Hongshang Peng

Luminescent Europium(III) Nanoparticles for Sensing and Imaging of Temperature in the Physiological Range

Europium(III) Nanoparticles are fabricated for sensing and imaging of physiological temperatures (see image). The material shows visible-light excitation, line-like emission, inertness to external perturbers (such as oxygen in air), and a dynamic range that covers temperatures encountered in medicine and (cellular) biology. The resolution is ±0.3 °C. The nanoparticles may also be incorporated into a (conceivably sprayable) sensor film.

A Nanogel for Ratiometric Fluorescent Sensing of Intracellular pH Values

A ratiometric fluorescent nanogel can sense pH over a range that is applicable to physiological studies. It can be easily prepared and made pH-responsive by addition of a pH probe and a FRET system that utilizes the gel to hold dyes in close proximity (see picture; overlay of coumarin dye and Nile Red fluorescence in kidney cells).

Luminescent terbium and europium probes for lifetime based sensing of temperature between 0 and 70 °C

Organic europium (III) and terbium (III) complexes (refered to as Eu1, Eu2, and Tb-L1, Tb-L2, respectively) have been synthesized that display bright emission and small bandwidth. Tb-L1 and Tb-L2 show lifetimes in the order of almost 1 ms at room temperature, good color purity, and high relative photoluminescence quantum yields. This makes them excellent probes for sensing temperature via measurement of luminescence lifetime. Probes Eu1, Eu2, Tb-L1 and Tb-L2 were incorporated into various polymer matrices to give sensor films for use as temperature-sensitive paints (TSPs). Eu (III) complexes have the advantage of being effectively excited by purple light-emitting diodes with their peak wavelengths of 405 nm. All TSPs based on these europium and terbium probes display good sensitivities to temperature, in particular, TSP based on Tb-L1 and Tb-L2 can show temperature-lifetime sensitivities of −13.8 μs per °C and − 9.2 μs per °C, respectively. Assuming a precision of ± 1 μs in the determination of lifetime, this will enable temperature to be determined with a precision of around ± 0.1 °C. This temperature dependence is the highest one reported so far for lanthanide complexes.

Facile One-Step Synthesis and Transformation of Cu(I)-Doped Zinc Sulfide Nanocrystals to Cu1.94S–ZnS Heterostructured Nanocrystals

A facile one-pot heating process without any injection has been developed to synthesize different Cu-Zn-S-based nanocrystals. The composition of the products evolves from Cu(I)-doped ZnS (ZnS:Cu(I)) nanocrystals into heterostructured nanocrystals consisting of monoclinic Cu1.94S and wurtzite ZnS just by controlling the molar ratios of zinc acetylacetonate (Zn(acac)2) to copper acetylacetonate (Cu(acac)2) in the mixture of n-dodecanethiol (DDT) and 1-octadecene (ODE). Accompanying the composition transformation, the crystal phase of ZnS is changed from cubic zinc blende to hexagonal wurtzite. Depending on the synthetic parameters including the reaction time, temperature, and the feeding ratios of Zn/Cu precursors, the morphology of the as-obtained heterostructured nanocrystals can be controlled in the forms of taper-like, matchstick-like, tadpole-like, or rod-like. Interestingly, when the molar ratio of Cu(acac)2 to Zn(acac)2 is increased to 9:1, the crystal phase of the products is transformed from monoclinic Cu1.94S to the mixed phase composed of cubic Cu1.8S and tetragonal Cu1.81S as the reaction time is further prolonged. The crystal-phase transformation results in the morphological change from quasi-spherical to rice shape due to the incorporation of Zn ions into the Cu1.94S matrix. This method provides a simple but highly reproducible approach for synthesis of Cu(I)-doped nanocrystals and heterostructured nanocrystals, which are potentially useful in the fabrication of optoelectronic devices.

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.

Controllable synthesis of silver and silver sulfide nanocrystals via selective cleavage of chemical bonds

A one-step colloidal process has been adopted to prepare silver (Ag) and silver sulfide (Ag₂S) nanocrystals, thus avoiding presynthesis of an organometallic precursor and the injection of a toxic phosphine agent. During the reaction, a layered intermediate compound is first formed, which then acts as a precursor, decomposing into the nanocrystals. The composition of the as-obtained products can be controlled by selective cleavage of S-C bonds or Ag-S bonds. Pure Ag₂S nanocrystals can be obtained by directly heating silver acetate (Ag(OAc)) and n-dodecanethiol (DDT) at 200 ° C without any surfactant, and pure Ag nanocrystals can be synthesized successfully if the reaction temperature is reduced to 190 ° C and the amount of DDT is decreased to 1 ml in the presence of a non-coordinating organic solvent (1-octadecene, ODE). Otherwise, the mixture of Ag and Ag₂S is obtained by directly heating Ag(OAc) in DDT by increasing the reaction temperature or in a mixture of DDT and ODE at 200 ° C. The formation mechanism has been discussed in detail in terms of selective S-C and Ag-S bond dissociation due to the nucleophilic attack of DDT and the lower bonding energy of Ag-S. Interestingly, some products can easily self-assemble into two- or three-dimensional (2D or 3D) highly ordered superlattice structures on a copper grid without any additional steps. The excess DDT plays a key role in the superlattice structure due to the bundling and interdigitation of the thiolate molecules adsorbed on the as-obtained nanocrystals.

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.