A dual-mode sensing platform coupling two-signal ratiometric and colorimetric methods for detecting Au3+ based on surface state-regulated carbon nanodot.

The considerable risk posed by Au3+ residues to the environment and human health has sparked interest in researching Au3+ monitoring techniques. The detection results in the usual ratio mode are more reliable. In this work, we develop a dual-mode strategy based on reducing carbon dots coupling with two-signal ratiometric and colorimetric methods for high-sensitivity, good-selectivity, and wide-range detection of Au3+. Cyan carbon dots (C-CDs) were synthesized by a simple and efficient one-step hydrothermal method. The C-CDs with rich amino group used m-phenylenediamine as carbon source, which made it have the potential as a reducing agent. After the addition of Au3+, Au3+ was reduced to Au0, generating stable gold nanoparticles (AuNPs). The fluorescence signal (F490) of C-CDs decreased. At the same time, the large size of AuNPs enhances the second-order scattering signal (S770) and produces the UV-visible absorption peak of AuNPs. Therefore, the dual-mode sensing strategy combining S770/F490 ratiometric and colorimetric detection of Au3+ is realized with high accuracy and sensitivity. Au3+ was determined in real samples and a good recovery was obtained. The dual-mode method has good performance and practicality, so it shows great potential for environment testing in a simple and reliable way.

One-step synthesis of aldehyde-functionalized dual-emissive carbon dots for ratiometric fluorescence detection of bisulfite in food samples.

Bisulfite (HSO3-) is used as a food additive for its antibacterial and antioxidant properties. However, excessive intake of HSO3- is harmful to humans. Here, for the first time, aldehyde-functionalized dual-emissive carbon dots (D-CDs) are synthesized in one-step for direct ratiometric sensing of HSO3-. Due to the nucleophilic addition reaction between HSO3- and aldehyde of D-CDs, the fluorescence transforms from green to deep-blue. The linear range of the probe is 0.1-30 µmol/L with a detection limit of 42 nmol/L. Moreover, D-CDs show good selectivity and a fast reaction time (<5 min) toward HSO3-. The probe has been applied to trace HSO3- detection in food samples. The recoveries range from 96.5 % to 107.0 % with relative standard deviations below 6.5 %. In addition, a smartphone sensing platform has been designed, which provides a wider application prospect for the real-time monitoring of HSO3- in food.