Efficient Fluorescent Probe Research Articles

Facile one-step synthesis of highly luminescent N-doped carbon dots as an efficient fluorescent probe for chromium(vi) detection based on the inner filter effect

Label-free fluorescence assay system is designed for Cr(iv) detection.

Molecular engineering of the photo switching in the ortho chromophores of the nanostructured green fluorescence protein

Green fluorescent protein (GFP) has attracted wide attention as an efficient fluorescent probe for photophysical properties studies in the biological and biochemical sciences. In this work, the effect of different substituents (OMe, OEt, NO2, Br, CN, and CF3) in the para position of the phenyl ring in 4-(2-hydroxybenzylidene)-1,2-dimethyl-1H-imidazol-5(4H)-one (o-HBDI), an analogue of the core chromophore of the GFP, on their photophysical properties were explored in both gas and solution phases by using TD-DFT method at PBE0/6-311++G(d,p) and M06-2X/6-311++G(d,p) levels of theory. The potential energy surfaces (PESs) were evaluated along the reaction coordinate (RC = dOH) at the ground S0 and excited S1 states of the three o-HBDI derivatives composed of electron donating and accepting substitutes in both gas and solution phases. The structural, electronic and photophysical properties, the atomic charges and electron density at critical points were examined. The results show the photophysical properties of o-HBDI are dependent on substitution patterns and solvents. In contrast to S0 state, the excited-state intramolecular proton transfer (ESIPT) process at S1 state in these compounds is expected to be approximately less barrier height. The ESIPT process in all three solvents is predicted to be an exergonic reaction. Depending on the strength of the electronic accepting or donating of the substituents, a wide tunable range of the fluorescence emissions from 460nm (visible blue light) to 642nm (visible red light) was predicted in the solvent media. By comparing wavelengths, the maximum value of the stoke shift is observed for CN-o-HBDI and TF-o-HBDI. Chromophores composed of the electron donating substituents (OMe and OEt) represent greatest red-shift in non-polar solvent cyclohexane. Our computed results are in good agreement with the experimental observations and have the potential applications in manipulating and tuning photo-physical properties of the technologically and biologically important fluorescent protein.

Molecular Engineering of α-Substituted Acrylate Ester Template for Efficient Fluorescence Probe of Hydrogen Polysulfides.

In this article, hydrogen polysulfide (H2Sn)-mediated Michael addition/cyclization cascade reactions toward acrylate ester analogues were exploited and utilized to construct novel and robust H2Sn-specific fluorescence probe for the first time. Through rational molecular engineering of the α-substituted acrylate ester template, the optimal candidate probe FP-CF3 containing trifluoromethyl-substituted acrylate ester group as recognition unit and 3-benzothiazol-7-hydroxycoumarin dye BHC as signal reporter can highly selectively detect H2Sn over other reactive sulfur species, especially biothiols including cysteine (Cys) and homocysteine (Hcy)/glutathione (GSH), with a rapid and significant turn-on fluorescence response (less than 60 s for response time and over 44-fold for signal-to-background ratio). The fast response and high selectivity of FP-CF3 for H2Sn could be attributed to a kinetically and spatially favored pentacyclic addition produced by the dual nucleophilic reaction of H2Sn with the CF3-substituted acrylate group. The big off-on fluorescence response is due to the pentacyclic intermediate results in the release of the highly fluorescent BHC. Moreover, it has been successfully applied in imaging of endogenous H2Sn fluctuation in living cells.

Novel fluorene/fluorenone DNA and RNA binders as efficient non-toxic ds-RNA selective fluorescent probes

A series of structurally similar 1-substitued heteroaryl fluorene derivatives were prepared in a simple single step reaction, oxidized to fluorenones and then both, fluorenes and fluorenones, were methylated to enhance the solubility and increase the affinity to DNA/RNA. Interactions of both, fluorene and fluorenone analogues with various ds-DNA, ds-RNA revealed strong ds-DNA/RNA binding, and various thermal stabilization effects. Most intriguingly, some fluorene derivatives showed opposite fluorescence change (increase for ds-RNA and decrease for ds-DNA), which was not previously reported for any fluorene analogue. CD experiments along with other methods support ds-DNA minor groove binding and major groove ds-RNA binding. All compounds showed negligible interaction with G-quadruplex DNA. Very low cell cytotoxicity of studied compounds combined with very efficient cellular uptake makes these fluorescent dyes safe for laboratory applications. Moreover, especially compounds which show opposite fluorescence response to ds-DNA and ds-RNA, are promising lead compounds for further studies aimed toward ds-RNA-specific fluorescence markers.

