SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Luminescence

172

Highly efficient room-temperature ultraviolet (UV) luminescence is obtained in heterostructures consisting of 10-nm-thick ultrathin ZnO films grown on Si nanopillars fabricated using self-assembled silver nanoislands as a natural metal nanomask during a subsequent dry etching process. Atomic layer deposition was applied for depositing the ZnO films on the Si nanopillars under an ambient temperature of 200°C. Based on measurements of photoluminescence (PL), an intensive UV emission corresponding to free-exciton recombination (approximately 3.31 eV) was observed with a nearly complete suppression of the defect-associated, broad-range visible emission peak. As compared to the ZnO/Si substrate, the almost five-times-of-magnitude enhancement in the intensity of PL, which peaked around 3.31 eV in the present ultrathin ZnO/Si nanopillars, is presumably attributed to the high surface/volume ratio inherent to the Si nanopillars. This allowed considerably more amount of ZnO material to be grown on the template and led to markedly more efficient intrinsic emission.

Concepts: Ultraviolet, Titanium dioxide, Luminescence, Zinc oxide, Sunscreen, Surface-area-to-volume ratio, Intensive and extensive properties, Nanopillar

48

The sensing and differentiation of explosive molecules is key for both security and environmental monitoring. Single fluorophores are a widely used tool for explosives detection, but a fluorescent array is a more powerful tool for detecting and differentiating such molecules. By combining array elements into a single multichannel platform; faster results can be obtained from smaller amounts of sample. Here, five explosives are detected and differentiated using quantum dots as luminescent probes in a multichannel platform - 2,4-dinitrotoluene (DNT), 2,4,6-trinitrotoluene (TNT), tetryl (2,4,6-trinitrophenylmethylnitramine), cyclotrimethylenetrinitramine (RDX) and pentaerythritol tetranitrate (PETN). The sharp, variable emissions of the quantum dots, from a single excitation wavelength, make them ideal for such a system. Each colour quantum dot is functionalised with a different surface receptor via a facile ligation process. These receptors undergo non-specific interactions with the explosives, inducing variable fluorescence quenching of the quantum dots. Pattern analysis of the fluorescence quenching data allows for explosive detection and identification with limits-of-detection in the ppb range.

Concepts: Fluorescence, Light, Quantum dot, Luminescence, Plastic explosive, Trinitrotoluene, Pentaerythritol tetranitrate, Semtex

28

Zn(II) complexes of the following new, fluorine-containing, benzothiazole-derived ligands have been synthesized and characterized crystallographically: 2-(3,3,3-trifluoro-2-oxopropyl)benzothiazole (3), 4,5,6,7-tetrafluoro-2-(3,3,3-trifluoro-2-oxopropyl)benzothiazole (4), 4,5,6,7-tetrafluoro-2-(2-hydroxyphenyl)benzothiazole (12), 2-(3,4,5,6-tetrafluoro-2-hydroxyphenyl)-4,5,6,7-tetrafluorobenzothiazole (13), and 2-(3,4,5,6-tetrafluoro-2-hydroxyphenyl)benzothiazole (16); the Cu(II) complex of ligand 4 is also reported. These are analogs of the important photo- and electroluminescent material [Zn(BTZ)(2)](2), where H-BTZ = 2-(2-hydroxyphenyl)benzothiazole. DFT calculations indicate that HOMO and LUMO energy levels in these materials are substantially lowered by fluorination. The fluorinated ZnL(2) complexes are mononuclear (in contrast to the dinuclear, nonfluorinated material [Zn(BTZ)(2)](2)). They easily sublime and show broad visible photoluminescence. A common crystallographic feature is the existence of pairs of fluorinated ZnL(2) molecules related by inversion centers, with their π systems facing one another.

Concepts: Following, Benzene, Ligand, Complex, Luminescence, Material, HOMO/LUMO, Electroluminescence

28

Biothiols, such as cysteine (Cys) and homocysteine (Hcy), play very crucial roles in biological systems. Abnormal levels of these biothiols are often associated with many types of diseases. Therefore, the detection of Cys (or Hcy) is of great importance. In this work, we have synthesized an excellent “OFF-ON” phosphorescent chemodosimeter 1 for sensing Cys and Hcy with high selectivity and naked-eye detection based on an Ir(III) complex containing a 2,4-dinitrobenzenesulfonyl (DNBS) group within its ligand. The “OFF-ON” phosphorescent response can be assigned to the electron-transfer process from Ir(III) center and C^N ligands to the DNBS group as the strong electron-acceptor, which can quench the phosphorescence of probe 1 completely. The DNBS group can be cleaved by thiols of Cys or Hcy, and both the (3) MLCT and (3) LC states are responsible for the excited-state properties of the reaction product of probe 1 and Cys (or Hcy). Thus, the phosphorescence is switched on. Based on these results, a general principle for designing “OFF-ON” phosphorescent chemodosimeters based on heavy-metal complexes has been provided. Importantly, utilizing the long emission-lifetime of phosphorescence signal, the time-resolved luminescent assay of 1 in sensing Cys was realized successfully, which can eliminate the interference from the short-lived background fluorescence and improve the signal-to-noise ratio. As far as we know, this is the first report about the time-resolved luminescent detection of biothiols. Finally, probe 1 has been used successfully for bioimaging the changes of Cys/Hcy concentration in living cells.

Concepts: Amino acid, Disulfide bond, Luminescence, Cysteine, Phosphorescence, Thiol, Methionine, Photoluminescence

28

Chemically modified CdSe/ZnS quantum dots (QDs) are used as fluorescent probes for the analysis of explosives, and specifically, the detection of trinitrotoluene (TNT) or trinitrotriazine (RDX). The QDs are functionalized with electron-donating ligands that bind nitro-containing explosives, exhibiting electron-acceptor properties, to the QD surface, via supramolecular donor-acceptor interactions leading to the quenching of the luminescence of the QDs.

