Fluorescence Emission Response Research Articles

Novel Peptide-Based Fluorescent Probe for Simultaneous Sensing of Chymotrypsin and Hydrogen Peroxide.

The developed multifunctional fluorescent probe enables the simultaneous detection of chymotrypsin as a model protease and hydrogen peroxide as a representative of reactive oxygen species (ROS) in biologically relevant concentration ranges. The chymotrypsin sensing is based on the cleavage of its selectively recognizable peptide sequence and the consequent disruption of FRET between coumarin (DEAC) and fluorescein (FL). Analogously, the presence of hydrogen peroxide causes the gradual degradation of the H2O2-labile benzopyrylium-coumarin (BC) dye. Considering the fluorescence emission responses of individual chymotrypsin-peroxide probe-attached fluorophores after their excitation at 425 nm, the sole presence of either chymotrypsin (50-1000 ng/mL) or hydrogen peroxide (10-200 μM) in a sample could be unambiguously confirmed or refuted. In addition, reliable simultaneous detection and approximate quantification of both studied species in the concentration ranges of 100-1000 ng/mL and 20-200 μM for chymotrypsin and H2O2, respectively, could be performed as well. The obtained results are summarized and visualized in the graphical models.

Restricted intramolecular vibrations assisted enhanced fluorescence emission response of probe: A new experimental and theoretical approach for the detection of hydrogen peroxide

Hydrogen peroxide (H2O2) is a harmful chemical used as a signature compound in forming easily synthesizable peroxide-based explosives. Therefore, detecting H2O2 vapors and solutions is imperative to avoid terroristic activities. Aggregation induced emission enhancement (AIEE) active probe PATdetected H2O2 based on geometry-dependent hydrogen bonding. Unlike frequently reported fluorescent probes, probePATexhibited a strong fluorescence emission enhancement response for H2O2 due to restrictions in intramolecular vibrations of probe. This unique sensing phenomenon enhances our probe's versatility and potential applications in the selective and sensitive detection of H2O2. 1H NMR titration experiments and extensive density functional theory (DFT) calculations explained the distinct sensing mechanism. As a result of efficient interaction, probe could detect H2O2 with critical features of excellent selectivity, nanoscale level detection (LOD; 10 nM), fast response (20 sec.), and distinguished photostability. Conveniently, probePAT-embedded fluorescent strips were successfully employed as a portable sensing tool for rapidly recognizing H2O2 vapors. Moreover, probePATwas also capable of H2O2 determination in industrial water, orange juice, milk samples and commercially available products. Therefore, our probe holds promising features for trace detection of H2O2 in vapor and solution phase that make it highly useful.

Carbazole-based Schiff base: A sensitive fluorescent ‘turn-on’ chemosensor for recognition of Al(III) ions in aqueous-alcohol media

Carbazole-based Schiff base chemosensor was synthesized in one-pot synthesis using 2-hydroxy-1-naphtaldehyde for fluorescent sensing of Al3+ ions. Characterization of the ligand (L) was revealed through spectroscopic and physicochemical techniques. The fluorescence emission responses of L to various metal ions and anions were investigated. The chelation was studied by UV–vis, 1H NMR, LC-MS/MS, fluorescence titration and Job’s plot analysis. Bathochromic shift resulted from charge transfer from L to electrophilic Al3+ ion was observed in the chelation of L with Al3+. The potentiality of L to be a distinguished probe to detect Al3+ ions was due to a chelation enhanced fluorescence (CHEF) effect, concomitant with noticeable fluorescent enhancement. A significant fluorescence enhancement at 533 nm was observed in ethanol–water (1:1, v/v) solution upon addition of Al3+ along with a distinct color change from yellow to white. Non-fluorescent ligand exposed highly sensitive turn-on fluorescent sensor behavior for selectively sensing Al3+ ions via 1:1 (ligand:metal) stoichiometry. The ligand’s specificity in the existence of other tested metal ions and anions indicated no observation in color change. The ligand-Al3+ complex formation was reversible upon addition of chelating agent EDTA. The ligand interacted with Al3+ ions with an association constant of Ka = 5 × 104 M−1. The limit of detection (LOD) was found to be 2.59 × 10-7 M. The synthesized Schiff base could efficiently detect Al3+ ions as a fluorescent sensor.

