Objective   Water-soluble PEG400-modified ZnS:Cu quantum dots (QDs) were prepared by hydrothermal method in search for an applicable rapid detection method on diquat.

  Method  The QDs were characterized by their quenching intensities using a fluorescence spectrophotometer, an FTIR, and a UV-Vis spectrophotometer. Effect of PEG400 on the ZnS:Cu QDs was examined to determine the optimal modification for the establishment of a methodology to rapidly detect the toxicity of diquat on microorganisms. The correlation between QD quenching intensity and diquat concentration was examined for the methodology development.

  Result  Under appropriate reaction conditions at the diquat concentration in the range of 1.45×10⁻⁶−8.7×10⁻⁶mol·L⁻¹, the fluorescence quenching degree of QDs had an excellent linear relationship with diquat concentration of a correlation coefficient of 0.999 9. The detection limit of the method was 2.071×10⁻⁷mol·L⁻¹.

  Conclusion  The obtained PEG400-modified ZnS:Cu QDs was considered adequate to be applied for rapid detection of diquat in support of further development of related analytical methodology.