Detection of extracellular H₂O₂ released from human liver cancer cells based on TiO₂ nanoneedles with enhanced electron transfer of cytochrome c

The high conductive TiO₂ nanoneedles film is first employed as a support matrix for immobilizing model enzyme, cytochrome c (cyt c) to facilitate the electron transfer between redox enzymes and electrodes. Reversible and direct electron transfer of cyt c is successfully achieved at the nanostructured TiO₂ surface with the redox formal potential (E ⁰′) of 108.0 ± 1.9 mV versus Ag|AgCl and heterogeneous electron transfer rate constant (k_s) of 13.8 ± 2.1 s ^-1. Experimental data indicate that cyt c is stably immobilized onto the TiO₂ nanoneedles film and maintains inherent enzymatic activity toward H₂O₂. On the basis of these results, the cyt c-TiO₂ nanocomposits film is capable of sensing H₂O ₂ at a suitable potential, 0.0 V (vs Ag|AgCl), where not only common anodic interferences like ascorbic acid, uric acid, 3,4-dihydroxyphenylacetic acid but also a cathodic interference, O₂, are effectively avoided. Besides high selectivity, the present biosensor for H₂O₂ shows broad dynamic range and low detection limit. These remarkable analytical advantages, as well as the characteristic of TiO₂ nanoneedles film such as high conductivity, biocompatibility, and facile ability to miniaturize establishes a novel approach to detection of extracellular H₂O ₂ released from human liver cancer cells.