Ag+-coordinated oligonucleotides on gold nanoparticles for anodic-stripping voltammetric immunoassay of cancer antigen 125 for cervical carcinoma

Abstract

A simple and enzyme-free electrochemical immunoassay was developed for the sensitive screening of cancer antigen 125 (CA 125; one biomarker for epithelial ovarian tumors and cervical carcinoma) using anodic-stripping voltammetry (ASV). The electrochemical immunosensor was constructed through immobilization of monoclonal anti-CA 125 antibody on an activated glassy carbon electrode on the basis of a classical carbodiimide coupling method. Cytosine (C)-rich oligonucleotide strands and polyclonal anti-CA 125 antibody labeled onto gold nanoparticles (AuNPs) were used as detection probes to quantify the target analyte with a sandwiched assay format. The voltammetric signal derived from the coordinated silver ions (Ag⁺) on the AuNPs through the C–Ag⁺–C coordination chemistry. Accompanying the formation of target-induced immunocomplexes, the coordinated Ag⁺ ions exhibited good voltammetric characteristics within the applied potentials. Under optimal conditions, the C–Ag⁺–C-based immunoassay displayed sensitive responses toward target CA 125 within a dynamic linear range of 0.01–100 U mL⁻¹ at a limit of detection of 6.8 mU mL⁻¹. Good reproducibility, high specificity and acceptable accuracy of this method were acquired for analysis of human serum specimens. Importantly, this immunoassay system offers a promising protocol for the detection of disease-related biomarkers without the need for natural enzymes.