Multiplexed immunoassay biosensor for the detection of serum biomarkers — β-HCG and AFP of Down Syndrome based on photoluminescent water-soluble CdSe/ZnS quantum dots

A multiplexed immunoassay biosensor for detecting serum biomarkers was developed by using photoluminescent (PL) aqueous CdSe/ZnS quantum dots (QDs) with high efficiency and stability as fluorescence labels and carboxyl functionalized microporous nylon membrane as a matrix. Two main biomarkers of Down Syndrome (DS), β-human chorionic gonadotrophin (β-HCG) and α-fetal protein (AFP), were selected for detection in this biosensor system. For specific detection of DS, antibody-immobilized microporous nylon membrane first captured the targeted antigens from the physiological samples and formed immunocomplexes (antibody–antigen) on the membrane surface. Then the immunocomplexes continued to react with QDs conjugated antibodies (labeled antibodies), and formed triplex “sandwich” structure, which was confirmed by AFM and confocal microscopy. Quantitative detection of β-HCG and AFP was also realized, the detectable level of this new biosensor was as low as 1 × 10−6 IU/L for β-HCG and 1 ng/mL for AFP in a relatively short assay time without any enrichment.