Selective Fluorescence Response Research Articles

An isophorone-fused near-infrared fluorescent probe with a large Stokes shift for imaging endogenous nitroxyl in living cells and zebrafish.

Nitroxyl (HNO) plays an important role in multiple physiological and pathological processes, but the detailed generation mechanism of the endogenous HNO still remained to explore and perfect further. There is an urgent need to develop an excellent fluorescent probe for selective recognition and sensitive detection of HNO in biological systems. Near-infrared (NIR) fluorescent probes with a large Stokes shift are an ideal tool for bioimaging applications. Here, we have developed a NIR fluorescent probe with a large Stokes shift, namely, NIR-HNO, to monitor HNO in cells and zebrafish. NIR-HNO consists of an isophorone-fused NIR fluorescence reporter and a diphenylphosphinobenzoyl HNO-responsive unit. Based on an aza-ylide intramolecular ester aminolysis reaction, NIR-HNO showed a rapid selective NIR fluorescent turn-on response for HNO, high sensitivity (detection limit was 39.6 nM), and large Stokes shift (265 nm). The biological imaging results indicate that NIR-HNO is a good candidate for imaging of endogenous HNO in living systems.

Design two large conjugate triazolopyrimidine analogs and apply them to detect 2,4,6-trinitrophenol

The aim of this study is to construct N-containing heterocyclic probes with large conjugate structures. Two triazolopyrimidine analogs LK-1 and LK-2 were designed and synthesized. Between them, LK-2 has a higher fluorescence quantum yield and selected as a fluorescent probe for detecting 2,4,6-trinitrophenol (TNP). Whether DMF or H2O as solvent, probe LK-2 shown low detection limit apparently (0.025 and 0.44 μM), fast and highly selective fluorescence response to TNP compared to other nitro-aromatic compounds. The static quenching mechanism is demonstrated by fluorescence lifetime. Nuclear magnetic titration and theoretical calculations further explain the identification process. What's more, application of LK-2 in actual water samples and test strip experiments demonstrate the potential of probe in practical significance.

A Dye@MOF composite as luminescent sensory material for selective and sensitive recognition of Fe(III) ions in water

Dye encapsulated metal-organic framework (MOF) composites have emerged as one of the promising platforms toward chemical recognition. Herein, a highly potent hydrolytically stable luminescent sensory probe was crafted exhibiting selective fluorescence response for Fe3+ ions in water medium. Encapsulation of a cationic dye inside a porous anionic MOF was successfully achieved via an ion-exchange process. Confinement of dye molecules inside the MOF serving as a crystalline flask prohibits the aggregation-induced quenching of dye molecules thereby manifesting a Dye@MOF luminescent composite material. The Dye@MOF composite shows selective response toward Fe3+ ions with remarkable luminescence quenching even in presence of other metal ions. Additionally, a high Ksv (quenching coefficient) value of 5.5 × 104 M−1 and low limit of detection (LOD) of 1.1 ppm was observed for Fe3+ ions.

Near-Infrared Hybrid Rhodol Dyes with Spiropyran Switches for Sensitive Ratiometric Sensing of pH Changes in Mitochondria and Drosophila melanogaster First-Instar Larvae.

Near-infrared hybrid rhodol dyes (probes A and B) for sensitive ratiometric visualization of pH changes were prepared by incorporating hemicyanine dyes into traditional rhodol dyes. This approach was based on π-conjugation changes involving a rhodol hydroxyl group as a spiropyran switch upon pH changes. Electronic spectra of probes A-2 and B-2 contain sharp absorption peaks at 535 nm and fluorescence peaks at 558 nm with similar π-conjugation and a closed spiropyran form at a basic pH of 10.2. However, acidic pH conditions break down the hemiaminal ether groups, leading to indolenium moieties and significantly extending the π-conjugation within the rhodol fluorophores, resulting in additional near-infrared emissions for probes A-1 and B-1. As a result, probes A and B exhibit gradual decreases of the absorption peaks at 535 nm and gradual increases in absorption peaks at 609 and 622 nm upon transition from basic to acidic pH, respectively. Both probes display ratiometric fluorescence sensing responses to pH downgrades from 10.2 to 3.6 with visible fluorescence decreases at 558 nm, as well as corresponding increases of the near-infrared fluorescence peaks at 688 and 698 nm, respectively. They exhibit fast, sensitive, and selective fluorescence responses with clearly defined ratiometric features to pH changes and show low cytotoxicity and excellent cell permeability. Our probes were successfully applied to ratiometrically detect pH changes in mitochondria, D. melanogaster first-instar larvae, and to visualize the mitophagy process caused by either cell nutrient starvation or drug treatment.

