Copper doped carbon dots as the multi-functional fluorescent sensing platform for tetracyclines and pH

The copper doped fluorescent carbon dots (Cu-CDs) with excellent biocompatibility were prepared from l-tryptophan and copper chloride as precursors through a facilely hydrothermal method. As-prepared Cu-CDs exhibited the bright blue fluorescence and excellent optical stability. In the presence of tetracyclines antibiotics (TCs), the intensely fluorescent quenching of Cu-CDs occurred from internal filtration effect (IFE), providing the foundation of TCs quantification. Meanwhile, the fluorescence intensity of Cu-CDs decreased gradually along with the increasing of pH and a sigmoidal curve was well fitted with the pKa12.49 and pKa2 6.21, respectively. The Cu-CDs as a multi-functional fluorescence sensing platform demonstrated great accuracy and selectivity for tetracyclines (TCs) and pH. On account of practical application, as-synthesized Cu-CDs not only were effectively employed for determination of TCs in antibiotic tablets and milk products, but also could trace nuclear and had been extended to sense and visualize pH fluctuations in cells due to low toxicity and biocompatibility. As a facile and effective multi-functional fluorescent sensor, the proposed Cu-CDs have a significant potential for biosensing and biomedical imaging.