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Peroxynitrite (ONOO−), as an important reactive oxygen species (ROS), plays a significant role in pathological and physiological processes, and abnormal levels of ONOO− will lead to many diseases. Thus, novel fluorescent probe for detecting ONOO− is in urgent need. Herein, we constructed a probe TPPB with aggregation-induced emission (AIE) characteristic based on triphenylamine and boronate group. The probe TPPB possesses remarkable performances including high selectivity in the presence of other ROSs, low detection limit (32 nM) and large Stokes shift (215 nm) toward ONOO−. Besides, probe TPPB shows low cytotoxicity and good imaging ability of ONOO− in living cells. [Display omitted] [ABSTRACT FROM AUTHOR]

A protein structure-dependent probe (OTB) for human serum albumin (HSA) was designed. Molecular simulation were used to assist probe design. OTB exhibited favorable selective HSA sensitivity and strong HSA binding ability. As a cationic molecule, OTB could form a stable amphipathic complex with water-soluble pillar [5]arene (WP5). More interestingly, the WP5-OTB complex possessed better HSA responsiveness and stronger HSA binding ability than OTB. The detection limit (3σ/k) of WP5-OTB towards HSA was determined to be 0.33 μM. WP5-OTB complex possessed excellent anti-interference ability in the selective recognition of HSA. Common commercial drugs, fluorescent amino acids, and fatty acids had almost negligible effect on the HSA responsiveness of the complex. The WP5-OTB complex self-assembled into supramolecular fluorescent probe in aqueous solution, and the supramolecular probe possessed favorable HSA-induced bioimaging property, pH-sensitive drug delivery property, and photodynamic activity. [Display omitted] • A cationic ICT probe OTB was designed by fully considering its interaction with HSA. • OTB exhibited favorable serum albumin sensitivity and strong HSA binding ability. • The WP5-OTB complex possessed better HSA responsiveness and binding ability than OTB. • The WP5-OTB complex self-assembled into supramolecular fluorescent probe in solution. • The supramolecular probe had good bioimaging and chemo-photodynamic therapy properties. [ABSTRACT FROM AUTHOR]

Thyroid cancer has been increasingly prevalent in recent years. The main diagnostic methods for thyroid are B-ultrasound scan, serum detection and puncture detection. However, these methods are invasive and complex. It is a pressing need to develop non-invasive or minimally invasive methods for thyroid cancer diagnosis. Fluorescence method as a non-invasive detection method has attracted much attention. Butyrylcholinesterase (BChE) is a common enzyme in the human body, and many diseases affect its reduction. We found that BChE is also a marker for thyroid cancer. Therefore, it is of certain clinical value to explore the expression of BChE in thyroid cancer cells through a customized fluorescent probe to provide valuable experimental data and clues for studying the expression of thyroid cancer marker to reflect thyroid status. In this study, we customized a fluorescent probe named Kang-BChE, which is easy to synthesize with a high yield. The experimental results show that the probe Kang-BChE can detect BChE in the linear range of 0–900 U L−1 (R2 = 0.9963), and the detection limit is as low as 3.93 U L−1 (λ ex/em = 550/689 nm). In addition, Kang-BChE probes have low cytotoxicity, good specificity, and can completely eliminate interference from acetylcholinesterase (AChE). Kang-BChE showed excellent stability in the detection of complex biological samples in serum recovery experiments (95.64–103.12 %). This study was the first time using Kang-BChE to study the low expression of BChE in thyroid cancer cells (Tpc-1 cells). In addition, we observed that H 2 O 2 concentration in Tpc-1 cells was positively correlated with BChE activity. Kang-BChE is expected to be an important tool for monitoring the change of BChE content in complex biological environments due to its excellent performance. Kang-BChE can also be used to explore the influence of molecules in more organisms on the change of BChE content due to its excellent anti-interference ability. We expect that Kang-BChE can play a significant role in the clinical diagnosis and treatment of thyroid cancer. [Display omitted] • Kang-BChE was first to observe the change of BChE content in Tpc-1 cells. • Kang-BChE can completely eliminate the interference of AChE. • Kang-BChE has good stability in complex biological samples. • Kang-BChE observed positive correlation between H 2 O 2 and BChE in Tpc-1 cells. [ABSTRACT FROM AUTHOR]

On the basis of classical Schiff base reaction, two novel and efficient fluorescent probes (DQNS , DQNS1) were designed and synthesized by introducing Schiff base structure into dis-quinolinone unit for structural modification, which can be used to detect Al 3+ and ClO −. [Display omitted] • The double-recognition fluorescent probes with the same site designed based on ICT and PET mechanism has the characteristics of simple synthesis method. • Preliminary speculation, the probe (DQNS) has continuity in identifying Al3+and ClO−. • The probes (DQNS) can primarily screen and analyze environmental samples and living cells containing Al3+and ClO−. On the basis of classical Schiff base reaction, two novel and efficient fluorescent probes (DQNS , DQNS1) were designed and synthesized by introducing Schiff base structure into dis-quinolinone unit for structural modification, which can be used to detect Al3+ and ClO−. Because the power supply capacity of H is weaker than that of methoxy, DQNS shows better optical performance: a large Stokes Shift (132 nm), identify Al3+ and ClO− with high sensitivity and selectivity, low detection limit (29.8 nM and 25 nM) and fast response time (10 min and 10 s). Through the working curve and NMR titration experiment, the recognition mechanism of Al3+ and ClO− (PET and ICT) probes are confirmed. Meanwhile, it is speculated that the probe has continuity for the detection of Al3+ and ClO−. Furthermore, DQNS detection of Al3+ and ClO− was applied to real water samples and living cell imaging. [ABSTRACT FROM AUTHOR]

