Synthesis of carbon dots using wild Citrullus lanatus var citroides for drug delivery applications

Nanomaterials are widely explored in the various fields such as medicine and biomedical engineering, catalysis and environmental pollution detection. Research in nanotechnology has led to the discovery of fluorescent carbon dots (CDs), which are biocompatible, resistant to photobleaching and have high fluorescence intensity compared to traditional fluorescent probes. CDs may be synthesized from cheap carbon material and herein, this study reports an economical and environmentally friendly hydrothermal synthesis of CDs using wild melon ( Citrullus lanatus var citroides ) peels. The as-prepared CDs were spherical with an amorphous structure and possessed an average size of 1.2 nm. The CDs were also successfully used for bacterial cell labelling of E. coli and S. aureus , which indicated that the CDs were able to attach and possibly penetrate the cells. The interaction of bacterial cells with CDs resulted in fluorescence increase of the cells. Finally, AMP-Na was successfully conjugated to the as-prepared CDs and the conjugate (AMP-Na/CDs) exhibited enhanced antibacterial activity compared to bare CDs and bare AMP Na. The conjugate showed capability of bacterial inhibition for both Gram-positive ( S. aureus ) and Gram-negative ( E. coli , P. aeruginosa ) as well as AMP-Na resistant P. aeruginosa , where in all cases the conjugate showed substantial zones of inhibition. For this study, fluorescing CDs with good physicochemical properties, excellent bacteria labelling, and as antibacterial conjugate were successfully synthesized. Antibiotic-conjugated CDs could be used as more efficient, targeted antimicrobial drug delivery systems. Biological applications of CDs should also be extended to use in vivo in animal models as an imaging entity. • Eco-friendly hydrothermal method for preparation of CDs using from C. lanatus var citroides melon peels. • Structure, size and morphology of CDs determined using FTIR, XRD, AFM, SEM and Raman. • Photoluminescence properties studied using Uv-Vis and fluorescence spectroscopy. • CDs demonstrated excellent candidate for labelling E. coli and S. aureus. • Conjugated CDs/AMP-Na when compared to bare AMP-Na exhibited high zones of inhibition for all test bacteria.