Controlled Polymerization of Norbornene Cycloparaphenylenes Expands Carbon Nanomaterials Design Space.

Carbon-based materials—such as graphene nanoribbons, fullerenes, and carbon nanotubes—elicit significant excitement due to their wide-ranging properties and many possible applications. However, the lack of methods for precise synthesis, functionalization, and assembly of complex carbon materials has hindered efforts to define structure–property relationships and develop new carbon materials with unique properties. To overcome this challenge, we employed a combination of bottom-up organic synthesis and controlled polymer synthesis. We designed norbornene-functionalized cycloparaphenylenes (CPPs), a family of macrocycles that map onto armchair carbon nanotubes of varying diameters. Through ring-opening metathesis polymerization, we accessed homopolymers as well as block and statistical copolymers constructed from “carbon nanohoops” with a high degree of structural control. These soluble, sp2-carbon-dense polymers exhibit tunable fluorescence emission and supramolecular responses based on composition and sequence. This work represents an important advance toward bridging the gap between small molecules and functional carbon-based materials.

Plasmon enhanced linear and nonlinear optical properties of natural curcumin dye with silver nanoparticles

The interactions between silver nanoparticles and bio molecules have potential significance in many interesting applications like sensing, imaging etc. In the present work, the variation in the fluorescence emission and nonlinear optical response of natural Curcumin dye extracted from the Curcuma longa with laser synthesized silver nanoparticles was studied. The formation and optical properties of silver nanoparticles and Curcumin dye solutions were analyzed using UV–Visible absorption spectroscopy, fluorescence emission spectroscopy and fluorescence life time studies. The third order nonlinear optical behavior of the Curcumin dye samples with incorporation of varying concentration of silver nanoparticles were investigated using open aperture Z-scan method. A substantial enhancement was observed for the entire optical behavior such as non-linear optical response, optical limiting properties and fluorescence emission of the Curcumin samples with silver nanoparticles, which progressively improved with the concentration of the silver nanoparticles incorporated into the system.

A Novel Polydopamine Grafted 3D MOF Nanocubes Mediated GR-5/GC DNAzyme Complex with Enhanced Fluorescence Emission Response toward Spontaneous Detection of Pb(II) and Ag(I) Ions.

In this work, we have proposed a novel DNAzyme/MnCoPBAs-PDANCs complex-based fluorescence biosensor for subsequent detection of Pb2+ and Ag+ ions. The GR-5/GC-rich DNAzymes are strongly anchored or quenched on the surface of polydopamine hybridized 3D metal–organic framework MnCoPBAs-PDANCs by π–π stacking interaction. Addition of Pb2+ ions has exhibited a catalytic inner cleavage of DNAzyme complex and disturbs to release shorter GC-rich sequence over the surface of MnCoPBAs-PDANCs complexes. Later on, addition of intercalating dye ThT interacts with free GC-rich substrate strand to form a G-quadruplex-ThT structure and thereby effectively enhanced the fluorescence intensity (“turn-on”). Interestingly, subsequent addition of Ag+ ions has an uncoiled GQ-ThT structure to provide a robust double-stranded DNA featuring C–Ag+–C, which diminishes (“turn-off”) the fluorescence intensity. This improved hybrid sensor exhibited a linear response in a concentration range of 3–9 nM for Pb2+, while 4–20 nM for Ag+ ions with a lower detection limit of 1.6 and 4.2 nM, respectively. Further, the method was successfully implemented for the analysis of Pb2+ and Ag+ ions in real water samples with a good regaining and high efficacy for practical analysis.

Two similar Schiff-base receptor based quinoline derivate: Highly selective fluorescent probe for Zn(II).

