Fabrication of Carbon Quantum Dots From <i>Caesalpinia sappan</i> L. for Antibacterial Applications and Fluorescent Detection of Ciprofloxacin

ABSTRACT This study demonstrates a one‐step hydrothermal synthesis of carbon quantum dots (CQDs) using Caesalpinia sappan L. as carbon source. The CQDs were characterized with TEM, FT‐IR, XPS, and UV–vis. The CQDs exhibit potent, dose‐dependent antibacterial activity against S. aureus and E. coli with MICs of 0.33 and 0.22 µg/mL, primarily through electrostatic binding and hydroxyl radical generation. Simultaneously, the CQDs function as a highly selective fluorescent “turn‐on” sensor for ciprofloxacin, achieving a low detection limit of 0.039 µmol/L via a mechanism driven by hydrogen bonding and electron transfer. This work presents a cost‐effective, eco‐friendly multifunctional platform with significant potential for combating bacterial infections and monitoring antibiotic residues in environmental and food safety applications.