Dicyanoisophorone-based near-infrared fluorescent probe with large Stokes shift for the monitoring and bioimaging of hypochlorite

Hypochlorite (ClO-), as one of reactive oxygen species (ROS), is closely linked to various illnesses and is essential for the proper functioning of immune system. Hence, monitoring and assessing ClO- levels in organisms are extremely important for the clinical diagnosis of ClO--related disorders. In this study, a novel ClO--selective fluorescent probe, DCP-ClO, was synthesized with dicyanoisophorone-xanthene unit as parent fluorophore, which displayed excellent selectivity towards ClO-, near-infrared emission (755 nm), large Stokes shift (100 nm), real-time response to ClO-, high sensitivity (LOD = 3.95 × 10-8 M), and low cytotoxicity. The recognition mechanism of DCP-ClO towards ClO- was confirmed to be a typical ICT process by HPLC-MS, HR-MS, 1H NMR and theoretical calculations. Meanwhile, DCP-ClO demonstrated remarkable efficacy in monitoring ClO- levels in water samples and eye-catching ability in imaging endogenous/exogenous ClO- in living organisms, which verified its potential as a powerful tool for the recognition of ClO- in complex biological systems.

Near-infrared Rhodols-based fluorescent probe with large Stokes shift for tracking of H2S in food spoilage and living cells

Hydrogen sulfide (H2S), as a biomarker signaling gas, is not only susceptible to food spoilage, but also plays a key function in many biological processes. In this work, an activated near infrared (NIR) H2S fluorescent probe was designed and synthesized with quinoline-conjugated Rhodols dye as fluorophore skeleton and a dinitrophenyl group as the responsive moiety. Due to the quenching effect of dinitrophenyl group and the closed-loop structure of Rhodols fluorophore, probe itself has a very weak absorption and fluorescence background signal. After the H2S-induced thiolysis reaction, the probe exhibits a remarkable colormetric change and NIR fluorescent enhancement response at 716 nm with large Stokes shift (116 nm), and possesses high sensing selectivity and sensitivity with a low detection limits of 330 nM. The response mechanism is systematically characterized by 1H NMR, MS and DFT calculations. The colorimetric change allows the probe to be used as a test strips to detect H2S in food spoilage, while NIR fluorescent response helps the probe monitor intracellular H2S.

A near-infrared fluorescence probe with large Stokes shift for selectively monitoring nitroreductase in living cells and mouse tumor models

Hypoxia is commonly regarded as a typical feature of solid tumors, which originates from the insufficient supply of oxygen. Herein, the development of an efficient method for assessing hypoxia levels in tumors is strongly desirable. Nitroreductase (NTR) is an overexpressed reductase in the solid tumors, has been served as a potential biomarker to evaluate the degrees of hypoxia. In this work, we elaborately synthesized a new near-infrared (NIR) fluorescence probe (MR) to monitor NTR activity for assessment of hypoxia levels in living cells and in tumors. Upon exposure of NTR, the nitro-unit of MR could be selectively reduced to amino-moiety with the help of nicotinamide adenine dinucleotide. Moreover, the obtained fluorophore emitted a prominent NIR fluorescence, because it possessed a classical "push-pull" structure. The MR displayed several distinguished characters toward NTR, including intense NIR fluorescent signals, large Stokes shift, high selectivity and low limit of detection (46 ng/mL). Furthermore, cellular confocal fluorescence imaging results validated that the MR had potential of detecting NTR levels in hypoxic cells. Significantly, using the MR, the elevated of NTR levels were successfully visualized in the tumor-bearing mouse models. Therefore, this detecting platform based on this probe may be tactfully constructed for monitoring the variations of NTR and estimating the degrees of hypoxia in tumors.

Nitrogen, sulfur-doped carbon quantum dots with large Stokes shift for real-time monitoring of pH in living cells

Construction of carbon quantum dots-based (CQDs) fluorescent probes for real-time monitoring pH in cells is still unsatisfied. Here, we propose the synthesis of nitrogen, sulfur-doped CQDs (N,S-CQDs) using one-pot hydrothermal treatment, and serve it as fluorescent probes to realize the real-time sensing of intracellular pH. These pH-responsive N,S-CQDs were proved exhibited a diversity of admirable properties, including great photostability, nontoxicity, favorable biocompatibility, and high selectivity. Particularly, due to the doping of nitrogen and sulfur, N,S-CQDs possessed long-wavelength emission and large Stokes Shift (190 nm), which could avoid self-absorption of tissue to realize high contrast and resolution bioimaging. The response of the probes to pH showed a good linear in range of 0.93-7.00 with coefficient of determination of 0.9956. Moreover, with advantages of high signal-to-noise ratio and stability against photobleaching, the as-prepared N,S-CQDs were successfully applied to monitor pH in living cells via bioimaging. All findings suggest that N,S-CQDs have significant potential for practical application for sensing and visualizing pH fluctuation in living systems.

A D-π-A-based near-infrared fluorescent probe with large Stokes shift for the detection of cysteine in vivo

D-π-A dyes are an ideal strategy for building near-infrared fluorescent probes that have a large Stokes shift due to their excellent properties of adjustable emission wavelength and Stokes shift. Developing a near-infrared (NIR) fluorescent probe (JTPQ-Cys) capable of detecting cysteine (Cys) was the aim of this study. In JTPQ-Cys, julolidine served as the electron donor (D) and quinoline as the electron acceptor (A), with 3,4-ethylenedioxythiophene as the π-bridge. The π-conjugation and vibrational/rotational activity of the molecule were increased by the introduction of 3,4-ethylenedioxythiophene, causing the molecule to exhibit NIR emission and a large Stokes shift. When JTPQ-Cys was used to detect Cys, a clear fluorescence turn-on signal was observed at 741 nm, together with a Stokes shift of 268 nm. The limit of detection of JTPQ-Cys for Cys is 24 nM. Moreover, JTPQ-Cys has been utilized successfully for imaging studies of Cys in cells and zebrafish because it has good photostability, low cytotoxicity, and a high signal-to-noise ratio. Overall, our findings demonstrate the potential of JTPQ-Cys to be one of the best choices for detecting Cys in biological systems, and JTPQ is an ideal fluorophore to construct fluorescence dyes for bioimaging.

