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 H2O2 to the axial position of one of the active copper sites of the oxy-Tyr during the catalase cycle to produce deoxy-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.Graphical Abstract

L-cysteine capped ZnS:Mn quantum dots for room-temperature detection of dopamine with high sensitivity and selectivity

“…In particular, Mn-doped ZnS (ZnS: Mn) QDs with intrinsic solubility in water have appeared as a potential fluorescent probe since they exhibit high resistance to photobleaching, broad absorption with relatively-narrow and symmetric emission, high quantum yield, and strong resistance to degradation. Their main features are not only analogous to those observed in Cd (Se, Te) QDs (most used as standards), but also ZnS:Mn QDs are nontoxic in a wide range of concentrations (Diaz-Diestra et al, 2015;Li et al, 2011b;Sotelo-Gonzalez et al, 2013;Zhang et al, 2011). In addition, the Mn-doping into the ZnS host further advances multiplicity of decay times, flexible bioconjugation approaches, enhanced surface passivation, large-effective Stokes shifts, intermittency under continuous excitation, and optical tunability (DiazDiestra et al, 2015;Liu et al, 2008a;Quan et al, 2009).…”

“…The phosphorescent spectrum shows a prominent orange emission band at $ 598 nm, which is associated to the internal Mn 2 þ ion transition between the 4 T 1 first excited state (spin 3/2) and the 6 A 1 ground state (spin 5/2) (Beltran-Huarac et al, 2013). Note that the blue band at $416 nm (ascribed to the nanostructure surface states) typically observed in dual-emitting ZnS:Mn QDs was not detected by the spectrometer since it was operated in phosphorescence mode (Ertas et al, 2015) The blue band of the QDs when the spectrometer is operated in fluorescence mode was reported in our previous work (Diaz-Diestra et al, 2015). The internal transition is assumed to cause energy transfer from s-p electronhole pair band states (host ZnS nanocrystal) to the Mn 2 þ ion delectron states.…”

“…Quantum dots (QDs) used as fluorescent probes in chemo/ biosensing offer significant advantages over organic molecules, genetically-encoded fluorophores and conventional dyes, in terms of simultaneously detecting multiple signals, producing long-term stabilities, and enriching both the biological targeting efficiency and substrate specificity (Alivisatos, 1996;Diaz-Diestra et al, 2015;Liao et al, 2014). In particular, Mn-doped ZnS (ZnS: Mn) QDs with intrinsic solubility in water have appeared as a potential fluorescent probe since they exhibit high resistance to photobleaching, broad absorption with relatively-narrow and symmetric emission, high quantum yield, and strong resistance to degradation.…”

Engineering Quantum Dots with Ionic Liquid: A Multifunctional White Light Emitting Hydrogel for Enzyme Packaging

“…The reasons for selecting Mn 2+ ‐doped ZnS QD are due to their bio‐friendly properties, such as ease of processability in aqueous media and lower toxicity. 29 Alternatively, the cholinium‐based ionic liquid also proved to be biocompatible 30–32. Thus, it is reasonable to say that the QD‐IL composite might also be bio‐compatible.…”

“…This result suggests that the structural integrity of the QD in the presence of an IL is maintained. However, the presence of the characteristic peaks of the functional groups such as OH stretching (3380 cm −1 ), alkyl CH stretching (2930 and 2850 cm −1 ), aromatic CC stretching (1625 cm −1 ), CH 2 bending (1481 cm −1 ), the asymmetric stretching vibration of OSO (1192 and 1129 cm −1 ), the symmetric stretching vibration of OSO (1037 cm −1 ), CC stretching (1009 cm −1 ), the anti‐symmetric stretching of quaternary ammonia (952 cm −1 ), p ‐disubstituted benzene (810 cm −1 ), the stretching vibration of the CS (685 cm −1 ) in the IL in the FTIR spectrum of IL‐treated QDs supports the incorporation of IL on the surface of the QD (Figure 1E; Table S1, Supporting Information) 32–34. In addition, the changes in the surface charge from +16.0 to +11.6 mV for QD, upon addition of IL, supports the modification of the surface of the QD through electrostatic interaction between the anions of IL and the excess cations present on the surface of QD (Figure 1F).…”