An Automated Microrobotic Platform for Rapid Detection of C. diff Toxins.

Clostridium difficile (C. diff) infection leads to hundreds of nosocomial infections, and early diagnosis of this toxin-mediated disease is important. This paper aims to develop a microrobotic system and related methods that enable the automated and rapid detection of toxins secreted by C. diff that exist in patient's stool. We utilize the fluorescent magnetic spore-based microrobot (FMSM), a microscale mobile sensing tool, to efficiently detect C. diff toxins by utilizing its property of selective fluorescence responses to C. diff toxins. A plug-and-play (PnP) electromagnetic coil system integrated with fluorescence microscopy is developed for actuation, control and observation of FMSMs. In order to track in real time and accurately obtain the fluorescence parameters of a FMSM under varied background noise in fluorescence signal, an image gradient-based method is proposed. For accelerating the FMSM-toxin interaction in different samples, an automated navigation control scheme for the FMSM is proposed and implemented. Moreover, data post-processing methods that can optimally extract the fluorescence decay trend from the dense and fluctuated fluorescence data are developed. This automated mobile detection process finishes within only 20 minutes, and the toxin detection result is immediately given by adopting the proposed system and methods. Experimental results on different biological samples confirm the qualitative detection capability. And, C. diff toxins are automatically detected from the clinical stool of infectious patients and the relationship between the fluorescence decay and the toxin concentration is calibrated for semi-quantitative detection purpose. The proposed automated microrobotic platform provides a rapid and low-cost detection technique for C. diff toxins, and it has good competency for future clinical use.

Aminoantipyrine based efficient chemosensor for Zn(II) ions and its effectiveness in live cell imaging

A simple imine based receptor NA-1 has been synthesized for detection of Zinc ions. Probe NA-1 showed the selective colorimetric changes with Zinc (II) ions whereas other metal ions didn't showed any observable colorimetric changes. The probe showed the very selective turn-on fluorescence response with Zn(II) ions among other rival metal ions like Cd(II) and Hg(II). The mode of binding was studied by 1H-nmr titrations and fluorescence spectroscopy. Jobs plot analysis confirming that the probe NA-1 forms 1:1 complex with Zn(II). The observed fluorescence and absorption change further supported by theoretical calculations. The turn-on fluorescence of the probe NA-1 is probably attributable to the interruption of intramolecular charge transfer as well as ESIPT. The limit of detection of the probe for Zn(II) sensing is in the range of 14 nano molar. Cytotoxicity (MTT) assay of the probe in live HeLa cells is showing that the probe is least toxic to cells. The probe NA-1 is effectively applied to detect Zn(II) ions in HeLa cells and suggesting the probe is NA-l permeable to cell wall and viable for Zinc(II) ions imaging in live cells.

Self-assembly of pyrene boronic acid-based chemodosimeters for highly efficient mercury(II) ion detection

A new chemodosimeter consisting of pyrene and boronic acid (1) for the detection of Hg2+ ions is described. The amphiphilic nature of 1 leads to self-assembly in aqueous solution and the high electron density throughout the aggregated pyrene units provides an outstanding platform for energy and electron transport. Self-assembled 1 exhibits a selective and sensitive fluorescence response to Hg2+ ions, where the Hg2+ ion allows a fast transmetallation of 1, which drastically reduces its fluorescence. The Stern-Volmer (SV) quenching constant for the fluorescence quenching of self-assembled 1 by Hg2+ ions is approximately 1.8 × 106 M−1, and Hg2+ ions can be sensed with a detection limit of 6.6 × 10−9 M. In addition, self-assembled 1 exhibits excellent sensing performance at nano-molar concentration levels for Hg2+ ion contamination of tap water, fresh water, and seawater.

Synthesis and optical properties of copper(II) and nickel(II) complexes of a highly fluorescent morpholine-derivative

A morpholine substituted methyl 3-hydroxy-2-naphthoate was synthesized. The morpholine derivative displayed an intense fluorescence. Owing to the presence of suitable donor atoms, it was employed for the detection of transition metal ions. The crystals of copper and nickel complexes of the fluorescence active ligand were grown via vapor diffusion method. The ligand structure and its metal complexes were characterized using 1H NMR, IR, HR-MS and single crystal X-ray crystallography. The synthesized ligand displayed selective turn-off fluorescence response in the presence of Cu2+ and Ni2+ ions. Fluorescence active letters were encoded successfully on filter paper utilizing metal complexes as a tool towards digital writing.

