Microplasma-synthesized <i>Citrus</i> -derived carbon quantum dots: antibacterial properties and nanoprobe sensitivity

This study introduces an environmentally friendly and cost-efficient approach for producing carbon quantum dots (CQDs) from <i>Citrus nobilis deliciosa via</i> a microplasma-assisted technique. The obtained CQDs demonstrated excitation-dependent fluorescence accompanied by a red shift, which can be ascribed to quantum size effects and the influence of surface chemical functionalities. The synthesized CQDs demonstrated remarkable antibacterial properties, achieving growth inhibition rates of 99.24% against <i>Staphylococcus aureus</i> and 98.12% against <i>Escherichia coli</i> at a concentration of 50 μg mL^-1. The antibacterial mechanism was primarily driven by membrane destabilization and oxidative stress induction, making CQDs a promising alternative to conventional antimicrobial agents. Additionally, the CQDs served as highly responsive fluorescent probes for Cd(ii) ion detection, exhibiting a linear response range spanning 1-14 μg mL^-1, a minimum detectable concentration of 0.12 μg mL^-1, and a Stern-Volmer quenching constant (<i>K</i> _SV) of 0.45 μg mL^-1. These findings highlight the dual functionality of CQDs as potent antibacterial agents and efficient fluorescence-based sensors for heavy metal detection. The eco-friendly synthesis, combined with the excellent biocompatibility and adjustable optical characteristics of CQDs, highlights their potential for applications in biosensing, environmental monitoring, and biomedical fields.