Detection of pathogens using luminescent CdSe/ZnS dendron nanocrystals and a porous membrane immunofilter

A biosensor system for detection of pathogens was developed by using CdSe/ZnS core/shell dendron nanocrystals with high efficiency and stability as fluorescence labels and a flowing chamber with a microporous immunofilter. The antibody-immobilized immunofilter captured the targeted pathogens, Escherichia coli O157:H7 as an example for bacteria and hepatitis B being a model system for viruses. The CdSe/ZnS core/shell dendron nanocrystals were conjugated with the corresponding antibodies and then passed through the microporous membrane where they attached to the membrane-antigen-antibody. The efficient and stable photoluminescence (PL) of the CdSe/ZnS nanocrystals on the formed "sandwich" structure complexes (membrane-antigen-antibody conjugated with the nanocrystals) was used as the detection means. The effects of the pore size of the membranes, buffer pH, and assay time on the detection of E. coli O157:H7 were investigated and optimized. The detectable level of this new system was as low as 2.3 CFU/mL for E. coli O157:H7 and 5 ng/mL for hepatitis B surface Ag (HBsAg). The assay time was shortened to 30 min without any enrichment and incubation.