Sensitive electrochemical immunoassay with signal enhancement based on nanogold-encapsulated poly(amidoamine) dendrimer-stimulated hydrogen evolution reaction.

A new electrochemical immunosensor with signal enhancement was designed for sensitive detection of disease-related protein (human carbohydrate antigen 19-9, CA 19-9 used in this case). The assay was carried out on a capture antibody-modified screen-printed carbon electrode with a sandwich-type mode by using detection antibody-functionalized nanogold-encapsulated poly(amidoamine) dendrimer (AuNP-PAAD). The AuNP-PAAD was first synthesized through the in situ reduction method and functionalized with the polyclonal rabbit anti-human CA 19-9 antibody. Upon target CA 19-9 introduction, a sandwiched immunocomplex could be formed between the capture antibody and detection antibody. Accompanying the AuNP-PAAD, the electrocatalytic activity of the carried gold nanoparticles toward the hydrogen evolution reaction (HER) allowed the rapid quantification of the target analyte on the electrode. The amplified electrochemical signal mainly derived from AuNP-catalyzed HER in an acidic medium. Under optimal conditions, the immuno-HER assay displayed a wide dynamic concentration range from 0.01 to 300 U mL(-1) toward target CA 19-9 with a detection limit (LOD) of 6.3 mU mL(-1). The reproducibility, precision, specificity and stability of our strategy were acceptable. Additionally, the system was further validated by assaying 13 human serum specimens, giving well matched results obtained from the commercialized enzyme-linked immunosorbent assay (ELISA) method.