Two microcell flow-injection analysis (FIA) platforms for capacitive silicon-based field-effect sensors

pH- and penicillin-sensitive electrolyte-insulator-semiconductor (EIS) sensors (Al/Si/SiO2/Ta2O5 and penicillinase) have been successfully integrated into a commercial flow-injection analysis (FIA) system. For the FIA set-up, a miniaturised home-made flow-through cell of plexiglass with a variable internal volume from 12 to 48 μl has been developed. As a second platform, an SU-8 based miniaturised flow-through cell, also combined with a pH-sensitive EIS structure, has been fabricated at wafer level. The application of SU-8 as a photoresist with good qualities (distinct chemical resistance, high aspect ratio, good mechanical and dielectric behaviour) is favoured. Different channel/sensor layouts have been realised with sensitive areas of the EIS sensors of 1.7-8.2 mm2 and sample volumes of 0.3-4 μl, respectively. FIA parameters (sample volume, flow rate, distance between injection valve and sensor) have been optimised in terms of high throughput, minimum dispersion, fluid consumption, sensitivity and reproducibility.