High-Density Single Nickel Sites via an Encapsulation-Substitution Strategy for Nonenzymatic Glucose Sensing

The content of metal single atoms is an important factor for restricting the electrocatalytic activity. In this work, the substitution-encapsulation strategy was reported to obtain high-density nickel single atoms (Ni SAs). This strategy was not only based on ion exchange between Zn nodes and adsorbed Ni²⁺ ions but also utilized porous ZIF-8 as a host to trap metal precursor guests in situ in their cages. The synergistic effect of ion exchange and precursor encapsulation significantly increased the content of Ni SAs. The structures of the Ni SAs were studied via transmission electron microscopy (TEM), high-angle annular dark-field scanning TEM (HAADF-STEM), X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), and atomic absorption spectroscopy (AAS). Electrochemical studies revealed that the prepared high-density Ni SA catalyst is beneficial for increasing the electrocatalytic activity toward glucose. The sensitivity and the detection limit were 653.9 μA·mM^–1·cm^–2 and 0.51 μM, respectively. Furthermore, a sensor based on high-density Ni SAs can achieve highly sensitive determination of glucose content in energy drinks and serum samples. This work provides an idea for designing highly active electrocatalysts to improve glucose electrochemical sensing.