Yellow Fluorescent Nitrogen and Bromine Co-doped Graphene Quantum Dots for Bioimaging

Currently, the large- scale commercial/industrial application of graphene quantum dots (GQDs) is generally limited by their low production and lack of diverse photoluminescence (PL) properties such as GQDs with long-wavelength emissions and high quantum yields. Herein, for the first time, a facile deflagration method was developed for the ultrafast and gram-scale synthesis of N and Br co-doped GQDs (NBr-GQDs) with bright yellow PL emissions. NBr-GQDs exhibited an excitation-independent emission property with a central PL wavelength of similar to 579 nm. The results of theoretical calculations revealed that N and Br co-doping may reduce the band gap between the excited singlet states and decrease the intersystem crossing effect of excited electrons from the singlet to the triplet state, thus considerably improving the quantum yield (as high as 52%). Moreover, a series of experiments were performed, and their results showed that the synthesized NBr-GQDs achieved excellent pH tolerance, long PL lifetime, and low cytotoxicity. Using HeLa cells as specimens, it was demonstrated that NBr-GQDs could successfully enter the HeLa cytoplasm and achieve high-quality fluorescent labeling, indicating their great potential in the bioimaging field.

Automated summary

A new method was developed for the efficient synthesis of N and Br co-doped GQDs, exhibiting excitation-independent emission properties and high quantum yields, along with excellent cytotoxicity and biological labeling potential.