The novel bacteria-affinitive photothermal carbon dots can specifically bind to bacteria and destroy its cell walls, killing bacteria more effectively than current carbon dots.
As much as antibiotics had fought off bacterial infections, the abuse of antibiotics has led to the emergence and widespread prevalence of “super bacteria”, where usual antibiotic medicines can no longer kill or stop their spread. In recent years, such antibiotic resistance has made the treatment of infectious diseases more challenging than it already is.
Photothermal therapy is where light energy is converted into localised physical heat to kill target microorganisms and is not known to cause resistance. As such, they provide an alternative to antibacterial treatment.
In a study published in Frontiers in Bioengineering and Biotechnology, researchers from the Suzhou Institute of Biomedical Engineering and Technology (SIBET) of the Chinese Academy of Sciences have designed bacteria-affinitive photothermal carbon dots that can specifically bind to bacteria and rapidly heat up with laser irradiation and destroy bacterial cell walls, effectively killing the bacteria.
“PTT uses targeted recognition to accumulate photothermal materials near the target tissue and convert light energy into thermal energy via an external light source, usually near-infrared light, to kill bacteria,” said Song Yizhi, co-corresponding author of the study.
However, many photothermal materials cannot specifically identify bacteria, which may lead to thermal damage to normal tissues. Therefore, there is a need to develop a bactericidal photothermal material that is specific.
Peptidoglycan is an important component of bacterial cell walls and the enzyme MurD ligase is involved in its synthesis. As cell walls protect the cells from the external environment and high internal osmotic pressure, this makes MurD ligase an excellent target for antibacterials as cell wall synthesis can be disrupted.
In previous years, many carbon dots with antibacterial properties have been developed but there are not many studies on carbon dot-based targeted photothermal technology. The team’s novel bacteria-affinitive photothermal carbon dots were developed from D-Glu and o-phenylenediamine by a solvothermal method.
“[Bacteria-affinitive photothermal carbon dots] have an excellent photothermal effect. The temperature of the [carbon dots] solution with different concentrations can increase and stabilise within 10 minutes,” said Dr. Qie Xingwang, the first author of the study. The maximum temperature of the carbon dots increased with the increase of material concentration and laser power.
Through their experiments, the synthesised carbon dots had effective and quick antibacterial properties under NIR light irradiation. Only about 80 per cent of E.coli and 89 per cent of S.aureus killed by the novel carbon dots without NIR irradiation, whereas when irradiated with NIR, only 3 per cent of E.coli survived and all of the S.aureus were killed by the increasing temperature.
“Combined with the advantage of high stability, high fluorescence quantum efficiency, good water solubility and non-toxicity of the carbon dots itself, the [bacteria-affinitive photothermal carbon dots] have a very good application prospect,” said Dong Wenfei, co-corresponding author of the study. [APBN]
Source: Qie et al.(2022). Design, synthesis, and application of carbon dots with synergistic antibacterial activity. Frontiers in Bioengineering and Biotechnology, 10.