Two-photon fluorescent probe for hydrogen sulfide based on a red-emitting benzocoumarin dye

Hydrogen sulfide (H2S) is an endogenous gasotransmitter and plays intriguing biological roles. To study the biological role of H2S, efficient fluorescent probes are in great demand. For imaging of H2S in deep-tissue, a two-photon probe that emits in the red wavelength region is of choice to avoid the autofluorescence from intrinsic biomolecules. Here, we disclose such a probe, which, developed based on an acetyl benzocoumarin fluorophore, can be excited at 900 nm under two-photon excitation and emit in the red region. The probe shows high reactivity, selectivity, and sensitivity in in vitro assays. Two-photon microscopic imaging of H2S in HeLa cells aided by the probe demonstrates that it is potentially useful to study H2S level changes in cells and tissues influenced by external stimuli.

Effect of clay in controlling the non-fluorescence H-dimeric states of a cationic dye Nile Blue Chloride (NBC) in hybrid Langmuir–Blodgett (LB) film

Present communication reports the effect of amphiphilic matrices and nano-clay platelets on the aggregation properties of a water soluble cationic fluorescent dye Nile Blue Chloride (NBC) in Langmuir-Blodgett (LB) films. In-situ Brewster Angle Microscopic (BAM) studies showed distinct domain structures of complex and hybrid Langmuir monolayer at the air-water interface. UV–vis absorption spectra showed non-fluorescent H-dimeric band in concentrated aqueous solution of NBC and in complex LB film of NBC with stearic acid. By changing various parameters, a great control over H-dimeric states has been achieved in clay incorporated hybrid LB films. These films can act as efficient fluorescence probe.

Highly efficient fluorescence probe for copper (II) ions based on gold nanoclusters supported on wool keratin

A highly efficient fluorescence gold nanoclusters probe for copper (II) (Cu2+) ions among various ions has been prepared through wool keratin as chelating and reducing agent. The main features of fluorescent gold nanoclusters supported on wool keratin (AuNCs@WK) probe are the high fluorescence in aqueous solution, the simplicity of synthesis and the hypotoxicity for living cells. The fluorescence probe exhibits high stability of pHs and shows more sensitivity under acidic condition. Upon exposure to various metal irons, only AuNCs@WK system with Cu2+ ions shows a fluorescence turnoff response changing from red to blue under UV light, which lead to the dramatically decreased fluorescent intensity of AuNCs@WK at 690 nm. Moreover, the high sensitivity of AuNCs@WK around 1 µM meets the need of detection standards. The slope of Stern–Volmer plot at low concentration of Cu2+ ions is greater than it at high concentrations, which indicates the aggregated AuNCs are from small amounts to large numbers with the increasing concentration of Cu2+ ions. The design mechanism of AuNCs@WK probe is the coordination of reactive groups to produce the complex (wool keratin-Cu-wool keratin) at 1:2 between Cu2+ ions and fluorescence probe. Furthermore, the cytotoxicity in cells indicates that AuNCs@WK system is safe for the selective imaging of copper ions in living cells.

Technical Review: Microscopy and Image Processing Tools to Analyze Plant Chromatin: Practical Considerations.

In situ nucleus and chromatin analyses rely on microscopy imaging that benefits from versatile, efficient fluorescent probes and proteins for static or live imaging. Yet the broad choice in imaging instruments offered to the user poses orientation problems. Which imaging instrument should be used for which purpose? What are the main caveats and what are the considerations to best exploit each instrument's ability to obtain informative and high-quality images? How to infer quantitative information on chromatin or nuclear organization from microscopy images? In this review, we present an overview of common, fluorescence-based microscopy systems and discuss recently developed super-resolution microscopy systems, which are able to bridge the resolution gap between common fluorescence microscopy and electron microscopy. We briefly present their basic principles and discuss their possible applications in the field, while providing experience-based recommendations to guide the user toward best-possible imaging. In addition to raw data acquisition methods, we discuss commercial and noncommercial processing tools required for optimal image presentation and signal evaluation in two and three dimensions.