SO 2 , the fourth endogenous gaseous signaling molecule, plays an important role in cells. Besides, SO 2 derivatives are used as preservatives in food and drinks. To understand the level of SO 2 derivatives in body and food, we developed a FRET-based fluorescent probe CPO. CPO had high energy transfer efficiency and high selectivity toward SO 2 derivatives. It could fast respond toward SO 2 derivatives in an aqueous solution (3 min) and possessed a low detection limit (68 nM). Furthermore, the SO 2 derivatives in tap water, sugar, vermicelli and cells were detected by probe CPO. In addition, probe CPO had a high colocalization coefficient (0.95) for lipid droplets. [Display omitted] • A novel FRET-based water-soluble fluorescent probe for fast response to HSO 3 − was reported. • The probe had good sensitivity and selectivity to HSO 3 −. • The probe was applied to detect HSO 3 − in tap water, food and cells. • The probe preferred to load on lipid droplets with a high Pearson's coefficient. [ABSTRACT FROM AUTHOR]

The abnormality of Cys concentration in organism could lead to a series of diseases, so its effective detection is of great importance in disease diagnosis. Here we developed a novel ESIPT fluorescent probe HBT-IDAc based on the classic ESIPT fluorophore 2-(2′-hydroxyphenyl)benzothiazole (HBT) and indanone, which could selectively and sensitively detect Cys with a large Stokes shift up to 210 nm and the detection limit to 0.89 μM. In addition, the probe exhibited good anti-interference and low cytotoxicity, and has been successfully applied to monitor Cys in cells. • A novel ESIPT fluorescent probe for selective and sensitive detection of Cys was developed. • The probe has the large stokes shift (210 nm) and good LOD (0.89 μM) in aqueous environment. • The probe exhibits low cytotoxicity and has been applied for imaging Cys in cells. [ABSTRACT FROM AUTHOR]

Mercury ion (Hg2+) is highly toxic to the environment and organisms, therefore, monitoring and quantitative detection of Hg2+ is of great significance. In this work, a new fluorescent probe TPEH that integrated tetraphenylethene (TPE) and 2-(2 ′ -hydroxyphenyl)benzothiazole was designed and synthesised. In EtOH/HEPES (2:8, v/v, pH = 7.2) solution, TPEH displays fluorescence turn on detection of Hg2+ with the advantages of swift response (<100 s), high selectivity and strong disturbance-resistant, a large Stokes shift (220 nm), and low limit of detection (81.7 nM). The sensing mechanism was proved to be Hg2+-triggered releasing of the aggregation-induced emission (AIE)-active precursor compound 2. TPEH has been successfully applied to detect Hg2+ in seafood and tea, and image Hg2+ in living cells. In addition, TPEH can be used to detect the content of Hg2+ in actual water samples with the aid of smartphone. [Display omitted] • A new AIE-based fluorescent probe TPEH for Hg2+ detection has been developed. • TPEH has the advantages of rapid response (<100 s), a large Stokes shift (220 nm), and a low detection limit (81.7 nM). • TPEH can detect Hg2+ in seafood and tea, and image Hg2+ in living cells. • TPEH can detect Hg2+ in actual water samples with the help of smartphone. [ABSTRACT FROM AUTHOR]

Stress granules (SGs) are a fascinating type of membrane-less organelle that form through liquid-liquid phase separation in eukaryotic cells. Our previous investigations have been instrumental in the development of the first small-molecule fluorescent probe, named TASG , which can selectively identify SGs. However, the practical utility of TASG for monitoring SG dynamics in live cells has been hindered by the difficulty in visualizing small nascent SGs. To overcome this obstacle, the present study systematically modified the structure of TASG , with the aim of discovering fluorescent chemical probes that exhibit superior performance. Among the evaluated candidates, TASG-8 exhibited the most promising ability to image SGs. Importantly, TASG-8 possessed a critical advantage over TASG , in that it could effectively label small nascent SGs. The structure-activity relationship of the candidates was analyzed. Additionally, the underlying mechanism responsible for this enhancement was extensively explored. Collectively, our research presents a rational strategy for the development of innovative fluorescent probes that selectively target SGs, and introduces a powerful new tool, TASG-8 , which has the potential to facilitate more comprehensive and efficient investigations into the functions of SGs in cells. • The structure-activity relationship of benzothiazoles that target SGs is clarified. • TASG-8 is the first fluorescent probe capable of visualizing small nascent SGs. • Our study presents a novel concept for developing probes that are specific to SGs. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new H 2 S fluorescence probe with the thiolysis of dinitrophenyl ether is developed. • The probe can detect H 2 S with high selectivity and low LOD in aqueous solution. • The probe was successfully applied to detec H 2 S in test paper strips and food samples. • The probe was successfully used for imaging exogenous H 2 S in living cells. Small-molecular fluorescent probes are currently being developed for sensing of hydrogen sulfide and are attracted great attention because of the significant roles of H 2 S in food safety and living organisms. We report herein an efficient approach to modify the previous reported quinolinium-phenol vinylic conjugated fluorescent probes 4NS by combination of the accelerated nucleophilic addition of H 2 S to an aldehyde group followed by an intramolecular fast thiolysis of dinitrophenyl ether. The modified probe 4ANS can be able to efficient sense H 2 S and displays typical features, with good selectivity, high sensitivity (LOD = 15 nM), "naked-eye" colorimetric and turn-on fluorescent detection, rapid response time (<3 mins), and good biocompatibility. The mechanism involving thiolysis of dinitrophenyl ether was confirmed by HRMS analysis, and the practical application to detect H 2 S in food spoilage and cell imaging was successfully demonstrated. [ABSTRACT FROM AUTHOR]

