Strong Fluorescence Emission Research Articles

Eu-doped ZnO quantum dots with solid-state fluorescence and dual emission for high-performance luminescent solar concentrators

Eu-doped ZnO quantum dots with strong solid-state fluorescence and dual emission are synthesized via a simple sol–gel method, which can be used for fabrication of high-performance luminescent solar concentrators.

Boron-doped and serine and histidine-functionalized graphene quantum dots with strong yellow fluorescence emissions for highly sensitive detection of carbofuran in cucumber and cabbage

The weak fluorescence of graphene quantum dots upon visible-light excitation limits their applications.

Two Cd(II) Coordination Compounds Based on the Flexible N-Bridging Ligands: Syntheses, Crystal Structures and Luminescent Properties

Two coordination compounds, Cd2(Рtt)2Cl4(H2O)2 (Ι) and [Cd(Dpb)2Cl2]n · nH2O (II) (Рtt = 3-(pyrid-2-yl)-5-(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl), Dpb = 1,4-bis(pyridin-3-ylmethoxy)benzene), were synthesized from hydro-solvothermal technique. Their structures have been characterized by infrared spectra, elemental analyses, single crystal X-ray diffraction analyses (CIF files CCDC nos. 1903141 (Ι), 1903138 (II)) and thermogravimetric analyses. Compound Ι is a dinuclear structure and II is a 1D chain. Moreover, the luminescent properties of Ι and II have been investigated with fluorescent spectra in the solid state, the two compounds display a strong fluorescent emission at room temperature and have potential applications as fluorescent-emitting materials.

Highly luminescent water-dispersed silicon quantum dots for fluorometric determination of oxytetracycline in milk samples.

A fluorescent probe based on silicon quantum dots (SiQDs) was developed for the selective and sensitive detection of oxytetracycline (OTC) via the inner filter effect (IFE). The water-soluble fluorescent SiQD was synthesized based on the reaction of 3-Aminopropyltriethoxysilane (APTES) and sodium citrate as precursors by the one-pot hydrothermal process. The strong fluorescence emission of quantum dots (QDs) was obtained at 440 nm when excited at 350 nm and OTC had a broad absorption band between 200 and 400 nm. The excitation spectrum of SiQDs was completely overlapped with the absorption spectrum of OTC. The light at an excitation wavelength of QDs absorbed by OTC caused a decrease in fluorescence intensity with an increase in the concentration of OTC. Under optimal conditions, the linear concentration range was 0.92–9.2 µg mL1 with a detection limit (LOD; S/N = 3) of 0.19 µg mL -1 . The proposed method was applied to the determination of OTC in milk samples and satisfactory recoveries (98.8–100.5%) with low RSD % values (0.93–2.31%) were achieved. This simple, selective, sensitive, rapid, and cheap method can be used as a promising tool for OTC analysis in food safety.

Robust Fabrication of Fluorescent Cellulosic Materials via Hantzsch Reaction.

Hantzsch reaction is one of the typical multicomponent reactions (MCRs), and it is employed herein to endow cellulosic materials with fluorescent properties. For example, acetoacetyl (ACAC)-bearing cotton fabric prepared via transesterification with tert-butyl acetoacetate is subjected to an aqueous Hantzsch reaction with formaldehyde and ammonium acetate at ambient temperature. A strong fluorescent emission around 460nm is achieved within 10min. XPS, fluorescent spectroscopy, and elemental analysis are used to confirm the presence of 1,4-dihydropyridine (DHP) rings on the surface of the fabric. TGA, SEM, XRD, and mechanical testing results show that the modification process has minimum impact on intrinsic properties of the fabric. The strategy is also shown to be generally applicable to various forms of cellulosic materials and different aldehydes. This fast and simple approach enriches the application of MCR in modification of cellulose and cellulose derivatives.

Rapid synthesis of dual proteins co-functionalized gold nanoclusters for ratiometric fluorescence sensing of polynucleotide kinase activity

