Near Infrared (NIR) absorbing dyes as promising photosensitizer for photo dynamic therapy

Photo Dynamic Therapy (PDT) is regarded as an effective therapeutic approach for cancer, which employs light and photosensitizing chemical substances. The successful demonstration of this technique by Dougherty et al. paved a new way for tumor treatment. Since then the technique has been continuously evolving to keep up its promises in medical science. The basic idea of PDT is to administer photoactive small molecules within tumor cells. The photoactive molecules, well known as Photosensitizers (PS) absorb light from external light source depending on its absorption property and goes to excited state. In this excited state they react with molecular oxygen of the living tissues and forms reactive oxygen species (ROS). These ROS are very toxic to the cells as they instantly oxidize important biomolecules such as proteins and nucleic acids (DNA, RNA), which leads to the dysfunction of the cells and eventually results in the cell death. In this context, PS which absorb broad region of energy ranging to Near Infrared Region (NIR) is desired as NIR, with better penetration efficiency into deep tissues as compared to visible light. One single review would be inadequate to consolidate all aspects of PDT on its design and efficacy. Each step needs a lot of standardizations and efforts and every step is equally important. This review is an attempt to give a comprehensive overview about the recent advancement in NIR absorbing dyes such as BODIPYs, Keio Fluors, Aza-BODIPY, Chorin, Phthalocyanines, Cyanine dyes, and Nano particles based NIR photosensitizers and their potential in PDT. Herein, we have also given deep insights into the recent trends in this field which emphasizes the potential of this technique to become a first line of treatment for tumours of diverse range.