A large transistor-based sensor array chip for direct extracellular imaging

This paper describes the development and evaluation of a large transistor-based sensor array chip for direct extracellular imaging. All of the sensors and electronics are designed and fabricated using an unmodified CMOS process. The sensor array chip consists of a 16×16 pixel array of ISFETs along with signal acquisition and readout circuitry. Each ISFET employs a floating gate electrode structure and uses the passivation layer as a pH sensitive membrane. The chip layout is optimised so that the surface topography allows cultured cells to be grown directly above the pixel array. On return from the foundry, a double layer of SU-8 photoresist is used to provide a biocompatible and waterproof package for the chip. An elastomer-based microfluidic chamber is fabricated and integrated for conducting long term cell culture experiments. The performance of the chip is evaluated using an electrolyte and a well-established confluent cell line. The fabricated circuit provides a linear operating range of 2.5 V that allows each ISFET to operate as a pH sensor in the array. The ISFETs have a threshold voltage of − 1.5 V and a sensitivity of 46 mV/pH.