Homogeneous immunoassay for alpha-fetoprotein based on the quenching of the fluorescence of quantum dots by antibody labelled with complexed copper ion tags

A homogeneous fluorescent immunoassay is described for the determination of alpha fetoprotein (AFP) relying on the interaction between copper ion complex and quantum dots (QDs). The copper ion complex-labelled antibody can be employed as a quencher of fluorescence of QDs and capture probe of AFP in homogeneous solution. The labelled antibody is mixed with QDs to form the immune ensemble probe. Upon the addition of AFP, the labelled antibody is stripped away from QDs by antigen-antibody combination leading to the increase in the fluorescence signal. Thus, the determination of AFP can be realized by fluorometry (best measured at excitation/emission wavelengths of 360/520 nm). The fluorescence intensity shows a good linear relationship with the AFP concentration ranging from 40 to 640 ng mL⁻¹, and the LOD is 26 ng mL⁻¹. The proposed method provides a new approach to incorporate metal complexes into QD-based biomolecule sensing.