Hierarchical Co3O4@ZnO binary oxide microstructures for high-performance photoelectrochemical glucose sensing

Binary metal oxides with hierarchical architectures have emerged as promising platforms for non-enzymatic glucose sensing due to their tunable optoelectronic properties and intrinsic redox activity. In this work, we report a sustainable, additive-free synthesis of a 3D Co₃O₄@ZnO heterostructure via a one-pot hydrothermal method followed by inert-gas calcination, effectively minimizing oxygen interference and preserving structural integrity. The composite integrates the redox-rich, narrow-bandgap Co₃O₄ with UV-active, high-mobility ZnO to form a type-II heterojunction that enables broad-spectrum light absorption, efficient charge separation, and suppressed carrier recombination. These features also enhance the electrochemical behavior of the material, yielding an ultra-low charge transfer resistance (R_ct = 3.35 Ω) and facilitating rapid electron transport and ion diffusion at the electrode/electrolyte interface. As a result, the Co₃O₄@ZnO heterostructure supports high-performance dual-mode glucose sensing under both dark and illuminated conditions. In the absence of light, the sensor exhibits a sensitivity of 114 μA cm⁻² mM⁻¹, a wide linear range (0.2–4 mM), and a fast response time (21 s). Upon illumination, a photoinduced internal electric field at the heterojunction interface significantly boosts performance, achieving a photoelectrochemical sensitivity of 231 μA cm⁻² mM⁻¹ with a rapid response of 11 s. Photocurrent studies further reveal response and recovery times of 5 s and 4 s, respectively. Importantly, the sensor also demonstrates reliable glucose detection in real urine samples, confirming its suitability for real-time physiological monitoring. These results highlight the Co₃O₄@ZnO heterostructure as an efficient and eco-friendly platform for stable, reliable, and high-performance dual-mode glucose sensing.