Graphene quantum dots on TiO₂ nanotubes as a light-assisted peroxidase nanozyme

Hybrid nanozyme graphene quantum dots (GQDs) deposited TiO₂ nanotubes (NTs) on titanium foil (Ti/TiO₂ NTs-GQDs) were manufactured by bestowing the hybrid with the advantageous porous morphology, surface valence states, high surface area, and copious active sites. The peroxidase-like activity was investigated through the catalytic oxidation of chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H₂O₂, which can be visualized by the eyes. TiO₂ NTs and GQDs comprising oxygen-containing functional groups can oxidize TMB in the presence of H₂O₂ by mimicking peroxidase enzymes. The peroxidase-mimicking activity of hybrid nanozyme was significantly escalated by introducing light illumination due to the photosensitive features of the hybrid material. The peroxidase-like activity of Ti/TiO₂ NTs-GQDs enabled H₂O₂ determination over the linear range of 7 to 250 μM, with a LOD of 2.1 µM. The satisfying peroxidase activity is possibly due to the unimpeded access of H₂O₂ to the catalyst's active sites. The porous morphology provides the easy channeling of reactants and products. The periodic structure of the material also gave rise to acceptable reproducibility. Without material functionalization, the Ti/TiO₂ NTs-GQDs can be a promising substitute for peroxidases for H₂O₂ detection.