Gold Nanoparticles Deposited Polyaniline–TiO₂ Nanotube for Surface Plasmon Resonance Enhanced Photoelectrochemical Biosensing

A novel ternary composite composed of TiO₂ nanotubes (TiONTs), polyaniline (PANI), and gold nanoparticles (GNPs) was prepared for photoelectrochemical (PEC) biosensing. PANI was initially coated on TiONTs with an oxidative polymerization method, and 12-phosphotungstic acid was then used as a highly localized photoactive reducing agent to deposit GNPs on TiONT-PANI. The morphology and composition of the composite were characterized by various spectroscopic and microscopic methods. Electrochemical impedance spectroscopy was also conducted to demonstrate the excellent electrical conductivity of the composite. A PEC biosensor was fabricated by immobilizing a mixture of lactate dehydrogenase and the composite onto ITO electrodes, which regenerated nicotinamide adenine dinucleotide (NAD⁺) to complete the enzymatic cycle and led to an improved method for PEC detection of lactate. Because of the surface plasmon resonance enhanced effect of GNPs, the electrochromic performance of PANI, and excellent conductivity and biocompatibility of the composite, this method showed a dynamic range of 0.5–210 μM, sensitivity of 0.0401 μA μM^–1, and a detection limit of 0.15 μM