title: Biocompatible ZnS:Mn quantum dots for reactive oxygen generation and detection in aqueous media.
abstract: We report here the versatility of Mn-doped ZnS quantum dots (ZnS:Mn QDs) synthesized in aqueous medium for generating reactive oxygen species and for detecting cells. Our experiments provide evidence leading to the elimination of Cd-based cores in CdSe/ZnS systems by substitution of Mn-doped ZnS. Advanced electron microscopy, X-ray diffraction, and optical spectroscopy were applied to elucidate the formation, morphology, and dispersion of the products. We study for the first time the ability of ZnS:Mn QDs to act as immobilizing agents for Tyrosinase (Tyr) enzyme. It was found that ZnS:Mn QDs show no deactivation of Tyr enzyme, which efficiently catalyzed the hydrogen peroxide (H2O2) oxidation and its eventual reduction (-0.063 V vs. Ag/AgCl) on the biosensor surface. The biosensor showed a linear response in the range of 12 μmol/L-0.1 mmol/L at low operation potential. Our observations are explained in terms of a catalase-cycled kinetic mechanism based on the binding of H2O2to the axial position of one of the active copper sites of theoxy-Tyr during the catalase cycle to producedeoxy-Tyr. A singlet oxygen quantum yield of 0.62 in buffer and 0.54 in water was found when ZnS:Mn QDs were employed as a photosensitizer in the presence of a chemical scavenger and a standard dye. These results are consistent with a chemical trapping energy transfer mechanism. Our results also indicate that ZnS:Mn QDs are well tolerated by HeLa Cells reaching cell viabilities as high as 88 % at 300 µg/mL of QDs for 24 h of incubation. The ability of ZnS:Mn QDs as luminescent nanoprobes for bioimaging is also discussed.
authors.affiliation: Molecular Sciences Research Center, University of Puerto Rico, San Juan, PR 00926 USA ; Department of Chemistry, University of Puerto Rico - Río Piedras, San Juan, PR 00936 USA.
authors.forename: Daysi
authors.initials: D
authors.lastname: Diaz-Diestra
authors.affiliation: Molecular Sciences Research Center, University of Puerto Rico, San Juan, PR 00926 USA ; Department of Physics, University of Puerto Rico - Río Piedras, San Juan, PR 00936 USA.
authors.forename: Juan
authors.initials: J
authors.lastname: Beltran-Huarac
authors.affiliation: Molecular Sciences Research Center, University of Puerto Rico, San Juan, PR 00926 USA ; Department of Biology, University of Puerto Rico - Río Piedras, San Juan, PR 00931 USA.
authors.forename: Dina P
authors.initials: DP
authors.lastname: Bracho-Rincon
authors.affiliation: Molecular Sciences Research Center, University of Puerto Rico, San Juan, PR 00926 USA ; Department of Biology, University of Puerto Rico - Río Piedras, San Juan, PR 00931 USA.
authors.forename: José A
authors.initials: JA
authors.lastname: González-Feliciano
authors.affiliation: Molecular Sciences Research Center, University of Puerto Rico, San Juan, PR 00926 USA ; Department of Biology, University of Puerto Rico - Río Piedras, San Juan, PR 00931 USA ; Department of Biochemistry, School of Medicine, University of Puerto Rico - Medical Sciences, San Juan, PR 00936 USA.
authors.forename: Carlos I
authors.initials: CI
authors.lastname: González
authors.affiliation: Molecular Sciences Research Center, University of Puerto Rico, San Juan, PR 00926 USA ; Department of Chemistry, University of Puerto Rico - Río Piedras, San Juan, PR 00936 USA.
authors.forename: Brad R
authors.initials: BR
authors.lastname: Weiner
authors.affiliation: Molecular Sciences Research Center, University of Puerto Rico, San Juan, PR 00926 USA ; Department of Physics, University of Puerto Rico - Río Piedras, San Juan, PR 00936 USA.
authors.forename: Gerardo
authors.initials: G
authors.lastname: Morell
keywords: Biosensing; Photodynamic therapy; Quantum dots; Singlet oxygen; Tyrosinase; ZnS:Mn