A smart fluorescent probe DPAS-Cys has been rationally designed based on a typical AIEgen DPAS and an acrylate moiety. The probe DPAS-Cys not only can be used for the detection of cysteine (Cys) selectively with large Stokes shift (200 nm) and relatively low detection limit (2.4 μM), but also shows lipid droplets (LDs) targeting property. The response mechanism for Cys was carefully verified. Importantly, due to the aggregation-induced emission characteristic, the introduction of considerable percentage of traditional organic solvent is avoidable, which makes it suitable for bioimaging in physiological systems. In addition, the confocal fluorescence imaging demonstrates that DPAS-Cys is able to detect Cys in LDs of different cell lines with universality. Our study opens a new avenue to understand the importance of LDs in biosystem, for which the gap between the essential biothiol Cys and the energy storage organelle LDs was bridged for the first time. Image 1 • A smart fluorescent probe DPAS-Cys is developed for selective detection of cysteine. • DPAS-Cys shows aggregation-induced emission characteristic and large Stokes shift. • DPAS-Cys exhibits lipid droplets targeting property with universality. [ABSTRACT FROM AUTHOR]

The ability to visualize enzyme activity in a cell, tissue, or living organism can greatly enhance our understanding of the biological roles of that enzyme. While many aspects of cellular signaling are controlled by reversible protein phosphorylation, our understanding of the biological roles of the protein phosphatases involved is limited. Here, we provide an overview of progress toward the development of fluorescent probes that can be used to visualize the activity of protein phosphatases. Significant advances include the development of probes with visible and near-infrared (near-IR) excitation and emission profiles, which provides greater tissue and whole-animal imaging capabilities. In addition, the development of peptide-based probes has provided some selectivity for a phosphatase of interest. Key challenges involve the difficulty of achieving sufficient selectivity for an individual member of a phosphatase enzyme family and the necessity of fully validating the best probes before they can be adopted widely. [ABSTRACT FROM AUTHOR]

A novel N,N -dithenoyl-rhodamine based fluorescent and colorimetric Fe3+ probe 1 was designed and synthesized by only one step from Rhodamine B hydrazide and 2-thiophenecarbonyl chloride. The structure of probe 1 was characterized by 1H NMR/13C NMR spectroscopy, IR spectroscopy, and HRMS spectrometry. Accompanying with significant changes in visual color and fluorescent spectrum, probe 1 displayed good sensitivity for Fe3+ with an abroad pH span. The detection limit (3.76 μmol/L, 0.2 mg/L) for Fe3+ was lower than WHO recommended value (0.3 mg/L) for drinking water. Using two thiophene carbonyl groups as coordinating functional recognition group, probe 1 showed excellent selectivity towards Fe3+ over diverse coexistent metal ions and anions. The sensing mechanism between dithenoyl-substituted probe 1 and Fe3+ was further confirmed by 1H NMR and IR titration experiments, binding constants study, and Job's plot analysis. Furthermore, probe 1 also exhibited good cell membrane permeability and could be used as an efficient Fe3+ probe in living human cells. Image 1 [ABSTRACT FROM AUTHOR]

The nitrogen and sulfur co-doped carbon dots (NSCDs) were synthesized using cysteine as precursor by hydrothermal approach, which showed good aqueous solubility, high fluorescent quantum yield (QY = 38.7%) and good photostability. The experiments with cells demonstrated that NSCDs possessed excellent biocompatibility and their cytotoxicity was low (cell viability ≥90%) in both normal and cancer cell lines. Furthermore, NSCDs as fluorescent probes could be used for the imaging of cells, which showed a good membrane permeability and strong resistance to photobleaching. In addition, the cellular uptake of NSCDs presented a time-dependent saturation. The imaging applicability of NSCDs in different cancer cells (MCF-7, A375, Hela and U251 cells) has also been demonstrated. Therefore, NSCDs are considered as promising candidates for the design of low cytotoxicity bioimaging agents and a cellular location system based on fluorescence measurements. Unlabelled Image • NSCDs show well-dispersed, high QY of 38.7% and good photostability. • NSCDs possess excellent biocompatibility in normal and cancer cell lines. • NSCDs are as fluorescent probes for cancer cell imaging and locating • The cellular uptake of NSCDs presents a time-dependent saturation. . [ABSTRACT FROM AUTHOR]

Cys is one of the important biothiols and its abnormal concentration may pose a threat to human health. Therefore, the monitoring of Cys in organisms is of great significance. GSH and Hcy, as the other two biothiols, have similar chemical structures and active sites to Cys. Consequently, developing fluorescent probes to independently detect Cys has become a challenging problem. Keeping this in mind, α-β unsaturated ketone as a recognition group was integrated into the coumarin group skeleton to synthesize a fluorescent probe SC. After the nucleophilic addition reaction of Cys with SC , the conjugated system of SC was blocked and the fluorescent enhanced obviously. SC was able to detect Cys specifically under the same excitation with a low detection limit (11.1 nM). SC showed a rapid respond to Cys (120 s) and good fluorescent stability over a wide pH range. In addition, it achieved extracorporeal circulation in the presence of H 2 O 2 or NEM. In the end, SC could be applied to detecting endogenous and exogenous Cys under biological condition due to its slight cytotoxicity and good biocompatibility. This provided a powerful tool for studying the physiological function of Cys exclusively. Image 1 • The probe SC possessed a high specificity of Cys over Hcy and GSH under the same excitation and test system. • SC had satisfactory reversibility in the presence of NEM or H 2 O 2. • SC displayed a fast response to Cys (120 s). • Cytotoxicity test indicated that probe SC had very low cytotoxicity even at the concentration of 100 µM. • The probe SC could be used to monitor endogenous and exogenous Cys in living cells. [ABSTRACT FROM AUTHOR]

