Highly Sensitive Non‑Enzymatic Glucose Sensor Based on Mesoporous NiO Nanopetals Grown on FTO

Abstract

We report a non‑enzymatic glucose sensor built on mesoporous, well‑aligned nickel oxide (NiO) nanopetals (NPs) hydrothermally grown on fluorine‑doped tin oxide (FTO) glass. Structural analysis (XRD, SEM, TEM, AFM, EDX, XPS) confirms a dense, vertically oriented NP morphology with an average thickness of 25–30 nm. Brunauer–Emmett–Teller (BET) surface area of 115 m² g⁻¹ and a pore size of 3.7 nm indicate excellent electrochemical accessibility. The sensor delivers a linear response from 50 µM to 1.2 mM glucose with a sensitivity of 3.9 µA µM⁻¹ cm⁻² at 0.5 V, a detection limit of 1 µM, and a response time under 1 s. It shows negligible interference from ascorbic acid, uric acid, and dopamine, making it a reliable non‑enzymatic glucose probe.

Background

Diabetes management hinges on accurate, real‑time glucose monitoring. Conventional enzymatic sensors rely on glucose oxidase (GOx) and suffer from limited lifespan and sensitivity to temperature, pH, and toxic reagents. Metal‑oxide based non‑enzymatic sensors circumvent these issues by directly oxidizing glucose on the electrode surface. NiO, CuO, TiO₂, and ZnO nanostructures have emerged as promising candidates due to their high surface‑to‑volume ratio and catalytic activity. Nanostructuring further increases active surface area, improving sensor performance. Here, we present NiO nanopetals grown on FTO, engineered for optimal glucose oxidation.

Experimental

Nickel nitrate and potassium persulfate were mixed with a trace of ammonium solution to guide the alignment of NiO NSs. The precursor solution was hydrothermally treated at 150 °C for 5 h on FTO glass, rinsed, dried, and annealed at 250 °C for 2 h. XRD (Rigaku SmartLab, Cu‑Kα, λ = 1.54 Å), SEM (Zeiss Supra55), TEM, AFM (Bruker MultiMode 8‑HR), EDX (Oxford Instruments), and XPS (SPECS) characterized the structure and composition. BET analysis (Quantachrome Autosorb iQ) quantified surface area and porosity. Electrochemical measurements used a Keithley 2450‑EC workstation in a three‑electrode setup with Ag/AgCl (1 M KCl) reference and Pt wire counter electrodes, employing 0.1 M NaOH as electrolyte.

Results and Discussion

The SEM and AFM images (Figure 1) reveal densely packed, rose‑petal‑like NiO structures uniformly covering the FTO substrate. Each petal is 25–30 nm thick, with fine thorn‑like features enhancing the surface area. TEM confirms the morphology, and EDX demonstrates high‑purity NiO with minimal Sn from the substrate. XPS shows Ni²⁺ in Ni–O bonds and confirms the crystalline FCC structure (XRD peaks at 43°, 37°, 63°, 76°, 79°). BET measurements indicate a mesoporous network with a surface area of 114.936 m² g⁻¹ and a pore size distribution centered at 3.7 nm (Figure 2).

Electrochemical tests (Figure 3) show that the NiO‑NPs@FTO electrode is surface‑controlled: the peak current scales linearly with scan rate, indicating efficient charge transfer. Cyclic voltammetry in 0.1 M NaOH reveals a pronounced oxidation peak between 0 V and 0.6 V. In the presence of 5 mM glucose, the peak current doubles, confirming glucose oxidation. The reaction pathway involves NiO forming NiO(OH), which oxidizes glucose to gluconolactone and subsequently to gluconic acid, producing measurable current (sensitivity 3.9 µA µM⁻¹ cm⁻²). Electrochemical impedance spectroscopy (EIS) shows a reduced semicircle and steeper low‑frequency line upon glucose addition, corroborating the sensor’s electrochemical activity.

Calibration curves (Figure 4) display linearity (R² = 0.9948) across 100 µM–1.2 mM glucose, with an amperometric response at +0.5 V yielding a sub‑second response and excellent repeatability. Selectivity tests against uric acid, ascorbic acid, and folic acid demonstrate negligible interference, while the sensor’s current decreases after glucose spikes, indicating reusability. Compared to recent non‑enzymatic sensors, the NiO‑NPs electrode offers superior sensitivity and rapid response.

Conclusions

Hydrothermally grown, densely packed NiO nanopetals on FTO provide a highly sensitive, non‑enzymatic glucose sensor. With a detection limit of 1 µM, a response time under 1 s, and robust selectivity, this platform is well‑suited for biomedical diagnostics and pharmaceutical analysis.

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