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(2)O(2)) 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 TiO(2) nanoneedle film (Au/TiO(2) film), and both anodic and cathodic currents of the redox reaction at the Au/TiO(2) 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/TiO(2) film in the presence of cyt. c is in a good agreement with the surface plasmon absorption spectrum of Au NPs deposited onto the TiO(2) 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/TiO(2) film and maintains inherent enzymatic activity toward H(2)O(2) 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/TiO(2) film even after continuous visible-light illumination, subsequently provide the enhanced analytical performance in determination of H(2)O(2). The sensitivity of the present biosensor for H(2)O(2) is 4-fold larger than that obtained without visible-light irradiation, the detection limit is achieved to be 4.5 x 10(-8) M and the dynamic detection linear range extends from 1 x 10(-7) M to 1.2 x 10(-2) M.