ABSTRACT
Periodically patterned Au nanorods in TiO2 nanocavities (Au NRs@TiO2) were fabricated via magnetron sputtering followed by a thermal dewetting process. This innovative Au NRs@TiO2 heterostructure was used as a plasmonic sensing platform for photoelectrochemical detection of glucose and lactose. This Au NRs@TiO2 patterned heterostructure possesses superior sensing properties to other Au nanoparticle-based sensors because (i) localized surface plasmon resonance (LSPR) generated at Au/TiO2 interfaces enhanced sensitivity of glucose (lactose) amperometric detection; (ii) periodic Au nanocrystals in TiO2 nanocavities accelerated charge separation and transfer rate, especially under monochromatic blue light irradiation; (iii) discrete planar architectures comprising Au NRs immobilized on TiO2 substrates significantly improved stability and reusability of the sensors. A low detection limit of 1 µM (10 µM) and a high sensitivity of 812 µA mM-1 cm-2 (270 µA mM-1 cm-2) were achieved on the Au NRs@TiO2 heterostructures for glucose (lactose) detection without the addition of enzymes. Good selectivity and superb stability over more than 8 weeks was also demonstrated using these Au NRs@TiO2 heterostructures for glucose (lactose) detection. Additionally, this cost-efficient technique can be easily extended to other photoelectrochemical sensing systems when considering the combination of sensing and visible or infrared light source enhancement.
ABSTRACT
Novel Au@TiO2 plasmonic films were fabricated by individually placing Au nanoparticles into TiO2 nanocavity arrays through a sputtering and dewetting process. These discrete Au nanoparticles in TiO2 nanocavities showed strong visible-light absorption due to the plasmonic resonance. Photoelectrochemical studies demonstrated that the developed Au@TiO2 plasmonic films exhibited significantly enhanced catalytic activities toward oxygen reduction reactions with an onset potential of 0.92 V (vs reversible hydrogen electrode), electron transfer number of 3.94, and limiting current density of 5.2 mA cm-2. A superior ORR activity of 310 mA mg-1 is achieved using low Au loading mass. The isolated Au nanoparticle size remarkably affected the catalytic activities of Au@TiO2, and TiO2 coated with 5 nm Au (Au5@TiO2) exhibited the best catalytic function to reduce oxygen. The plasmon-enhanced reductive activity is attributed to the surface plasmonic resonance of isolated Au nanoparticles in TiO2 nanocavities and suppressed electron recombination. This work provides comprehensive understanding of a novel plasmonic system using isolated noble metals into nanostructured semiconductor films as a potential alternative catalyst for oxygen reduction reaction.
