Silica immobilized porphyrin-culnS2/ZnS quantum dot conjugates for coliform bacteria photoinactivation in water

Abstract

Chlorination is a widely used chemical disinfection technique in South African water treatment facilities. However, it fails to combat emerging pollutants, drug resistant microbes and carcinogenic by-products, resulting in the inability of water treatment plants (WTPs) to meet standard regulations. Thus, alternative techniques to combat these challenges must be developed. Among the reported procedures, antimicrobial photodynamic inactivation (aPDI) is reportedly promising. aPDI is a photoinactivation technique employed for combating prevalent and drug-resistant pathogenic microbes. The efficacy of aPDI is independent of existing drug-resistance and is not associated with promoting drug-resistance after a photoinactivation process. In this study, the synthesis, characterization, photochemical properties and aPDI efficacy of a metal-free and indium (III) porphyrin conjugated to CuInS2/ZnS core-shell quantum dots (QDs) against E. coli and S. aureus when immobilized on mesoporous silica is reported. The effect of conjugation and metalation of porphyrin with indium (III) on aPDI efficacy, singlet oxygen quantum yields, fluorescence lifetimes, fluorescence quantum yields, triplet lifetimes and antimicrobial log reductions was studied. This study finds indium (III) porphyrin and CuInS2/ZnS QDs to generate more reactive oxygen species and singlet oxygen through conjugation. The singlet oxygen quantum yield of nanoconjugates was determined to be higher when compared to non-conjugated porphyrins. As such, the photoinactivation efficacy of nanoconjugates was greater.