Macroporous silicon based capacitive affinity sensor-fabrication and electrochemical studies

Abstract

We report the fabrication and characterization of capacitive immunosensors based on electrolyte-insulator-porous silicon (EIS) structures. The sensor structure, gold|silicon|porous silicon |SiO₂|aminosilane|glutaraldehyde|antibody|phosphate-buffered-saline (PBS)|platinum, is fabricated with a low thermal budget process and is found to be five times more sensitive than an immunosensor on polished silicon with identical die area. Macroporous silicon was prepared by electrochemical etching of polished <1 0 0> oriented p-type silicon wafers and characterized using SEM, optical microscopy, cyclic voltammetry and impedance spectroscopy. Columnar macroporous structures of different column densities and column sizes were used as the sensor substrates. The capacitive immunosensors were fabricated by anodic oxidation of these porous silicon substrates to form oxide followed by covalent immobilization of antibody (mouse IgG). Antibody-analyte (goat anti-mouse IgG) interactions were monitored via fluorescence microscopy and by change in the measured capacitance. Sensor response was dependent on both the porous silicon column structure and oxide quality.