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.Cd S 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 m L-1at a detection limit（LOD）of 68 pg m L-1.The relative standard deviations（RSD）were below9.09%and 10.54%for the intra-and inter-assay,respectively.Additionally,six human serum specimens were determined on CdISE-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.