A novel imidazo[1,2-a]pyridine-rhodamine ratiometric fluorescent probe IP-Hg for Hg2+ based on a fluorescence resonance energy transfer mechanism has been developed. The probe has been proved to show high sensitivity and high selectivity toward Hg2+. Furthermore, it could be used for imaging Hg2+ in cells and in polluted water. Image 1 • A ratiometric fluorescent probe for sensing Hg2+ based on new imidazo[1,2-a]pyridine fluorophore has been synthesized. • The probe exhibits highly sensitivity and selectivity toward Hg2+ (LOD: 9.1 nM). • The ratiometric fluorescent probe displays a remarkable emission shift (220 nm). • The probe show low cytotoxicity and can image in cells. [ABSTRACT FROM AUTHOR]

Abnormal levels of Cys, Hcy and GSH are associated with various diseases, thus monitoring biothiols is of great significance. In this work, a dual-emission responsive near-infrared fluorescent probe NIR-NBD for detecting Hcy and Cys/GSH was developed based on the conjugation of a dicyanoisophorone based fluorophore (NIR-OH) and 7-nitrobenzofurazan (NBD). To our surprise, the addition of Hcy induced significant fluorescence enhancement at both 549 and 697 nm; while Cys/GSH resulted in major fluorescence emission at 697 nm. The detection limit was determined to be 33.2 nM for Cys, 33.5 nM for Hcy, and 34.4 nM for GSH. Therefore, the probe can be used for discriminative detection of Hcy and Cys/GSH. Moreover, fluorescence imaging of HeLa cells indicated that the probe was cell membrane permeable and could be used for visualizing Hcy and Cys/GSH in living cells. Image 1 • A novel NIR fluorescent probe for discriminative sensing of Hcy and Cys/GSH in dual channel was developed. • The probe can measure Hcy level in serum samples. • The probe could sense intracellular Hcy and Cys/GSH in living HeLa cells. [ABSTRACT FROM AUTHOR]

A fluorescence-enhanced and lysosome-targeted Al3+ probe (1) based on a pyrazole-containing hydrazone was developed in this work. The fluorescent probe 1 displays an OFF–ON fluorescence response to Al3+ in the lysosome pH environment. In addition, the resultant 1 –Al3+ complex could act as an ON–OFF fluorescence sensor for F−. Fluorescence imaging shows that 1 is suitable for visualization of Al3+ in lysosomes of HeLa cells. Image 1 • A quite simple hydrazone-based fluorescent probe for Al3+ has been developed. • The probe displayed an OFF-ON response toward Al3+ in aqueous solution. • The resultant Al3+ complex of the probe could act as an on-off fluorescent sensor for F−. • The probe has been used for imaging of Al3+ in lysosomes of HeLa cells. [ABSTRACT FROM AUTHOR]

• A dicyanoisophorone-based fluorescent probe was developed for sensing H 2 S with a large Stokes shift (155 nm). • The probe showed faster time response and high sensitivity for H 2 S. • The probe can be used to detect exdogenous and endogenous H 2 S in living HeLa cells. Due to the importance of hydrogen sulfide (H 2 S) in physiology and pathology, the development of fluorescence probes for the detection of H 2 S has attracted extensive attention of researchers. We developed a H 2 S fluorescence probe (DCN-S) based on dicyanoisopentanone using dithioether and ester groups as the reaction sites. Under the nucleophilic substitution of H 2 S, disulfide bond of DCN-S was broken. Then the probe changed into dicyanoisophorone derivative and emitted an orange fluorescence band from 530 nm to 700 nm (centred 580 nm). Upon response for H 2 S, DCN-S exhibited high sensitivity (88 nM detection limit) and large stokes shift (155 nm). Importantly, the probe also was successfully used for endogenous and exogenous imaging of living cells. [ABSTRACT FROM AUTHOR]

In this study, we developed a new fluorescent probe (CMM) based on coumarin dye and malononitrile, for highly sensitive and selective detection of hypochlorite ion (ClO−). CMM showed a 45-fold fluorescence enhancement at 459 nm in the presence of ClO− and displayed an excellent selectivity over other competing species. The probe featured a fast response time (<15 s), which could be in favor of the real-time detection towards ClO−. Meanwhile, probe CMM could effectively monitor ClO− in physiological pH condition and the detection limit was estimated to be as low as 5.7 nM. Furthermore, its preeminent recognition properties made the successful application for monitoring ClO− in environmental water samples and labeling ClO− in living biological cells. Image 1 • A coumarin-based "turn-on" fluorescent probe for hypochlorite was developed. • The probe detect ClO− with high selectivity and low detection limit. • The probe is able to detect ClO− within 15 s. • The probe is successfully applied to detect ClO− in real water samples and living cells. [ABSTRACT FROM AUTHOR]

