A novel
ternary composite composed of TiO<sub>2</sub> 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<sup>+</sup>) 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<sup>–1</sup>, and a detection limit of 0.15 μM
