Efficient chemiluminescence harnessing via slow photons in sensitized TiO2 nanotubes for the photoelectrochemical biosensing

TiO2 nanotubes (TNTs) were fabricated by anodic oxidation and the partially reduced black-TNTs (B-TNTs) were obtained by electrochemical reduction. After the sensitization of B-TNTs with thioflavin T (B-TNTs-Th-T), the photoelectrode was used as a photoelectrochemical (PEC) biosensing of glucose. The uniform porous architecture of TNTs with a high surface to volume ratio is responsible for the photo-generated charge transfer and Th-T absorption and sensitization broadened the light absorption range and intensity. The favorable matching of energy levels between Th-T and B-TNTs allowed a fast electron transfer from excited Th-T to TNTs under chemiluminescence (CL). Furthermore, the bandgap of TNTs was red-shifted after the formation of B-TNTs and the red edge of the photonic stop-band was deliberately tuned to overlap with both the bandgap of the semiconducting material and the CL emission spectrum, by leading dual enhancement effects which enhanced the photocurrent unprecedentedly mainly owing to the "slow light effect". The photo-electrode yielded 40 times higher photocurrent compared to TiO2 thin film coated counterpart indicating effectively harnessing of CL. The biosensor has a large linear measurement range of 0.027-5 mM with a LOD of 8 mu M for glucose. The phenomenon "slow light effect" will pay the way for efficient light harnessing and management for commercially available more sensitive and inexpensive PEC devices in the future.