Gold nanoparticle triggered dual optoplasmonic-impedimetric sensing of prostate-specific antigen on interdigitated porous silicon platforms

A porous silicon (PSi) platform with interdigitated NiCr electrodes has been used for the impedimetric biosensing of prostate specific antigen (PSA), a cancer biomarker. The first step involved the formation of a conductive PSi structure through the ion beam creation of 250 nm deep interdigitated slots, followed by their filling with NiCr electrodes deposited by plasma sputtering. In the second step, a biorecognition interface was formed by modification of the PSi surface with (3-Glycidyloxypropyl)-trimethoxysilane. A sandwich assay was performed in which PSA was first recognized by a surface-anchored antibody and then by a secondary antibody tethered to 100 nm gold nanoparticles (GNPs). The changes in the impedance upon analyte binding at different concentrations have been monitored showing that the PSA concentration exhibits a linear dependence with the series resistance defined from the device equivalent circuit. A limit of detection in the range of 1 ng/mL PSA has been determined. A dark-field study of the PSi surface after the sandwich bioassay allowed an optoplasmonic demonstration of the increasing density of GNPs at higher PSA concentrations, which was confirmed by using scanning electron microscopy. The results confirm the dual optoplasmonic-electric labelling effect of the 100 nm GNPs and their role in an internally controlled detection of PSA.