Anodic SnO₂ Nanoporous Channels Functionalized with CuO Quantum Dots for Selective H₂O₂ Biosensing

In this work, we explore the nonenzymatic detection of H2O2 using anodic SnO2 nanoporous channels (NPC) decorated with CuO quantum dots (QDs). The open-top and crack-free morphology of SnO2 NPC was obtained by modified anodization. The samples were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray analysis (EDAX), high-resolution transmission electron microscopy (HRTEM), Raman and X-ray photoelectron (XPS) spectroscopy. FESEM and HRTEM results show that SnO2 has a uniform channel width and pore size with an average diameter of around 40 nm. XRD, EDAX, XPS, Raman, and HRTEM measurements confirm the high purity of anodic SnO2 NPC with successful deposition of CuO QDs. Pristine (SnO2) and hybrid (SnO2-CuO) electrodes were used directly as the nonenzymatic H2O2 biosensor. The hybrid electrode demonstrated an ultrahigh sensitivity of ∼85,250 μA mM–1 cm–2 with an extremely low limit of detection (0.001 μM), broad linear detection ranges of 5–95 and 25–450 μM, and a quick response time (less than 1.9 s) toward H2O2 detection. This can be attributed to the advanced SnO2 nanoporous structure, the reduced band gap, and the formation of additional surface sites as a result of CuO QD decoration. H2O2 measurement in human blood serum demonstrates high sensitivity, good accuracy, and excellent selectivity of the fabricated hybrid electrode compared to the commercially available biosensor. Density functional theory results indicate that the formation of SnO2-CuO is energetically favorable. H2O2 is strongly and selectively adsorbed over the SnO2-CuO nanostructure possessing a large negative adsorption energy (−1.89 eV) and evinces a significant decrease in the band gap (up to 1.59 eV) of the hybrid structure. The fabricated biosensor showed the highest sensitivity, excellent selectivity, good reproducibility, repeatability, and stability, thus confirming it as a favorable candidate for nonenzymatic H2O2 sensing and quantification.