Label-free electrochemical immunosensor determination of CA125 using Cu2+ and hemin dual-functionalized PEI/SiO2 nanoparticles

In this paper, using a strong coordination of the multi-amino groups of polyethylenimine (PEI)/SiO 2 nanoparticles with Cu 2+ and the weaker carboxyl-amine interactions with heme chloride (hemin), novel Cu 2+ -hemin dual-functionalized PEI/SiO 2 nanoparticles (abbreviated as Cu 2+ /hemin/PEI/SiO 2 NPs) were conveniently synthesized. The Cu 2+ /hemin/PEI/SiO 2 NPs exhibit both the peroxidase-like activity of hemin and the electrochemical signaling properties of Cu 2+ . Moreover, a large number of hemin molecules were successfully loaded onto Cu 2+ /PEI/SiO 2 NPs through electrostatic interactions. This not only prevented their self-aggregation-induced inactivation in aqueous solutions, but also catalytically amplified the electrooxidation signal of Cu 2+ /PEI/SiO 2 NPs by shortening the electron transfer distance. Subsequently, these nanoparticles spontaneously assembled on the overoxidized polypyrrole-modified reduced graphene oxide (abbreviated as OPPy/rGO) electrode surface through Cu N coordination between OPPy and Cu 2+ , and π-π stacking interactions between hemin and rGO. As a novel immunosensing platform, a label-free electrochemical immunosensor for carbohydrate antigen-125 (CA125), a specific biomarker for epithelial ovarian cancer was developed by covalently immobilizing CA125 capture antibodies onto the Cu 2+ /hemin/PEI/SiO 2 NPs@OPPy/rGO hybrid nanomaterials. Elevated serum CA125 levels correlate significantly with ovarian cancer progression. With the increasing concentration of CA125 antigen, the current responses of this immunosensor were decreased due to the formation of antigen-antibody insulating immune complexes. The proposed immunosensor exhibited excellent performances within a wide linear range from 5 × 10 −5 to 200 U·mL −1 for CA125 and a low detection limit of 1.2 × 10 −5  U·mL −1 (S/N = 3). Additionally, this immunosensor demonstrated good stability, reproducibility, and selectivity, making it a promising tool in clinical screening, early diagnosis, and prognostic monitoring of ovarian cancer.