Investigation of europium(Ⅲ)-doped ZnS for immunoassay

Biofunctional europium (Ⅲ)-doped ZnS (ZnS:Eu) nanocrystals are prepared by a sol-gel method. The characteristic luminescence of ZnS:Eu is used as a probe signal to realize sensitive immunoassay. The luminescence intensity of the Eu³⁺ in the ZnS matrix shows strong concentration dependence, and the optimal doping concentration is 4%. However, the emission wavelengths of the ZnS:Eu nanocrystals are not dependent on doping concentration nor the temperature (from 100 K to 300 K). Our results show that these features allow for reliable immunoassay. Human immunoglobulin, used as a target analyte, is captured by antibody modified ZnS:Eu probe and is finally enriched on gold substrate for detection. High specificity of the assay is demonstrated by control experiments. The linear detection range is 10 nM-800 nM, and the detection limit is about 9.6 nM.