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

Abstract

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.

Anodic SnO2 Nanoporous Structure Decorated with Cu2O Nanoparticles for Sensitive Detection of Creatinine: Experimental and DFT Study

“…40−42 The XRD pattern of the pristine sample annealed at 450 °C (Figure 5a, red curve) exhibits welldefined diffraction peaks with improved intensity. 34 It shows outstanding relationship with the international center for diffraction data (ICDD = 01-086-8925) and the literature. 16 The sheet (Figure S4a, red curve) confirms the formation of amorphous SnO 2 .…”

“…The pristine sample calcined at 350 °C in air confirms the rutile phase formation with a tetragonal structure (Figure a, black spectrum). The peak positions appearing at ∼ 26.5, 33.8, 37.9, 51.7,57.7, 61.8, and 65.2° correspond to the reflections from (110), (101), (200), (211), (002), (310), and (112) crystal planes of SnO 2 . − The XRD pattern of the pristine sample annealed at 450 °C (Figure a, red curve) exhibits well-defined diffraction peaks with improved intensity . It shows outstanding relationship with the international center for diffraction data (ICDD = 01-086-8925) and the literature .…”

“…Rutile SnO 2 having space group P 4 2 / mnm and point group D 4h with 2 SnO 2 molecules per unit cell and 15 optical phonons corresponding to this symmetry is given by normalΓ = normalA 1 normalg + normalA 2 normalg + normalA 2 normalu + normalB 1 normalg + normalB 2 normalg + 2 normalB 1 normalu + normalE normalg + 3 normalE normalu where B 1g , A 1g , E g , and B 2g are the Raman active modes. The Raman spectrum of the SnO 2 nanoporous structure (green curve in Figure b) is composed of three major peaks found at ∼470, 636, and 773 cm –1 , which can be assigned to SnO 2 rutile structure . The peak located at 470 cm –1 can be attributed to E g , which is due to the surface defect-related band and vibration of oxygen.…”

“…Raman spectroscopy is a very sensitive technique used to find defects in materials. Defects in different morphologies of SnO 2 nanocrystals have been reported , using Raman spectroscopy. Raman spectroscopy also helps to determine the extent of functionalization of NPs or quantum dots on the substrate surface .…”

“…A 0.1 mol/L phosphate buffer solution (PBS) electrolyte having 7.5 pH was utilized in all electrochemical measurements. 34 For creatinine detection, 1 mmol stock solution was prepared in DI water and then diluted according to the requirement. 2.6.…”