Development of a pH sensor with integrated reference electrode for cell culture monitoring

The possibility to monitor the acidification of cell culture medium is of great interest in several fields of application, where it can provide information on the culture status and on the cell metabolism. To realise a highly integrated system with high throughput, ISFET sensors are good candidates. In order to realise these structure, a MOS process with appropriate gate dielectric needs to be implemented. A possible technological solution with lower costs and lower technological constraints can rely on extended gate structures, where a capacitor made of the sensitive material is connected to an external high impedance readout circuitry. One drawback of electrochemical pH sensors is the need of bulky external reference electrodes, which limits the actual integration of the system. Recently, reference electrodes based on polymeric layers doped with lipophilic salts to provide electrical conductivity, have provided promising results in term of potential stability and long term viability of the device. In this paper, we present the development of a sensor system including a “all-solid state” integrated reference electrode based on a PVC solid electrolyte with different types of lipophilic salts for the integration with a sensor array. As regards the sensing element, we compare the performances of ISFETs with Si3N4 dielectric used as sensitive material and extended gate structures.