Isocyano-functionalized, 1,8-naphthalimide-based chromophore as efficient ratiometric fluorescence probe for Hg2+ in aqueous medium

Abstract A type of isocyano-functionalized, 1,8-naphthalimide-based chromophore (M2) was successfully synthesized from its primary amine-derivatived precursor (M1) compound. The chemical structure of M2 was verified by FT-IR, NMR and HRMS analyses. The presence of electron-withdrawing isocyano group brought significant influence to the optical properties of M2. Distinct from the yellowish green emission of its precursor (M1), M2 emitted ultraviolet light (with the emission peak at ∼389 nm, excited by 352 nm) in THF-water [VTHF/Vwater = 3/7, buffered with 5 mM sodium dihydrogen phosphate-disodium hydrogen phosphate (PB), pH = 7.4] co-solvent system. Interestingly, M2 exhibited distinctive and selective optical response (with significant enhancement of emission at ∼560 nm) toward Hg2+. In Hg2+ titration process, PL spectra of M2 displayed contiguous ratiometric alteration (simultaneous decreasing at 389 nm and increasing at 560 nm). Hg2+-assisted hydration of isocyano group to amino group on M2 was proposed as the plausible probing mechanism in this current case.

Fluorescence turn-on sensing of thiamine based on Arginine – functionalized graphene quantum dots (Arg-GQDs): Central composite design for process optimization

A low-cost, sensitive and convenient fluorescent probe of highly fluorescent Arginine – functionalized graphene quantum dots (Arg-GQDs) was designed and synthesized by a facile one–pot hydrothermal treatment of citric acid in the presence of Arginine. The fabricated Arg-GQDs with oxygen-rich functional groups exhibit a strong blue emission with 28.3% quantum yield (QY). It is found that such Arg-GQDs with high QY can be used as efficient fluorescent probe for thiamine determination. In the detection, photoluminescence (PL) intensity of the Arg-GQDs was reversibly quenched and recovered by Ag+ and thiamine, respectively. The effect of different parameters were optimized by central composite design (CCD) combined with response surface methodology (RSM). Furthermore, results of CCD were evaluated by standard analysis of variance (ANOVA) to assess the accuracy and suitability of the quadratic model. Under optimal conditions, the fluorescence “Off-On” process showed a sensitive response to thiamine in the concentration range of 0.1–8.0μM with a detection limit of 53nM. Finally, the Arg-GQDs based fluorescence method was applied to the analysis of thiamine in pharmaceuticals and foodstuff samples with satisfying recoveries for the spiked samples.

Current Application of Quantum Dots (QD) in Cancer Therapy: A Review.

Semiconductor quantum dots proved themselves as efficient fluorescent probes in cancer detection and treatment. Their size, high stability, non-photobleaching and water solubility made them a unique fluorophore in place of conventional organic dyes. Newly emerged theranostic drug delivery system using quantum dots helped us in better understanding of the drug delivery mechanism inside the cells. Surface modified Quantum dots and their applications became wide in bioimaging, immunohistochemistry, tracking intracellular drug and intracellular molecules target. We have highlighted various applications of quantum dots in cancer treatment, drug delivery, flow cytometry, and theranostics.

Highly fluorescent nitrogen-doped carbon dots derived from Phyllanthus acidus utilized as a fluorescent probe for label-free selective detection of Fe3+ ions, live cell imaging and fluorescent ink

A facile, economical and one-step hydrothermal method is used to synthesize highly durable fluorescent nitrogen-doped carbon dots (FNCDs) by utilizing Phyllanthus acidus (P. acidus) and aqueous ammonia as the carbon and nitrogen sources, respectively. The synthesized FNCDs have an average size of 4.5±1nm and showed bright blue fluorescence under the irradiation of UV-light at an excitation wavelength of 365nm. It exhibits a quantum yield (QY) of 14% at an excitation wavelength of 350nm with maximum emission at 420nm. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy characterizations clearly showed the formation of FNCDs that predominantly consists of nitrogen and hydroxyl groups which can provide more adsorption sites. In addition, the above study reveals the successful bonding of nitrogen with carbon (C–N) in the FNCDs. The synthesized FNCDs with high QY can be used as efficient fluorescent probes for the detection of Fe3+. Based on the linear relationship between normalized fluorescence intensity and concentration of Fe3+ ions, the prepared FNCDs can be used for label-free sensitive and selective detection of Fe3+ ions in a wide concentration range of 2–25μM with a detection limit of 0.9μM. The present study proves that synthesized FNCDs has durable fluorescence, soluble in water very well and thus act as a promising candidate for the diverse applications such as label-free sensitive and selective detection of Fe3+, fluorescent ink and cellular imaging with good biocompatibility and low cytotoxicity.

A Boron 2-(2'-pyridyl) Imidazole Fluorescence Probe for Bovine Serum Albumin: Discrimination over Other Proteins and Identification of Its Denaturation.

