A ratiometric fluorescence and colorimetric dual-mode sensing platform based on sulfur quantum dots and carbon quantum dots for selective detection of Cu2.

A new dual-mode ratiometric fluorescence and colorimetric probe for selective determination of Cu2+ was developed based on blue-emission sulfur quantum dots (SQDs) and yellow-emission carbon quantum dots (CQDs). The fluorescence and absorbance of CQDs increased in the presence of Cu2+ due to the Cu2+ -oxidized o-phenylenediamine group on the surface of the CQDs. Because of the inner filter effect between SQDs and CQDs-Cu2+, the fluorescence response of SQDs decreased following the introduction of Cu2+. Furthermore, in the presence of Cu2+, the dual-mode SQD-CQD probe showed visible color changes under both ultraviolet light and sunlight. Under optimal conditions, the dual-mode probe was used to quantitatively detect Cu2+ with a linear range of 0.1-5.0 µM for ratiometric fluorescence and colorimetry, with a limit of detection of about 31 nM and 47 nM, respectively. Finally, the dual-mode probe was used for the determination of Cu2+ in practical samples to expand the practical application, and the difference between ratiometric fluorescence and colorimetric methods was compared. The recovery results confirmed the high accuracy of the dual-mode probe, showing that it has immense potential for sensitive and selective detection of Cu2+ in practical samples.

Sensitive and selective determination of tetracycline in milk based on sulfur quantum dot probes.

A novel fluorescent probe based on sulfur quantum dots (SQDs) was fabricated for sensitive and selective detection of tetracycline (TC) in milk samples. The blue emitting SQDs were synthesized via a top-down method with assistance of H2O2. The synthesized SQDs showed excellent monodispersity, water solubility and fluorescence stability, with a quantum yield (QY) of 6.30%. Furthermore, the blue fluorescence of the obtained SQDs could be effectively quenched in the presence of TC through the static quenching effect (SQE) and inner filter effect (IFE) between TC and SQDs. Under the optimum conditions, a rapid detection of TC could be accomplished within 1 min and a wide linear range could be obtained from 0.1 to 50.0 µM with a limit of detection (LOD) of 28.0 nM at a signal-to-noise ratio of 3. Finally, the SQD-based fluorescent probe was successfully applied for TC determination in milk samples with satisfactory recovery and good relative standard deviation (RSD). These results indicate that the SQD-based fluorescent probe shows great potential in practical analysis of TC in real samples with high rapidity, selectivity, and sensitivity.