Capacitive microsensors for biochemical sensing based on porous silicon technology

Porous EIS (electrolyte-insulator-semiconductor) structures of n-Si/SiO2/Si 3N4 with a mean pore diameter of about 1 mu m and a mean pore depth of abou t 2 mu m have been realized for capacitive pH sensors. For the fabrication of the porous microsensors (down to "spot'' sizes of 10 mu m X 10 mu m), th e n-doped silicon substrates have been photolithographically patterned by m eans of mask-matching technique using polyimide as a passivation material. The average pH sensitivity of the porous pH microsensor amounts about 56 mV /pH in the concentration range between pH 4 and pH 8. In order to prepare p orous EIS biosensors the enzyme penicillinase has been adsorptively immobil ized inside the porous structure. In the case of the porous biosensors an a verage penicillin sensitivity of about 90 mV/mM in the concentration range from 0.01 to 1 mM exists. Microreference electrodes, also prepared by the s ame porous silicon technology as for the pH- and biosensors, show a potenti al stability of more than 1 week in the long term. (C) 2000 Elsevier Scienc e S.A. All rights reserved.