Hypochloric acid (HOCl) plays vital roles in cell signaling and homeostasis which involved in many related diseases. Therefore, the accurate detected level of OCl− for discussing the complex contributions of OCl− to human health is of great significance. In this study, a novel mitochondrion-targeting fluorescent probe DMI bearing a carbon-carbon double bond as an OCl−-responsive site has been developed. Probe DMI exhibited specific fluorescence response toward OCl− with fast response (within 4 s) and high sensitivity (detection limit is 0.05 μM), where the obvious color changes could be observed by the naked eye. More importantly, DMI could be applied in the bioimaging of OCl− in living A549 cells successfully benefited from its good sensing properties and low toxicity. Fluorescence co-localization test was further carried out and confirmed mitochondria-targetable ability of DMI which can be used for investigating physiological function of HOCl at organelle levels. Image 1 • Probe DMI is a mitochondria-targeting visual fluorescence probe. • DMI could highly sensitive and selective detected of hypochlorite. • The mechanism of DMI has been proved to be via oxidation fracture of C C. • DMI can be used to imaging of OCl− in living A549 cells. [ABSTRACT FROM AUTHOR]

Two different colors of water-soluble core-shell quantum dots CdTe/CdS (green and orange red) have been synthesized and characterized in this paper. The formation of core-shell quantum dots not only improves the fluorescence quantum yield, but also reduces the biological toxicity of quantum dots, and improves the fluorescence lifetime. Two novel fluorescent bioprobes, CdTe/CdS (λ em = 545 nm)-5-Fu and Bio-CdTe/CdS (λ em = 600 nm)-TAM, have been synthesized via the interaction of these two core-shell quantum dots with anticancer drugs (5-Fu) and P-gp inhibitors (TAM), respectively. These two fluorescent probes have been simultaneously used in fluorescence imaging of human breast cancer cells MDA-MB-231/MDR. It can be observed that under the action of P-gp inhibitors distributed on the cell membrane, anticancer drugs can be retained in cancer cells. According to the color of quantum dots on the probe, the visualization results of the action of anticancer drugs and P-gp inhibitors can be obtained. This study shows that to prepare functional bioprobes using core-shell quantum dots CdTe/CdS has great potential in the field of biomedical research such as anticancer drugs. Image 1 • CdTe/CdS core-shell QDs has higher fluorescence quantum yield and lower biological toxicity. • Simultaneous imaging of two bioprobes (CdTe/CdS-5-Fu, Bio-CdTe/CdS-TAM) in cancer cells. • Surface functionalization of quantum dots by anticancer drugs 5-Fu and P-gp inhibitors TAM. • Two colors bioprobes visualize the Interaction between Anticancer Drugs and P-gp Inhibitors. [ABSTRACT FROM AUTHOR]

Lipid droplets (LDs) are an important organelle as the main energy storage site in cells. LDs viscosity controls the material and energy exchange between it and other organelles. Furthermore, the LDs metabolic abnormalities, cell dysfunction, some diseases may be attributed to the singular LDs viscosity. Currently, the fluorescent probes for sensing the variations of LDs viscosity are still scarce and expose some drawbacks of low fluorescence quantum yield, low sensitivity and LDs polarity interference. Thus, the development of high performance probes is significant to detect LDs viscosity. We hereby provide a lipophilic fluorescent probe (TPE-BET) with high fluorescence quantum yield (Φ f , 0.91 in glycerol) for imaging LDs viscosity in living cells. With the increase of viscosity from 0.54 cp to 934 cp, the fluorescence at λ ex /λ em = 405/520 nm and the fluorescence quantum yield of TPE-BET linearly increased by 64.9 and 128.5 folds, respectively. Meanwhile, the outstanding LDs staining capability of TPE-BET may provide a high spatial resolution for LDs imaging. The cell imaging of TPE-BET not only successfully observed the viscosity variations of LDs in cell stress models, e.g., ferroptosis, inflammation and mitophagy, but also revealed the increased viscosity and extracellular delivery of LDs in heavy metal cell injury models (Hg/As) for the first time, which may supply concrete evidence for understanding the structure and function of LDs. This represents a new fluorescent probe TPE-BET with high fluorescence quantum yield for imaging LDs viscosity, which may decrease the dose of probe and excitation light intensity along with the improvement on signal noise ratio (S/N). The imaging results of TPE-BET clarified that LDs viscosity may be an appraisal index on cell differentiation, state evaluation and drug screening. [Display omitted] • A lipophilic probe (TPE-BET) with high fluorescence quantum yield was developed for imaging lipid droplet (LDs) viscosity. • TPE-BET shows high spatial resolution, which provide information including the distribution, size and morphology of LDs. • The LDs viscosity was detected in various cell models such as ferroptosis, mitophagy and heavy metal cell injury models. • LDs viscosity may be an appraisal index on cell differentiation, state evaluation and drug screening. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new benzobodipy-based HOCl fluorescent probe has been designed and developed. • The probe exhibits an excellent sensitivity and low detection limit to HOCl. • The probe could be applied for real-time fluorescence imaging of HOCl in live cells and zebrafish. Hypochlorous acid (HOCl) is an essential endogenous reactive oxygen species in biological systems, playing a critical role in various physiological processes. Real-time monitoring of HOCl concentration in living organisms is essential for understanding its biological functions and pathological roles. In this study, we developed a novel fluorescent probe based on benzobodipy, BBDP , for rapid and sensitive detection of HOCl in aqueous solutions. The probe exhibited a significant fluorescence turn-on response to HOCl based on its specific oxidation reaction towards diphenylphosphine, with high selectivity, instantaneous response (less than 10 s), and low detection limit (21.6 nM). Furthermore, bioimaging results illustrated that the probe could be applied for real-time fluorescence imaging of HOCl in live cells and zebrafish. The development of BBDP may provide a new tool for exploring the biological functions of HOCl and its pathological roles in diseases. [ABSTRACT FROM AUTHOR]