Herein, we reported a facile strategy for rapidly synthesizing gold nanoclusters co-functionalized by dual proteins (bovine serum albumin and lysozyme, BL-AuNCs). The BL-AuNCs exhibited intense fluorescence emission at 640 nm and good biochemical stability. And a sensitive and simple ratio fluorescent method was constructed for polynucleotide kinase (PNK) activity analysis by utilizing BL-AuNCs and dsDNA-intercalating dye-SYBR Green I (SGI) as sensing receptors for the first time. BL-AuNCs were modified with specific designed double-stranded DNA (dsDNA) (BL-AuNCs-dsDNA). SGI, a specific intercalator of dsDNA, displayed strong fluorescence emission at 526 nm when intercalated into the dsDNA on BL-AuNCs. With adenosine triphosphate (ATP), PNK can catalyze phosphorylation of dsDNA at 5′-terminus. Phosphorylated dsDNA was specially recognized and degraded by λ exonuclease (λ exo) to produce single-stranded DNA and mononucleotides, which lacked ability to combine with SGI. Therefore, the fluorescent signal at 526 nm would decrease, while the BL-AuNCs fluorescence at 640 nm kept unaffected and was employed as the reference signal. The PNK activity was detected by monitoring variation of the ratio of fluorescence intensity (F526/F640) with a low detection limit of 0.012 U mL−1. This ratio fluorescent strategy was also applied for PNK determination in cell lysates with satisfying results.

Azaaromatic Functionalized Rhodamine Based Fluorescent Probes for Selective Dual Channel Detection of ClO− and Cu2+ in Water Samples and Living Cells

Two efficient probes were presented for dual channel simultaneous distinguishing detection of ClO− and Cu2+. Strong color changes and fluorescent emissions driven by ClO− induce irreversible oxidat...

Efficient Synthesis of Novel 1,3,4-Oxadiazoles Bearing a 4-N,N-Dimethylaminoquinazoline Scaffold via Palladium-Catalyzed Suzuki Cross-Coupling Reactions.

Two series of novel (symmetrical and unsymmetrical) quinazolinylphenyl-1,3,4-oxadiazole derivatives were synthesized using palladium-catalyzed Suzuki cross-coupling reactions. The presented synthetic methodology is based on the use of bromine-substituted 2-phenyl-4-N,N-dimethylaminoquinazolines and either a boronic acid pinacol ester or a diboronic acid bis(pinacol) ester of 2,5-diphenyl-1,3,4-oxadiazole. The reactions are conducted in a two-phase solvent system in the presence of catalytic amounts of [1,1′-bis(diphenylphosphino)ferrocene]-dichloropalladium(II), sodium carbonate, and tetrabutylammonium bromide, which plays the role of a phase-transfer catalyst. The luminescence properties of the obtained compounds are discussed in the context of applying these compounds in optoelectronics. Specifically, two highly-conjugated final products: N,N-dimethyl-2-phenyl-6-(4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl)quinazolin-4-amine (8f) and 6,6′-(4,4′-(1,3,4-oxadiazole-2,5-diyl)bis(4,1-phenylene))bis(N,N-dimethylquinazolin-4-amine (9f), which contain a 1,3,4-oxadiazole moiety connected to a quinazoline ring by a 1,4-phenylene linker at the 6 position, exhibit strong fluorescence emission and high quantum yields.

Characterization and luminescence sensing behaviour of a newly constructed hydrolytic stable Pb(II) coordination polymer

Sensing and detecting toxic pollutants like Fe3+, chromate anions and trinitrophenol (TNP) in water are especially important due to their hazardous effects on environmental and ecological systems. In this work, the hydrolytic stable Pb(II) CP {[Pb(asba)(obix)]•2H2O}n (1) [H2asba = 2-amino-4-sulfobenzoic acid, obix = 1, 2-(methylenebenzene)bisimidazole] was constructed and well characterized. 1 exhibits reversible de-/re-hydration behavior. The wide indirect band gap was obtained through the analysis of the solid-state diffuse reflectance UV–Vis spectrum of 1, which is consistent with the calculated value using the CASTEP program in Materials Studio. 1 keeps its crystallinity and structural integrity in various solvents. Interestingly, 1 shows solvent-dependent fluorescence emissions. A strong blue fluorescence emission occurs in water. 1 can sense the Fe3+ and chromate anions selectively and sensitively in the presence of the co-existent different metal cations and inorganic anions, respectively. Moreover, 1 also shows efficient sensing of Fe3+ in the simulative biological system. Furthermore, 1 demonstrates sensitive sensing of TNP. 1 displays excellent recyclability in sensing of these analytes. 1 can determine the related trace analytes in ppm level.