As is known, Zn2+ plays a vital role in a variety of biological processes but excessive exposure of Zn2+ to human beings can cause toxicity, inducing a series of overt poisoning symptoms and neurodegenerative disorders. Thus, we designed and synthesized two quinoline-derived Schiff-bases HL1 and HL2, and investigated the fluorescence emission responses of these two Schiff-bases to various metal ions. A significant enhancement in fluorescence emission band centered at 450nm was observed in the ethanolic solution of HL1 with addition of Zn2+, while remarkably lower fluorescence emission enhancement was obtained in the case of HL2 in which one methyl group was introduced to the azomethine carbon. In addition, HL1 showed good selectivity and high sensitivity towards Zn2+ in the existence of other various interfering metal ions, and the reversibility and regeneration of HL1 were also perfect for extending its applications in environmental and biological systems. Therefore, HL1 could be identified as a fluorescent probe for sensing Zn2+ environmentally and biologically.

A multi-responsive crown ether-based colorimetric/fluorescent chemosensor for highly selective detection of Al3+, Cu2+ and Mg2.

A novel multi-response chemosensor L based on coumarin-chalcone-crown ether was designed and synthesized, which exhibited a high selectivity for the colorimetric detecting Al3+ and Cu2+ and fluorescent recognizing Al3+ and Mg2+ in ethanol. L can monitor Al3+ and Cu2+ via distinct color changes from a slight yellow to pink and to orange, respectively. The sensor L can also monitor Al3+ and Mg2+ by fluorescence emission responses at 592nm and 547nm with low detection limits of 0.31μM and 0.23μM, respectively. The selectivity of L toward Al3+, Cu2+ and Mg2+ was not interfered by a large number of coexisting ions and was found to be reversible. By means of spectrometric titration, Job's plot, mass spectrometry, 1H NMR titration and IR spectroscopy analysis, it was unanimously confirmed that the sensor L had a stoichiometric ratio of 1:1 with Cu2+ and Mg2+, and 1:2 with Al3+. The order of the stability of the complexes formed by L and Al3+, Cu2+, Mg2+ was as follows: L-Al3+>L-Cu2+>L-Mg2+. At the same time, some possible bonding modes and sensing mechanisms were further proposed, and the optimized structure of the sensor L and its sensing mechanism for Al3+, Cu2+ and Mg2+ were confirmed by the calculations of DFT/B3LYP and TD-DFT methods in a suite of Gaussian 09 programs.

Real-time detection of airborne fluorescent bioparticles in Antarctica

Abstract. We demonstrate, for the first time, continuous real-time observations of airborne bio-fluorescent aerosols recorded at the British Antarctic Survey's Halley VI Research Station, located on the Brunt Ice Shelf close to the Weddell Sea coast (lat 75°34′59′′ S, long 26°10′0′′ W) during Antarctic summer, 2015. As part of the NERC MAC (Microphysics of Antarctic Clouds) aircraft aerosol cloud interaction project, observations with a real-time ultraviolet-light-induced fluorescence (UV-LIF) spectrometer were conducted to quantify airborne biological containing particle concentrations along with dust particles as a function of wind speed and direction over a 3-week period. Significant, intermittent enhancements of both non- and bio-fluorescent particles were observed to varying degrees in very specific wind directions and during strong wind events. Analysis of the particle UV-induced emission spectra, particle sizes and shapes recorded during these events suggest the majority of particles were likely a subset of dust with weak fluorescence emission responses. A minor fraction, however, were likely primary biological particles that were very strongly fluorescent, with a subset identified as likely being pollen based on comparison with laboratory data obtained using the same instrument. A strong correlation of bio-fluorescent particles with wind speed was observed in some, but not all, periods. Interestingly, the fraction of fluorescent particles to total particle concentration also increased significantly with wind speed during these events. The enhancement in concentrations of these particles could be interpreted as due to resuspension from the local ice surface but more likely due to emissions from distal sources within Antarctica as well as intercontinental transport. Likely distal sources identified by back trajectory analyses and dispersion modelling were the coastal ice margin zones in Halley Bay consisting of bird colonies with likely associated high bacterial activity together with contributions from exposed ice margin bacterial colonies but also long-range transport from the southern coasts of Argentina and Chile. Dispersion modelling also demonstrated emissions from shipping lanes, and therefore marine anthropogenic sources cannot be ruled out. Average total concentrations of total fluorescent aerosols were found to be 1.9 ± 2.6 L−1 over a 3-week period crossing over from November into December, but peak concentrations during intermittent enhancement events could be up to several tens per litre. While this short pilot study is not intended to be generally representative of Antarctic aerosol, it demonstrates the usefulness of the UV-LIF measurement technique for quantification of airborne bioaerosol concentrations and to understand their dispersion. The potential importance for microbial colonisation of Antarctica is highlighted.

