Carbon Dots' Light-activated Antimicrobial Activities against Bacterial Pathogens

Introduction: Infectious diseases caused by bacterial pathogens have been a constant threat to the public health. Photo-activated antimicrobial technology is developing rapidly in response to the demand for development of effective treatments to control and prevent bacterial infections. Carbon dots (CDots) are generally small carbon nanoparticles with various surface passivation. The photoinduced redox processes in CDots have been credited for the photocatalytic activities that make carbon dots excellent candidates as antibacterial agents.

Purpose: The objectives of this study were to validate and compare the light-activated antibacterial function of CDots against Gram positive and Gram negative bacteria, to investigate the correlation of CDots’ antibacterial function with its quantum yield, and to explore the optimization of CDots’ antimicrobial activity by a combination of its properties and treatment conditions.

Methods: A series of specifically prepared Cdots with 2,2’-(ethylenedioxy)bis(ethylamine) as the surface functionalization molecule (EDA-CDots), whose fluorescence quantum yields (Φ_F) ranged from 7.5% to 27%, were synthesized. The traditional surface plating method was used to determine the viable cell reduction of Escherichia coli and Bacillus subtilis cells after treatment with these CDots under light illumination to evaluate the light-activated antibacterial function.

Results: Cdots’ light-activated antibacterial function toward both E. coli and B. subtilis, under different light conditions, was validated and compared. Gram positive B. subtilis cells were more susceptible to CDots treatment. The results of this first study revealed there was a correlation between CDots’ light-activated antibacterial efficiency and their quantum yields. A combination of the selected fluorescence quantum yields (Φ_F), dots concentration, and treatment time could achieve ~5 log viable cell reduction.

Significance: This study demonstrated that CDots have a great potential to be a class of low cost, low to no toxicity, highly efficient photo-activated antimicrobial agents against bacterial pathogens.