High-Density Single\nNickel Sites via an Encapsulation-Substitution\nStrategy for Nonenzymatic Glucose Sensing

The\ncontent of metal single atoms is an important factor for restricting\nthe electrocatalytic activity. In this work, the substitution-encapsulation\nstrategy was reported to obtain high-density nickel single atoms (Ni\nSAs). This strategy was not only based on ion exchange between Zn\nnodes and adsorbed Ni<sup>2+</sup> ions but also utilized porous ZIF-8\nas a host to trap metal precursor guests in situ in their cages. The\nsynergistic effect of ion exchange and precursor encapsulation significantly\nincreased the content of Ni SAs. The structures of the Ni SAs were\nstudied via transmission electron microscopy (TEM), high-angle annular\ndark-field scanning TEM (HAADF-STEM), X-ray diffractometry (XRD),\nX-ray photoelectron spectroscopy (XPS), and atomic absorption spectroscopy\n(AAS). Electrochemical studies revealed that the prepared high-density\nNi SA catalyst is beneficial for increasing the electrocatalytic activity\ntoward glucose. The sensitivity and the detection limit were 653.9\nμA·mM<sup>–1</sup>·cm<sup>–2</sup> and\n0.51 μM, respectively. Furthermore, a sensor based on high-density\nNi SAs can achieve highly sensitive determination of glucose content\nin energy drinks and serum samples. This work provides an idea for\ndesigning highly active electrocatalysts to improve glucose electrochemical\nsensing.