Catecholate Dye-Assisted Decoration of Ag on TiO₂ Nanoparticles for Detection of Cancer-Related MicroRNA Biomarkers on a Multiplexed Photoelectrochemical Platform

Photoelectrochemical (PEC) signal transduction has emerged as a powerful technique for ultrasensitive biosensing with a low background in complex media. However, it remains challenging to create PEC biosensors found on stable materials that are easily biofunctionalized. Herein, we report the development of a one-pot synthesis method for TiO 2 nanoparticles (NPs) decorated with Ag NPs. In this nanomaterial synthesis process, TiO 2 NPs are modified with hematoxylin (HTX) dye to achieve enhanced photoreduction and direct nucleation of Ag NPs. The resulting TiO 2 /HTX/Ag NP heterostructure showed significantly enhanced photocurrent generation, necessary for achieving high sensitivity in PEC biosensing, through the combined effects of plasmon resonance and photoelectron injection. TiO 2 /HTX/Ag NP is very easily biofunctionalized through thiol–metal complexation. This was taken as an advantage to create a multiplexing PEC microRNA sensor for the analysis of urine samples, which demonstrated a low limit of detection of 172 fM and a high dynamic range of 100 fM–100 nM, while showing a high degree of specificity.