Boron 2-(2'-pyridyl) imidazole complex (BOPIM) derivatives, BOPIM-1 and BOPIM-2, involving twisted intra-molecular charge transfer (TICT) characteristic, were investigated to probe bovine serum albumin (BSA). BOPIM-1 was demonstrated to be an efficient fluorescence probe to discriminate BSA from other proteins including human serum albumin (HSA). The encapsulation of BOPIM-1 in the hydrophobic subdomain IIA of BSA inhibited the TICT state and resulted in 70-fold emission enhancement of BOPIM-1. Besides, it was found that BOPIM-1 could distinguish denatured BSA from the native, due to the difference of 15 nm emission wavelength at least. The denaturation of BSA leads to the exposure of binding sites and resulted in an increase in the accessibility of the fluorophore to the BSA cavity, which made a great contribution to the further restraint of TICT state of BOPIM-1. The tracking of BSA denaturizing process was easily achieved, through the change of BOPIM-1 emission wavelength from 485 to 465 nm. Thus, a promising pharmacological dual-functional probe was provided for both the selective recognization of BSA and the identification of denatured BSA from the native.

Efficient Two-Photon Fluorescent Probe for Glutathione S-Transferase Detection and Imaging in Drug-Induced Liver Injury Sample.

Drug-induced liver injury (DILI) is a potential complication of any prescribed medication. So far, the diagnosis of DILI is still a clinical challenge due to the lack of efficient diagnosis method. Glutathione S-transferase (GST), with a high concentration in liver cytosol, can reduce toxicity and facilitate urinary excretion by catalyzing the conjugation of glutathione (GSH) with reactive metabolites in liver. When liver is seriously damaged, GST and GSH will be released into plasma from liver cytosol, which caused a lower GST activity in liver cytosol. Therefore, monitoring the level of GST activity in liver tissue may be a potential strategy for diagnosis of DILI. Here, we reported a two-photon probe P-GST for GST activity detection for the first time. In the proposed design, a donor-π-acceptor (D-π-A) structured naphthalimide derivative with efficient two-photon properties was chosen as the fluorescent group, and a 2,4-dinitrobenzenesulfonate group was employed as the GST recognition unit, which also acted as the fluorescence quencher. In the present of GST and GSH, the recognition unit was removed and the fluorophore was released, causing a 40-fold enhancement of fluorescence signal with a detection limit of 35 ng/mL. At last, P-GST was successfully applied in two-photon imaging of GST in cells and DILI samples, which demonstrated its practical application in complex biosystems as a potential method for diagnosis of DILI.

Responsive mechanism of three novel hypochlorous acid fluorescent probes and solvent effect on their sensing performance**Project supported by the National Natural Science Foundation of China (Grant Nos. 11374195 and 11404193) and the Taishan Scholar Program of Shandong Province, China.

Optical properties and responsive mechanisms of three newly synthesized fluorescent probes for hypochlorous acid (HOCl) are investigated by employing time-dependent density functional theory. The computational results show that the absorption and emission properties of these probes change obviously when they react with hypochlorous acid. It is found that the probe FHZ has the best performance according to the probing behavior. Moreover, the responsive mechanisms of the probes are studied by analyzing the distributions of molecular orbitals and charge transfer, which are shown as the photon-induced electron transfer (PET) for FHZ and the intramolecular charge transfer (ICT) for the other two probes. Specially, solvent effect on optical properties of the probe FHZ before and after reaction is studied within the polarizable continuum model (PCM). It is shown that performance of the probe depends crucially on the solvent polarity. Our computational results agree well with the experimental measurement, and provide information for design of efficient two-photon fluorescent probes.

A novel imidazo[1,5-a]pyridine-rhodamine FRET system as an efficient ratiometric fluorescent probe for Hg2+ in living cells

An imidazo[1,5-a]pyridine-rhodamine-based ratiometric fluorescent probe was designed and successfully synthesized. The probe shows a large Stokes shift (204 nm), high sensitivity and high selectivity. The detection limit was calculated to be as low as 0.93 nM. The probe could quickly (5 min) detect Hg2+ over a wide pH range from 4 to 10. Furthermore, it could be used for imaging Hg2+ in living cells.

