# The effects of the combined use of carbon quantum dots and antibacterial agents on pathogenic bacteria

## TL;DR

This study explores how carbon quantum dots combined with antibiotics can effectively combat drug-resistant bacteria.

## Contribution

The novel synthesis of codoped carbon quantum dots and their synergistic antibacterial effects with antibiotics are presented.

## Key findings

- CCQDs-2 showed synergistic effects with antibiotics like gentamicin and clindamycin against bacteria.
- CCQDs demonstrated high quantum yield and fluorescence with antibacterial activity against G+ and G− strains.
- Citric acid removal from CCQDs influenced antibacterial efficacy and interactions with antibiotics.

## Abstract

This study evaluates the challenges associated with overcoming antimicrobial resistance and innovative approaches to combat multidrug-resistant (MDR) bacterial infections.

Novel codoped carbon quantum dots (CCQDs) were synthesized using citric acid as the carbon source and L-cysteine as the nitrogen codoping atom. The formulation in which citric acid was retained was designated as CCQDs-1, whereas the purified version, from which citric acid was removed, was termed CCQDs-2. The antibacterial properties of CCQDs-1 and CCQDs-2 were compared using the agar well diffusion method. This study comprehensively characterizes these nanomaterials and evaluates their antibacterial potential, both alone and in combination with antibiotics, against a spectrum of gram-positive (G+) and gram-negative (G−) bacterial strains.

The study demonstrates the significant antibacterial efficacy of CCQDs, with notable variations observed between citric acid-containing and citric acid-neutralized formulations. The QDs exhibited remarkable characteristics, including a quantum yield of 90.3%–90.6%, intense fluorescence, and distinctive interactions with various antibiotics. In addition to their intrinsic antibacterial activity, the QDs also exhibited synergistic effects when combined with certain antibiotics. A synergistic effect was particularly observed when CCQDs-2 were combined with antibiotics such as gentamicin, levofloxacin, and clindamycin, suggesting potential mechanisms such as membrane permeability disruption and efflux pump saturation.

These findings underscore the promising potential of carbon-based QDs as innovative, biocompatible solutions to address the critical global challenge of antimicrobial resistance.