Au Nanoparticle@AgNCs Nanocomposites:a New Class Of Bioprobe For High Sensitivity Immunosensor

Abstract:Gold nanoparticles, with exceptional electron transfer property, high surface-to-volume ratio and good biocompatibility, are an excellent nano-catalytic material. Silver nanoclusters, with few to tens of silver atoms and ultrasmall size (<2nm), are also a superior nano-catalytic material due to their size effect, large surface-to-volume ratio and strong surface activity. AuNPs@AgNCs nanocomposites with an AuNPs core and an AgNCs-doped mesoporous shell have been successfully synthesized by simple DNA hybrization process. The DNA duplex provides a dielectric spacer between the AuNPs and AgNCs, and spatially well separated AgNCs on the AuNPs surface. Therefore, AuNPs@AgNCs nanocomposites are not only able to provide good biocompatibility to protein, but also offer electron transfer path effectively and play a role of the nano micro-electrodes to accelerate electron transfer between the electrode and the analyte. Moreover, AuNPs@AgNCs nanocomposites exhibit increased electro-catalytic property due to the synergistic catalytic effect of AuNPs and AgNCs.In this paper, an ultrasensitive electrochemical immunosensor for measurement of prostate-specific antigen (PSA) was fabricated based on AuNPs@AgNCs nanocomposites. The chitosan-graphene was immobilized on electrode surface to accelerate the electron transfer, and the capture antibody (Ab1) was covalently linked to the amino group on chitosan.The DNA sequences functionlized AuNPs facilitated the DNA encapsulated AgNCs loading on AuNPs and signal antibody (Ab2) to label the signal probeby the interaction between SA and biotin.With a sandwich-type immunoreaction, the AuNPs@AgNCs labeled Ab2was captured on the surface of an immunosensor to further catalyze the electroactive species. The electro-catalytic signal of theelectroactive species was used to monitor the immunoreaction. Here, we apply the immunosensor to catalyze the deposited Ag and H2O2, respectively.After finishing the immunosensor, silver deposition enhancement was induced to the immunosensor surface. The electrochemical stripping signal of the deposited AgNCs was used to monitor the immunoreaction. The resulted immunosensor had a wide linear range from1fg mL-1to1ng mL-1and a low detection limit with0.2fg mL-1. Meanwhile, this immunosensor were applied to discriminate the breast cancer patient by measuring their prostate-specific antigen (PSA) level in women serum. In breast cancer patients’serum, the immunosensor could detect PSA concentration successfully. Thus, this unique immunosensor may provide potential applications in early clinical diagnosis.After completing the immunosensor, two electrodes modified f-PSA and t-PSA, respectively, were put a electrolyte to measure f-PSA and t-PSA simultaneously. The electro-catalytic reduction signal of the H2O2was used to monitor the immunoreaction. The resulted immunosensor had a wide linear range from1pg mL-1to10ng mL"1and a low detection limit with0.2pg mL-1and0.3pg mL-1, respectively. Meanwhile, the immunosensors were applied to measure f-PSA and t-PSA level simultaneously in serum of patient with prostate cancer or benign prostatic hyperplasia samples. The f-PSA, t-PSA contents and f/t-PSA ratio detected by the immunosensor agreed well with the ELISA measurement. The developed unique immunosensor may provide potential applications in clinical diagnosis.