Modifying optical properties of reduced/graphene oxide with controlled ozone and thermal treatment in aqueous suspensions

Graphene possesses a number of advantageous properties, however, does not exhibit optical emission, which limits its use in optoelectronics. Unlike graphene, its functional derivative, graphene oxide (GO) exhibits fluorescence emission throughout the visible. Here, we focus on controlled methods for tuning the optical properties of GO. We introduce ozone treatment of reduced graphene oxide (RGO) in order to controllably transform it from non-emissive graphene-like material into GO with a specific fluorescence emission response. Solution-based treatment of RGO for 5–45 min with ∼1.2 g l−1 ozone/oxygen gas mixture yields a drastic color change, bleaching of the absorption in the visible and the stepwise increase in fluorescence intensity and lifetime. This is attributed to the introduction of oxygen-containing functional groups to RGO graphitic platform as detected by the infrared spectroscopy. A reverse process: controllable quenching of this fluorescence is achieved by the thermal treatment of GO in aqueous suspension up to 90 °C. This methodology allows for the wide range alteration of GO optical properties starting from the dark-colored non-emissive RGO material up to nearly transparent highly ozone-oxidized GO showing substantial fluorescence emission. The size of the GO flakes is concomitantly altered by oxidation-induced scission. Semi-empirical PM3 theoretical calculations on HyperChem models are utilized to explore the origins of optical response from GO. Two models are considered, attributing the induced emission either to the localized states produced by oxygen-containing addends or the islands of graphitic carbon enclosed by such addends. Band gap values calculated from the models are in the agreement with experimentally observed transition peak maxima. The controllable variation of GO optical properties in aqueous suspension by ozone and thermal treatments shown in this work provides a route to tune its optical response for particular optoelectronics or biomedical applications.

Synthesis, characterization and photophysical properties of novel azole derivatives.

This paper concerns the design, synthesis, structural characterization, thermal stability evaluation and fluorescence properties of novel triazolothiadiazole derivatives. The target compounds 6a-e were synthesized by condensing 4-amino-3-(4-methoxybenzyl)-1H-1,2,4-triazole-5 (4H)-thione (5) with biphenyl, naphthyl, p-terphenyl, pyrenyl and ferrocenyl carboxylic acid in the presence of phosphorous oxychloride. The structures of newly synthesized compounds were characterized by IR, (1)H NMR and (13)C NMR analysis. The photophysical properties of synthesized compounds were measured in a variety of organic solvents of variable polarities. Spectral properties of the compounds were highly dependent on the nature of the substituent and coupling components attached to the triazolothiadiazole skeleton as well as slightly affected by the solvent polarities. Correlation of the absorption spectra and fluorescence emission response of 6a-e with the substituent revealed that the fluorescent properties can easily be tuned by varying conjugation length of side coupled groups. The newly synthesized derivatives represent a new type of fluorescent materials with efficient visible absorption and surpassing brightness which could be a promising candidate for bioimaging, photonic applications, organic light emitting diodes and dye sensitized solar cells.

Optical properties of some novel 2,5-disubstituted 1,3,4-oxadiazole derivatives and their application as an efficient cell staining azo dyes.

A series of six 2,5-disubstituted 1,3,4-oxadiazole derivatives with various length of conjugation have been synthesized and their optical properties including UV-visible absorption spectra, fluorescence emission spectra, molar absorption co-efficient, Stokes shift and the relative fluorescence quantum yield were measured in a variety of organic solvents. Correlation of the absorption spectra and fluorescence emission response of the 2,5-disubstituted 1,3,4-oxadiazole derivatives with the substituent effect revealed that the optical response can easily be tuned toward red shift by increasing conjugation length. The synthesized compounds were further employed in bioimaging assay in order to investigate their potential as an efficient cell staining agent using L-929 cells under confocal fluorescence microscope which showed scrupulous cell permeability and no toxicity as assessed by MTT assay.