An off-on fluorescent probe (NS-CDs-AgNPs) was synthesized based on a one-pot microwave process by utilizing N, S co-doping carbon dots (NS-CDs) and silver nitrate as precursors. The significant peak of NS-CDs-AgNPs at 393 nm in ultraviolet spectrum indicated silver nanoparticle (AgNPs) were successfully synthesized. A faint blue fluorescence emission (442 nm) was displayed when excited NS-CDs-AgNPs at 371 nm. A remarkable fluorescence recovery was observed upon adding of trance Hg2+, whereas the other heavy metal ions did not elicit this response. The reason for this phenomenon was revealed in this work that a spontaneous redox reaction occurred between NS-CDs-AgNPs and Hg2+, which leaded to the formation of NS-CDs-Ag n -2NPsHg complexes. On the basis of this mechanism, a new off-on fluorescent analytical method was constructed for Hg2+ detection with linear range of 10–400 nM (R 2 = 0.9941), and the detection limit (LOD) of 5.16 nM. Additionally, satisfactory recovery (90.28%–106.13%) and the relative standard deviation (RSD) (RSD＜5.21%) were obtained in water sample detection. More importantly, the NS-CDs-AgNPs exhibited lower cytotoxicity and better biocompatibility, indicating a huge potential in cell imaging and clinical medicine. [Display omitted] • An off-on fluorescent probe NS-CDs-AgNPs was constructed on the basis of the in-situ formation of silver nanoparticles (AgNPs) through one-step microwave-assisted method. • The spontaneous redox reaction of NS-CDs-AgNPs with Hg2+ was confirmed as the main recognition mechanism. • The NS-CDs-AgNPs is not only highly selective for Hg2+ with a LOD of 5.16 nM (S/N = 3), but also have a lower cytotoxicity and satisfactory biocompatibility. [ABSTRACT FROM AUTHOR]

[Display omitted] The biological microenvironment includes important parameters such as viscosity, polarity, temperature, oxygen content and pH. In particular, abnormal cell viscosity is associated with the development of major diseases. Sulphur dioxide (SO 2) serves not only as an essential atmospheric pollutant but also an influential signalling molecule in biological cells, predisposing individuals to increased respiratory disease. In this work, we designed and synthesized a novel fluorescent probe CouCN-V&S with dual response to micro environmental viscosity and SO 2. The probe monitored viscosity and SO 2 separately through dual emission channels with a difference of 135 nm. The probe responded sensitively to SO 2 (<1s) and exhibited satisfactory immunity to interference and pH stability. The probe was successfully applied to imaging cellular, intra-zebrafish viscosity and SO 2 changes. Interestingly, we took onion epidermal cells as model and explored the capability of probe CouCN-V&S to image SO 2 in plant cells for the first time. [ABSTRACT FROM AUTHOR]

Herein, a two-photon mitochondria-targeting fluorescent probe (TPNP) which can be activated by the azo reductase (AzoR) has been developed for imaging the hypoxic microenvironment of tumors in vivo. The probe TPNP showed a low detection limit (LOD = 1.85 eq), high selectivity, and considerable steadiness in different pH conditions (3.0–11.0). In living cells, it could co-locate with the commercial dye in the mitochondria (co-localization coefficient: 0.92) and indicate hypoxia in both one-photon and two-photon fluorescence imaging. Its AzoR-activation mechanism was further verified by the docking simulation as well as the experiments of adding AzoR or electron transporter inhibitors. Moreover, the in vivo real-time fluorescence imaging proved that TPNP could monitor hypoxia and the tumor progression in mouse tumor models. Overall, this designed probe exhibited high sensitivity, synthetic ease, and excellent fluorescent properties, which might therefore enlighten new ideas for the diagnosis of tumors in future studies. • A new hypoxia-sensitive fluorescent probe (TPNP) for tumor detection is reported. • TPNP exhibited high sensitivity, synthetic ease, and impressive fluorescent properties. • TPNP can monitor the presence of solid tumors in the xenograft mice model. [ABSTRACT FROM AUTHOR]

Hypochlorous acid (HOCl) is a crucial reactive oxygen species in biological systems, and its abnormal metabolism is associated with various diseases. Therefore, it is essential to accurately detect HOCl to understand its biological function and develop related therapeutic strategies for diseases. In this work, we developed a novel fluorescence probe, BCy-S , based on the twisted intramolecular charge transfer (TICT) mechanism for rapid and sensitive detection of HOCl in an aqueous solution. The probe exhibited a significant turn-on fluorescence response to HOCl, with high selectivity, rapid kinetics (less than 40 s), large Stokes shift (about 170 nm), and low detection limit (35.2 nM), based on the specific oxidation reaction of HOCl with sulfur atoms. Additionally, the outcomes of the bioimaging experiment showed that BCy-S was capable of real-time fluorescence visualization of HOCl in living HeLa cells and zebrafish. The development of BCy-S presents a new tool for investigating the physiological function of HOCl and its pathological role in diseases. [Display omitted] • A new TICT-based HOCl fluorescent probe has been designed and developed. • The probe exhibits an excellent sensitivity, large Stokes Shift and low detection limit to HOCl. • The probe could be applied for real-time fluorescence imaging of HOCl in live HeLa cells and zebrafish. [ABSTRACT FROM AUTHOR]

