Metal sulfide quantum dots-aggregated PAMAM dendrimer for cadmium ion-selective electrode-based immunoassay of alpha-fetoprotein

An ion-selective electrode (ISE)-based immunoassay has been innovatively designed for the sensitive detection of liver cancer biomarker (alpha-fetoprotein, AFP), using metal sulfide quantum dot (QD)-based nano labels. CdS QDs-aggregated PAMAM dendrimer (QD-DE) was first synthesized and functionalized with polyclonal rabbit anti-human AFP antibodies. Thereafter, a sandwich immunoreaction was implemented on monoclonal mouse anti-human AFP antibody-coated microplate by using antibody-functionalized QD-DE as the secondary antibody. Accompanying the immunocomplex, subsequent potentiometric detection of cadmium ion dissolved from the QD-DE under acidic condition was conducted on a portable cadmium ion-selective electrode (Cd-ISE). Results revealed that the electrode potential of the Cd-ISE increased with the increment of AFP concentration from 0.1 to 100 ng mL(-1) at a detection limit (LOD) of 68 pg mL(-1). The relative standard deviations (RSD) were below 9.09% and 10.54% for the intra- and inter-assay, respectively. Additionally, six human serum specimens were determined on Cd- ISE-based immunosensor by using commercial human AFP ELISA kit as the reference, and gave good relationship between two methods. Importantly, Cd-ISE-based immunoassay offers the promise for simple and cost-effective screening of disease-related biomarkers.