A highly selective fluorescence turn-on detection of Al3+ and Ca2+ based on a coumarin-modified rhodamine derivative

A fluorescent chemosensor 1 was synthesized containing a coumarin moiety bound to rhodamine B hydrazide. Compound 1 displayed different fluorescence emission responses to Al3+ and Ca2+ ions with high quantum yields (0.64 and 0.15, respectively) and low detection limits (3.0×10–8 and 9.4×10–8M, respectively). The possible binding modes of compound 1 with Al3+ and Ca2+ ion were calculated using a Job plot, HRMS, 1H NMR spectroscopic titration and IR spectroscopy. Moreover, the calcium in 1-Ca2+ could be displaced by Al3+ ions, resulting in another ratiometric sensing signal output, which indicates that 1-Ca2+ could detect Al3+ ions in a ratiometric way. Bioimaging results also demonstrated that compound 1 could act as an intracellular Al3+ ion imaging sensor.

Coumarin modified rhodamine derivative: Fluorescent chemosensor selectively recognizing Al3+ and Ca2+

A fluorescent probe with a coumarin moiety bound to rhodamine 6G hydrazide(1) was synthesized. Its sensing behavior toward various metal ions was investigated with fluorescence methods. Compound 1 displays different fluorescence emission responses to Al3+ and Ca2+ at the same excitation wavelength in the visible light region, while no changes occur after the addition of other metal ions. The binding ratios of the complexs of 1-Al3+ and 1-Ca2+ are both 2:1 according to the Job plot and high resolution mass spectrometer(HRMS) experiments. Moreover, emission spectrum of 1-Ca2+ complex and absorption spectrum of the rhodamine dyes overlap largely. When Al3+ was added to the 1-Ca2+ system, calcium in complex 1-Ca2+ can be displaced by Al3+, resulting in the output of another ratiometric sensing signal, which demonstrates that the 1-Ca2+ complex can be served as a new and effective fluorescence resonance energy transfer(FRET) donor for rhodamine derivatives.

Metal–organic coordination polymers of Tb2−xEux(BDC)3(H2O)nwith tunable fluorescence and smart response toward aldehydes (0 ≤ x ≤ 2, BDC = 1,4-benzenedicarboxylate)

A family of leaf-shaped lanthanide metal–organic coordination polymers, Tb2−xEux(BDC)3(H2O)n (0 ≤ x ≤ 2, BDC = 1,4-benzenedicarboxylate), was prepared through a surfactant-assisted one step method at room temperature, which showed tunable fluorescence emission and smart response toward aldehydes.

Novel Naphthalene Based Lariat-Type Crown Ethers Using Direct Single Electron Transfer Photochemical Strategy

This study explored a direct SET-photochemical strategy to construct a new family of thioene conjugatednaphthalamide fluorophore based lariat-crown ethers which show strong binding properties towards heavy metal ions. Irradiations of designed nitrogen branched (trimethylsilyl)methylthio-terminated polyethylenoxytethered naphthalimides in acidic methanol solutions have led to highly efficient photocyclization reactions to generate naphthalamide based lariat type thiadiazacrown ethers directly in chemo- and regio-selective manners which undergo very facile secondary dehydration reactions during separation processes to produce their corresponding amidoenethio ether cyclic products tethered with electron donating diethyleneoxy- and diethyenethio-side arm chains. Fluorescence and metal cation binding properties of the lariat type enamidothio products were examined. The photocyclized amidoenethio products, thioene conjugated naphthalamide fluorophore containing lariat-thiadiazacrowns exhibited strong fluorescence emissions in region of 330-450 nm along with intramolecular exciplex emissions in region of 450-560 nm with their maxima at 508 nm. Divalent cation Hg 2+ and Pb 2+ showed strong binding to sulfur atom(s) in side arm chain and atoms in enethiadiazacrown ether rings which led to significant enhancement of fluorescence from its chromophore singlet excited state and concomitant quenching of exciplex emission. The dual fluorescence emission responses towards divalent cations might provide a new guide for design and development of fluorescence sensors for detecting those metals.

