Photodynamic therapy: A special emphasis on nanocarrier-mediated delivery of photosensitizers in antimicrobial therapy

Resistance to antimicrobial drugs is an impending healthcare problem of growing significance. In the post-antibiotic era, there is a huge push to develop new tools for effectively treating bacterial infections. Photodynamic therapy involves the use of a photosensitizer that is activated by the use of light of an appropriate wavelength in the presence of oxygen. This results in the generation of singlet oxygen molecules that can kill the target cells, including cancerous cells and microbial cells. Photodynamic therapy is shown to be effective against parasites, viruses, algae, and bacteria. To achieve high antimicrobial activity, a sufficient concentration of photosensitizer should enter the microbial cells. Generally, photosensitizers tend to aggregate in aqueous environments resulting in the weakening of photochemical activity and lowering their uptake into cells. Nanocarrier systems are shown to be efficient in targeting photosensitizers into microbial cells and improve their therapeutic efficiency by enhancing the internalization of photosensitizers into microbial cells. This review aims to highlight the basic principles of photodynamic therapy with a special emphasis on the use of nanosystems in delivering photosensitizers for improving antimicrobial photodynamic therapy.