Concepts: Fluorescence, Chemistry, Quantum dot, Luminescence, Explosive material, Trinitrotoluene, Dynamite, RDX

28

Fluorescent probes based on boron dipyrromethene functionalized with a phenylboronic acid group (BODIPY-PBAs) were synthesized in high yield for the first time by Suzuki coupling of bis(pinacolato)diboron and 8-(4-bromophenyl)-1,3,5,7-tetramethyl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY). Wavelength tuning of the fluorophores was achieved by attaching an auxochromic substituent to the 5-position of the BODIPY core structure through Knoevenagel condensation. The emission intensity of fluorophores increases when binding to the analytes with diol groups and forming boronic esters at fixed pH. These compounds can detect monosaccharides in the concentration range of 0.1-100 mM. Whereas glycogen was found to quench the fluorescence of BODIPY-PBAs in an aqueous solution due to the self-quenching of the fluorophores after attaching in the extensively branched and compact glucose polymer, further addition of d-fructose to the solution can release the fluorophores from the polymer and the fluorescence regains. The BODIPY-PBA fluorophore has been applied in polymeric optodes containing anion exchangers to perform repetitive measurement. Such sensors respond to different monosaccharides in the range of 0.1-100 mM and demonstrate an improved selectivity toward d-fructose over other saccharides, compared to the results obtained from homogeneous assay.

Concepts: Amino acid, Glucose, Light, Concentration, Chemistry, Luminescence, Monosaccharide, Boronic acid

28

In this study, we have demonstrated the reconstruction of encrypted information by employing photoluminescence spectra and lifetimes of a phosphorescent Ir(III) complex (IrHBT). IrHBT was constructed on the basis of a heteroleptic structure comprising a fluorescent N(∧)O ancillary ligand. From the viewpoint of information security, the transformation of the Ir(III) complex between phosphorescent and fluorescent states can be encoded with chemical/photoirradiation methods. Thin polymer films (poly(methylmethacrylate), PMMA) doped with IrHBT display long-lived emission typical of phosphorescence (λ(max) = 586 nm, τ(obs) = 2.90 μs). Meanwhile, exposure to HCl vapor switches the emission to fluorescence (λ(max) = 514 nm, τ(obs) = 1.53 ns) with drastic changes in both the photoluminescence color and lifetime. Security printing on paper impregnated with IrHBT or on a PMMA film containing IrHBT and photoacid generator (triphenylsulfonium triflate) enables the bimodal readout of photoluminescence color and lifetime.

Concepts: Spectroscopy, Luminescence, Phosphorescence, Security, Photoluminescence, Triphenylsulfonium triflate, Triflates, Sulfonium

28

The lux operon derived from Photorhabdus luminescens incorporated into bacterial genomes, elicits the production of biological chemiluminescence typically centered on 490 nm. The light-producing bacteria are widely used for in vivo bioluminescence imaging. However, in living samples, a common difficulty is the presence of blue-green absorbers such as hemoglobin. Here we report a characterization of fluorescence by unbound excitation from luminescence, a phenomenon that exploits radiating luminescence to excite nearby fluorophores by epifluorescence. We show that photons from bioluminescent bacteria radiate over mesoscopic distances and induce a red-shifted fluorescent emission from appropriate fluorophores in a manner distinct from bioluminescence resonance energy transfer. Our results characterizing fluorescence by unbound excitation from luminescence, both in vitro and in vivo, demonstrate how the resulting blue-to-red wavelength shift is both necessary and sufficient to yield contrast enhancement revealing mesoscopic proximity of luminescent and fluorescent probes in the context of living biological tissues.

Concepts: Fluorescence, Gene, Bacteria, Light, Fungus, Luminescence, Bioluminescence, Chemiluminescence

27

Fluorescence imaging is one of the most versatile and widely used visualization methods in biomedical research. However, tissue autofluorescence is a major obstacle confounding interpretation of in vivo fluorescence images. The unusually long emission lifetime (5-13 μs) of photoluminescent porous silicon nanoparticles can allow the time-gated imaging of tissues in vivo, completely eliminating shorter-lived (<10 ns) emission signals from organic chromophores or tissue autofluorescence. Here using a conventional animal imaging system not optimized for such long-lived excited states, we demonstrate improvement of signal to background contrast ratio by >50-fold in vitro and by >20-fold in vivo when imaging porous silicon nanoparticles. Time-gated imaging of porous silicon nanoparticles accumulated in a human ovarian cancer xenograft following intravenous injection is demonstrated in a live mouse. The potential for multiplexing of images in the time domain by using separate porous silicon nanoparticles engineered with different excited state lifetimes is discussed.

Concepts: Nanoparticle, Animal testing, In vivo, Silicon, In vitro, Luminescence, Excited state, Imaging

27

Rare-earth upconversion nanophosphors (UCNPs) have become one of the most promising luminescent materials for bio-applications, but their use still meets some limitations by difficulties in obtaining biocompatible UCNPs. To address this problem, we have developed a simple and versatile strategy for converting hydrophobic UCNPs into hydrophilic ones by amphiphilic silane modification with ultrathin thickness at room temperature (RT). In this strategy, the coating layers can also afford the place for loading with Eu(TTA)3(TPPO)2 complex which displays down conversion luminescence (DCL). Due to the UC and DC properties, we achieved the dual mode physiological range temperature sensing and dual mode cell imaging. Such novel nanomaterials offer a new surface modification strategy for the NPs that are formed in the oil phase for bio-applications.

Concepts: Chemical properties, Developed country, Solubility, Trigraph, Materials science, Luminescence