were employed. The I2C module was moved to the edge of the chip prevent exposing cells to unacceptably high temperatures during viability studies.