Controllable Cobalt Oxide/Au Hierarchically Nanostructured Electrode for Nonenzymatic Glucose Sensing

Abstract

By electrodeposition and galvanic replacement reaction, we developed a facile, time-saving, cost-effective, and environmentally friendly, two-step synthesis route to obtain a controllable cobalt oxide/Au hierarchically nanostructured electrode for glucose sensing. The nanomaterials were characterized by transmission electron microscopy, scanning electron microscopy, Raman spectroscopy, energy-dispersive spectrometry, and X-ray photoelectron spectroscopy, meanwhile, the sensing performance was investigated by cyclic voltammetry and amperometric response. The results revealed that this novel electrode exhibited excellent electrocatalytic performance toward glucose oxidation, with a wide double-linear range from 0.2 μM to 20 mM and a low detection limit of 0.1 μM based on a signal-to-noise ratio of 3, which was mainly attributed to the ability of loading a small amount of Au with good electron conductivity on the surface of cobalt oxide nanosheets with large active surface area and synergistic electrocatalytic activity of Au and cobalt oxide toward glucose electrooxidation. This facile, sensitive, and selective glucose sensor is also proven to be suitable for the detection of glucose in human serum.

Nanostructured Inorganic Materials at Work in Electrochemical Sensing and Biofuel Cells

“…The low detection limit (LOD) is estimated to be 1 μM (S/N = 3) for the CoOX/FTO electrode (linear ranges of 2 μM to 0.2 mM, and 1 mM to 20 mM), and 0.1 μM for the Au/Co3O4/FTO electrode (linear ranges of 0.2 μM to 0.2 mM, and 0.5 mM to 20 mM); the LOD was calculated as LOD = 3s/m (s is the standard deviation which was estimated from a small segment of the amperometric response curve obtained before the first addition of glucose, and m is The CV experiments for the electrooxidation behavior of glucose at both cobalt oxide and cobalt oxide/Au electrodes show that the oxidation of glucose starts at ca. 0.40 and 0.25 V vs. Ag|AgCl|KCl sat on CoO x /FTO and Au/Co 3 O 4 /FTO electrodes, respectively [93]. This significant negative shift of E onset towards the lower potential range is assigned to the presence of AuNPs tethered to Co 3 O 4 within the material.…”

“…The CV experiments for the electrooxidation behavior of glucose at both cobalt oxide and cobalt oxide/Au electrodes show that the oxidation of glucose starts at ca. 0.40 and 0.25 V vs. Ag|AgCl|KClsat on CoOx/FTO and Au/Co3O4/FTO electrodes, respectively [93]. This significant negative shift of Eonset towards the lower potential range is assigned to the presence of AuNPs tethered to Co3O4 within the material.…”

“…Then, cobalt electrodeposition (Equation (4) As an alternative to noble metals, cobalt (Co) is another promising candidate as an electrocatalyst. Su et al [93] combined the electrodeposition method and galvanic replacement reaction to design a controllable cobalt oxide/Au hierarchically nanostructured electrode that has glucose-sensing ability with a wide linear range from 0.2 µM to 20 mM and a low detection limit of 0.1 µM (S/N = 3). Typically, the galvanic replacement is a simple and well-established chemical way to fabricate metal (especially noble metal) nanostructures [94][95][96].…”

“…This significant negative shift of E onset towards the lower potential range is assigned to the presence of AuNPs tethered to Co 3 O 4 within the material. According to the literature, the mechanism of the electrochemical oxidation of glucose catalyzed by Co 3 O 4 has been proposed to be that Co 3 O 4 is oxidized to CoOOH, and then CoOOH is further oxidized to CoO 2 , which finally oxidizes glucose to generate gluconolactone and CoOOH (Equations (6)- (8)) [93,97]. Based on this mechanism, the performance mostly depends on the reversibility of the CoO 2 /CoOOH redox couple as an electron transfer agent.…”

“…Amperometric measurements carried out at 0.60 V vs. Ag|AgCl|KCl sat on CoO X /FTO and 0.30 V on Au/Co 3 O 4 /FTO by the successive injection of glucose into 0.1 M NaOH under stirring are displayed within Figure 7. The low detection limit (LOD) is estimated to be 1 µM (S/N = 3) for the CoO X /FTO electrode (linear ranges of 2 µM to 0.2 mM, and 1 mM to 20 mM), and 0.1 µM for the Au/Co 3 O 4 /FTO electrode (linear ranges of 0.2 µM to 0.2 mM, and 0.5 mM to 20 mM); the LOD was calculated as LOD = 3s/m (s is the standard deviation which was estimated from a small segment of the amperometric response curve obtained before the first addition of glucose, and m is the slope of the calibration curve at low glucose concentrations) [93]. The comparison with other reported glucose sensors based on cobalt oxide and gold electrodes (see Table 1 of Reference [93]) indicates the good performance of Au/Co 3 O 4 /FTO heterogeneous material, likely due to the excellent conductivity of gold and the synergistic electrocatalytic activity of gold and cobalt oxide.…”