Nanoscaled approach to formulate photosensitizers for improved photodynamic therapy and imaging

Abstract

In this thesis, an effort is made to create a biocompatible, biodegradable nanoformulation of photosensitizer (PS) that can be more effective for photodynamic therapy and imaging. Rhodamine 6G (R6G) was chosen as PS. R6G exhibit fluorescent properties that has been studied for its potential use in various application, including photodynamic therapy (PDT). Even though R6G has shown promise in some studies, there are also potential issues and challenges associated with its use like photobleaching, limited tissue penetration, toxicity, tumor selectivity, biocompatibility and biodegradability. Here some nanomaterials are chosen to overcome these drawbacks. Nanomaterials such as gold nanoparticle (AuNP), chitosan-alginate hydrogel (Cs-Alg), calcium alginate (Alg), oxidized sodium alginate (OSA) was chosen as a carrier of R6G. Poor aqueous solubility and decreased sensitivity of R6G prevent its use as a photosensitizer in PDT, necessitating the development of nanocarriers to enhance its bioavailability, targeted distribution, and ROS-quantum yield. Gold nanoparticle was chosen among the metal nanoparticle, since it offers numerous advantages, particularly in the field of nanomedicine. Their unique optical, electronic, and catalytic properties make them valuable for various applications. Their size-dependent properties enable precise control over their behavior, facilitating targeted drug delivery in medicine. Additionally, gold nanoparticles exhibit excellent biocompatibility and can be functionalized for specific purposes, enhancing their utility in diagnostics and imaging. The study is concentrated on investigating the nanoformulated PS for the generation of higher quantum yield and theranostic application. newlineR6G conjugated AuNP was synthesized using citrate reduction method. The prepared nanoformulations was characterized at each stage using various instruments including UV-visible spectrophotometer, spectrofluorometer, particle size analyzer, SEM, and TEM. The ability to generate ROS was investigated using the iodide method. R6G conjugated AuNP showed the higher ROS generation than R6G alone. Compare to R6G in water the quantum yield of AuNP- R6G showed three time higher. At optimal concentrations, R6G-AuNP generated 0.9 singlet oxygen whereas R6G generated 0.3, three times more than free R6G. Similar study was conducted using other formulations like, R6G encapsulated Cs-Alg-R6G, Alg-R6G and OSA-R6G, where the quantum yield of Cs-Alg- R6G was calculated as 0.9. The ROS quantum yield increased from 0.30 in an aqueous environment to 0.51 when using an alginate-based formulation, and it was further enhanced to 0.81 in the case of OSA. Optical imaging revealed that the fabricated particles containing R6G could serve as an effective optical probe. Subsequent CT imaging validated the potential of the conjugated AuNP-R6G for use as a contrast agent in CT, enhancing diagnostic capabilities for various medical conditions. Using the MTT test and cumulative hatchability study, the biocompatibility evaluations were performed in both in vitro and in vivo, and showed nontoxic behavior and no abnormality on embryos. newlineGenerally, all the studies concluded that the nanoformulated PS poses a theranostic approach with increased ROS production, reduced toxicity, and improved imaging. newline newline