Highly Efficient Non-Enzymatic Glucose Sensor Based on CuO Modified Vertically-Grown ZnO Nanorods on Electrode

Abstract

There is a major challenge to attach nanostructures on to the electrode surface while retaining their engineered morphology, high surface area, physiochemical features for promising sensing applications. In this study, we have grown vertically-aligned ZnO nanorods (NRs) on fluorine doped tin oxide (FTO) electrodes and decorated with CuO to achieve high-performance non-enzymatic glucose sensor. This unique CuO-ZnO NRs hybrid provides large surface area and an easy substrate penetrable structure facilitating enhanced electrochemical features towards glucose oxidation. As a result, fabricated electrodes exhibit high sensitivity (2961.7 μA mM^-1 cm^-2), linear range up to 8.45 mM, low limit of detection (0.40 μM), and short response time (<2 s), along with excellent reproducibility, repeatability, stability, selectivity, and applicability for glucose detection in human serum samples. Circumventing, the outstanding performance originating from CuO modified ZnO NRs acts as an efficient electrocatalyst for glucose detection and as well, provides new prospects to biomolecules detecting device fabrication.

Figure 1

Schematic illustration. Non-enzymatic glucose sensor electrode fabrication and its application in glucose detection.

Figure 2

(a) XRD patterns of as-synthesized ZnO NRs and CuO modified ZnO NRs. (b) Low- and (c) high-resolution FESEM images of as-grown ZnO NRs. (d) Low-, (e) high-resolution, and (f) cross sectional FESEM view of CuO modified ZnO NRs.

Figure 3

XPS analysis. XPS spectrum of ZnO NRs and CuO modified ZnO NRs showing full scan survey (a) and corresponding deconvoluted peaks in the high resolution spectra for O 1 s (b), Zn 2p (c), and Cu 2p (d) elements.

Figure 4

Typical Nyquist semicircle plots of EIS spectra. Electrode fabrication step measured in a mixture of 5 mM [Fe(CN)₆]^3-/4- and 0.1 M KCl solutions at an applied amplitude of ± 5 mV within a frequency range of 0.01 Hz-100 MHz. (a) Bare FTO electrode, (b) ZnO NRs/FTO electrode, (c) 10 s CuO modified ZnO NRs/FTO electrode, (d) 20 s CuO modified ZnO NRs/FTO electrode, and (e) 30 s CuO modified ZnO NRs/FTO electrode. Inset FESEM images show the surface morphology of the electrodes. Randles equivalent circuit model is shown in inset, where C_dl, R_s, R_et, and Z_w are double layer capacitor, solution resistor, electron transfer resistance, Warburg resistor, respectively.

Figure 5

Typical CV curve of electrodes. (a) CV response of FTO, ZnO NRs/FTO, and CuO-ZnO NRs/FTO electrodes in blank NaOH solution (scan rat, 100 mVs⁻¹). (b) CVs in the presence of glucose at different electrode (scan rat, 100 mVs⁻¹). (c) CVs for CuO-ZnO NRs/FTO in 0.1 mM glucose at scan rats from 20 to 200 mVs⁻¹. (d) Corresponding calibration plot of peak current versus scan rate.

Figure 6

Non-enzymatic detection of glucose. (a) Amperometric response of CuO-ZnO NRs/FTO electrode at +0.62 V (versus Ag/AgCl) in 0.1 M NaOH solution with different glucose concentration from 0.001 to 14.95 mM and inset response curve shows the magnified view of low concentration range of glucose (0.001–3.95 mM). (b) Corresponding calibration plot of current response versus glucose concentration. (c) Anti-interference ability test. Amperometric response of the CuO-ZnO NRs/FTO electrode with the addition of 0.1 mM glucose and 0.02 Mm of each possible interfering species i.e. (a) AA, (b) UA, (c) DA, (d) NADH, (e) Mg²⁺, (f) Ca²⁺, (g) Cys, (h) NaCl, (i) lactose, (j) sucrose, (k) maltose, and (l) mannose in the 0.1 M NaOH solution at +0.62 V (versus Ag/AgCl). (d) Real sample glucose detection. Amperometric response of CuO-ZnO NRs/FTO electrode at +0.62 V (versus Ag/AgCl) in 9.5 mL 0.1 M NaOH solution after injecting 0.5 mL blood serum (i) and freshly drawn whole human blood (ii). The upper inset shows the photograph of serum and whole blood samples and lower inset shows the histogram of glucose concentration compared with blood chemistry analyzer result.