RETRACTED ARTICLE: A fluorescent coordination polymer for TNP detection and protection effect on cough after infection by up-regulates the activity of neuroendopeptide enzyme in respiratory tract mucosa

Through utilizing the mixed-ligand method, a novel coordination polymer based on Zn(II) ions as nodes was synthesized under hydrothermal condition via applying 1,4-cyclohexanedicarboxylic acid (1,4-H2chdc) and 2-(4-fluoro-phenyl)-1H-imidazo[4,5-f][1,10]phenanthroline (L), a π-electron rich ligand, as co-ligand, and its chemical formula is [Zn(1,4-chdc)(L)(H2O)]n (1). Because of its strong ambient temperature fluorescent emission and outstanding water stability, the complex 1 could be utilized as the sensitive sensor for the 2, 4, 6-trinitrophenol (TNP) via fluorescence quenching, and the constant of quenching can reach 2.794 × 105 M−1. The following experiment was further conducted to detect the treatment activity of the synthetic compound against post-infectious cough. The release of inflammatory cytokines and endopeptidase from respiratory tract mucosa was determined through enzyme linked immunosorbent assay (ELISA). Next, the fluorescent probe of DCFH-DA was utilized to detect the accumulation of ROS in the respiratory mucosal epithelial cells.

Synthesis and spectral studies of coumarin derivatives as fluorescent probes for Fe3+

Three novel coumarin derivatives were designed and facilely synthesized, namely 6-[bis-(2-acetoxyethyl)aminomethyl]-4-methyl coumarin (BAMC), 4-(trans-4-methylformate-styryl)-6-[bis-(2-acetoxyethyl)aminomethyl]-coumarin (TSAC) and Trans-4-[2-(benzimidazole-2-substituted)vinyl]-6-methyl coumarin (TBVC). The synthesis route via various reactions including Pechmann, Wittig and substitution, etc. Three strategies are applied in the construction of the coumarin fluorescent probe. That is the electron push-pull effect, extended electronic conjugated system, as well as the strong fluorescence emission group. The compounds BAMC and TSAC are proved to be selective Fe3+ fluorescent probes based on ICT mechanism. TBVC exhibits strong fluorescent emission in tetrahydrofuran. The relationship between the structure and fluorescence mechanism for coumarin probes were explored.

Synthesis of biocompatible and highly fluorescent N-doped silicon quantum dots from wheat straw and ionic liquids for heavy metal detection and cell imaging

Silane-based precursors for the synthesis of water-dispersible silicon quantum dots (SiQDs) present harmful effects on both researchers and the environment, due to their high toxicity. Though waste wheat straw is an abundant source of natural silicon, its application towards the synthesis of biocompatible SiQDs for metal detection has not yet been explored. In this study, N-doped SiQDs demonstrating uniform spherical morphologies, excellent water dispersity and strong fluorescence emission with a quantum yield of 28.9% were facilely synthesized by using wheat straw (WS) as silicon source and allyl-3-methylimidazolium chloride (AMIMCl) as nitrogen source. The wheat straw based SiQDs (WS-SiQDs) showed linear fluorescence quenching ((F0-F)/F) with Cr(VI) and Fe(III) concentration in the range of 0–6 × 10−4 M. Following immobilization on hydrophilic silica hydrogels, WS-SiQDs@silica hydrogels demonstrated enhanced fluorescence emission which can selectively detect Cr(VI) and Fe (III) to the limits of 142 and 175 nM, respectively. Moreover, cell imaging results reflected that WS-SiQDs can penetrate the membranes of dental pulp stem cells and react with the nucleuses of the stem cells. The stem cells maintained high viability under the conditions of 24 h incubation and SiQD concentration below 50 mg·L−1, thus indicating low cytotoxicity of WS-SiQDs. The as-prepared SiQDs demonstrated notable structural and fluorescent properties, therefore representing promising biocompatible fluorescent nanomaterials for metal detection and cell imaging.

A novel barbituric-based fluorescent probe with aggregation induced emission for the highly sensitive ratiometric detection of cyanide anions

A new tetraphenylethylene-based barbituric acid derivative (TPEB) with an aggregation induced emission effect is synthesized as a fluorescent probe for CN−. The fluorescence spectra of TPEB in a DMSO–H2O mixture changed with different water fractions (fw). Nano-aggregates of TPEB are formed with the strongest fluorescence emission when fw beyond 60%. TPEB displays high selectivity and anti-interference toward CN− in DMSO–H2O (fw 70%) system at pH around 6, even in the presence of other competitive anions (AcO−, F−, Cl−, Br−, I−, NO3−, SO42−, ClO4−, PO43−, SCN−, HS−, S2− and H2O2). The linear curve is excellently matched between the fluorescence intensity and CN− concentration at 500 nm. By the equation 3σ/S, the limit of detection of TPEB for CN− reaches 0.767 × 10–6 mol L−1. The probe TPEB operates via intramolecular charge transfer mechanism, attributed to the unique nucleophilic addition reactions between TPEB and CN−, which is further confirmed by LC–MS spectra, Job's plot and DFT calculations. By colorimetry and fluorescence approach, CN− ions can be easily detected by the TPEB testing strip. The probe can be used to distinguish the acidity and basicity of the solution qualitatively.

