Covalent Framework Particles Modified with MnO₂ Nanosheets and Au Nanoparticles as Electrochemical Immunosensors for Human Chorionic Gonadotropin

A covalent organic framework (COF)/manganese dioxide (MnO2) nanocomposite (COF/MnO2) was prepared via a green and facile method. Using an etched halloysite nanotube (eHNT) as a material on the sensing platform and the COF/MnO2 nanocomposite for signal amplification, an electrochemical biosensor was constructed for detecting human chorionic gonadotropin (HCG). Gold nanoparticles (Au NPs) decorated with eHNT were used to immobilize primary antibodies (Ab1). Subsequently, Au/COF/MnO2 composites were prepared for immobilizing secondary antibodies (Ab2) and abundant redox signals of TB to form the Ab2/TB/Au/COF/MnO2 bioconjugate. Furthermore, in the presence of H2O2, the amplified electrochemical signal was further obtained, since the catalytic ability of eHNT and Ab2 bioconjugate improved the electrocatalysis of H2O2 reduction. Under the optimum conditions, the constructed electrochemical sensor showed a wider linear range of 0.0005–100 mIU mL–1. Our prepared sensor was used to measure HCG in serum with ultrasensitivity, good reproducibility, and excellent specificity. Amplified current of the immunosensor was caused by outstanding charge transfer properties of the Au/eHNT, COF/MnO2 nanocarrier, and Au NPs electrocatalyst. This work not only provided a facile method for preparation of the COF/MnO2 nanocomposite but also developed an ultrasensitive assay for the electrochemical detection of HCG.