Design and fabrication of dual functional sulfur nanodots with reducibility and fluorescence properties for sensitive and selective analysis of metal ions in environmental water samples

Reduced-state sulfur nanodots (r-SDs) with reducibility, satisfactory fluorescence properties and high stability were synthesized for the sensitive and selective analysis of metal ions, including Hg2+, Fe3+ and Cu2+. The reduction property of SDs was discovered for the first time, and the detailed reduction mechanisms of r-SDs were investigated. The reducibility of r-SDs exhibits the in situ reduction of Au3+ to Au nanoparticles (AuNPs/r-SDs) and also the reduction of Fe3+ and Cu2+ to Fe2+ and Cu+, respectively. On the one hand, selective analysis of Hg2+ can be achieved through dual-mode fluorescence and colorimetric probes of thymine-modified AuNPs/r-SDs (T-AuNPs/r-SDs) on account of the special bonding of T-Hg2+-T, as verified by density functional theory simulations. Furthermore, the fluorescent probes r-SDs-1, 10-Phenanthroline (r-SDs-Phen) and r-SDs-neo-cuproine (r-SDs-Nc) were applied to the quantitative analysis of Fe3+ and Cu2+ by the specific recognition of Phen-Fe2+ and Nc-Cu+ after the reduction of Fe3+ and Cu2+ to Fe2+ and Cu+ by r-SDs. The linear ranges of T-AuNPs/r-SDs, r-SDs-Phen, and r-SDs-Nc for Hg2+, Fe3+, and Cu2+ were 5.0-70.0 nmol/L (fluorescence), 10.0-500.0 nmol/L (colorimetric), 1.0-100.0 mu mol/L, and 1.0-50.0 mu mol/L, with limits of detection of 0.82 nmol/L, 4.05 nmol/L, 0.36 mu mol/L, and 0.56 mu mol/L, respectively. In addition, good recoveries for practical applications in environmental water samples can be obtained to confirm the analysis accuracy. The successful results provided a new idea for the application of nanomaterials with reducibility and fluorescence properties in analytical chemistry.

Automated summary

In this study, reduced-state sulfur nanodots (r-SDs) with reducibility, satisfactory fluorescence properties, and high stability were synthesized for the sensitive and selective analysis of metal ions. The reduction property of SDs was discovered for the first time, and the detailed reduction mechanisms were investigated. The r-SDs showed in situ reduction of Au3+ to Au nanoparticles and also reduction of Fe3+ and Cu2+ to Fe2+ and Cu+, respectively. Hg2+ was selectively analyzed through dual-mode fluorescence and colorimetric probes, while Fe3+ and Cu2+ were quantitatively analyzed using specific recognition after reduction by r-SDs. The linear ranges and limits of detection for the different analytes were determined. Good recoveries were obtained for practical applications in environmental water samples.