SnO–Sn(OH)2 nanoflakes as non-enzymatic glucose sensor for human serum analysis using EIS

Abstract

A porous film, composed of tin oxide and hydroxide nanoflakes (SnE/SnO@Sn(OH)₂), was successfully grown on a bare Sn electrode and used as a non-enzymatic sensor for glucose detection using electrochemical impedance spectroscopy (EIS). The sensor was developed in a single step via anodic oxidation in a 0.1 M Na₂SO₄ solution. Various characterization techniques, including CV, EIS, chronoamperometry, SEM, XRD and ATR-FTIR, were employed to confirm and analyze the modification process. Unlike conventional SnO₂-based or MOF-based sensors, the unique SnO–Sn(OH)₂ hybrid system combines the high electrical conductivity and catalytic activity of SnO with the abundant hydroxyl functional sites of Sn(OH)₂, yielding a synergistic enhancement in glucose oxidation performance. EIS technique was used as the detection method because of its high sensitivity to interfacial changes at low analyte concentrations, allowing precise monitoring of glucose oxidation kinetics that might be overlooked by faster but less surface-sensitive techniques such as amperometry or cyclic voltammetry. Several parameters were optimized to enhance the sensor's efficiency, i.e. deposition potential, accumulation time, temperature, electrolyte type, and pH. Under optimal conditions, the modified electrode demonstrated the best response in NaOH solution, showing a significant enhancement in electrocatalytic activity for glucose oxidation. The as-prepared sensor demonstrated the ability to detect glucose over a wide concentration range, up to 2.0 μM, with a detection limit of 0.4 μM, a quantification limit of 1.8 μM, and a notable sensitivity of 0.04 mA mM⁻¹ cm⁻². Additionally, the SnE/SnO@Sn(OH)₂-5 sensor exhibited excellent selectivity in the presence of various interfering species. It also displayed good repeatability (RSD = 0.49 %) and reproducibility (RSD = 0.91 %). The sensor's reliability and precision were further confirmed by its satisfactory performance in human serum, with recovery values ranging from 96 % to 101 %. In summary, our study introduces an innovative and cost-effective electrochemical sensor based on a modified tin electrode, offering sensitive and accurate glucose detection.