Fluorescent probes with high pKa values based on traditional, near-infrared rhodamine, and hemicyanine fluorophores for sensitive detection of lysosomal pH variations.

Sterically hindered fluorescent probes (A-C) have been developed by introducing 2-aminophenylboronic acid pinacol ester to a traditional, A, a near-infrared rhodamine dye, B, and a near-infrared hemicyanine dye, C, forming closed spirolactam ring structures. Probe A was non-fluorescent under basic pH conditions whereas probes B and C were moderately fluorescent with fluorescence quantum yields of 9% and 5% in pH 7.4 PBS buffer containing 1% ethanol, respectively. With all probes increasing acidity leads to significant increases in fluorescence at 580 nm, 644 and 744 nm for probes A, B and C with fluorescence quantum yields of 26%, 21% and 10% in pH 4.5 PBS buffer containing 1% ethanol, respectively. Probes A, B and C were calculated to have pKa values of 5.81, 5.45 and 6.97. The difference in fluorescence under basic conditions is ascribed to easier opening of the closed spirolactam ring configurations due to significant steric hindrance between the 2-aminophenylboronic acid pinacol ester residue and an adjacent H atom in the xanthene derivative moiety in probe B or C. The probes show fast, reversible, selective and sensitive fluorescence responses to pH changes, and are capable of sensing lysosomal pH variations in living cells.

Rapid and specific assays for intracellular pH fluctuations based on pH-dependent disassembly-assembly of conjugated polymer nanoparticles

Intracellular pH (pHi) is a critical factor that governs many physiological and pathological processes. Accurate measurement and visual imaging of pHi is of importance and in high demand for biological research and clinical diagnosis. In this paper, a novel strategy of pH-dependent disassembly-assembly of conjugated polymer nanoparticles was developed and successfully applied in constructing an efficient fluorescent probe for intracellular pH sensing and imaging. The nanoparticles-based probe (PTNPs) was prepared by reprecipitation method from a polythiophene derivative (PTNEt2) with diethylamine group on its side chains. As the acidity of system increased, the disassembly of PTNPs took place due to the electrostatic repulsion between protonated PTNEt2 chains at low pH. Conversely, once the system recovered to weak alkalinity, the dispersed polymer chains reassembled to form nanoparticles owing to their poor water-solubility at high pH. Thus, PTNPs showed a rapid, highly selective and reversible fluorescence response to pH. Besides, the probe exhibited an ideal pKa value of 5.71, which was suitable for quantification of intracellular pH values with a linearly proportional range of 4.0–8.0. In view of easy modification properties of conjugated polymers, this proposed strategy could offer a general way for quantifying various biological events inside living cells.

Determination of Cyanide in Water and Food Samples Using an Efficient Naphthalene-Based Ratiometric Fluorescent Probe.

Monitoring cyanide levels in water and food samples is crucial. Herein, we rationally developed a simple and efficient fluorescent probe for cyanide determination. The probe displayed selective ratiometric fluorescent response to cyanide. In addition, after treatment with cyanide, the fluorescence ratios (I509/I466) exhibited a good linearity with cyanide concentration in the range of 0–60 μM, and the detection limit was determined to be 0.23 μM (S/N = 3). Significantly, the practical application demonstrated that the probe was able to quantitatively detect cyanide concentration in natural water samples. Monitoring of endogenous cyanide in cherry nut by the probe was also successfully conducted. Notably, upon fabrication of test strips, the probe could be conveniently utilized for field measurement of cyanide in bitter almond without relying on sophistical instruments. Furthermore, the cyanide in potato tissues was determined for the first time by means of fluorescence imaging.

A coumarin-based near-infrared fluorescent probe with a large stokes shift for the sequential recognition of Ni2+ and CN−: Performance research and quantum calculation

The design and synthesis of bifunctional probes have gradually become a new research focus in the field of fluorescent probes. In this work, a reversible colorimetric and NIR fluorescent probe (Ni−3) for the sequential detection of Ni2+ and CN− was developed based on 3-benzothiazolyl-7-hydroxycoumarin. This probe featured a large Stokes shift (145 nm) and excellent anti-fatigue performance for the sequential detection of Ni2+ and CN−. Ni−3 showed a highly colorimetric response to Ni2+ and the selectivity could be distinguished by naked eyes. Besides, Ni−3 also exhibited selective NIR fluorescence response toward Ni2+ due to the paramagnetic effect and the chelation-enhanced quenching (CHEQ) effect. Additionally, the in situ generated complex [2 Ni−3 + Ni2+] showed highly sensitive and selective sensing ability for CN− via Ni2+ displacement approach. The limit of detection toward CN− (1.29 μM) was lower than the maximum acceptable concentration level of cyanide in drinking water (1.9 μM) set by WHO. Furthermore, a “paralleled-coordination” mode between Ni−3 and Ni2+ was proposed and demonstrated with the aid of quantum calculations.

