Cascade redox cycling amplification enabled by COF-confined Co3O4 for enhanced immunosensing

Abstract

Herein, an enzyme-free and highly efficient sandwich-type electrochemical immunosensor for cTnI detection was developed using covalent organic framework (COF) confined Co3O4 nanoparticles (NPs) as the signal probe and enhancing the sensitivity with electrochemical-chemical-chemical (ECC) redox cycle amplification (RCA) strategy. The multifunctional COF, with high surface area and rich nitrogen, serves not only as a substrate material but also as a scaffold for Co2+ entrapment, enabling the confined growth and uniform distribution of ultrafine Co3O4 NPs as signal amplification platform, thereby providing abundant catalytic active sites for ECC redox cycling reactions. COF confined Co3O4 NPs with variable valence states (Co3+/Co2+) serve as a redox-active electrode material that can enhance the current signal substantially. The ECC redox cycle is triggered by the redox reaction between Co3+ at the electrode and electroactive hydroquinone (HQ), while HQ was regenerated by the reducing agent tris (2-carboxyethyl) phosphine (TCEP), resulting in a significant amplification of the current signal for cTnI analysis. The constructed immunosensor exhibited excellent performance with a wide linear range from 1 fg mL- 1 to 100 ng mL-1, and a low detection limit of 0.88 fg mL-1. Furthermore, the immunosensor successfully applied to detected cTnI in human serum, proving its clinical potential.