Characterization of a vertically aligned silica nanospring-based sensor by alternating current impedance spectroscopy IOPselect

In this study, the initial phase of development of a vertically aligned (silica) nanospring (VANS)-based sensor utilizing alternating current impedance spectroscopy is presented. The sensor is a capacitor consisting of two glass substrates coated with indium tin oxide, where the VANS are grown on one substrate, following a top-down approach, serving as the dielectric spacer layer. The sensitivity of the VANS sensors was evaluated using deionized water (of an effective 10-3 mM monovalent ion concentration) and saline-phosphate (SP) solutions of pH 7.3 with concentrations 0.1, 1, 10 and 100 mM. Similar tests were performed with sensors without VANS or blank sensors. The modeling of the VANS impedance spectra required an equivalent circuit consisting of eight elements compared to four elements for the blank sensor. VANS sensors exhibited greater sensitivity to changes in the SP concentration relative to the blank sensors. The enhanced sensitivity is attributed to the addition of an ionic diffusion barrier at the VANS--solution interface and to ionic diffusion within the VANS.