Three-Dimensional TiO₂@Cu₂O@Nickel Foam Electrodes: Design, Characterization, and Validation of O₂-Independent Photocathodic Enzymatic Bioanalysis

This work reports the innovative design and application of a three-dimensional (3D) TiO2@Cu2O@nickel foam electrode synergized with enzyme catalysis toward the proof-of-concept study for oxygen-independent photocathodic enzymatic detection. Specifically, a 3D-nanostructured photoelectrode has great potential in the semiconductor-based photoelectrochemical (PEC) biological analysis. On the other hand, using various photocathodes, cathodic PEC bioanalysis, especially the photocathodic enzymatic detection, represents an attractive frontier in the field. Different from state-of-the-art photocathodic enzymatic studies that are oxygen-dependent, herein, we present the ingenious design, characterization, and implementation of 3D TiO2@Cu2O@nickel foam photocathodes for the first oxygen-independent example. In such a configuration, the Cu2O acted as the visible-light absorber, while the TiO2 shell would simultaneously function as a protective layer for Cu2O and as a desirable substrate for the immobilization of enzyme biomolecules. Especially, because of the proper band positions, the as-designed photocathode exhibited unique O2-independent PEC property. Exemplified by glucose oxidases, the as-developed sensor exhibited positive response to glucose with good performance. Because various oxidases could be integrated with the system, this protocol could serve as a universal O2-independent platform for many other targets. This work is also anticipated to catalyze more studies in the advanced 3D photoelectrodes toward innovative enzymatic applications.