title: Correlation between defects in capped ZnO nanoparticles and their antibacterial activity.
abstract: Antibacterial activity of ZnO nanoparticles (NPs) triggered by generation of reactive oxygen species (ROS) depends on the fate of photoexcited charge carriers. Batches of wide band gap ZnO NPs of 7-9nm sizes, capped with polyethylene glycol (PEG), ascorbic acid (AsA), mercaptoacetic acid (MAA) and polysorbate 80 (T-80) were synthesized by precipitation method. These capped ZnO NPs exhibited ROS induced antibacterial activity, where the ROS was measured by TBARS assay. The PEG capped and AsA capped ZnO NPs exhibited weaker antibacterial activity and were correlated with strong and broad green emission peak owing to oxygen vacancies. The oxygen vacancies were trap sites of photoexcited electrons which inhibited interaction between the photoexcited electrons and oxygen on the surface of the ZnO NPs and accounted for lesser ROS generation and subsequently weaker antibacterial activity. Contrastingly MAA capped and T-80 capped ZnO NPs did not exhibit significant green emission peak, but exhibited 13% and 43% inhibition of growth of E. coli, respectively. The lack of oxygen vacancy defects in MAA capped and T-80 capped ZnO NPs perhaps led to lesser trapping of charge carriers, which is favorable for higher ROS generation and consequently higher antibacterial activity.
authors.affiliation: Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, India. duttafcy@iitr.ernet.in
authors.forename: Raj Kumar
authors.initials: RK
authors.lastname: Dutta
authors.forename: Bhavani P
authors.initials: BP
authors.lastname: Nenavathu
authors.forename: Mahesh K
authors.initials: MK
authors.lastname: Gangishetty
mesh_terms: D000900:Anti-Bacterial Agents / Q000737:chemistry* / Q000494:pharmacology*; D001205:Ascorbic Acid / Q000737:chemistry; D048168:Escherichia coli K12 / Q000187:drug effects / Q000378:metabolism; D015227:Lipid Peroxidation / Q000187:drug effects; D053758:Nanoparticles; D055620:Optical Phenomena; D011092:Polyethylene Glycols / Q000737:chemistry; D011136:Polysorbates / Q000737:chemistry; D017382:Reactive Oxygen Species / Q000378:metabolism; D013329:Structure-Activity Relationship; D017392:Thiobarbituric Acid Reactive Substances / Q000378:metabolism; D013864:Thioglycolates / Q000737:chemistry; D015034:Zinc Oxide / Q000737:chemistry* / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D011136:Polysorbates; D017382:Reactive Oxygen Species; D017392:Thiobarbituric Acid Reactive Substances; D013864:Thioglycolates; D011092:Polyethylene Glycols; C017487:2-mercaptoacetate; D001205:Ascorbic Acid; D015034:Zinc Oxide
keywords: Antibacterial activity; Capping agents; Oxygen vacancies; Reactive oxygen species; TBARS assay; ZnO NPs