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Photon-upconversion nanoparticles as a background-free label in rapid immunoassays for diclofenac

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FARKA Zdeněk HLAVÁČEK Antonín MICKERT Matthias Jürgen KNOPP Dietmar SKLÁDAL Petr GORRIS Hans-Heiner

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Fakulta / Pracoviště MU

Středoevropský technologický institut

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Popis Enzyme-linked immunosorbent assays (ELISAs) are widely used for detecting various analytes in complex matrices. However, they are limited by inherent instability of enzymes and time-consuming signal development. Thus, novel nanomaterial labels can offer several advantages, such as high stability and relatively easy preparation and storage. Photon-upconversion nanoparticles (UCNPs) are particularly suitable as background-free luminescent labels for immunoassays. We have developed an indirect and direct formats for the competitive upconversion-linked immunosorbent assay (ULISA). The target analyte was the pharmaceutical diclofenac (DCF), which is a common micropollutant in waters. The indirect assay involves a UCNP-labeled secondary antibody, while the tracer in the direct assay consists of UCNP enclosed by a carboxylated silica shell and coated with DCF-conjugated bovine ?-globulin. The protein coating prevents non-specific adsorption and provides a structurally flexible linker for surface-exposed DCF to allow efficient competition with free DCF in real water samples. The single-step direct assay has a limit of detection (LOD) of 20 pg mL-1 and reduces the analysis time to only 70 min. The optimized ULISA is comparable in sensitivity to the conventional ELISA while providing shorter analysis time of 70 min. Currently, we are able to visualize individual UCNP-labelled immunocomplexes, which provides essentially absolute sensitivity and allows to further enhance the immunoassay performance.
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