Silicon–glass instrumented solid-phase extraction–zone electrophoresis microchip with thin amorphous silicon film electrodes: performance in immunoaffinity analysis

Silicon–glass microchips were designed and fabricated for on-chip solid phase extraction (SPE) and zone electrophoresis studies. The solvent channels for extraction and the separation channels for analyses were fabricated sequentially on the silicon device. Electrical contacts were integrated in a fused silica glass lid. Amorphous silicon thin film electrodes were fabricated for high voltage and conductivity detection. A chip installation rack with electrical and fluidic contacts was constructed to facilitate the experiments. Simulation was used to elucidate both the liquid flow and the electric field distribution. The operational performance of the microchips was demonstrated by using a fluorescein isothiocyanate (FITC)-labelled testosterone derivative as the model analyte and fluorescein as both the negative control and the calibration compounds. In SPE an immunosorbent, based on recombinant anti-testosterone Fab-fragments, was immobilized to activated Sepharose gel. Simultaneous monitoring of the movement of FITC-testosterone from SPE cavity through the channel to the detection point was performed with a laser-induced fluorescence detector. The observed limit of detection for FITC-testosterone was 2 μM.