Fangtian You

Biocompatible fluorescent core–shell nanoparticles for ratiometric oxygen sensing

Ratiometric fluorescent core–shell nanoparticles (NPs) with good biocompatibility are successfully prepared by a one-step reprecipitation–encapsulation method for sensing dissolved oxygen. The particle core comprises the oxygen probe platinum(II) octaethylporphine (PtOEP), the reference dye coumarin 6 (C6) and a third fluorophore dinaphthoylmethane (DNM). Upon single 381 nm excitation, C6 gives oxygen-insensitive referenced green fluorescence via intraparticle FRET from DNM, whilst PtOEP yields highly oxygen-sensitive red phosphorescence with a quenching response of 94%. The fluorescence quenching of the NPs against oxygen follows a linear Stern–Volmer behavior, which is fundamental for practical sensing. Moreover, positively charged poly-L-lysine molecules are in situ self-assembled onto the surface of NPs during synthesis. The resultant core–shell NPs with functional groups exhibit low cytotoxic effects as well as effortless cellular uptake, indicating targeted intracellular oxygen sensing is very promising using the oxygen nanosensors.

Poly-L-lysine assisted synthesis of core–shell nanoparticles and conjugation with triphenylphosphonium to target mitochondria

In this paper, we report a facile route to synthesize mitochondria-targeted core-shell nanoparticles (NPs). Firstly, PLL-coated NPs are prepared by a one-step reprecipitation-encapsulation method assisted by positively charged poly-l-lysine (PLL). The effect of the molecular weight of PLL on the formation of particles is studied in terms of morphology, size and zeta potential, and medium-sized PLL (MH-PLL) is proved to be the optimum one. By means of crosslinking with different amounts of glutaraldehyde, amino groups in MH-PLL-NPs are characterized by zeta potential and fluorescamine assay, respectively. The results indicate that in the PLL shell, only a small portion of amino groups (surface amino groups, SAGs) are available for conjugation, while the other groups exclusively contribute to zeta potential. Subsequently, a known mitochondriotropic ligand, triphenylphosphonium (TPP), is conjugated with SAG via a carbodiimide reaction, which is evaluated by NMR and absorption spectra, respectively. The TPP-MH-PLL-NPs exhibit a low cytotoxic effect tested by the MTT method, as well as efficient cellular uptake microscopically observed after a fluorescent dye, coumarin 6, is incorporated. Most importantly, the TPP-conjugated NPs can selectively target mitochondria, demonstrated by the merged z-stacked images in co-localization experiments with MitoTracker-stained mitochondria. Given that many hydrophobic species could be loaded into the particle core, TPP-MH-PLL-NPs are very promising as mitochondria-targeted nanocarriers for imaging or anti-cancer therapies.

Hydrothermal preparation and persistence characteristics of nanosized phosphor SrS: Eu2+, Dy3+

Abstract Nanosized long-persistent phosphors SrS: Eu 2+ , Dy 3+ were prepared by the hydrothermal method. The samples were characterized by X-ray powder diffraction, transmission electron microscopy, and charge-coupled device spectrometry. The persistence characteristic was studied using the decay curves. The results showed that the emission intensity decreased sharply with temperature increasing, although the particle size increased. The S 2– vacancies caused by oxidization served as shallow traps, and Dy 3+ served as deep traps in SrS: Eu 2+ , Dy 3+ . The afterglow intensity of SrS: Eu 2+ , Dy 3+ was higher than that of SrS: Eu 2+ prepared at the same temperature. However, the minimization span of initial afterglow with temperature for the former sample was larger than that for the latter. Binary-doped phosphor decayed more slowly than the singly doped one. The afterglow of SrS: Eu 2+ , Dy 3+ decayed more quickly with the increase of sintering temperature.

Targetable Phosphorescent Oxygen Nanosensors for the Assessment of Tumor Mitochondrial Dysfunction By Monitoring the Respiratory Activity

Cellular respiration is a worthwhile criterion to evaluate mitochondrial dysfunction by measuring the dissolved oxygen. However, most of the existing sensing strategies merely report extracellular (ec-) or intracellular (ic-) O2 rather than intramitochondrial (im-) O2 . Herein we present a method to assess tumor mitochondrial dysfunction with three phosphorescent nanosensors, which respond to ec-, ic-, and im-O2 . Time-resolved luminescence is applied to determine the respective oxygen consumption rates (OCRs) under varying respiratory conditions. Data obtained for the OCRs and on (intra)cellular O2 gradients demonstrate that mitochondria in tumor cells are distinctly less active than those of healthy cells, resulting from restrained glucose utilization of and physical injury to the mitochondria. We believe that such a site-resolved sensing strategy can be applied to numerous other situations, for example to evaluate the adverse effects of drug candidates.

Ultraviolet to near-infrared energy transfer in NaYF4:Nd3+,Yb3+ crystals

Abstract To convert ultraviolet (UV) light into near-infrared (NIR) light in phosphors is demanded for the development of solar cells. A series of NaYF4:Nd3+,Yb3+ white powder samples were prepared via the hydrothermal method. The crystal structure and photoluminescence properties of the samples were carefully studied using X-ray diffractometry (XRD) and photoluminescence spectra. The excitation and emission spectra of NaYF4:Nd3+,Yb3+ samples and the luminescence decay curves of Nd3+ and Yb3+ revealed an efficient energy transfer process from Nd3+ to Yb3+. This process resulted in the Yb3+ NIR fluorescent emission at 980 nm. Moreover, the lifetime of the Nd3+ 4F3/2 level decreased with the increase of Yb3+ doping concentration. The build-up time of the decay curves of the Yb3+ 2F5/2 level further verified the energy transfer process. Meanwhile, energy transfer efficiency based on different Yb3+ doping concentrations was achieved.