[Display omitted] • A colorimetric and near-infrared fluorescent F- based on malononitrile isophorone derivatives have been designed and synthesized. • It can selectively make Si-O bond breakage probes that can respond specifically to F- and have high sensitivity with a detection limit of 6.59 × 10-7 mol/L. The probe YC-Si has a large Stokes shift at 678 nm (168 nm). • In cell imaging experiments it was demonstrated that YC-Si has cell permeability and low cytotoxicity and can be used to detect F- in living cells. In this study, we have successfully designed and synthesized a colorimetric and near-infrared fluorescent probe YC-Si for F- detection based on malononitrile isophorone derivatives which can selectively make Si-O bond breakage probes that can respond specifically to F- and have high sensitivity with a detection limit of 6.59 × 10-7 mol/L. The probe YC-Si has a large Stokes shift at 678 nm (168 nm). In cell imaging experiments it was demonstrated that YC-Si has cell permeability and low cytotoxicity and can be used to detect F- in living cells.. [ABSTRACT FROM AUTHOR]

Ferroptosis is a novel Fe(II)-mediated oxidative cell death form, and is closely related with endoplasmic reticulum (ER). Exploring the fluctuation of ER polarity during ferroptosis is highly important for the in-depth study of the biological roles of ER in ferroptosis. Herein, we present a ratiometric probe (BNS) for revealing the changes of the ER polarity in the living cells experiencing ferroptosis. BNS employed a D-π-A-π-D type structure as the polarity-sensitive fluorophore, and selected p -toluenesulfonamide as the ER-targeting unit. Theoretical calculations suggested that the response mechanism of BNS to polarity was based on ICT, and two ICT processes appeared when BNS was at excited state. Cell imaging results demonstrated that BNS possessed desirable ER-targeting capability, and erastin-induced ferroptosis could increase the ER polarity of the living cells. Moreover, similarly to vitamin E (VE) and deferoxamine (DFO), dihydrolipoic acid (DHLA) could inhibit the changes of the ER polarity during erastin-induced ferroptosis. We expect that the probe could provide a convenient method to rapidly monitor ferroptosis and design novel drugs for the treatment of ferroptosis-relevant diseases. [Display omitted] • A D-π-A-π-D type structure-based fluorescent probe (BNS) was developed for detecting the changes of ER polarity in the living cells. • Two ICT processes appeared when the probe BNS responded to polarity. • Ratiometric fluorescence imaging demonstrated that ferroptosis could increase ER polarity in living cells. • Fluorescence imaging demonstrated that dihydrolipoic acid (DHLA) could show prominent inhibition effect to ferroptosis. [ABSTRACT FROM AUTHOR]

[Display omitted] • A fluorescent probe was synthesized based on benzopyran-chromone for detection of ONOO−. • The probe shows short response time for ONOO− (<30 s). • The probe shows specifically selectivity and a very low detection limit of 22.4 nM for ONOO−. • The probe can accurately identify endogenous and exogenous ONOO− in HeLa cells. Peroxynitrite is widely present in organisms and closely related to many pathophysiological functions. Therefore, it is of great physiological significance to develop capable probes for detecting ONOO−. In this work, a novel fluorescent probe B-Ch was designed based on the intramolecular charge transfer (ICT) effect. By means of molecular engineering, the replacement from diethylamine group to hydroxyl group has improved the detection sensitivity of the probe. After the addition of ONOO−, the solution color and fluorescence showed noticeable changes, which were visible to the naked eye. The probe showed excellent advantages: visualization, good selectivity, low sensitivity (22.4 nM), good stability and biocompatibility, exogenous and endogenous imaging of ONOO− in HeLa cells. [ABSTRACT FROM AUTHOR]

The abnormal changes of intracellular potassium ion (K+) concentration are usually associated with various diseases, therefore, real-time monitoring of intracellular K+ dynamic balance is crucial for disease research. Herein, we present a design strategy based on conjugated polymers (CPs) as potassium ion fluorescence probes. Six novel CP-based K+ sensors (P1 , P2 , P3 , PP1 , PP2 and PP3) were synthesized. These probes have different conjugated length backbones composing of stilbenzene, fluorene, thiophene, and/or benzothiadiazole units and different numbers of K+ selective ligands of triazacryptand (TAC), so as to study their spectral characteristics and response to K+. Among them, PP3 exhibits exceptional responsiveness and selectivity to K+. With a longer conjugated backbone, it shows a longer emission at 628 nm compared to other probes. Especially, the fluorescence intensities of PP3 showed a linear relationship with the concentrations of K+ in the range of 0–250 mM. PP3 has been successfully applied to detect the dynamic equilibrium of potassium ion concentration in living cells. This study proposes and validates the feasibility of the CP-based K+ fluorescence probe design strategy and expands the range of K+ probes, providing a new tool for understanding disease pathogenesis. [Display omitted] • A new design strategy of K+ sensor based on cross-conjugated CPs was proposed. • Six new cross-conjugated CPs K+ sensors were designed and synthesized. • PP3 is the first CPs probe that can detect the dynamic equilibrium of K+ in cells. • The design strategy based on cross-CPs K+ sensor has been proved to be feasible. [ABSTRACT FROM AUTHOR]

