A chemodosimeter for the ratiometric detection of hydrazine based on return of ESIPT and its application in live-cell imaging

Cyanide Boosting Copper Catalysis: A Mild Approach to Fluorescent Benzazole Derivatives from Nonemissive Schiff Bases in Biological Media

An application of nucleophilic cyclization and oxidation of nonemissive Schiff bases via cyanide boosting copper catalysis to synthesize fluorescent benzazole derivatives in high conversion yield is disclosed. This approach is highlighted by broad substrate scope, fast reaction time, and mild conditions and can efficiently proceed in living cells or Arabidopsis root tissues. Furthermore, this methodology can be applied for selective detection of Cu²⁺ and CN^-.

A coumarin-fused 'off-on' fluorescent probe for highly selective detection of hydrazine

Hydrazine is a kind of widely used industrial raw material and a toxic biochemical reagent. Due to its toxic to organisms, hydrazine has been classified to be a hazardous environmental pollutant. It is urgent to develop fluorescent probe tools for selective sensitivity detection of hydrazine in the environment and the body. We developed here a new coumarin-based fluorescent probe for hydrazine detection. The probe can selectively detect hydrazine over other environmental and endogenous interfering analytes with a large off-on fluorescence response. The detection limit is 8.55 ppb, which is well below the allowed threshold limit value. The sensing mechanism is hydrazine-induced pyrazole ring formation, which is confirmed by HRMS and DFT calculation methods. Additionally, the probe could also be applied for hydrazine imaging in living HeLa cells.

A Natural Light Visible Colorimetric Responses Fluorescent Probe for Hydrazine Detection

A natural light visible colorimetric responses fluorescent probe (Probe 1) was developed for N2H4 detection. The recognition mechanism of Probe 1 for hydrazine is based on addition-cyclization. The LOD of Probe 1 for N2H4 was 80.3 nM (0.0026 mg/L), which is below the national limited standard (0.02 mg/L). When various concentrations of N2H4 were added, the color of the Probe 1 solution was graded gradually from yellow to colorless, which could be observed under natural light. The changing course only takes 5 min. Furthermore, Probe 1 was successful applied to detect N2H4 in mineral water, seawater, tap water and river water. The obtained recovery ranged from 91.91 - 100.00%. Probe 1 has great potential, developed as a visual tool for N2H4 rapid detection.

Phenothiazine-based fluorescence probe for ratiometric imaging of hydrazine in living cells with remarkable Stokes shift

By modifying the 10-butyl-2-methoxy-10H-phenothiazine-3-carbaldehyde with malonontrile group, a new fluorescent sensor PBM for selective detection of hydrazine in ratiometric mode has been developed. Probe PBM owned the advantages of quick response (10 min), remarkable Stokes shift (168 nm for PBM, 161 nm for PBM-NH₂), excellent selectivity, high sensitivity (detection limit of 63.2 nM was obtained from in vitro experiment), profound ratiometric change (82-fold) and low cytotoxicity in response to hydrazine. Additionally, it could be utilized to monitor hydrazine in gas state with various concentrations through vivid color changes and imaged hydrazine in living MCF-7 cells with excellent performance.

A turn-on fluorescent sensor for selective detection of hydrazine and its application in Arabidopsis thaliana

In this work, a primary method was constructed for detecting hydrazine in plant, thus accomplished the closed-loop monitoring of hydrazine circulation within manufacture, environment, plants, animals and human. From a series of sensors, QYL-1 was selected to present the hydrazine sensing properties. As a preliminary tool, QYL-1 suggested the ultra-wide linear range (0-20.0 equivalent) and high selectivity, which were extremely essential for linking the monitoring in various scale and field. For the first time, concentration-dependent tracking of hydrazine was successfully performed in Arabidopsis Thaliana root tips. Afterwards applications in water samples and living MCF-7 cells then fulfilled the demonstration of closing the loop by linking both the upstream and downstream nodes. More than raising a practical method, this work offered initial information for the closed-loop monitoring of hydrazine circulation, which might be significant for the ideal systematic managing in future.