Aggregation-Induced Emission-Active 1,4-Dihydropyridine-Based Dual-Phase Fluorescent Sensor with Multiple Functions.

A N-2-phenylethyl-substituted 1,4-dihydropyridine derivative (NDHP) containing 5,5-dimethylcyclohexane-1,3-dione and naphthylethylene was designed and synthesized. NDHP acts as a multifunctional fluorescent sensor in dual phases. The crystal structure analysis confirms that the NDHP molecules have highly twisted conformations. The twisted conformation results in aggregation-induced emission properties and solid-state emission, by restricting the intramolecular free rotation in the aggregated or solid state. In the solid state, NDHP exhibits reversible mechanochromic properties as a result of the transition between the amorphous and crystalline states. NDHP also exhibits a rare phenomenon of acid-fumed solid-state emission enhancement owing to the change in packing mode from a zigzag arrangement to J-aggregation. The solid-state stimuli-responsive fluorescence switching is applied to realize a rewritable optical recording media and a multiple output combinational logic system. In solution, NDHP shows a selective fluorescence response for environmentally harmful Hg2+ , with a limit of detection of 2.7 nm. This results from the "turn-on" responsive behavior owing to the Hg2+ -triggered aggregation of the NDHP molecules. NDHP is also used in the imaging of intracellular Hg2+ in HeLa cells. These findings provide a feasible and attractive route for developing multifunctional fluorescent sensors for use in dual phases.

Specific detection of hypochlorite: a cyanine based turn-on fluorescent sensor

Judiciously designed cyanine based fluorogenic probe (L) can exhibit interesting solvent polarity induced isomerization. The probe displayed a highly selective TURN-ON fluorescence response towards hypochlorite among various reactive oxygen species (ROS) and analytes in a mixed aqueous medium. The sensing process was attributed to the formation of a probe-OCl adduct which results in restricting the donor-acceptor extended conjugation. The detection limit was found to be as low as 3 $$\upmu \hbox {M}$$ . The proposed sensing mechanism is supported by mass spectrometric analysis and HPLC study. Cyanine based fluorogenic probe (L) selectively detect hypochlorite among various ROS with a detection limit of 3 $$\upmu \hbox {M}$$ in mixed aqueous medium through TURN-ON fluorescence response.

Ultrasensitive Detection of Sulfur Mustard via Differential Noncovalent Interactions.

In this work, we fabricate two types of hierarchical microspheres, i.e., one coassembled from two fluorene-based oligomers (1 and 2) and one self-assembled from a fluorene-based oligomer (1), for ultrasensitive and selective detection of trace sulfur mustard (SM) vapor. On the basis of distinct fluorescence responses of 1-2 coassembled and individual 1 hierarchical microspheres that originate from differential noncovalent interactions between analytes and these sensors, SM vapor can be ultrasensitively detected (30 ppb) and easily discriminated from various sulfides and other potential interferents. Our work that utilizes differential noncovalent interactions to give sensitive and selective fluorescence response patterns represents a new detection approach for SM and other hazardous chemicals.

A Pyrene-Functionalized Metal-Organic Framework for Nonenzymatic and Ratiometric Detection of Uric Acid in Biological Fluid via Conformational Change.

In this work, a water-stable, pyrene-functionalized Hf-based mixed-ligand metal-organic framework (MOF) with UiO-66 (UiO = University of Oslo) framework topology was designed and synthesized for the fluorimetric detection of uric acid (UA) in aqueous medium. The free pyrene-functionalized ligand changes its conformation (monomer to excimer) upon framework formation, which was confirmed via fluorescence spectral studies. The MOF material showed a fast, selective, sensitive (detection limit 1.4 μM), and ratiometric fluorescence response toward UA in pure aqueous medium. During sensing, a further conformational change (excimer to monomer) of the ligand molecule was observed within the MOF. These dual conformation changes helped us to utilize the MOF material for the sensing of UA. Detailed experimental studies showed that the sensing mechanism involves hydrogen-bonding interactions between UA and the framework ligand, which is responsible for the change in conformation and fluorescence emission properties of the pyrene-functionalized ligand molecule. The MOF probe could be reused up to five cycles of sensing events. The MOF material was also utilized for the detection of UA present in serum and urine samples. Moreover, MOF-coated paper test strips were developed for the on-site fluorimetric detection of UA.

