Plasmon-induced enhancement in analytical performance based on gold nanoparticles deposited on TiO₂ film

This paper demonstrates a novel approach for developing the analytical performance of electrochemical biosensors in which hydrogen peroxide (H ₂O₂) is selected as a model target, based on surface plasmon resonance of gold nanoparticles (Au NPs) deposited onto a TiO ₂ nanoneedle film. Direct electron transfer of cytochrome c (cyt. c) is realized at Au NPs deposited onto a TiO₂ nanoneedle film (Au/TiO₂ film), and both anodic and cathodic currents of the redox reaction at the Au/TiO₂ film upon visible-light irradiation are amplified. Meanwhile, in the presence of oxidized or reduced states of cyt. c, cathodic or anodic photocurrents are generated respectively by the Au/TiO ₂ film, suggesting that the amplified anodic and cathodic currents are ascribed to the visible-light excitation. The photocurrent action spectrum obtained at the Au/TiO₂ film in the presence of cyt. c is in a good agreement with the surface plasmon absorption spectrum of Au NPs deposited onto the TiO₂ film, and maximum photocurrent is also consistent with the plasmon absorption peak of Au NPs themselves. It indicates that the enhanced photocurrents generated by visible-light irradiation are attributed to the surface plasmon resonance of Au NPs. On the other hand, experimental results reveal that cyt. c is stably immobilized onto the Au/TiO₂ film and maintains inherent enzymatic activity toward H2O₂ even under continuous visible-light illumination. The amplified redox currents of cyt. c produced by surface plasmon resonance of Au NPs, combined with the stability and enzymatic activity of cyt. c confined on the Au/TiO₂ film even after continuous visible-light illumination, subsequently provide the enhanced analytical performance in determination of H₂O₂. The sensitivity of the present biosensor for H₂O₂ is 4-fold larger than that obtained without visible-light irradiation, the detection limit is achieved to be 4.5 x 10^-8 Mand the dynamic detection linear range extends from 1 x 10^-7 M to 1.2 x 10^-2 M.