WO₃ nanostructures facilitate electron transfer of enzyme: Application to detection of H₂O₂ with high selectivity

The WO₃ nanoparticles film is first employed as a support matrix for confining cytochrome c (cyt. c), an excellent model for studying electron transfer between the redox enzymes and the electrode. The surface pK_a of nanostructured WO₃ film is estimated to be ∼2.74 using electrochemical method. The present WO₃ surface with negative charge at the neutral solution is very benefit for the adsorption of cyt. c with positive charge and facilitates electron transfer of cyt. c. As a result, direct and fast electron transfer of cyt. c is realized at the nanostructured WO₃ surface with the redox formal potential (E⁰′) of -133.5 ± 1.7 mV (n = 4) versus Ag/AgCl and heterogeneous electron transfer rate constant of 5.57 ± 0.54 s^-1. Experimental data indicate that cyt. c is stably confined onto the WO₃ nanoparticles film, possibly due to the electrostatic interaction between WO₃ nanostructures and cyt. c, and processes its enzymatic activity toward H₂O₂. Based on these results, the third-generation biosensor for H₂O₂ is developed with high selectivity, free from not only common anodic interferences like ascorbic acid, uric acid, 3,4-dihydroxyphenylacetic acid, and so on, but also cathodic interference-O₂. The remarkable analytical advantages, as well as the characteristic of WO₃ nanoparticles film such as biocompatibility, low-cost, and facile to miniature give a strong basis for continuous, on-line detection of H₂O₂ under pathophysiological conditions.