Sustainable synthesis of carbon quantum dots from banana peel waste using hydrothermal process for in vivo bioimaging

Banana peel is a common solid biowaste. This paper reports a sustainable synthesis of carbon quantum dots (CQDs) from banana peel waste by a simple hydrothermal method. The resulting CQDs have a narrow size distribution, and the average particle size was measured as 5 nm. The nitrogen-containing and oxygen-containing functionalities on/in the surface of carbon structure were observed in the resulting CQDs. CQDs emit intense blue fluorescence under the excitation of UV-light (365 nm) with a good quantum yield of 20% without any surface passivation chemicals. Besides, CQDs exhibit excellent water solubility and excitation-dependent emission performance. Furthermore, the banana peel waste-derived CQDs had almost no photobleaching under UV-light irradiation for a long-time, suggesting that they have high photostability. Since no chemical reagent was involved in the synthesis of CQDs, the synthesized CQDs were confirmed to have lower toxicity for nematodes even at a high concentration of 200 μg mL−1. Because of the intense fluorescence with excellent fluorescence stability and biocompatibility, CQDs can be used for bioimaging in nematodes. The CQDs efficiently stained into the whole body of the nematodes and brightly illuminated the multicolor by varying the excitation wavelength. Therefore, fluorescent CQDs would be a great potential candidate for bioimaging applications.