Antibacterial Activity of Ciprofloxacin-Based Carbon Dot@Silver Nanoparticle Composites

The combined green synthesis of carbon dots (CDs) from the hydrothermal conversion of ciprofloxacin and silver nanoparticles (AgNPs) using sodium alginate as a reducing and stabilizing agent results in arrangements of nanostructures (CD@AgNP composites) with positive surface charge that electrostatically interact with Gram-positive and Gram-negative bacteria in the planktonic form and also biofilm forms, inhibiting their growth and adhesion on surfaces. Outstanding performance for CD-based materials results in a 5-log reduction in colony-forming units (CFU/mL) of <i>E. coli</i> after 1 h of treatment and a decrease of 99.32% in the consolidated biofilm of <i>S. aureus</i>. These nanostructures result in the intrinsic fluorescence of CDs and an overall eco-friendly preparation process that can be explored in disinfection procedures based on the direct administration of a sanitizer based on nanoparticles dispersed in an aqueous solution. This process is justified by the adequate conversion of antibiotics in positively charged CDs and composites with AgNPs, resulting in nanocomposites in which the prevailing cationic effect facilitates their incorporation and diffusion into bacterial membrane cells.