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A new fluorescent probe based on phosphorus-doped cow milk-derived carbon quantum dots (P-CMCQDs) for the detection of Au 3+ was studied in water samples. P-CMCQDs were prepared by hydrothermal method with cow milk as carbon source and phosphoric acid as dopant. P-CMCQDs show green fluorescence under ultraviolet light and can be partially quenched by Au 3+ . However, the excellent fluorescence characteristics of P-CMCQDs-ascorbic acid (AA) were obtained and can be used to detect trace Au 3+ by simply mixing the P-CMCQDs with AA. The sensing mechanism is based on the reduction of Au 3+ to AuNPs by P-CMCQDs and AA, and then AuNPs induce the fluorescence quenching of P-CMCQDs through synergistic static quenching and internal filtering effect. The fluorescence intensity of P-CMCQDs-AA varies with the concentration of Au 3+ (10-140 μmol/L), the detection limit is 4.2 nmol/L, indicating that the P-CMCQD S -AA probe has excellent sensitivity. In the detection of Au 3+ in tap water and lake water, it is found that the recovery is between 99.6% and 100.5%, and the relative standard deviation is between 1.7% and 3.2%. This method is fast, efficient, and sensitive, and can be used to detect Au 3+ in actual water samples. Practical ApplicationsAlthough the element gold is chemically inert, soluble gold salts remaining in the environment in the form of ions are toxic and serious damage the peripheral nervous system, causing other health issues. Therefore, it seems necessary to design an efficient and sensitive method to detect Au 3+ in environment. Among many detection methods, fluorescence sensing method is more suitable for on-site, rapid detection.However, the complex system, high limit of detection and environmental pollution caused by metal luminescence limit its application. In this paper, the biomass P-CMCQDs was synthesized from cow milk by hydrothermal method. By adding AA in the synthesized P-CMCQDs, the limit of detection (LOD) was greatly improved, and the trace Au 3+ detection in tap water and lake water was highly selective and sensitive.

Summary A fluorescent probe based on carbon dots (CDs) for the detection of sulfoquinoxaline (SQX) in food was studied. White pitaya peel‐derived carbon dots (WCDs) were synthesised by hydrothermal method. The obtained WCDs exhibit excellent fluorescence response towards SQX due to the inner filter effect (IFE) and aggregation‐caused quenching(ACQ), which cause the fluorescence to be quenched. The prepared fluorescent probe has a good linear relationship, and the detection limit of SQX is 24.5 μg L−1. The practicability of the fluorescent probe was further validated in milk, honey, eggs, carp, pork, chicken, beef and pork liver, and the recoveries of SQX range from 93.38% to 103.86%. The fluorescent probe based on WCDs has high selectivity, specificity, sensitivity, reliability and good reproducibility for the detection of SQX.