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 Eu~(3+) 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.