A Sandwich-Type Electrochemical Immunosensor for Insulin Detection Based on Au-Adhered Cu₅Zn₈ Hollow Porous Carbon Nanocubes and AuNP Deposited Nitrogen-Doped Holey Graphene

Rapid, accurate, and sensitive insulin detection is crucial for managing and treating diabetes. A simple sandwich-type electrochemical immunosensor is engineered using gold nanoparticle (AuNP)-adhered metal–organic framework-derived copper–zinc hollow porous carbon nanocubes (Au@Cu5Zn8/HPCNC) and AuNP-deposited nitrogen-doped holey graphene (NHG) are used as a dual functional label and sensing platform. The results show that identical morphology and size of Au@Cu5Zn8/HPCNC enhance the electrocatalytic active sites, conductivity, and surface area to immobilize the detection antibodies (Ab2). In addition, AuNP/NHG has the requisite biocompatibility and electrical conductivity, which facilitates electron transport and increases the surface area of the capture antibody (Ab1). Significantly, Cu5Zn8/HPCNC exhibits necessary catalytic activity and sensitivity for the electrochemical reduction of H2O2 using (i–t) amperometry and improves the electrochemical response in differential pulse voltammetry. Under optimal conditions, the immunosensor for insulin demonstrates a wide linear range with a low detection limit and viable specificity, stability, and reproducibility. The platform's practicality is evaluated by detecting insulin in human serum samples. All these characteristics indicate that the Cu5Zn8/HPCNC-based biosensing strategy may be used for the point-of-care assay of diverse biomarkers.