Novel blue-green emitting NLOphoric triphenylamine-imidazole based donor-π-acceptor compound: Solvatochromism, DFT, TD-DFT and non-linear optical studies

Novel Donor (D)-π-Acceptor (A) NLOphoric triphenylamine-imidazole based dye 9 was designed, synthesized, and confirmed by Mass, ¹³C NMR, and ¹H NMR analysis. Photophysical properties of 9 were studied in solvents of different polarities and compared with analogues compounds 7 and 8. Phenonthroline acceptor based dye 9 shows highly bathochromic shifted absorption and emission compared to dyes 7 and 8. Positive solvatochromism was noticed in 7, 8, and 9 which was supported by the linear (i.e. Lippert-Mataga and Mac-Rae polarity functions) and multi-linear (i.e. Kamlet-Taft and Catalan parameters) analysis. Moreover, solvent polarizability (d_SP) and solvent dipolarity (C_SdP) are the major factors responsible for red shift in absorption as well as in emission spectra. Charge transfer descriptors as well as the polarity graphs are in good relation with Generalized Mulliken-Hush (GMH) parameters. NLO properties of 7, 8, and 9 were studied by using solvatochromic and computational methods. The static first hyperpolarizability (β₀) and relevant microscopic parameters (μ,α₀,α,β,γ) were determined using DFT with B3LYP, BHHLYP, and CAM-B3LYP functionals. Third-order NLO properties of nitrogen containing phenanthroline based compound 9 were observed to be several times higher than those of the compounds 7 and 8, justify the design approach.

An ICT-based fluorescent probe with a large Stokes shift for measuring hydrazine in biological and water samples

As a strong reductant and highly active alkali, hydrazine (N₂H₄) has been widely used in chemical industry, pharmaceutical manufacturing and agricultural production. However, its high acute toxicity poses a threat to ecosystem and human health. In the present study, a ratiometric fluorescent probe for the detection of N₂H₄ was designed, utilizing dicyanoisophorone as the fluorescent group and 4-bromobutyryl moiety as the recognition site. 4-(2-(3-(dicyanomethylene)-5,5-dimethylcyclohex-1-enyl) phenyl 4-brobutanoate (DDPB) was readily synthesized and could specially sense N₂H₄ via an intramolecular charge transfer (ICT) pathway. The cyclization cleavage reaction of N₂H₄ with a 4-bromobutyryl group released phenolic hydroxyl group and reversed the ICT process between hydroxy group and fluorophore, turning on the fluorescence in the DDPB-N₂H₄ complexes. DDPB exhibits a low cytotoxicity, reasonable cell permeability, a large Stokes shift (186 nm) and a low detection limit (86.3 nM). The quantitative determination of environmental water systems and the visualization fluorescence of DDPB test strips provides a strong evidence for the applications of DDPB. In addition, DDPB is suitable for the fluorescence imaging of exogenous N₂H₄ in HeLa cells and zebrafish.

Rational design of a novel turn-on fluorescent probe for the detection and bioimaging of hydrazine with barbituric acid as a recognition group

A novel turn-on fluorescent probe with barbituric acid as a unique recognition group has been rationally designed and synthesized using a facile method for detecting hydrazine.

A hepatocyte-targeting fluorescent probe for imaging isoniazid-induced hydrazine in HepG2 cells and zebrafish

A novel hepatocyte-targeting fluorescent N₂H₄ probe was first prepared. The probe can be used to image N₂H₄ produced by the hydrolysis of isoniazid in HepG2 cells and the liver of zebrafish in situ.

Twisted Schiff-base macrocycle showing excited-state intramolecular proton-transfer (ESIPT): assembly and sensing properties

A Schiff-base macrocyclic host showing ESIPT-based AIEE and nanoparticle assembly.

A selective and sensitive near-infrared fluorescent probe for in vivo real time tracking of exogenous and metabolized hydrazine, a genotoxic impurity

The hydrazine level in the liver and kidneys of mice after administration of isoniazid was monitored by using probe Hcy-DB.

Mechanistic insights into heavy metal ion sensing by NOS2-macrocyclic fluorosensors via the structure-function relationship: influences of fluorophores, solvents and anions

The sensing properties of heavy metal ions by macrocycle-based fluorosensors are sensitive not only to cation–receptors and cation–fluorophore interactions but also to cation–anion (endo/exo-coordination modes) and/or cation–solvent interactions.

New simple molecular fluorescent probes for rapid and highly selective sensing of hydrazine by aggregate-induced emission

A rapid, selective, and sensitive method is developed and employed in the detection of hydrazine in water and living cells.

