Synthesis of high quantum yield orange carbon dots as multifunctional fluorescence probe in VB12 detection and bio-imaging.

Unique orange-emissive carbon dots (O-CDs) are synthesised via a solvothermal method by safranin T and 2,2'-dithiodibenzoic acid in ethanol. O-CDs show a maximum emission peak at 595 nm and a quantum yield of 81.63% when dissolved in dichloromethane. O-CDs are able to be fabricated into fluorescent hydrogels, powders and films exhibiting excellent fluorescence performance. The linear relationship is observed in the concentration range of 0-200 µM with R2 of 0.9973, and the limit of detection is 0.19 µM. Meanwhile, this method is effectively utilized to analyze real food samples, such as egg yolk and milk, with recoveries ranging from 99.21% to 101.8%. Sensing mechanism is found to be the inner filter effect and dynamic quenching. Furthermore, O-CDs exhibit low toxicity and nice biocompatibility, facilitating the applications in bioimaging of B16F10-2 cells as well as zebrafish, and enabling VB12 detection in live cells. Therefore, the novel O-CDs developed present broad application prospects including food safety, biosensing, bioimaging and fluorescent films.