Study on Ruthenium Complexes and Methylene Blue Based Photosensitizers for Visible Light Bactericidal Action

Abstract

The combined use of photosensitizer (PS) and light to kill cancerous and microbial cells newlinehas emerged as photodynamic therapy (PDT), and photodynamic antimicrobial chemotherapy (PACT), respectively. PSs are known to generate reactive oxygen species (ROS) on photo excitation that has the ability to kill cells. Moreover, recent studies indicate that PACT agents have been useful for light induced water disinfection. The PSs can be organic compounds, transition metal complexes, bioconjugates or nanoparticle systems. The recovery of homogeneous PS by adsorption from disinfected water is important to obtain water free of microbes and PS. Ruthenium complexes as PSs for visible light water disinfection and their removal from water after disinfection have not been studied. A photostable PS which retains its activity after adsorption, and newlinedoes not leach is desirable. Furthermore, nano hybrid systems of PS and nanoparticles newlineare known. However, their effect on bacterial photoinactivation has not been well studied. Light emitting diodes (LEDs) are emerging as suitable and promising light sources for photoinactivation of bacteria. A brief introduction on all the above facts is newlinepresented in chapter 1. Gap in the literature, on the use of PSs for photoinactivation of bacteria is presented in chapter 1. Two ruthenium complexes namely, newline[Ru(bpy)2(phendione)]2+, [Ru(phendione)3]2+ have been demonstrated to kill both Grampositive and Gram-negative bacteria in water using LED as visible light source. These complexes were also effectively removed from water using activated carbon (AC) and newlinesilica, and these results are presented in Chapter 2. Further, ruthenium complexes newline([Ru(bpy)2(phendione)]2+, [Ru(bpy)3]2+) adsorbed onto AC were shown to inactivate newlinebacteria without leaching of complexes and reused for at least 5 cycles (Chapter 3). newlineNano hybrid systems consisting of positively charged [Ru(bpy)3]2+ and negatively charged Ag-GSH showed the ability to completely photoinactivate both Gram-positive and Gram-negative bacteria in water.