An extra-large Stokes shift near-infrared fluorescent probe for specific detection and imaging of cysteine

Cysteine (Cys) plays a crucial role in numerous physiological and pathological processes. Therefore, it is imperative to design a highly selective and sensitive near-infrared (NIR) fluorescent probe to monitor Cys. In this study, we have developed a novel NIR fluorescent probe XA based on Xanthene hybrid tetrahydro-acridine salt dye for specifically tracking of Cys, where a chlorine-substituted tetrahydro-acridine acts as a high Cys-reactive site and water-soluble group. Probe XA exhibits a remarkable "turn-on" NIR emission (830 nm) with an extra-large Stokes shift (305 nm) for monitoring Cys. It also has a high selectivity, rapid response time (6 min) and high sensitivity (LOD as 0.5 μM). We fully characterized and discussed the sensing mechanism of XA toward Cys using HPLC and MS spectrums, as well as quantum theory calculations. Furthermore, the excellent properties of NIR fluorescent detection allow this novel probe to successfully monitor fluctuations of exogenous and endogenous Cys concentration levels in living cells and in vivo.

A series of fluorescent dyes based on 4-phenylacetylene-1,8-naphthalimide: Synthesis, theoretical calculations, photophysical properties and application in two-color imaging and dynamic behavior monitoring of lipid droplets and lysosomes

A series of fluorescent dyes (NapPAs) based on 4-phenylacetylene-1,8-naphthalimide were synthesized and characterized, whose conjugated structures were extended by the introduction of phenylethynyl. Furthermore, changes in the photophysical properties of the dyes when substituents with varying electron richness were introduced at the p-position of phenylacetylene were studied. The theoretical calculation of the dye molecules was carried out by B3LYP functional and 6-31G(d,p) basis set, and the effects of different substituents at the p-position of phenylacetylene on the electronic structure and photophysical properties of the dyes were studied by theoretical calculation results. Theoretical calculations provided a reliable means of predicting the properties of dyes, which could help in the design of more efficient and novel dyes. To verify the practicability of the dyes, two dyes with excellent photophysical properties (large Stokes shift, high polarity-viscosity sensitivity, good biocompatibility) were selected as fluorescent probes for visualization of LDs and two-color imaging of LDs and lysosomes. Cell imaging showed that NapPA-LDs and NapPA-LDs-Lyso serve as excellent imaging tools to monitor the dynamic changes, movements, and behaviors of LDs and lysosomes in real time. Notably, NapPA-LDs-Lyso held promise as a potential tool to study the interaction between LDs and lysosomes.

HClO imaging in vivo and drug-damaged liver tissues by a large Stokes shift fluorescent probe

Drug-induced liver injury (DILI), as a classic acute inflammation, has attracted widespread concern due to its unpredictability and severity. Among the various reactive oxygen species, HClO has been used as a marker for the detection of DILI process. Thus, we designed and synthesized a "turn-on" fluorescent probe FBC-DS by modifying 3'-formyl-4'-hydroxy-[1,1'-biphenyl]-4-carbonitrile (FBC-OH) with N, N-dimethylthiocarbamate group for sensitively sensing HClO. Probe FBC-DS showed a low detection limit (65 nM), fast response time (30 s), an enormous Stokes shift (183 nm) and 85-fold fluorescence enhancement at 508 nm in the detection of HClO. Probe FBC-DS could monitor exogenous and endogenous HClO in living HeLa cells, HepG2 cells and zebrafish. In addition, probe FBC-DS has been successfully utilized in biological vectors for imaging acetaminophen (APAP)-induced endogenous HClO. Moreover, DILI caused by APAP is evaluated by probe FBC-DS through imaging over-expression of endogenous HClO in the mice liver injury models. All in all, we have every reason to believe that probe FBC-DS can be a potential tool to study the complex biological relationship between HClO and drug-induced liver injury.

A near-infrared fluorescent probe with remarkably large stokes shift for specifical imaging of peroxynitrite fluctuations in Hela cells

Peroxynitrite (ONOO-), an endogenous reactive nitrogen species, plays an important role in maintaining intracellular homeostasis. Abnormal levels of ONOO- in cells could cause protein oxidation which is confirmed that related with Alzheimer's diseases, so accurate monitoring of ONOO- in cells is crucial. Herein, a novel fluorescent probe (XPC) based on dicyanomethylene-4H-benzothiopyran was developed by regulating its intramolecular charge transfer (ICT) effect to detect ONOO-. Once reaction with ONOO-, the fluorescence of XPC was turned on and the emission wavelength could reach up to 750 nm. Furthermore, XPC exhibited satisfactory performances for ONOO- such as large Stokes shift (200 nm), good sensitivity (Limit of detection = 13 nM), high selectivity to ONOO- over other a reactive nitrogen species (RNS)/reactive oxygen species (ROS). More importantly, XPC was successfully applied for monitoring the fluctuations of ONOO- in living cells.

γ-Glutamyltranspeptidase-Activated Near-Infrared fluorescent probe for visualization of Drug-Induced liver injury

Drug-induced liver injury (DILI), induced by overdose or chronic administration of drugs, has become the leading cause of acute liver failure. Therefore, an accurate diagnostic method for DILI is critical to improve treatment efficiency. The production of γ-glutamyltranspeptidase (GGT) is closely related to the progression of drug-induced hepatotoxicity. KL-Glu exhibits a prominent GGT-activated NIR fluorescence (734 nm) with a large Stokes shift (137 nm) and good sensitivity/selectivity, making it favorable for real-time detection of endogenous GGT activity. Using this probe, we evaluated the GGT up-regulation under the acetaminophen-induced liver injury model. Moreover, KL-Glu was successfully used to assess liver injury induced by the natural active ingredient triptolide and the effective amelioration upon treatment with N-acetyl cysteine (NAC) or Glutathione (GSH) in cells and in vivo by fluorescent trapping the fluctuation of GGT for the first time. Therefore, the fluorescent probe KL-Glu can be used as a potential tool to explore the function of GGT in the progression of DILI and for the early diagnosis and prognostic evaluation of DILI.

A Reaction-Based ESIPT Fluorescent Probe for the Detection of Hg2+ with Large Stokes Shift

A novel reaction-based fluorescent probe 1 for Hg2+ was designed and synthesized. 1 was almost nonfluoresent due to inhibition of the ESIPT process between hydroxy group and imid carbonyl oxygen by diphenylphosphinothioate group. After reacting with Hg2+, the fluorescence intensity of 1 exhibited significant enhancement owing to recovery of the ESIPT process via Hg2+-promoted desulfurization-hydrolysis of the diphenylphosphinothioate moiety and cleavage of the P-O bond. 1 not only showed rapid response, high sensitivity, excellent selectivity for Hg2+ over other metal ions, but also could detect Hg2+ with large Stokes shift (165 nm), which was attributed to the ESIPT process. Moreover, the reaction mechanism was fully validated by absorption spectra, fluorescence spectra, fluorescence color as well as ESI-MS analysis. 1 is the reaction-based ESIPT fluorescent probe for the detection of Hg2+ with large Stokes shift, rapid response, high sensitivity and selectivity.

