Cinnamic acid-derived carbon dots by microwave irradiation synergise the ciprofloxacin effect against Staphylococcus aureus and promote its skin permeability†

Aqueous solubility and biocompatibility have encouraged the development of carbon dots (CDs) for multiple applications. Considering the significance of natural molecules as precursors, cinnamic acid (CA) was used to develop carbon dots (CA-CDs) using an efficient microwave irradiation method which gave a higher quantum yield in comparison with other conventional methods. The positively charged CA-CDs showed a broad spectrum of action against Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria. Unlike ciprofloxacin (CIP), CA-CDs showed potent inhibition of clinically resistant S. aureus (SA-DR) while reducing biofilm production, leading to synergy with CIP. CA-CDs also acted as carriers to enhance the skin-permeability of CIP through their ionic complex (CIP-CA-CDs). The complex retained the antimicrobial properties and showed the ability to gradually release CIP like a reservoir. Considering the poor permeability of CIP as a limitation, this work can encourage the translational application of CIP for topical application. This work provides a novel method of developing CDs for antimicrobial properties and can encourage their use as a complementary therapy or as carriers for further application.