Construction of Supramolecular Organogel with Circularly Polarized Luminescence by Self-Assembled Guanosine Octamer

SUMMARYGel formation using guanosine self-assembly is an important process in supramolecular chemistry. Here, we report the stepwise construction of circularly polarized luminescent supramolecular organogels from self-assembled guanosine quadruplexes. A lipophilic guanosine derivative (aldG) is designed and synthesized for the formation of a well-defined G8-octamer. The diamine linkers are used to connect G8-octamer units by imine formation to facilitate the construction of the supramolecular gel networks. 1H NMR experiments show that the pre-assembled aldG8-octamer remains intact and is crucial for transparent and stiff organogel formation. With extended conjugation, the aldG organogels exhibit strong green fluorescence emission and circularly polarized properties without the assistance of any external fluorescent dyes, suggesting an alternative approach to construct molecular probes for biological and material applications.

Sub-Surface Molecular Analysis and Imaging in Turbid Media Using Time-Gated Raman Spectral Multiplexing.

Obtaining molecular information deeper within optically turbid samples is valuable in many applications. However, in many cases this is challenging, in particular when the sample elicits strong laser-induced fluorescence emission. Here, we investigated the use of time-gated and micro-spatially offset Raman spectroscopy (micro-SORS) based on spectral multiplexing detection to obtain sub-surface molecular analysis and imaging for both fluorescing and non-fluorescing samples. The multiplexed spectral detection achieved with a digital micromirror device (DMD) allowed fast acquisition of the time-gated signals to enable three-dimensional Raman mapping (raster scanning in the lateral x,y plane and using time-of-flight calibration for the axial z-direction). Sub-millimeter resolution molecular depth mapping was achieved with dwell times on the order of seconds per pixel. To suppress fluorescence backgrounds and enhance Raman bands, time-gated Raman spectroscopy was combined with micro-SORS to recover Raman signals of red pigments placed behind a layer of optically turbid material. Using a defocusing micro-SORS approach, both fluorescence and Raman signals from the surface layers were further suppressed, which enhanced the Raman signals from the deeper sublayers containing the pigment. These results demonstrate that time-gated Raman spectroscopy based on spectral multiplexed detection, and in combination with micro-SORS, is a powerful technique for sub-surface molecular analysis and imaging, which may find practical applications in medical imaging, cultural heritage, forensics, and industry.

Functionalized multi-walled carbon nanotubes with strong fluorescence emission

Multi-walled carbon nanotubes (MWCNTs) with strong visible fluorescence were synthesized via oxidation and amination. A large number of oxygen-containing surface functional groups contributing to fluorescence emission have been found, and the novel structure of carbon nanoclusters with the diameter of 20–30 nm are formed at the tips of MWCNTs. The fluorescent MWCNTs exhibit distinct excitation-wavelength dependence and pH response. Furthermore, the temperature sensitivity of fluorescence has been described carefully. The fluorescence intensity first increases and then decreases upon increasing temperature, and the maximum emission is achieved when the functionalized MWCNTs are dried at 150 °C.

A Light-Up Strategy with Aggregation-Induced Emission for Identification of HIV-I RNA-Binding Small Molecules.

Fluorescence methods are important tools to identify RNA-binding small molecules and further employed to study RNA-protein interactions. Most reported fluorescence strategies are based on covalent labeling of ligand or RNA, which can impede the binding between them to some extent, or light-off fluorescent indicator displacement methods, which ask for particular indicators. Herein, a label-free fluorescence strategy based on the light-on aggregation-induced emission (AIE) feature of tetraphenylethene (TPE) derivative to screen RNA-binding small molecules is presented. As a result of electrostatic interaction, the selected peptides can induce self-assembly of the TPE derivative to produce strong fluorescent emission; when the peptides are bound to RNA molecules, the TPE derivative is in the deaggregated form and shows no or minimum fluorescence. Based on the phenomenon, a competitive displacement assay combined with the TPE reporter was employed to characterize selected small molecules for their binding abilities to HIV-I RNAs. This AIE feature enables the fluorescence-off state of the TPE derivative in the presence of RNA-peptide complex to be "lightened up" quickly as the RNA-binding molecule is introduced and the peptide is competitively released. This strategy was carried out to test several small molecule binders, and the results are consistent with previous reports. This report gives an inspiring example of AIE-based fluorescent assay for HIV-I RNA-binding molecule screening, which may further be explored to build a drug screening platform for RNA-protein interference.