3D dynamic tracking Aβ plaques in live brains using vinyl-bridged dyes with two-photon excitation/NIR emission and large Stokes shifts

Real-time studies of biomarkers for neurological disorders present significant opportunities for diagnosing and treating related diseases, and fluorescent probes offer a promising approach to brain imaging. However, intracerebral fluorescence imaging is often limited by blood-brain barrier permeability and penetration depth. Moreover, only very few probes have rapid intracerebral metabolic properties, which are critical for in vivo imaging. Here, we developed a novel class of fluorescent dyes with two-photon excitation and near-infrared (NIR) emission (920/705 nm). The representative WAPP-4 probe exhibits a large Stokes shift (Δλ = 324 nm in ethanol) and excellent blood-brain barrier permeability. Notably, using WAPP-4, we achieved in vivo 3D dynamic imaging of Aβ plaques in the brains of living mice with Alzheimer's disease (AD). In addition, super-resolution imaging showed that WAPP-4 could effectively characterize the distribution and shape of Aβ plaques in isolated brain slices. This study demonstrates that newly developed fluorescent dyes with large Stokes shifts and blood-brain barrier permeability enable real-time imaging of amyloid plaques, which will contribute to the development of other valuable tools for near-infrared imaging and super-resolution imaging in the brain.

A novel near-infrared fluorescent probe with large Stokes shift for imagining hydrogen sulfide

Hydrogen sulfide (H₂S) plays an important role in regulating varieties of important physiological and pathological processes. Thus the development of fluorescent probe for the detection of H₂S is of great significance and has attracted much attention recently. Herein, we reported a novel near-infrared (NIR) emitting fluorescent probe WFP-PC, which contained a positive charged hemicyanine-based WFP-OH as fluorophore and thiobenzoate unit as a specific reaction site. After treated with H₂S, the probe exhibited significant fluorescence enhancement and response time within 4 min and detection limit as low as 0.47 μM, accompanied by color changes from purple to blue. The probe was successfully applied to imaging the exogenous/endogenous H₂S in cells and mice, suggesting it could be a promising molecular tool for H₂S detection in living systems.

An aggregation induced emission chalcone fluorescent probe with large Stokes shift for biothiols detection

The homeostasis of biothiols is closely related to the health of organisms. In view of the important role of biothiols, a fluorescent probe (7HIN-D) for the detection of intracellular biothiols was developed based on a simple chalcone fluorophore 7HIN with "ESIPT + AIE" characteristics. The probe 7HIN-D was obtained by introducing a biothiols specific DNBS (2,4-dinitrobenzenesulfonyl) unit as a fluorescence quencher to the fluorophore 7HIN. The nucleophilic substitution reaction between biothiols and probe 7HIN-D will release the DNBS unit and the fluorophore 7HIN, which exhibits a "turn on" AIE fluorescence with a large Stokes shift of 113 nm. The probe 7HIN-D displays high sensitivity and good selectivity to biothiols, and the detection limits value of probe 7HIN-D for GSH, Cys and Hcy were 0.384 μmol/L, 0.471 μmol/L and 0.638 μmol/L, respectively. In addition, the probe has been successfully used for fluorescence detection of endogenous biothiols in living cells due to its excellent performance, good biocompatibility and low cytotoxicity.

A tetraphenylethene-based Schiff base AIEgen with a large Stokes shift as probe for highly sensitive and selective detection of aqueous Cu2+ ions and its application in cell imaging

In this work, an AIE-active tetraphenylethene-based Schiff base fluorescent probe 3 with a large Stokes shift (247 nm) was designed and synthesized. It was found that the aggregated probe 3 exhibited very high selectivity and anti-interference ability for Cu²⁺ in PBS buffer (70% f_w) through a fluorescence "turn-off" strategy. Job's plot and NMR analysis indicated the two phenolic hydroxyl groups of the benzene ring and the N atom (-CH=N-) on probe 3 interacted with Cu²⁺ ions in a 1:1 stoichiometric ratio. A comprehensive analysis of the Stern-Volmer and binding constant indicated a rather strong interaction between probe 3 and Cu²⁺ ions. Probe 3 illustrated excellent sensitivity toward Cu²⁺ under ppb level (4.5 nM) and achieved more than 95% recovery in river, lake and tap water toward estimation of Cu²⁺ ions in the analytical applications. Moreover, probe 3 was able to realize bioimaging of HepG2 cells and be quenched by intracellular Cu²⁺ ions, making it promising as a sensitive Cu²⁺ sensor for organisms.

An edoplasmic reticulum-targeted NIR fluorescent probe with a large Stokes shift for hypoxia imaging

Hypoxia is closely linked to various diseases, including solid tumors. The level of nitroreductase (NTR) is usually abnormally upregulated in hypoxic conditions, which can be a biomarker of hypoxia. Herein, the first endoplasmic reticulum-targeting NIR fluorescent probe, ISO-NTR, was developed for highly selective and sensitive detection of NTR. It shows a large Stokes shift (185 nm) and a 5-fold increases in fluorescence intensity. Meanwhile, the ISO-NTR probe with a dicyanoisophorone derivative has excellent endoplasmic reticulum targeting in living systems with high Pearson's correlation coefficients (R_r = 0.9489). Molecular docking calculations and high binding energy between the probe and NTR (-10.78 kcal·mol^-1) may explain the high selectivity of ISO-NTR. Additionally, it has been successfully applied to NTR imaging in vitro and vivo due to its good sensitivity, high selectivity and large Stokes shift, which may provide an effective method for studying the physiological and pathological functions of NTR in living systems. This probe could be developed as a potential imaging tool to further explore the pathogenesis of hypoxia-related diseases in endoplasmic reticulum stress.

Novel red light-emitting two-photon absorption compounds with large Stokes shifts for living cell imaging

Three novel donor-π-acceptor two-photon absorption compounds (1PZPy, 2PZIm, 3CZPy) bearing the 10-butyl-10H-phenothiazine (9-butyl-9H-carbazole) donor, the pyridinium (benzimidazolium) acceptor, and the 2,5-divinylthiophene π-bridge were synthesized and fully characterized by ¹H NMR, ¹³C NMR, FT-IR, and HRMS. The linear and nonlinear photophysical properties were systematically investigated. Their absorption properties show a strong solvent dependence, while the emission properties are nearly independent of solvent polarity. All of them possess large Stokes shifts (Δλ=149-190 nm in H₂O). 1PZPy and 3CZPy exhibit red fluorescence emission centered at about 635 and 660 nm, respectively. The two-photon absorption cross-sections measured by the open aperture Z-scan technique are determined to be 486 (1PZPy), 601 (2PZIm), and 753 GM (3CZPy) in DMF. The density functional theory calculations were further carried out to reveal their electronic structures. All the target compounds are verified to have low cytotoxicity in the working solution and good capability for one- and two-photon excitation fluorescence imaging, suggesting their potential application in bioimaging. Moreover, they show the organelle targeting ability in living cells with the high Pearson's coefficients above 0.94 for the endoplasmic reticulum.

