Surface plasmon-enhanced gas sensing in single gold-peapodded silica nanowires

Abstract

An intriguing system featuring a wide band gap silica nanowire (SiO x NW) that absorbs visible light (532 nm) via the surface plasmons (SPs) of embedded gold nanoparticles (Au NPs) is reported for sensing applications. We report SP resonanceenhanced molecular oxygen sensing by single Au-NPs@SiO x NWs under 532-nm illumination (visible light) at room temperature. Excellent selectivity of the Au-NPs@SiO x NWs to molecular oxygen in air has been demonstrated. Illumination improved the sensing properties in terms of response and fast recovery time, which can be attributed to the photogenerated hole-mediated oxygen desorption. A general strategy of light-modulated sensing, vis-à -vis dark, is demonstrated in a wide band gap single NW system that could potentially open up routes for biosensing, because silica and Au both lack biotoxicity. NPG Asia Materials (2013) 5, e49; doi:10.1038/am.2013.17; published online 24 May 2013 Keywords: gas sensor; nanowire; silica; surface plasmon INTRODUCTION Oxide-based semiconductor nanostructured materials have been widely investigated for chemical and biosensing applications because of their biocompatibility, relatively easy large-scale synthesis, superior thermal and chemical stabilities and high surface-to-volume ratios. 1,2 However, improving the sensing performance requires improved sensitivity, good selectivity or specificity, short rise and fall times of signals (high-speed response and recovery) and an easily attainable working temperature, ideally in the room-temperature range. Because of their large surface areas, nanostructures such as nanowires (NWs), 3 nanotubes, 4,5 nanorods 6 and nanoparticles (NPs) 7 offer large reaction cross sections for signal generation. To further enhance the sensing performance of these nanostructures, surface modification, [8][9][10] applications of high electrical bias 11 and high operational temperatures (T4100 1C) 12 have been used.Improving the sensing performance with light has also been demonstrated using ZnO-based nanostructures under UV illumination. 13 However, most of these approaches have required high operational temperatures, high biases and light outside the visible range (400-800 nm), which has somewhat limited their general applicability. We demonstrated how Au NPs embedded in single amorphous silica NW (Au-NPs@SiO x silica NW) can be used as an oxygen gas sensor by amperometric routes in this work. According to that study, the silica shell is amorphous, containing various defects within the NW, such as nonbridging oxygen atoms, dangling bonds,

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