Design and fabrication of covalently linked PEGylated nanohybrids of ZnO quantum dots with preserved and tunable fluorescence

Non-toxicity, high photo stability, biocompatibility and long lasting narrow emissions are some prime factors for an efficient biological marker. Unfortunately, commercial dyes and Cd-based fluorescent probes do not have such characteristics. Therefore, an efficient fluorescent probe is extremely desirable. Herein, functionalized ZnO quantum dots (QDs) and their nanohybrids with polyethylene glycol (PEG) were prepared by a room temperature solution growth tactic using 3-isocyanatopropyltriethoxysilane (3-ICPTES) as a coupling agent. Isocyanato functional groups were hosted on the surface of as prepared ZnO QDs by introducing optimized stoichiometric amounts of 3-ICPTES. The ZnO QDs were further bonded covalently to PEG via urethane linkages by the reaction of isocyanato functionalized ZnO QDs and hydroxyl groups from PEG molecules. The fluorescence was tuned from cyan to yellowish color after the functionalization of ZnO QDs with 3-ICPTES. Moreover, PEGylated nanohybrids showed greater water dispensability with photoluminescence preserved for at least six months. The present synthesis and coupling strategy for QDs may open up new ways to achieve biocompatible nanohybrids with higher stability and efficient luminescence for bio-imaging and biomedical applications.

Artefact-free Evaluation of Metal Enhanced Fluorescence in Silica Coated Gold Nanoparticles

Metal nanoparticles can either quench or enhance the emission of dyes in their vicinity, but the precise measurement and understanding of this effect is still hindered by experimental artifacts, especially for particles in colloidal dispersion. Here, we introduce a new methodology to correct the inner filter effect of the metal on the dye emission. To test the method, we developed new hybrid nanoparticles with a gold core and a silica shell of precise thickness (tuned from 7 to 13 nm), with a high quantum yield perylenediimide dye on the surface. This novel approach effectively avoids fluorescence quenching, allowing us to measure emission enhancements of 5 to 30 times, with no change on the dye fluorescence lifetime. Being able to measure the emission enhancement in dye-metal hybrid nanoparticles in dispersion, free from inner filter and quenching artifacts, offers excellent prospects to guide the development of more efficient fluorescent probes, sensors and photonic devices.

Highly Efficient Multiple-Anchored Fluorescent Probe for the Detection of Aniline Vapor Based on Synergistic Effect: Chemical Reaction and PET.

A multiple-anchored fluorescent probe ((((hexane-1,6-diylbis(2,7-bis(4-formyl)-phenyl)-9H-fluorine-9,9-diyl))-bis(hexane-6,1-diyl))-bis(9H-carbazole-9,3,6-triyl))-tetrakis(benzene-4,1-diyl))-tetraformyl-(8FP-2F) with eight aldehyde groups was designed and synthesized. The molecule has four branches and highly twisted structure. Furthermore, it tends to self-assemble into nanospheres, which is beneficial for gaseous analyte penetration and high fluorescence quantum efficiency. Among gaseous analytes, detection of aniline vapor is extraordinarily important in the control of environmental issues and human diseases. Herein, 8FP-2F was introduced to detect aniline vapor with distinguished sensitivity and selectivity via simple Schiff base reaction at room temperature. After exposure to saturate aniline vapor, the 89% fluorescence of 8FP-2F was quenched in 50 s and the detection limit was as low as 3 ppb. Further study showed the suitable HOMO/LUMO energy levels and matched orbital symmetry between probe and aniline molecules ensured chemical reaction and PET process work together. The synergistic effect resulted in a significant sensing performance and fluorescence quenching toward aniline vapor. Moreover, the multiple active sites structure of 8FP-2F means it could be applied for constructing many interesting structures and highly efficient organic optoelectronic functional materials.

Fluorescent carbon dots with tunable negative charges for bio-imaging in bacterial viability assessment

Applying bio-imaging in bacterial viability assessment is vital to human health. Nitrogen, phosphorus co-doped carbon dots (NPCDs) with high visible fluorescence and tunable negative charges were synthesized by a feasible hydrothermal reaction. The as-prepared NPCDs possess abundant surface functional groups, excellent photostability and bio-compatibility. Especially, the surface negative charges of NPCDs can be adjusted by changing the kind of the precursors. The obtained NPCDs as a fluorescent dye could selectively stain dead bacteria instead of live ones due to electrostatic repulsion since the cell walls of bacteria possess negative charges. The NPCDs with less negative charges provides a low accurate mortality rate due to a weaker repulsion, while NPCDs with the most negative charges give a comparable mortality rate with traditional plate counting method but consumes shorter time. Our study suggests that NPCDs with highly negative charges could serve as a precise and efficient fluorescent probe to determine the living state of bacteria, widening the path for bio-imaging application in bacterial viability assessment.