A red-emitting Europium(III) complex as a luminescent probe with large Stokes shift for the sequential determination of Cu2+ and biothiols in real samples

In this work, a novel Eu³⁺-DTPA-bis(AMC) complex with red luminescence was designed and synthesized for sequential detection of Cu²⁺ and biothiols (Cys/Hcy/GSH) based on the displacement strategy with the good selectivity, high sensitivity, and large Stokes shift (288 nm). The possible detection mechanism was verified by UV-vis, the high-resolution mass spectrometry, and the fluorescence decay curve. The experimental parameters, including the solution pH, the incubation time, the concentration ratio of Eu³⁺-DTPA-bis(AMC) to Cu²⁺ and biothiols concentration, were optimized. Under the optimal conditions, it shows a good linear relationship between the concentration (0-10 μM) of Cu²⁺ and the fluorescence intensity of Eu³⁺-DTPA-bis(AMC), with a low detection limit of 0.065 μM. The linear range and the limit of detection of the Eu³⁺-DTPA-bis(AMC)/Cu²⁺ system for Cys/Hcy/GSH were 2.5-22.5/5-45/5-50 μM and 0.11/0.07/0.05 μM, respectively. Surprisingly, the high or low concentration of Eu³⁺-DTPA-bis(AMC)/Cu²⁺ can significantly affect the selectivity of the sensing system to biothiols (Cys/GSH/Hcy). When the concentration of the Eu³⁺-DTPA-bis(AMC)/Cu²⁺ system is 10.0 μΜ, it could recognize biothiols (Cys/GSH/Hcy) from other substances, but when the concentration is as low as 3.3 μM, it could further specifically distinguished Cys from Hcy/GSH. Owing to the high anti-interference characteristics, accuracy and specificity, the sensing system was well applied to the cascade detection of Cu²⁺ in actual environmental samples and Cys in biological and food samples, including FBS, urine, milk, beverage, fresh juice with the satisfactory recoveries from 96.20 to 106.80 %.

Development of a NIR iridium(III) complex for self-calibrated and luminogenic detection of boron trifluoride

Boron trifluoride (BF3) is a potential environmental pollutant, and excess exposure to it may cause human diseases. However, the sensitive, rapid and accurate detection of BF3 for on-site purposes is still a challenge. In this work, we developed the first NIR iridium(III)-based probe with dual emission and a Stokes shift of 370 nm for self-calibrated and luminogenic detection of BF3. This probe exhibited a strong luminescence enhancement at around 650 nm to BF3 (0-100 μM) with almost no change in luminescence at 475 nm, displaying a 220-fold I650 nm/I475 nm enhancement at 100 μM of BF3 with a detection limit of 0.35 μM. Moreover, the probe showed a fast response time of less than 5 s to BF3 along with an obvious color change under UV irradiation for visual detection. Importantly, the desirable photophysical properties of the iridium(III)-based probe can be harnessed for time-resolved detection of BF3 in the presence of the fluorescence background. The applicability of the probe was further verified in an organic solvent waste-spiked system and on a glass pane. This work will provide a solid basis for the development of sensitive and on-site BF3 sensing toolkits for environmental monitoring.

A red-emissive benzothiazole-based luminophore with ESIPT and AIE natures and its application for detecting and imaging hypochlorous acid

A new "ESIPT + AIE" based dye of benzothiazole with red emission and a large Stokes shift was constructed by combining 2-(2'-hydroxyphenyl)benzothiazole as the ESIPT unit and α-cyanostilbene as the AIE unit. The compound BACN was found to be a ideal HClO chemosensor, and presented palpable fluorescence and colorimetric responses toward HClO via the HClO-trigged oxidation cleavage of the ethylene bridge activated by the electron withdrawing cyano group. BACN was capable of recognizing HClO rapidly (12 s) and sensitively under physiological conditions, with good selectivity over other biologically pertinent substances. Thanks to strong red emission (λ_em = 606 nm) and large Stokes shift (213 nm) resulted from the combination of ESIPT and AIE effects, it was successfully utilized for the recognition of exogenous and endogenous HClO in living HeLa cells.

Coumarin-based turn-on fluorescence probe with a large Stokes shift for detection of endogenous neutrophil elastase in live cells and zebrafish

Neutrophil elastase (NE), a serine proteinase, is a significant biomarker which is closely related to the progress of diseases. However, only few probes have been reported for detection of NE activity and cell imaging. And these probes have exhibited small Stokes shift, which leads to high fluorescence interferences. Furthermore, only one probe among them is able to image NE in vivo successfully. To overcome the above problems, we designed a novel coumarin-based fluorescent probe HNCOU-NE with large Stokes shift to visualize NE activity in living cells and zebrafish. The new probe HNCOU-NE for NE contains fluorophore HNCOU as the reporter and pentafluoroethyl as the enzyme-active trigger moiety. As expected, HNCOU-NE displays perfect detecting performance for sensing of NE, including good water solubility, large Stokes shift, high affinity and wide linear response concentration. In addition, HNCOU-NE has been successfully utilized for NE real-time detection and imaging in different living cells, exhibiting low cytotoxicity and excellent biocompatibility. Most importantly, endogenous NE fluorescence imaging experiments reveals that HNCOU-NE can distinguish liver cancer cells (HepG2) and other cells (293T, HeLa and SKOV3), illustrating its specific ability to diagnose liver cancer cells. Besides, probe HNCOU-NE also has the ability to specifically detect endogenous NE activity in living zebrafish. All the results indicate that HNCOU-NE is a valuable probe for qualitative and quantitative sensing of NE activity in vitro and in vivo.

Construction of novel coumarin-carbazole-based fluorescent probe for tracking of endogenous and exogenous H2S in vivo with yellow-emission and large Stokes shift

Recent medical studies have confirmed that endogenous H₂S serves as the third gas-messenger besides nitric oxide (NO) and carbon monoxide (CO), which is produced by enzyme-catalyzed metabolism of cysteine and takes part in multiple physiological processes. The abnormal levels induced by H₂S overproduction in mammals can destroy tissues and organ systems, which lead to certain serious diseases, such as neurodegenerative diseases, cardiovascular diseases, and various cancers. In this work, we developed a novel coumarin-carbazole fluorescent probe COZ-DNB with yellow emission and a large Stokes shift for H₂S detection. In probe COZ-DNB, the newly dye COZ-OH as a luminophore and the 2,4-dinitrophenyl ether moiety was chosen as a trigger group for H₂S. Probe COZ-DNB itself displayed nearly non-fluorescent. However, COZ-DNB gave the remarkable fluorescence with an 83-fold enhancement in the yellow region after interaction with H₂S. The sensing mechanism of COZ-DNB toward H₂S was checked by means of UHPLC, HRMS and DFT/TD-DFT calculations. What's more, probe COZ-DNB also exhibited fast response (2.0 min), high sensitivity (65.0 nM), a large Stokes shift (161.0 nm), high stability and excellent selectivity. Furthermore, COZ-DNB was applied for imaging of exogenous and endogenous H₂S in living HeLa cells and zebrafish with satisfactory performances. We anticipate COZ-DNB would be served as a potential tool for investigating the biological functions of H₂S in pathological processes.

