Introduction: Infections caused by fungi, bacteria, parasites, or viruses cause many severe diseases. Antibiotics have historically been the primary weapon in the fight against infectious diseases. However, due to the high cost and long pathways to new drugs discovery, clinical testing, and scaling up the production process, approval of the development of next- generation antibiotics takes longer. As a result of multidrug resistance (MDR), which is of particular concern for high- risk populations such as those in healthcare settings or for those with concurrent conditions, such as cancer, bacterial infections can severely worsen patient health; infections may also delay wound recovery even when treated, with some negative health impacts associated with current disinfection techniques many of these diseases will become more challenging to treat and result in higher medical costs and mortality rates.
Photodynamic inactivation of bacteria mediated by photoactive compounds, more precisely photosensitizer molecules (PSs), is one of the most promising techniques in the fight against MDR pathogens.
Photodynamic antimicrobial chemotherapy (PACT) is a fast, intense and challenging field that has been developed to address the growing antibiotic resistance among harmful bacteria.
Carbon dots (CDs) have been proposed as a potential fluorescent nanomaterial for identifying and inactivating different types of bacterial species among a wide variety of PSs, already used in the past. They have good photoelectric properties, high water solubility, and chemical durability. CDs also present low toxicity and have good biocompatibility, making them ideal for photocatalytic dye degradation, photocatalytic/electrical water splitting, solar devices, bioimaging, drug delivery, gene delivery, biosensors and fluorescent-labeling applications and even in LED technologies.
Methods: Top-down and bottom-up approaches are two commonly used approaches for preparing CDs. Chemical processes such as hydrothermal, pyrolysis, combustion, ultrasonic, microwave irradiation, thermal, and biogenic procedures, conversely, are used in the bottom-up approach.
Using a top-down technique, large-sized carbon materials, such as carbon nanotubes and graphite ash, are decomposed into small CDs, from the macro to the nanoscale. Different carbon sources are exposed to laser ablation, arc discharge, plasma treatment, chemical oxidation, electrochemical oxidation, and others.
Although many of the aforementioned synthesis methods can be found in the literature, hydrothermal treatment in either a top-down or bottom-up regime is most commonly employed. In particular, this method is favored amongst reports of carbon dot “green synthesis” from biomass, or natural precursors.
Currently, the main green synthesis processes for producing CDs include ultra-sonication, microwave irradiation, hydrothermal carbonization, self-exothermic synthesis, and ozone/hydrogen peroxide oxidation.
For the green synthesis process, toxic chemicals that are harmful to people’s health and the environment should be avoided.
Results: Thus far, much work has been performed on the cytotoxicity of CDs on mammalian cells, and it has been reported that they are non-toxic at proper concentrations both in vitro and in vivo. A high concentration of CDs will exert toxic effects on the central nervous system. Toxicology reports of GQDs indicate that although most existing studies support the safe use of GQDs, their toxicity may vary depending on the concentration and test method used in the synthesis technology. Studies have found that small-sized CDs are more toxic than large-sized CDs, and CDs with negative charged are more cytotoxic to mammalian cells. In order to solve the above problems, it is necessary to promote safe and controllable CDs synthesis strategies and application methods, and the safe application of CDs in the treatment of infectious diseases requires in-depth research on its possible toxic side effects and complications.
Conclusion: The CDs’ structure work as a photosensitizer in PACT is discussed in many aspects and applications in this paper.
CDs have been shown to be one of the most promising carbon classes of material to work properly as an antibacterial material because of their excellent physical and chemical properties, optical qualities, and photophysical and photochemical behavior associated with exceptional water solubility.
Conversely, CDs face some problems, limiting their practical application. The exact process of photoluminescence is unknown, and CDs with extended excitation and emission wavelengths are still uncommon, leading to complex tissue and biofilm penetration. Second, relatively few CDs have intrinsic microbe targeting ability, resulting in a significantly reduced antibacterial effect that is essential in developing antibacterial CDs. Finally, CDs’ water solubility and biocompatibility influence their microbial therapy usage.