title: Quantification of reactive oxygen species generation by photoexcitation of PEGylated quantum dots.
abstract: Photocatalytic generation of reactive oxygen species (ROS) from quantum dots (QDs) has been widely reported yet quantitative studies of ROS formation and their quantum yields are lacking. This study investigates the generation of ROS by water soluble PEGylated CdSe/ZnS QDs with red emission. PEGylation of QDs is commonly used to confer water solubility and minimise uptake by organs of the reticuloendothelial system; therefore studies of ROS formation are of biomedical relevance. Using non-photolytic visible wavelength excitation, the superoxide anion radical is shown to be the primary ROS species generated with a quantum efficiency of 0.35%. The yield can be significantly enhanced in the presence of the electron donor, nicotinamide adenine dinucleotide (NADH), as demonstrated by oxygen consumption measurements and electron paramagnetic resonance spectroscopy with in situ illumination. Direct production of singlet oxygen is not detectable from the QDs alone. A comparison is made with ROS generation by the same QDs complexed with a sulfonated phthalocyanine which can generate singlet oxygen via Förster resonance energy transfer between the QDs and the phthalocyanine.
authors.affiliation: Division of Surgery & Interventional Science, Charles Bell House, University College London, London, W1W 7EJ, UK.
authors.forename: Elnaz
authors.initials: E
authors.lastname: Yaghini
authors.forename: Katharina F
authors.initials: KF
authors.lastname: Pirker
authors.forename: Christopher W M
authors.initials: CW
authors.lastname: Kay
authors.forename: Alexander M
authors.initials: AM
authors.lastname: Seifalian
authors.forename: Alexander J
authors.initials: AJ
authors.lastname: MacRobert
mesh_terms: D004578:Electron Spin Resonance Spectroscopy; D008027:Light; D010101:Oxygen Consumption; D011092:Polyethylene Glycols / Q000737:chemistry*; D045663:Quantum Dots; D017382:Reactive Oxygen Species / Q000378:metabolism*
chemical_list: D017382:Reactive Oxygen Species; D011092:Polyethylene Glycols
keywords: EPR spectroscopy; quantum dots; singlet oxygen; spin trapping; superoxide anion radicals