A novel cysteine fluorescent probe with large stokes shift for imaging in living cells, zebrafish and living mice

The small molecule biological thiols, such as Cysteine (Cys), homocysteine (Hcy), and glutathione (GSH), play crucial roles in maintaining various cellular vital activities. In the organism, abnormal levels of small-molecule biological thiols have been associated with a variety of diseases. Therefore, quantitative determination of biological thiols, especially Cys, is significant for understanding their functions in various biological processes. Thus, in this work we designed a new fluorescent probe Ty-Cys1 with a large Stokes shift of 207 nm to monitor Cysteine. The maximum absorption wavelength of Ty-Cys1 was 418 nm, and the maximum emission wavelength was 625 nm. Significantly, the novel probe Ty-Cys1 was effectively in detecting of Cys changes in living cells, zebrafishes, and living mice.

A NIR fluorescence probe for monitoring Cys upregulation induced by balsam pear polysaccharide and imaging in zebrafish

In this work, we introduced the acrylate recognition group into dicyanoisophorone derivative DCI-C-OH to construct the NIR fluorescent probe DCI-C-Cys with a large Stokes shift (240 nm). DCI-C-Cys could specifically respond to Cys, resulting in a 22-fold increase in fluorescence intensity at 702 nm. Meanwhile, the probe has the advantages of good water solubility, high sensitivity (93 nM), and excellent biocompatibility. Moreover, DCI-C-Cys successfully monitored endogenous and exogenous Cys in HepG2 cells and zebrafish. Most importantly, we found that balsam pear polysaccharide could lead to the increase of intracellular Cys levels, which might be conducive to the further study of the antioxidant mechanism of balsam pear polysaccharide.

A ratiometric fluorescent probe with large Stokes shift and emission shift for sensing hydrazine in living organisms

As a highly toxic reagent, hydrazine (N₂H₄) is notorious to human beings and the environment. To simply and conveniently detect N₂H₄ in environmental and biological systems, a ratiometric fluorescent probe MA-N₂H₄ was developed with excellent sensitivity and selectivity. Probe MA-N₂H₄ was readily prepared based on a naphthalene as the fluorescent scaffold and an indanedione group as the responsive moiety for N₂H₄. This probe displayed a red-emitting fluorescence at 670 nm with a large Stokes shift (200 nm). After treatment with N₂H₄, a significant blue-shifted emission at 440 nm could be observerd, which led to an extremely large emission wavelength shift (230 nm). The fluorescent intensity ratio (I₄₄₀/I₆₇₀) of probe MA-N₂H₄ was rapidly and significantly increased (273-fold) within 18 min. The detection limit for N₂H₄ was 0.5 µM. In addition, the probe was successfully employed for tracking N₂H₄ in living cells and zebrafish through a ratiometric manner.

Development of a ratiometric fluorescent probe with large Stokes shift and emission wavelength shift for real-time tracking of hydrazine and its multiple applications in environmental analysis and biological imaging

As a tremendously noxious and extensively utilized chemical reagent, hydrazine (N₂H₄) has become a serious threat to ecosystem and human health. Thus, it is desirable to exploit an efficient method for real-time tracking of hydrazine. Here, a novel ratiometric fluorescent probe PBQ-AB for hydrazine was rationally constructed from isolongifolanone. This probe displayed an extremely large Stokes shift of 230 nm and could selectively recognize hydrazine in the presence of other competitive species within an extremely short time ( 40 s). PBQ-AB also displayed some fascinating merits in the detection of hydrazine, including low detection limit (48 nM), wide pH range (5-12), excellent photostability (>240 min), and well-resolved emission wavelength shift (148 nm). Moreover, this probe was utilized to fabricate a ready-to-use electrospinning nanofibrous membrane for convenient detection of hydrazine vapor by virtue of smartphone. Furthermore, PBQ-AB was capable of determining hydrazine contaminant in environmental soil and water samples. Additionally, its favorable performance for detecting hydrazine was successfully demonstrated in live HeLa cells as well as in live Arabidopsis thaliana tissues, manifesting its promising application for labeling hydrazine in living systems. Therefore, we believed that this probe has great potential in environmental analysis and health supervision.

Probe with large Stokes shift for effective cysteine imaging in living cells

A new fluorescence probe L, which featured with a large Stokes shift (216 nm), was designed for sensitive detection of cysteine (Cys) and a potential sensing mechanism derived from excited state intramolecular proton transfer (ESIPT) was proposed. More importantly, probe L exhibits higher selective to Cys than other amino acid due to its specific cyclization between acrylate group and Cys. Meanwhile, the probe L shows a low detection limit of 8.82 × 10^-8 M, which is enough for detecting Cys in organisms. Furthermore, this probe displays high biocompatibility and can image Cys in living cells.

A near-infrared fluorescent probe with large Stokes shift for imaging Cys in tumor mice

Cysteine (Cys), a kind of small molecule biological thiol, not only involves in the regulation of physiological processes, but also is considered a marker of tumor. However, it is challenging to develop suitable probe for detecting Cys in tumors. In this paper, a near-infrared (NIR) fluorescent probe named IX for Cys has been designed and synthesized. The probe shows a NIR emission peak at 770 nm with large Stokes shift (180 nm) upon adding Cys. It displays high sensitivity to Cys with 6-fold increase of fluorescence intensity. Meanwhile, IX has the high selectivity to Cys over other potential interference such as Hcy and GSH, which have similar structure with Cys. In addition, a possible mechanism of fluorescence enhancement is the reaction of IX with Cys to release IX-OH, which is verified by fluorescence spectra, MS and HPLC. Next, IX can selectively image Cys in HCT-116 cells thanks to the low cytotoxicity. Most important of all, the fluorescent probe IX has visualized Cys in HCT116-xenograft tumor mice due to the near-infrared properties with large Stokes shift.

