Abstract
Antimicrobial photodynamic therapy (aPDT) is a new-age therapeutic
technique that by principle, focuses on the eradication of target cells by highly
cytotoxic reactive oxygen species (ROS) generated through the activation of a chemical
photosensitizer (PS) molecule with visible light of appropriate wavelength. The
cytotoxic species can arise via two main mechanisms known as Type I and Type II
photoreactions: the former leads to the generation of ROS and the latter to the
formation of the singlet oxygen. These highly reactive oxidants can bring about
instantaneous oxidation of a great array of biological molecules, causing havoc to the
target cell. This technique provides significant advantages over conventional
antimicrobial therapies in practice which are now facing the burning threat of growing
complete resistance against them. To combat this world-wide health concern, new
treatment strategies are the need of the time while ensuring no further rise of resistance
against those alternative therapies, and aPDT appears to be highly promising in this
aspect by fulfilling all the demands at the same time. It appears not only equally
effective at killing both antibiotic-sensitive and multi-resistant bacterial strains, but also
highly selective, non-invasive and rapid in action than other antimicrobial agents, and
there have been no reports of resistance till date. The success of this phototherapy relies
on several factors, including the target cell type, reaction conditions, and the type,
molecular structure and cytolocalization of the PS; because its potency depends on the
distribution, high reactivity and short lifetime of ROS as well as the PS itself in
electronically excited states.