A seminaphthorhodafluor-based near-infrared fluorescent probe for hydrazine and its bioimaging in living systems

Hydrazine (N₂H₄) has been classified as a potential carcinogen with its high toxicity, which can be readily absorbed through the skin or via breathing directly. Although some fluorescent probes have been developed for imaging of N₂H₄, very little can be used for imaging of N₂H₄ in vivo because of its short emission wavelength. In this study, a new colorimetric and near-infrared (NIR) fluorescent probe CF-1 based on a seminaphthorhodafluor dye was successfully designed and used for hydrazine determination. Upon reaction with N₂H₄, probe CF-1 showed obvious off-on NIR emission spectrum centered at 657 nm, as well as a distinct color change that can be distinguished by the naked eye. The results of fluorescence spectrum experiments indicated that probe CF-1 has high selectivity and low detection limitation (40.6 nM in the solution). Probe CF-1 has low cytotoxicity and was applied to imaging hydrazine in mitochondria of HeLa cells and in zebrafish.

Chelation of specific metal ions imparts coplanarity and fluorescence in two imidazo[1,2-a]pyridine derivatives: Potential chemosensors for detection of metal ions in aqueous and biosamples

Synthesis and chelation induced fluorescence emission from two imidazo[1,2-a]pyridine derivatives are described. The nonfluorescent molecule 1 containing N and O donor atoms, achieves coplanarity upon interactions with trivalent cations Al³⁺, Fe³⁺ and Cr³⁺, that favors fluorescence emission. Molecule 2 containing two N donor atoms attains coplanarity upon interaction with the only Zn²⁺ and becomes fluorescent. Both molecules 1 and 2 form a 1:1 complex with interacting metal ions. Other trivalent metal ions (including Bi³⁺ and In³⁺) and common divalent metal ions (including Hg²⁺ and Cd²⁺) fail to form any complex with 1 or 2, and they do not interfere in the detection of Zn²⁺, Al³⁺, Fe³⁺ or Cr³⁺ ions. Noninterference of other metal ions renders 1 and 2 suitable for the detection of fungal cells contaminated with Zn²⁺, Al³⁺, Fe³⁺ or Cr³⁺ ions.

Ratiometric Fluorescent Strategy for Localizing Alkaline Phosphatase Activity in Mitochondria Based on the ESIPT Process

Fluorescent probes are powerful tools for detecting and mapping the species of interest in vitro and in vivo. Although the probes always show high selectivity and sensitivity, they are usually affected by some factors, such as detecting conditions and the probe concentrations. Ratiometric fluorescent strategies, possessing advantage of low background noise, would solve the problem effectively and lead to a higher sensing performance. Thus, an ESIPT-based ratiometric probe (HBTP-mito) was developed on the basis of a phosphorylated 2-(2'-hydroxyphenyl)-benzothiazole derivative for the determination of ALP activity. HBTP-mito is water soluble and emits green fluorescence in TBS buffer due to the blockage of ESIPT. Upon the introduction of ALP, the phosphate ester of HBTP-mito was hydrolyzed and the ESIPT process was restored. Accordingly, the fluorescence at 514 nm decreases, while emission at 650 nm shows a "turn-on" response. The ratio of intensity (I_514nm/I_650nm) decreases linearly with ALP activity increasing from 0 to 60 mU/mL, obtained an LOD of 0.072 mU/mL. The favorable performance of the probe enables its application not only in the detection of ALP activity in biological samples, but also in the localization of the ALP levels in living cells and in vivo.

A coumarin-based fluorescent probe for ratiometric detection of hydrazine and its application in living cells

A new ratiometric fluorescent probe (1) was developed for the detection of hydrazine. The probe was obtained by incorporating the recognition moiety of acetyl group onto a coumarin fluorophore. Probe 1 displayed a distinct cyan emission in a 100% aqueous phosphate buffer solution. In the presence of hydrazine, probe 1 undergoes a hydrazinolysis process to release the coumarin fluorophore, which exhibited significant hypsochromic shifts in both absorption and emission spectra, and thus achieving a ratiometric response. This ratiometric probe is highly selective and sensitive towards hydrazine detection. The limit of detection (LOD) was calculated to be 34 nM. Moreover, cellular toxicity and imaging experiments suggested that probe 1 is can be used to monitor hydrazine in live cells.

Cd(II) enhanced fluorescence and Zn(II) quenched fluorescence with phenylenevinylene terpyridine: A theoretical investigation

Phenylenevinylene terpyridine (mepvpt) shows chelation enhanced fluorescence (CHEF) with Cd(II) and chelation quenched fluorescence (CHQF) with Zn(II), respectively. To understand the behaviors, we studied their intrinsic optical properties using DFT/TDDFT methods. The results show that fluorescence quantum yields (FQY) of mepvpt, mepvpt-Cd and mepvpt-Zn are low due to high ISC rates from higher excited states rather than the S₁ excited state. When mepvpt chelates Cd(II), the molecular structure becomes more planar and S_3,4 → S₀ radiation rates become higher than that of mepvpt, which results in CHEF. When mepvpt chelates Zn(II), a new S₄ → S₀ emission with low oscillator strength occurs and high S₄ → T_n ISC rates appear, which leads to CHQF. This proposed mechanism of metal fluorescence enhancing/quenching suggests a design strategy for single-molecular multi-analyte sensors.