Near-infrared fluorescent probe with large stokes shift for detecting Human Neutrophil elastase in living cells

Human Neutrophil elastase (HNE) plays a great role in immune responses and inflammation, and is associated closely with lung cancer and acute lung injury (ALI). Accurate detection of its activity is imperative to understand its biological function and diagnosing the disease states through monitoring the dynamic changes. Herein, we report a new NIR fluorescent probe (F-1) with large Stokes shift (182 nm). Probe F-1 featured high sensitivity (LOD ~ 5.6 ng/mL), good selectivity, low toxicity and a bright NIR emission triggered by HNE. Moreover, F-1 was successfully applied as an indicator to track the HNE in the A549 cells. Thus, F-1 may be an excellent tool for detecting enzymatic activity for preclinical applications and NE related diseases.

In-vitro and in-vivo monitoring of gold(III) ions from intermediate metabolite of sodium aurothiomalate through water-soluble ruthenium (II) complex-based luminescent probe

Real-time monitoring of drug metabolism in vivo is of great significance to drug development and toxicology research. The purpose of this study is to establish a rapid and visual in vivo detection method for the detection of an intermediate metabolite of the gold (I) drug. Gold (I) drugs such as sodium aurothiomalate (AuTM) have anti-inflammatory effects in the treatment of rheumatoid arthritis. Gold(III) ions (Au³⁺) are the intermediate metabolite of gold medicine, and they are also the leading factor of side effects in the treatment of patients. However, the rapid reduction of Au³⁺ to Au⁺ by thiol proteins in organisms limits the in-depth study of metabolism of gold drugs in vivo. Here we describe a luminescence Au³⁺ probe (RA) based on ruthenium (II) complex for detecting Au³⁺ in vitro and in vivo. RA with large Stokes shift, good water solubility and biocompatibility was successfully applied to detect Au³⁺ in living cells and vivo by luminescence imaging, and to trap the fluctuation of Au³⁺ level produced by gold (I) medicine. More importantly, the luminescent probe was used to the detection of the intermediate metabolites of gold (I) drugs for the first time. Overall, this work offers a new detection tool/method for a deeper study of gold (I) drugs metabolite.

Novel near-infrared fluorescence probe with large Stokes shift for monitoring CCl4-induced toxic hepatitis

Toxic hepatitis which is induced by chemical substance is a serious threat to human health. More and more studies have shown that peroxynitrite (ONOO^-) is related with the development of toxic hepatitis. So it is important to find a tool to study ONOO^- change during the diagnosis and therapy of toxic hepatitis. Herein, a series of novel near-infrared (NIR) fluorescence dyes (DDM-R) with long emission wavelength (740-770 nm) and large Stokes shift (~200 nm) are developed. Among the dyes, DDM-OH with great spectral performance and facilely modified feature is used to construct probe DDM-ONOO^-. The probe have the preference of high sensitivity and excellent selectivity for ONOO^-. In addition, DDM-ONOO^- was applied in detecting exogenous and endogenous ONOO^- in cells and further used in detecting ONOO^- of CCl₄-induced toxic hepatitis in cells by fluorescence imaging, 3D quantification analysis, flow cytometry. More importantly, by visualizing ONOO^-, the probe was used to monitor the diagnosis of CCl₄-induced toxic hepatitis in mice and evaluate the therapeutic efficacy of hepatoprotective medicines (NAC, SM, DDB). The results show that the probe will provide a powerful tool for the diagnosis and treatment of toxic hepatitis.

A near-infrared fluorogenic probe with fast response for detecting sodium dithionite in living cells

Developing a reliable fluorescence probe is crucial for accurately monitoring sodium dithionite (Na₂S₂O₄, SDT) in biosystems, but the current reported azo-based ones suffers from short excitation/emission wavelengths and relative slow response speed. To address this issue, we herein present a novel near-infrared emissive fluorescence probe for SDT, namely DCM-MQ, consisting of a dicyanomethylene-benzopyran fluorogenic reporter and a 1-methylquinolinium as recognition moiety. On the basis of the specific reduction mechanism, DCM-MQ exhibited a rapid colorimetric and fluorescent recognition for SDT (less than 3 s) with large Stokes shift (112 nm) and high sensitivity (detection limit was 19 nM). The fluorescence imaging results demonstrate that DCM-MQ is competent for monitoring SDT in living systems.

A near-infrared fluorescent probe for hydrogen polysulfides detection with a large Stokes shift

Due to the crucial biological roles of hydrogen polysulfides (H₂S_n) in living systems, the selective determination of H₂S_n is essential. In this work, we reported a turn-on fluorescent probe, JSI-Sn, for H₂S_n with high sensitivity and good selectivity. Probe JSI-Sn displayed a near-infrared emission (λ_max^Em = 701 nm) and a large Stokes shift (123 nm) in the presence of H₂S_n in solution. Using probe JSI-Sn as an indispensable tool, the monitoring of intracellular H₂S_n in living cells and zebrafish were realized.

A dicyanoisophorone-based highly sensitive and selective near-infrared fluorescent probe for sensing thiophenol in water samples and living cells

Thiophenol (PhSH) is an important sulfhydryl compound in organic synthesis, but it is also a volatile environmental pollutant with high toxicity to organisms. Herein, we reported a novel near-infrared (NIR) probe (1) for turn-on fluorescence detection of PhSH. The probe was prepared by coupling 2,4-dinitrophenyl (DNP) to a dicyanoisophorone-based fluorophore (2). PhSH can specifically perform a nucleophilic aromatic substitution on probe 1 and result in the release of fluorophore 2, thus achieving a turn-on fluorescence response (λ_em = 693 nm). A dramatic color change from red (λ_abs = 525 nm) to blue (λ_abs = 668 nm) was also observed. This fluorescent assay displayed a large Stokes shift (∼133 nm) and a high sensitivity for PhSH, as well as a low detection limit (34 nM). Moreover, probe 1 was successfully applied to monitor PhSH in real water samples and image PhSH in living cells.

A pyrene-based ratiometric fluorescent probe with a large Stokes shift for selective detection of hydrogen peroxide in living cells

Hydrogen peroxide (H₂O₂) plays a significant role in regulating a variety of biological processes. Dysregulation of H₂O₂ can lead to various diseases. Although numerous fluorescent imaging probes for H₂O₂ have been reported, the development of H₂O₂ ratiometric fluorescent probe with large Stokes shift remains rather limited. Such probes have shown distinct advantages, such as minimized interference from environment and improved signal-to noise ratio. In this work, we reported a new pyrene-based compound Py-VPB as H₂O₂ fluorescent probe in vitro. The probe demonstrated ratiometric detection behavior, large Stokes shift and large emission shift. In addition, the probe showed high sensitivity and selectivity towards H₂O₂ in vitro. Based on these excellent properties, we successfully applied Py-VPB to the visualization of exogenous and endogenous H₂O₂ in living cells. Cell imaging study also showed that our probe was localized in the mitochondria. We envision that the probe can provide a useful tool for unmasking the biological roles of mitochondrial H₂O₂ in living systems.