Poly(1-amino-5-chloroanthraquinone): Highly Selective and Ultrasensitive Fluorescent Chemosensor For Ferric Ion

Poly(1-amino-5-chloroanthraquinone) (PACA) was firstly synthesized by a chemically oxidative interfacial polymerization. The PACA has been developed as a fluorescent sensor for the determination of Fe(III) in semi-aqueous solution at pH 7.0. The sensor exhibited remarkably high sensitivity toward Fe(3+) since the fluorescence of the polymer could be significantly quenched even though trace Fe(3+) was added. The sensor showed a linear fluorescence emission response over a wide concentration range from 1.0 × 10(-10) to 1.0 × 10(-4) M, with an ultra-low detection limit of 2.0 × 10(-11) M. The quenching of the fluorescence was found to be static one due to the formation of non-fluorescent complex in the ground state.

Highly Durable Double Sol–Gel Layer Ratiometric Fluorescent pH Optode Based on the Combination of Two Types of Quantum Dots and Absorbing pH Indicators

Long-term stable ratiometric fluorescent optical pH sensors (optodes) based on double sol-gel silica layers are prepared with the first layer embedding two types of quantum dots (QDs) and the second layer embedding light-absorbing pH indicators. The sensors are fabricated by a simple general sol-gel spin-coating method. The resulting double-layer pH optodes are designed as having long Stokes shift as well as ratiometric fluorescence emission response to pH in aqueous solutions of varying pH values. This optode has high durability against continuous light exposure, even under severe acidic condition (1 M HCl), and the storage stability is over a period of more than 6 months. These results indicate that the double-layer ratiometric fluorescence-based pH optode allows for long-term pH sensing. When two pH indicators of different pK(a) values with an optimized mixing ratio are embedded into the second layer, a double-layer pH optode with reproducible linear response in a wide pH range of over 6 pH units (from pH 4 to 10) can be designed and fabricated.

Preparation of a Library of EDTA Amide x-Aminenaphthalene-y-sulfonic Acid Derivatives on Solid Phase and Their Fluorescence Behavior toward Transition Metals

In this work, we report the synthesis of a combinatorial library of 80 derivatives of EDTA amide x-aminenaphthalene-y-sulfonic acid on four different supports with variable length linker. The sensing fluorescence behavior of these materials for transitions metals was studied by packing the beads into a conventional flow-through cell in a continuous flow injection set up. The fluorescence emission response of these materials shows that sensors supported in Argopore (a) with the fluorescence moiety of 1-aminenaphthalene-4-sulfonic acid behaves like dosimeter for copper.

A highly Li+-selective glass optode based on fluorescence ratiometry

This paper presents the preparation and characterization of a single-excitation, dual-emission ratiometric optical Li(+)-sensing device using a newly designed and synthesized highly Li(+)-selective fluoroionophore (KBL-01) carrying 14-crown-4 ether with tetramethyl and benzene blocking subunits as Li(+)-binding site and boron-dipyrromethene as fluorophore. The indicator dye was covalently immobilized on the surface of a porous glass support having a large internal surface area using a silane-coupling agent. The resulting Li(+)-selective glass optode shows dual fluorescence emission response in pseudo-serum at varying Li(+) concentrations, allowing ratiometric signal processing. The obtained signal is independent of the presence of possibly interfering cations (Na(+), K(+), Mg(2+) and Ca(2+)) and pH. The sensor response was found to be reversible within the Li(+) concentration range from 10(-4) to 10(-1) M, and showed good repeatability and light stability. The plots of the ratiometric signal versus the Li(+) concentrations in spiked real human serum go along with the response curve in pseudo-serum. These results indicate that the novel Li(+)-selective glass optode can be employed as a Li(+)-sensing device with high durability, sensitivity and accuracy for medical analyses.