Upconversion immunoassays for environmental control, food safety, and biomedicine
| Authors | |
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| Year of publication | 2021 |
| Type | Conference abstract |
| MU Faculty or unit | |
| Citation | |
| Description | Due to their anti-Stokes emission, photon-upconversion nanoparticles (UCNP) can be detected without optical background interferences. Therefore, the conjugates of UCNPs with appropriate biorecognition molecules are useful labels in immunochemical assays. We have developed upconversion-linked immunosorbent assays (ULISA) for the detection of environmental pollutants, food contaminants, and cancer biomarkers. We have established an indirect and direct ULISA for the pharmaceutical diclofenac (DCF), a common micropollutant in waters. The indirect assay involved a UCNP-labeled secondary antibody, while the tracer in the direct assay consisted of UCNPs enclosed by a carboxylated silica shell and coated with DCF-conjugated bovine ?-globulin. The single-step direct assay provided a limit of detection (LOD) of 20 pg/mL and reduced the analysis time to 70 min. Zearalenone (ZEA) is one of the most frequently encountered mycotoxins in food worldwide. We designed a ZEA-mimicking peptide and used it for the competition with free ZEA in an ULISA. As a label, streptavidin-conjugated UCNPs were prepared by click reaction using an alkyne-PEG-neridronate linker. With an LOD of 20 pg/mL, the ULISA was well-applicable for detecting ZEA at the levels set by the European legislation. Moreover, the unique optical properties enabled imaging of single UCNPs by wide-field epiluminescence microscopy and allowed the development of single-molecule (digital) immunoassays. We have applied the streptavidin-conjugated UCNPs to detect cancer biomarker prostate-specific antigen (PSA). The noise-surpassing digital readout (particle counting) resulted in 20× higher sensitivity than the analog readout (output light intensity) and provided an LOD of 23 fg/mL (800 aM) in 25% human serum. |
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