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The first pyrene-based fluorescent probe for H₂O₂ detection with ratiometric readout was presented.

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The probe has shown prominent properties in detecting H₂O₂, such as high sensitivity & selectivity and large Stokes shift.

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The probe was successfully applied to visualizing exogenous and endogenous H₂O₂ in living cells.

Synthesis of a far-red emitting flavonoid-based lysosome marker for live cell imaging applications

A bright far-red emitting flavonoid derivative (FuraET) was synthesized in good yields by inserting a π extension group (i.e., furan) into the flavonoid skeleton, via using the Suzuki-Miyaura cross-coupling reaction. FuaraET exhibited optical absorption at λ_ab ≈ 450 nm and emission λ_em ≈ 660 nm by recognizing as the first far-red emitting flavonoid derivative reported. FuraET exhibited a large Stokes shift (Δλ > 150 nm) high fluorescent quantum yield (φ_fl ≈ 0.2-0.4), and good photostability indicating excellent characteristics for an imaging probe. Live cell fluorescent confocal microscopy imaging revealed the exceptional selectivity of the FuraET towards cellular lysosomes (Mander's overlap coefficients >0.9). The observed non-alkalinizing nature and high biocompatibility (LC₅₀ > 50 µM) suggested that FuraET can a reliable lysosome marker for live cell imaging experiments. Our further study also indicated that FuraET may likely internalized into hydrophobic regions of the cellular lysosomes in contrast to acidic lysosomal lumen.

Two 8-hydroxyquinoline-based fluorescent chemosensors for ultra-fast and sensitive detection of water content in strong polar organic solvents with large Stokes shifts

It is of great significance to detect the moisture in organic solvents before used in water-sensitive reactions. Herein, two Schiff base quinoline derivatives, 8-hydroxyquinoline-2-carboxaldehyde thiosemicarbazone (HQCT) and 8-hydroxyquinoline-2-carboxaldehyde (pyridine-2-carbonyl)-hydrazine (HQPH), were designed and synthesized by a simple one-step reaction, and used as fluorescent chemosensors for ultra-fast and sensitive detection of water content in strong polar organic solvents. Based on excited-state intramolecular proton transfer (ESIPT) process, HQCT and HQPH exhibited strong fluorescence emissions with large Stokes shifts in dimethyl sulfoxide (DMSO) and N, N-dimethylformamide (DMF) solvents compared to other various organic solvents, and their fluorescence quenching and fluorescent color changes were obviously observed with increasing water content. The experimental results revealed that the hydroxyl groups substituted at the 8-position of HQCT and HQPH played a key role in the fluorescence emission processes. Dynamic light scattering (DLS) and ¹H NMR titration indicated that the sensing mechanism for the detection of water was based on inhibition of the ESIPT by H₂O via forming hydrogen bonds. In the range of 0.0-1.8 wt%, the fluorescence intensity of chemosensors changed as a linear function of water content. The detection limits of water in DMSO by HQCT and HQPH were as low as 0.0220 wt% and 0.0274 wt%, respectively. Moreover, HQCT and HQPH are successfully applied for the detection of moisture content in real commercial organic solvents.

Dimethylamino naphthalene-based fluorescent probes for hydrogen sulfide detection and living cell imaging

Hydrogen sulfide shows great importance in various physiological and biochemical processes. The development of fluorescence probes for facile and efficient detection of H₂S has attracted increasing attention of researchers. Herein, we synthesized two fluorescence probes based on simple naphthalene structure for detection of H₂S. Upon reaction with H₂S, the probe DN-DM exhibited a red fluorescence emission with large Stokes shift. The probe showed high sensitivity, pH insensitivity and good selectivity for H₂S over other analytes including common biothiols. The detection mechanism was based on the thiolysis of the dinitrophenyl ether moiety, which was confirmed by ¹H NMR spectral analysis. The DFT calculation was also performed for a deeper understanding of the photophysical properties. In addition, these probes showed good cell-membrane permeability and could be utilized for detection of H₂S in living cells.

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.

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.

Imidazo[1,5-α]pyridine-based fluorescent probe with a large Stokes shift for specific recognition of sulfite

By taking advantage of the intramolecular charge transfer (ICT) process, we presented a novel fluorescent probe IPY-SO₂ based on imidazo[1,5-α]pyridine derivative for detecting SO₃^2- with a low detection limit (70 nM). Combining its favorable turn-on fluorescence feature (75-fold), rapid response (5 min), high selectivity, large Stokes shift (174 nm) and low cytotoxicity, IPY-SO₂ was successfully applied to imaging SO₃² in living MCF-7 cells and zebrafish.

A novel gold nanocluster-based fluorometric biosensor for measuring prooxidant activity with a large Stokes shift

A chicken egg white protein-protected gold nanocluster (CEW-AuNC) based fluorogenic biosensor, where protein was used as both reducing and protecting agent, was developed to determine the Cu(II)-induced prooxidant activity of natural antioxidants abundant in food and biological samples. Gold nanoclusters, prepared using egg white proteins, exhibited strong fluorescence. The prooxidant activity of the tested antioxidants was indirectly measured by their reducing action on Cu(II) to Cu(I), and the reduced cuprous ion was bound to the thiol groups in the CEW-AuNC structure, causing a decrease in fluorescence intensity. Epicatechin, catechin, epigallocatechin gallate, morin, rutin, quercetin, gallic, chlorogenic, and rosmarinic acids, glutathione, cysteine, N-acetyl cysteine, bilirubin, resveratrol, and α-tocopherol were studied as natural antioxidants. A fluorometric method showing a large Stokes shift with excitation/emission maxima at 360∕640 nm was developed to sensitively measure the decrease in the fluorescence of CEW-AuNC associated with the binding of copper(I) to the protein structure. Total prooxidant activities of the binary, ternary, and quaternary synthetic mixtures and of some food and synthetic serum samples were determined. The biosensor response was statistically compared to that of its spectrophotometric counterpart. This method can be used for the control of the oxidative stability of foods with a prolonged shelf life.

A red-emitting fluorescent probe with large Stokes shift for real-time tracking of cysteine over glutathione and homocysteine in living cells

Fluorescent probes with high quality for highly selective detection of cysteine (Cys) are still urgently in demand because of the indispensable roles Cys plays in the biological systems. Herein, a red-emitting fluorescent probe CP was developed for the highly selective detection of Cys over glutathione (GSH) and homocysteine (Hcy) by incorporating acryloyl group as the recognition unit into the 2-(2-(4-hydroxystyryl)-6-methyl-4H-pyran-4-ylidene) malononitrile (P-OH) fluorophore which is characterized by red emission, noteworthy Stokes shift, and appreciable photostability. Basically, CP demonstrated appreciable sensing performance toward Cys including short response time of 4 min, high sensitivity with approximately 147-fold emission enhancement, low detection limit of 41.696 nM, and good selectivity both in the solution and living cells, indicating its promising potential of visualizing Cys in biological systems.

