Cobalt Phosphate Nanostructures for Non-Enzymatic Glucose Sensing at Physiological pH

Abstract

Nanostructured materials have great potential as platforms for analytical assays and catalytic reactions. Herein, we report the synthesis of electrocatalytically active cobalt phosphate nanostructures (CPNs) using a simple, low-cost, and scalable preparation method. The electrocatalytic properties of the CPNs toward the electrooxidation of glucose (Glu) were studied by cyclic voltammetry and chronoamperometry in relevant biological electrolytes, such as phosphate-buffered saline (PBS), at physiological pH (7.4). Using the CPNs, Glu detection could be achieved over a wide range of biologically relevant concentrations, from 1 to 30 mM Glu in PBS, with a sensitivity of 7.90 nA/mM cm 2 and a limit of detection of 0.3 mM, thus fulfilling the necessary requirements for human blood Glu detection. In addition, the CPNs showed a high structural and functional stability over time at physiological pH. The CPN-coated electrodes could also be used for Glu detection in the presence of interfering agents (e.g., ascorbic acid and dopamine) and in human serum. Density functional theory calculations were performed to evaluate the interaction of Glu with different faceted cobalt phosphate surfaces; the results revealed that specific surface presentations of undercoordinated cobalt led to the strongest interaction with Glu, suggesting that enhanced detection of Glu by the CPNs can be achieved by lowering the surface coordination of cobalt.Our results highlight the potential use of phosphate-based nanostructures as catalysts for electrochemical sensing of biochemical analytes.Potassium chloride (KCl, CAS no. 7440-09-7) was purchased from Chem-Supply. All the chemicals were used as received. High purity (Milli-Q) water with a resistivity of 18.2 MΩ cm was obtained from an inline Millipore RiOs/Origin water purification system.Instrumentation. X-ray photoelectron spectroscopy (XPS) spectra were acquired using an Axis Ultra X-ray photoelectron spectrometer (Kratos Analytical, UK), equipped with a 165 mm concentric hemispherical electron energy analyzer and a monochromated Al Kα incident Xray source (1486.6 eV). Survey (wide) scans were recorded in the binding energy range of 0-1200 eV, with 1.0 eV steps, a dwell time of 100 ms, and an analyzer pass energy of 160 eV.Multiplex (narrow) high-resolution spectra were recorded with a pass energy of 20 eV, with 0.05 eV steps, and a dwell time of 250 ms, resulting in an energy resolution (ΔE/E) of ~300 meV. The base pressure in the analysis chamber during data collection was 1-2 × 10 −9 mbar, and these data were processed using the software CasaXPS. All binding energies were calibrated using the C 1s level of adventitious carbon at 285.0 eV. Fourier transform infrared (FTIR) spectra were obtained on a Tensor II (Bruker) attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectrometer and analyzed using the software OPUS 7.8. The number of scans was 64. A minimum resolution of 4 cm −1 and the absorbance/transmittance mode were used. Scanning electron microscopy (SEM) images were o...

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