Ag+-coordinated oligonucleotides on gold nanoparticle for anodic-stripping voltammetric immunoassay of cancer antigen 125 for cervical carcinoma
A simple and enzyme-free electrochemicla 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 monocolonal 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 nanoparticle (AuNP) were used as the detection probes to quantify the target analyte with a sandwiched assay format. The voltammetric signal derived from the coordinated silver ion (Ag+) on the AuNP 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 the 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 accpetable 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 needs of natural enzymes.