Fluorescent AgInS/ZnS quantum dots microplate and lateral flow immunoassays for folic acid determination in juice samples.

A noninstrumental rapid test for folic acid (FA) detection with visual results evaluation utilizing bright water-stable AgInS/ZnS (AIS/ZnS) quantum dots (QDs) is reported . AIS/ZnS QDs are hydrophilic photostable nanocrystals with size < 7 nm and emission in the visible range. They were synthesized directly in the water phase by a simple method compared to the synthesis of other QDs and conjugated with monoclonal antibodies specific for FA via ligand carboxyl groups. The conjugate was used for the development of instrumental qualitative and rapid quantitative FA detection methods. The competitive fluorescent microplate immunosorbent assay provided a limit of detection of 0.1 ng/mL FA and half maximal inhibitory concentration (IC50) of 24 ng/mL FA. The analytical signal was measured at ʎex = 410 nm and ʎem=590 nm. The proposed method showed no cross-reaction with other group B vitamins. For FA screening in juice samples, the lateral flow immunoassay was developed with a visual cutoff level of 3 µg/mL. In our perception, the developed methods are convenient for proving the perception of the AIS/ZnS QDs application as a luminescent label for immunoassay and are effective for FA detection. Graphical abstract.