Energy transfer from Ce3+ to Tb3+, Dy3+ and Eu3+ in Na3Y(BO3)2

Abstract Energy transfer is a promising strategy to improve the visible light emitting efficiency of phosphors. A series of Ce 3+ , Tb 3+ , Dy 3+ and/or Eu 3+ doped Na 3 Y(BO 3 ) 2 (NYB) were prepared by solid-state reaction and their photoluminescence properties were studied in detail. The excitation and emission spectra of NYB:Ce 3+ ,Tb 3+ and NYB:Ce 3+ ,Dy 3+ revealed that an efficient energy transfer process from Ce 3+ to Tb 3+ or Dy 3+ occurred upon excitation Ce 3+ into 5d level. The dependence of the decay times of Ce 3+ 5d level on Tb 3+ or Dy 3+ concentration indicated that the energy transfer efficiency increased with increasing Tb 3+ or Dy 3+ content. So the UV excitation light could be converted into green or near-white emission. However, there was no obvious evidence of the existence of energy transfer from Ce 3+ to Eu 3+ in NYB.

Core-shell structure in doped inorganic nanoparticles: approaches for optimizing luminescence properties

Doped inorganic luminescent nanoparticles (NPs) have been widely used in both research and application fields due to their distinctive properties. However, there is an urgent demand to improve their luminescence efficiency, which is greatly reduced by surface effects. In this paper, we review recent advances in optimizing luminescence properties of doped NPs based on core-shell structure, which are basically classified into two categories: one is by use of surface coating with nonmetal materials to weaken the influence of surface effect and the other is with metal shell via metal enhanced luminescence. Different materials used to coat NPs are surveyed, and their advantages and disadvantages are both commented on. Moreover, problems in current core-shell structured luminescent NPs are pointed out and strategies furthering the optimization of luminescence properties are suggested.

Synthesis and optimization of ZnPc-loaded biocompatible nanoparticles for efficient photodynamic therapy

Zinc(ii) phthalocyanine (ZnPc) is a promising photosensitizer for PDT but suffers from aggregation in a physiological aqueous environment. In this paper, a class of biocompatible polymeric nanoparticles (NPs) was prepared to encapsulate ZnPc molecules. Mostly because of the planar structure, ZnPc molecules were difficult to be encapsulated into the polymeric NPs unless further coated with a thick poly-l-lysine (PLL) layer. The PLL shell endowed the NPs with good biocompatibility, efficient cellular uptake, and potential bioconjugation. The degree of aggregation (DOA) of ZnPc molecules in PLL-NPs was thoroughly investigated based on self-defined relative DOA, and a loading capacity of 4 wt% was deduced as the turning point for aggravating aggregation. Similarly, the optimal loading capacity of ZnPc was determined to be 4% according to the 1O2 generation rate, demonstrating the feasibility of the DOA approach. Polymers with large rigid units (PVK and PFO) were also utilized to relieve the aggregation of ZnPc in NPs. Taking advantage of the optimized ZnPc-loaded NPs, high PDT efficacy was demonstrated in HepG2 cells and in tumor-bearing mice as well. Both high in vitro and in vivo PDT efficacy and biocompatibility are demonstrated. Aside from affording a class of efficient biocompatible nanophotosensitizers, this work is also instructive to design other types of ZnPc-based nanocarriers, in which aggregation should be well considered.

Electrooptical characteristics of nanoscale and bulk long persistent phosphor SrAl2O4 : Eu, Dy

Nanoscale and bulk SrAl2O4 : Eu2+, Dy3+ were prepared, respectively, by auto-combustion of citrate gelatin (gel) and high temperature solid state method. The crystalline structure was examined by X-ray diffraction. The morphological and size aspects of nanoscale sample were carried out with transmission electron microscopy. Spectral shift of nanoscale phosphor was confirmed by measuring excitation and emission spectra. The current-voltage characteristic and optical power were measured with a Keithley source meter 2410. Ionic conductivity plays the leading role when the sample is not irradiated by light and electron conductivity should be in the charge of the current gain when the sample is irradiated by light. The result showed that light irradiation simultaneously increased the luminescence intensity and the current. The current increasing range of nanoscale phosphor is smaller than that of bulk phosphor. It was further concluded that the excited state energy levels of emission centre overlap partly with the conduction band of host crystal. Otherwise, surface effect was analysed deeply by comparing the decay curves of nanoscale and bulk SrAl2O4 : Eu2+, Dy3+.

Temperature-Dependent Emission of Pr3+ -Doped LaB3O6 under Vacuum Ultraviolet Excitation

Abstract The vacuum ultraviolet (VUV) luminescent properties of Pr3+ -activated LaB3O6 were investigated with high-energetic synchrotron radiation from 20 to 300 K. In the emission spectra, the parity-forbidden 4f2→4f2 and parity-allowed 4f5d→4f2 transitions were observed simultaneously. In addition, it was also observed that the intensity of 4f5d→4f2 emission bands increased relative to the intensity of 4f2→4f2 emissions with increasing temperature. The thermal equilibrium model of energy levels was employed with respect to the lowest 4f5d state and 1S0 state of LaB3O6: Pr3+, as a result of which the fitted curve had a good agreement with the experiment values, which clarified the physical nature of temperature-dependent emission characteristics of Pr3+ in LaB3O6.