Improving Photovoltaic and Enzymatic Sensing Performance by Coupling a Core–Shell Au Nanorod@TiO₂ Heterostructure with the Bioinspired <scp>l</scp>-DOPA Polymer

Abstract

The photoelectrochemistry (PEC) performance of TiO₂ is somewhat limited by its wide band gap and low quantum efficiency, and the innovation of its composite materials provides a promising solution for an improved performance. Herein, a composite of a Au nanorod@TiO₂ core-shell nanostructure (AuNR@TiO₂) and a melanin-like l-DOPA polymer (PD) is designed and prepared, where the outer layer PD tethered by TiO₂-hydroxyl complexation and the AuNR core can intensify the long-wavelength light harvesting, and the AuNR@TiO₂ core-shell structure can strengthen the hot-electron transfer to TiO₂. The photocurrent of PD/AuNR@TiO₂ is 8.4-fold improved versus that of commercial TiO₂, and the maximum incident photon-to-electron conversion efficiency reaches 65% in the UV-visible-near-infrared region. In addition, the novel PD/AuNR@TiO₂ photocatalyst possesses the advantages of good biocompatibility and stability, which can act as a versatile PEC biosensing platform for providing a biocompatible environment and improving detection sensitivity. Herein, a PEC enzymatic biosensor of glucose is developed on the basis of the immobilization of dual enzyme [glucose oxidase (GOx) and horseradish peroxidase (HRP)] in PD and the signaling strategy of biocatalytic precipitation. In phosphate buffer containing glucose and 4-chloro-1-naphthol, the HRP-catalyzed oxidation of 4-chloro-1-naphthol by GOx-generated H₂O₂ can form a precipitate on the electrode, by which the decrement of photocurrent intensity is proportional to the common logarithm of glucose concentration. The linear detection range is from 0.05 μM to 10.0 mM glucose, with a limit of detection of 0.01 μM (S/N = 3). Glucose in some human serum samples is analyzed with satisfactory results.