Bright red-emitting highly reliable styryl probe with large Stokes shift for visualizing mitochondria in live cells under wash-free conditions

Bright red-emitting pyridinium cyanine based styryl probe 2 is synthesized in good yields. Probe 2 demonstrated a large Stokes' shift (Δλ ≈ 128 nm, 4227 cm^-1 in DCM) and excellent fluorescent quantum yield (ϕ_fl ≈ 0.2 - 0.7) due to strong Intra-molecular charge transfer (ICT). Probe 2 found to exhibit exceptional selectivity for cellular mitochondria in both normal (COS-7) and cancer (A549) cell lines. Probe 2 is readily applicable as a "wash-free" dye to visualize mitochondria as it does not require post-staining washing prior to imaging. Styryl probe 2 also showed an excellent biocompatibility as the calculated LC₅₀ (lethal concentration, 50%) value was > 20 μM. Probe 2 emission did not show any interferences from anionic species or other biological molecules. Probe 2 is readily excitable (λ_ex ∼460 and λ_em ∼618 nm) with the available laser (454 nm) in commercial microscopes and thus it can be a useful probe for mitochondrial tracking in live cells.

A near-infrared fluorescent probe for imaging endogenous carbon monoxide in living systems with a large Stokes shift

Near-infrared (NIR) fluorescent probes with a large Stokes shift are very practical tools for bioimaging applications. Carbon monoxide (CO) is a key gaseous signal molecule and its imaging in living systems has attracted great attention in recent years. In this work, a very easy-to-get NIR fluorescent probe with a remarkable large pseudo-Stokes shift (238 nm) for detection of CO was reported. This probe was found to show a rapid NIR fluorescent turn-on response for CO with high selectivity, high sensitivity and a low detection limit (38 nM). Moreover, imaging CO in living cells and animals with this probe was successfully applied with a high signal-to-noise ratio. The results indicate that this probe can be used as a new practical tool for imaging of endogenous CO in living systems.

A novel ratiometric and reversible fluorescence probe with a large Stokes shift for Cu2+ based on a new clamp-on unit

A novel ratiometric and reversible chemosensor 4-((2-(Benzo[d]thiazol-2-yl)phenyl)ethynyl)-N,N-diethylaniline (BT-1) based on ortho-arylethynyl benzothiazole with large Stokes shift (Δλ≈190 nm) was designed and synthesized to recognize Cu²⁺. Copper ion induces a remarkable fluorescence enhancement and causes formation of a BT-1-Cu complex. The clamp-on coordination mode of BT-1 to Cu²⁺ was demonstrated using Job's plot, mass spectrum (MS) and DFT calculations. The calculations also indicate that Cu²⁺ was chelated to BT-1 through N and alkyne instead of S and alkyne. The probe could quantify Cu²⁺ with the detection limit of 3.2 × 10^-9 M. The in vitro imaging results indicated that the probe BT-1 was membrane-permeable and could be applied into the recognition of Cu²⁺ ions in living cells.

Effect of substituents on Stokes shift of BODIPY and its application in designing bioimaging probes

BODIPY-based probes have excellent fluorescence properties. However, small Stokes shifts approximately 5-15 nm greatly affect their detection sensitivity. In this study, we compared the Stokes shifts of reported BODIPY-based probes with various of substituents, and found that the phenyl groups on the specific position of BODIPY core could expand the Stokes shift of BODIPY-based probes, and methoxy groups on these phenyl substituents could enhance such effects. Then, by quantum chemical calculations, we found that the number of methoxy groups might also have obvious effect on the Stokes shift of BODIPY. Taking nitric oxide (NO) as analyte, 4,4-difluoro-8-(3,4-diaminophenyl)-3,5-bis(2,4-dimethoxyphenyl)-4-bora-3a,4a-diaza-s-indancene (DMOPB) with diaminophenyl substituents has been designed and synthesized. Compared with monomethoxy-phenyl substituted BODIPY-based probes (MOPBs) in our previous work, Stokes shift of DMOPB was expanded by 10 nm when using dimethoxyphenyl instead of monomethoxyphenyl, which is basically consistent with the quantum chemistry calculation of 11 nm. DMOPB can react with NO in only 2 min to form the triazole DMOPB-T with a fluorescence quantum yield of 0.32. An excellent linear relationship was observed in the range of NO concentration from 0.5 μM to 4 μM and the detection limit was 1 nM. The experimental results indicate that DMOPB with high sensitivity, excellent selectivity, low toxicity and dark background can be a great candidate for imaging NO in cells and tissues. Considering the lack of practical way to increase Stokes shift of small-molecule fluorescent probes based on specific fluorophore, the proposed strategy has great potential for the designing of probes with large Stokes shift.

A rapid and selective fluorescent probe with a large Stokes shift for the detection of hydrogen sulfide

We have successfully developed a new green-emitting H₂S fluorescence probe employing a 2,4-dinitrophenyl ether moiety as the sensing group based on 3'-formyl-4'-hydroxybiphenyl-4-carbonitrile. This probe displayed a rapid (2 min), sensitive (the detection limit was 0.18 μM) and selective with a large Stokes shift (183 nm) in response to H₂S, which was beneficial for fluorescence sensing and cell imaging studies. Moreover, this probe can qualitatively and quantitatively detect H₂S with a good linearity (R² = 0.9991). Importantly, this probe had been used for the detection of H₂S in living MDA-MB-231 cells with good performance.

A benzothiazole-based fluorescent probe for hypochlorous acid detection and imaging in living cells

A benzothiazole-based turn-on fluorescent probe with a large Stokes shift (190nm) has been developed for hypochlorous acid detection. The probe displays prompt fluorescence response for HClO with excellent selectivity over other reactive oxygen species as well as a low detection limit of 0.08μM. The sensing mechanism involves the HClO-induced specific oxidation of oxime moiety of the probe to nitrile oxide, which was confirmed by HPLC-MS technique. Furthermore, imaging studies demonstrated that the probe is cell permeable and can be applied to detect HClO in living cells.

A novel dicyanoisophorone based red-emitting fluorescent probe with a large Stokes shift for detection of hydrazine in solution and living cells

A novel dicyanoisophorone based fluorescent probe HP was developed to detect hydrazine. Upon the addition of hydrazine, probe HP displayed turn-on fluorescence in the red region with a large Stokes shift (180nm). This probe exhibited high selectivity and high sensitivity to hydrazine in solution. The detection limit of HP was found to be 3.26ppb, which was lower than the threshold limit value set by USEPA (10ppb). Moreover, the probe was successfully applied to detect hydrazine in different water samples and living cells.