Colorimetric and fluorometric dual-channel detection of α-fetoprotein based on the use of ZnS-CdTe hierarchical porous nanospheres

An immunoassay is described for either colorimetric and fluorometric determination of the cancer biomarker α-fetoprotein (AFP). It is making use of ZnS nanospheres modified with CdTe quantum dots (QDs). These display strong fluorescence due to the enrichment of the QDs onto the porous ZnS nanospheres. In this assay, the release of millions of zinc(II) ions can be triggered to form a purple complex (with an absorption maximum at 571 nm) on addition of the reagent 2-(5-nitro-2-pyridylazo)-5-(N-propyl-N-sulfopropylamino) phenol. This results in a sensitive colorimetric immunoassay which can also be used as a visual test. It represents an enzyme-free alternative to the commonly used ELISAs. It also can be evaluated by fluorometry (with excitation/emission maxima at 400/645 nm). The detection limits are 10 pg·mL−1 for fluorometry and 7 pg·mL−1 for colorimetry. This sensitivity is better by one order of magnitude than that of the commercial ELISA. The dual detection feature provides good complementarity and reduces the risk of false-positive or false-negative results.