An example of enhanced emission of a pyridine containing schiff base zinc2+ complex

▪A pentadentate Schiff-based ligand incorporating a pyridine binding moiety has been synthesized and characterized. This ligand is of potential interest in the development of a fluorescent chemosensor for the biologically relevant Zn2+. This mixed oxo and aza donor ligand shows highly selective fluorescent response to Zn2+ compared to alkali, alkaline, transition metal, and lanthanide ions, exhibiting a quantum yield of 1.60% when bound to Zn2+. The system exhibits a limit of detection of 7.2 µM. Examination of twelve other metal ions in competition with the ZnL complex found a unique augmentation in fluorescence upon addition of K, Ca, Mg, and Cd ions, an effect not previously observed in similar chemosensor systems. Cooperative binding of ligand, Zn, and K resulted in the largest increase in quantum yield to 2.71%.

Fluorescence-sensitive adsorbent based on cellulose using for mercury detection and removal from aqueous solution with selective "on-off" response.

A new fluorogenic bio-adsorbent was successfully synthesized for detection and adsorption of mercury ions in aqueous solution. It showed high sensitivity in removing Hg (II) at low concentration with a detection limit of 84 ppb which was below the maximum discharge standard in enterprise drain off water in China, besides, the adsorbent had good selectivity towards Hg (II) among numerous kinds of cations in water that it showed fluorescent quenching properties for Hg (II) ions due to photo-induced electron transfer. In addition, batch adsorption experiments were investigated to study the influence of initial concentration of metal ions, contact time, pH of the solution on the adsorption capacity. Equilibrium adsorption isotherms demonstrated the Hg (II) removing process fitted well with Langmuir isotherm model, and the maximum adsorption capacity for mercury was measured to be 143.88 mg/g. Furthermore, the adsorption kinetics was found to follow pseudo-second-order model. FTIR spectra and SEM-elemental mapping clearly confirmed the adsorbed heavy metal ions.

A New Tetrasubstituted Imidazole Based Difunctional Probe for UV-spectrophotometric and Fluorometric Detecting of Fe3+ Ion in Aqueous Solution

Two new compounds, 4-(2-bromophenyl-4,5-diphenyl-imidazol-1-yl)aniline(probe 1) and 4-[2,4,5-tris(4-bromophenyl)-1H-imidazol-1-yl]aniline(probe 2), were synthesized via a soft and high-efficiency one-pot microwave- assisted method under solvent-free conditions. Their sensing to different metal ions was detected by UV spectrophotometry and fluorescence spectrometry. Probe 2 revealed highly selective and sensitive UV and fluorescence response to Fe3+ ion. Upon the addition of Fe3+ ion, probe 2 showed obvious color change of the solution, conspicuous absorbance enhancement and relatively quick fluorescence quenching. The detection limit for Fe3+ ion was respectively calculated to be 0.72 μmol/L(fluorescent detection) and 0.48 μmol/L(UV-spectrum detection). Also, probe 2 was bound by Fe3+ ion to form a 1:1 complex. Moreover, preliminary application of probe 2 for detecting Fe3+ ion in aqueous solution was attempted, and satisfying results were obtained.

Schiff base functionalized PEG as a high efficient fluorescent chemosensor for Al3+ detection in 100% aqueous solution

A new simple Schiff base functionalized water-soluble polymer (PEGBN) was synthesized by one-step esterification of Schiff base derivative with carboxylated polyethylene glycol. PEGBN exhibited a sensitive and selective turn-on fluorescence response toward Al3+ over other competitive metal ions in 100% aqueous solution. The detection limit of PEGBN for Al3+ was as low as 6.15 × 10−9 M. PEGBN displayed high selectivity to Al3+ over a wide pH range from 5 to 9. The reusability of PEGBN was demonstrated successfully by multiple cycles of alternate addition of Al3+ and EDTA to PEGBN solution. Furthermore, an INHIBIT logic gate was constructed based on the fluorescence response of PEGBN with Al3+ and EDTA as two input signals.