A dual-excitation fluorescent probe EuIII-dtpa-bis(HBT) for hydrazine detection in aqueous solutions and living cells

The Eu^III-dtpa-bis(HBT) dual-excitation fluorescence probe has good selectivity and strong anti-interference ability for the detection of N₂H₄.

First-principles investigation of the double ESIPT process in a thiophene-based dye

Explanation of the experimental triple emission with theoretical tools requires advanced solvent models.

A hemicyanine-based fluorescent probe for hydrazine detection in aqueous solution and its application in real time bioimaging of hydrazine as a metabolite in mice

A fluorescent probe, Hcy-Ac, was developed for the monitoring of in situ hydrazine release during the metabolism of isoniazid.

Facile detection of organophosphorus nerve agent mimic (DCP) through a new quinoline-based ratiometric switch

Here a new quinoline-based (BIMQ) probe was developed which displayed ratiometric detection of organophosphorus chemical vapor threat, DCP.

An ESIPT based chromogenic and fluorescent ratiometric probe for Zn2+ with imaging in live cells and tissues

A benzothiazole based fluorescent probe for selective and efficient detection of Zn²⁺ showing potential application in human breast cancer cells.

An isophorone-based NIR probe for hydrazine in real water samples and hermetic space

The role of hydrazine in production is not to be underestimated due to its strong reducibility. However, every coin has two sides.

A dual-response sensor based on NBD for the highly selective determination of sulfide in living cells and zebrafish

A dual chemosensor, 1-NO₂, showing fluorogenic and colorimetric responses was developed for the detection of sulfide in vitro and in vivo.

A probe with double acetoxyl moieties for hydrazine and its application in living cells

As a common chemical reductant, hydrazine has been widely used in various fields. However, its high toxicity to human and environment have also attracted people's attention. In this work, a new fluorescence "turn-on" probe based on coumarin for hydrazine was successfully synthesized. The probe with double acetoxyl moieties as the reaction sites can obtain the detection limit as low as 2.98 nM for the detection of hydrazine in distilled water, which was lower than the U.S. Environmental Protection Agency standard (10 ppb). In addition, it also responded obvious fluorescence enhancement and high selectivity to hydrazine over other molecules. Furthermore, this probe could visualize the hydrazine in living cells.

A Highly Selective and Colorimetric Fluorescent Probe for Hydrazine Detection in Water Samples

A new highly selective and visible colorimetric fluorescent probe (probe 1) was developed to detect hydrazine (N₂H₄) concentration in real water samples. As different concentrations of N₂H₄ were added, the color of the probe solution was graded gradually from colorless to pink, which could be observed by the naked eye under UV light at 365 nm. Our research indicates that probe 1 offers a certain practical significance for use as a visible detection agent to detect N₂H₄ efficiently by distinct color response. Furthermore, our work showed that probe 1 can be successfully applied to detect N₂H₄ concentrations in real water samples.

Acid-Induced Shift of Intramolecular Hydrogen Bonding Responsible for Excited-State Intramolecular Proton Transfer

The significant progress recently achieved in designing smart acid-responsive materials based on intramolecular charge transfer inspired us to utilize excited-state intramolecular proton transfer (ESIPT) for developing a turn-on acid-responsive fluorescent system with an exceedingly large Stokes shift. Two ESIPT-active fluorophores, 2-(2-hydroxyphenyl)pyridine (HPP) and 2-(2-hydroxyphenyl)benzothiazole (HBT), were fused into a novel dye (HBT-HPP) fluorescent only in the protonated state. Moreover, we also synthesized three structurally relevant control compounds to compare their steady-state fluorescence spectra and optimized geometric structures in neutral and acidic media. The results suggest that the fluorescence turn-on was caused by the acid-induced shift of the ESIPT-responsible intramolecular hydrogen bond from the HPP to HBT moiety. This work presents a systematic comparison of the emission efficiencies and basicity of HBT and HPP for the first time, thereby utilizing their differences to construct an acid-responsive smart organic fluorescent material. As a practical application, red fluorescent letters can be written using the acid as an ink on polymer film.