Structurally-thrifty and visible-absorbing fluorophores.

Fluorophores with a minimal push-pull backbone are actively pursued due to their potentials in biological labelling. Herein a series of structurally-thrifty and visible-absorbing fluorophores (SDXs) were successfully constructed following the D'D-π-A design strategy, in which a secondary donor (D') was introduced in conjugation with the donor (D) to enhance its electron donating capability. For a very small scaffold, SDXs exhibit a surprisingly long-wavelength absorption band in the visible spectral range (λabs=420nm) and a strong green fluorescence emission (λem=530nm) with a fluorescence quantum yield up to 0.84. Notably, fluorescence of SDXs was quenched in hydrogen-bonding solvents, e.g. MeOH and H2O. This phenomenon renders SDXs feasibility for imaging of cellular non-hydrogen-bonding microenvironment, as demonstrated with BEAS-2B cells. These results proved that the D'D-π-A is a powerful design strategy to construct novel structurally-thrifty fluorophores.

Photophysical, DFT and molecular docking studies of Sm(III) and Eu(III) complexes of newly synthesized coumarin ligand

Herein, [M(HL)2(H2O)2]NO3·2H2O (M = Sm (III) /or Eu (III); HL = 4-(2-hydroxy benzylidene acetohyrazide)-7-hydroxy coumarin) were synthesized and characterized using several spectroscopic methods. The complexes stoichiometry with molar ratio 2L:1M were confirmed by Job's method. Tridentate ligand (HL) was coordinated to the lanthanide ions Sm(III) or Eu(III) through azomethine nitrogen atom, phenolic oxygen of hydrazide, and ketonic oxygen of the amide group. The photophysical properties of the ligand and its complexes were studied in different organic solvents and their fluorescence quantum yields were determined as well. Strong fluorescence emissions to red shifts of europium complex were observed at 580, 593, 617, 653, 693, 704 nm which were attributed to Eu(III) emission of 5D0→7F0, 5D0→7F1, 5D0→7F2, 5D0→7F3,5D0→7F4, and 5D0→7F5, respectively. First-principles DFT calculations were performed to evaluate the optimized structure and separation energies of the HL compound, using the B3LYP/6-311++g(d,p) basis set. Molecular docking studies were carried out to predict the binding modes between the HL compound and active site of the xanthine oxidase enzyme [EC# (1.17.3.2) PDB ID: 1FIQ] which produced from liver patients of hepatitis C. The observed activity of the HL gave rise to the conclusion that it might exert its action through inhibition of the xanthine oxidase enzyme.

Fluorescence Determination of Acrylamide in Snack, Seasoning, and Refreshment Food Samples with an iOS Gadget–Based Digital Imaging Colorimeter

The novelty of this research work lies in a simple, fast, and plausible analysis of acrylamide in food samples accomplished using an iOS gadgets–based digital imaging colorimeter (iOS gadgets–based DIC). This method is based on fluorescence color measurements obtained from digital images of derivatized acrylamide solution extracted from snack, seasoning, and refreshment food samples (fried banana chip, fried potato chip, fried taro chip, fried durian chip, cayenne pepper, paprika seasoning, tea, and instant coffee). This device represents a convenient and low-cost detection for immediate and simultaneous determination. In addition, there is no reported research using an iOS gadgets–based DIC for the analysis of acrylamide in food samples. In this research, acrylamide is degraded through Hofmann reaction, and a fluorescent product is produced by the vinyl amine reacting with fluorescein, resulting in strong fluorescence emission at 590 nm. Fluorescein was chosen instead of fluorescamine because fluorescein is about 10 times cheaper than fluorescamine. The linear range for the relationship between color value and acrylamide concentration is in the range 1.00–10.0 mg L−1 with the correlation coefficient (R2) of 0.9985. The limits of detection and quantitation were 0.53 and 1.78 mg L−1, respectively. The color values of acrylamide solution were tested for accuracy using food samples spiked with 1.00, 3.00, and 5.00 mg L−1 of standard acrylamide solutions. The recoveries for food samples are in the range 82.74–113.3%. There was no significant difference observed when comparing the results obtained with the DIC instrument with those obtained with fluorescence microplate reader and high-performance liquid chromatography.