Enhanced sensitivity in non-enzymatic glucose detection by improved growth kinetics of Ni-based nanostructures

Ni-based nanostructures are attractive catalytic materials for many electrochemical applications, among which are non-enzymatic sensing, charge storage, and water splitting. In this work, we clarify the synthesis kinetics of Ni(OH)₂/NiOOH nanowalls grown by chemical bath deposition at room temperature and at 50 °C. We applied the results to non-enzymatic glucose sensing, reaching a highest sensitivity of 31 mA cm^-2mM^-1. Using scanning electron microscopy, x-ray diffraction analysis and Rutherford backscattering spectrometry we found that the growth occurs through two regimes: first, a quick random growth leading to disordered sheets of Ni oxy-hydroxide, followed by a slower growth of well-aligned sheets of Ni hydroxide. A high growth temperature (50 °C), leading mainly to well-aligned sheets, offers superior electrochemical properties in terms of charge storage, charge carrier transport and catalytic action, as confirmed by cyclic voltammetry and electrochemical impedance spectroscopy analyses. The reported results on the optimization and application of low-cost synthesis of these Ni-based nanostructures have a large potential for application in catalysis, (bio)sensing, and supercapacitors areas.

Low-cost synthesis of pure ZnO nanowalls showing three-fold symmetry

ZnO nanowalls (NWLs) represent a non-toxic, Earth abundant, high surface-to-volume ratio, semiconducting nanostructure which has already showed potential applications in biosensing, environmental monitoring and energy. Low-cost synthesis of these nanostructures is extremely appealing for large scale upgrading of laboratory results, and its implementation has to be tested at the nanoscale, at least in terms of chemical purity and crystallographic orientation. Here, we have produced pure and texturized ZnO NWLs by using chemical bath deposition (CBD) synthesis followed by a thermal treatment at 300 °C. We examined the NWL formation process and the new obtained structure at the nanoscale, by means of scanning and transmission electron microscopy in combination with x-ray diffraction and Rutherford backscattering spectrometry. We have shown that only after annealing at 300 °C in nitrogen does the as-grown material, composed of a mixture of Zn compounds NWLs, show its peculiar crystal arrangement. The resulting ZnO sheets are in fact made by ZnO wurtzite domains (4-5 nm) that show a particular kind of texturization; indeed, they are aligned with their own c-axis always perpendicular to the sheets forming the wall and rotated (around the c-axis) by multiples of 20° from each other. The presented data show that low-cost CBD, followed by an annealing process, gives pure ZnO with a peculiarly ordered nanostructure that shows three-fold symmetry. Such evidence at the nanoscale will have significant implications for realizing sensing or catalyst devices based on ZnO NWLs.

Low-cost and facile synthesis of Ni(OH)2/ZnO nanostructures for high-sensitivity glucose detection

An efficient electrode for non-enzymatic glucose detection is produced with low-cost techniques on a Cu wire. ZnO nanorods (NRs) were grown on a Cu wire by chemical bath deposition and were used as the substrate for pulsed electrodeposition of nanostructured Ni(OH)₂ flakes. The effect of the electrodeposition potential on the final morphology and electrochemical behavior of the Ni(OH)₂/ZnO/Cu structures is reported. ZnO NRs resulted to be well dressed by Ni(OH)₂ flakes and were tested as glucose sensing electrodes in 0.1 M NaOH solution, showing high sensitivities (up to 3 mA mM^-1 cm^-2) and long-term stability. The presence of ZnO NRs was shown to improve the performance of the glucose sensor in terms of electrochemical stability over the time and sensitivity compared to Ni(OH)₂/Cu sample. The reported data demonstrate a simple, versatile and low-cost fabrication approach for effective glucose sensing system within a urban mines framework.

CeO₂ Nanorods Embedded in Ni(OH)₂ Matrix for the Non-Enzymatic Detection of Glucose

The electrode based on cerium oxide (CeO₂) nanorods embedded in nickel hydroxide (Ni(OH)₂) matrix were prepared and used for detecting glucose non-enzymatically. The materials were characterized by X-ray diffraction, transmission electron microscopy (TEM), and so on. The results indicate that the response of CeO₂/Ni(OH)₂ nanocomposite are significantly improved due to the synergetic effect between CeO₂ and Ni(OH)₂. The optimum CeO₂/Ni(OH)₂ nanocomposite electrode exhibits a detection range from 2 μM to 6.62 mM, a sensitivity of 594 μA mM-1 cm-2, an estimated detection limit of 1.13 μM, and a response time less than 5 s. In addition, this biosensor also shows good selectivity, long term stability, and accurate measurement in juice on sale.