Plasmonic nanostructures using self-assembled nanosphere templates for water splitting and DNA sensing

Abstract

Plasmonic metal nanostructures have emerged as a promising way to harness solar energy through the excitation of the surface plasmon resonance. They converse and transfer the solar energy through the energy or charge transfer, which can be utilized in the solar-to-fuel conversion or signal amplification. Here we present the plasmonic nanostructures based on the self-assembled polystyrene nanospheres as templates, for solar water splitting and DNA fluorescence sensing. First, we report sustainable photoelectrochemical water oxidation through the deposition of catalytic polyoxometaltates (POMs) onto a plasmonic Au/TiO$_2$ half-shell array photoanode, followed by the atomic layer deposition of a thin Al$_2$O$_3$ layer. The Al$_2$O$_3$ layer increased the photocurrent and delayed current attenuation by preventing the dissociation of Co$_4$POMs from the surface during the water oxidation. A thicker Al$_2$O$_3$ layer exhibited a higher protection effect on the POMs and also passivated the TiO$_2$ surface, improving electron transfer through the POMs/Au half-shell structure. Second, we propose a fast and sensitive DNA fluorescence sensing platform based on plasmon-based enhancing and quenching of the fluorescence using two kinds of plasmonic nanoparticles. As the enhancer, the Au half-shells on polystyrene nanosphere (Au/PS) exhibited 5-fold fluorescence enhancement when the Au/PS captured target and dye DNA via a sandwich hybridization. Then AuNPs, as the quencher, were introduced to the Au/PS with DNA solution for reducing the background fluorescence from the unhybridized dye DNA, improving the sensitivity 1,000 times (a limit of detection: 16 pM, within 1 h) with high specificity that discriminated the single-base difference. Target DNA was from the gene of the Klebsiella pneumoniae carbapenemase, one of the targets for pathogenic bacteria with drug resistance, showing the clinical applicability. These works suggest that the catalyst/plasmonic photoelectrode with a thin protection layer is a promising alternative to conventional semiconductor-based photoelectrodes for sustainable and efficient water oxidation and a novel DNA sensing platform using two kinds of plasmonic nanoparticles without an amplification, labeling, and purification step.