Monoamine oxidase A (MAO-A) is involved in various diseases such as heart failure (HF), prostate cancer (PCa), psychiatric disorders, etc. The precise sensing of MAO-A is important to elucidate its function in various biological processes, as well the diagnosis and treatment of related diseases. In this research, we created a brand-new fluorescence probe ANET for the specific detection of MAO-A. Propylamine moiety of ANET was specifically recognized for MAO-A and then the product EHBT was released. A well-calculated p K a value of 8.01 ± 0.02 was achieved for EHBT by pH-dependent spectra. The fluorescence at 700 nm of EHBT was observed at pH 8.0 due to the enhanced intramolecular charge transfer (ICT). The fluorescence intensity of EHBT at 559/700 nm was in a linear relationship with MAO-A concentration in the 0.375–1.50 μg/mL range. The detection limit was 19.8 ng/mL. It is well known that the environment of mitochondria is microalkaline (pH 8.0), however, other organelles are neutral or acidic. So the fluorescence at 700 nm of ANET could be notably turned on by MAO-A in mitochondria. In addition, ANET can selectively accumulate in the mitochondria through powerful electrostatic attractions. Finally, ANET was applied for specific imaging of MAO-A in mitochondria of SH-SY5Y, PC-3, and glucose-deprived (GD) H9c2 cells. [Display omitted] • A probe was developed for Monoamine Oxidases A (MAO-A) based on ICT. • ANET can selectively accumulate in the mitochondria through strong electrostatic interactions. • Since the p K a of EHBT matches the pH in mitochondria, fluorescence of EHBT can be specifically turned on at 700 nm. • ANET was capable of differentiating MAO-A overexpressing cells from other cells. [ABSTRACT FROM AUTHOR]

• Two polarity-sensitive fluorescent probes (NNap-LD-Ⅰ , NNap-LD-Ⅱ) with D-A-D structures were accurately synthesized by a simple synthetic method. • The two fluorescent probes (NNap-LD-Ⅰ , NNap-LD-Ⅱ) exhibit good photophysical properties, such as bright fluorescence, large Stokes shift, and resistance to chemical interference. • Both fluorescent probes (Nap-LD-Ⅰ , Nap-LD-Ⅱ) easily penetrate the cell membrane, specifically localize and aggregate in lipid droplets and lysosomes with low cytotoxicity, and yellow and red fluorescent lipid droplets and lysosomes can be observed. • Both fluorescent probes (NNap-LD-Ⅰ , NNap-LD-Ⅱ) were further investigated for the separate targeting of lysosomes and lipid droplets in HepG2 cells. • Both fluorescent probes (NNap-LD-Ⅰ , NNap-LD-Ⅱ) can be used for imaging of zebrafish. Lipid droplets (LDs) and lysosomes, vital subcellular organelles in cells, played irreplaceable roles in the areas involved in the synthesis of cell membranes, the movement of substances and the transfer of energy. Moreover, the imbalance of LDs could cause the occurrence of certain diseases, such as cardiovascular disease, liver cancer, atherosclerosis and diabetes. LDs and lysosomes interact in some biological processes. In this work, two polarity-sensitive fluorescent probes (NNap-LD-Ⅰ , NNap-LD-Ⅱ) were developed and synthesized by simple 1,8-naphthalimide scaffold modifications, which exhibited large Stokes shifts (173 nm and 190 nm), viscosity, pH stability and interference resistance. Notably, they were biocompatible and showed good targeting for bioimaging. LDs, lysosomes in HepG2 cells and zebrafish could be marked by bright yellow and red fluorescence after incubation with probes (NNap-LD-Ⅰ , NNap-LD-Ⅱ). In addition, HepG2 cells were stained for NNap-LD-Ⅰ and NNap-LD-Ⅱ to monitor the corresponding reduction in the number of LDs in starvation-treated cells. Similarly, the targeting of the probes to the lysosomes was diminished during imaging after the cells were treated with chloroquine (CQ), resulting in a reduction in lamellar fluorescence. These remarkable characteristics suggested that the probes NNap-LD-Ⅰ and NNap-LD-Ⅱ were quite efficient fluorescent probes with good visualization of LDs and lysosomes. [ABSTRACT FROM AUTHOR]

[Display omitted] • A near-infrared ratiometric fluorescent probe (DCPBCl 2 -Hz) was developed. • DCPBCl 2 -Hz exhibited excellent sensitivity and selectivity for hydrazine. • The probe can monitor gaseous hydrazine with a content down to 1 ppm (mg/m3). • The probe was applied for detecting hydrazine in solid and in live cells. Hydrazine (N 2 H 4) is a widely used raw material in the chemical industry, but at the same time hydrazine has extremely high toxicity. Therefore, the development of efficient detection methods is crucial for monitoring hydrazine in the environment and evaluating the biological toxicity of hydrazine. This study reports a near-infrared ratiometric fluorescent probe (DCPBCl 2 -Hz) for the detection of hydrazine by coupling a chlorine-substituted D-π-A fluorophore (DCPBCl 2) to the recognition group acetyl. Due to the halogen effect of chlorine substitution, the fluorophore has an elevated fluorescence efficiency and a lowered pKa value and is suitable for physiological pH conditions. Hydrazine can specifically react with the acetyl group of the fluorescent probe to release the fluorophore DCPBCl 2 , so the fluorescence emission of the probe system significantly shifted from 490 nm to 660 nm. The fluorescent probe has many advantages, such as good selectivity, high sensitivity, large Stokes shift, and wide applicable pH range. The probe-loaded silica plates can realize convenient sensing gaseous hydrazine with content down to 1 ppm (mg/m3). Subsequently, DCPBCl 2 -Hz was successfully applied to detect hydrazine in soils. In addition, the probe can also penetrate living cells and allow the visualization of intracellular hydrazine. It can be anticipated that probe DCPBCl 2 -Hz will be a useful tool for sensing hydrazine in biological and environmental applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • A series of probes NR-BS for H 2 S n were synthesized based on Nile red skeleton. • NR-BS4 can detect H 2 S n with high selective, wide linear range and broad pH tolerance. • The detection mechanisms of NR-BS4 were proved by LC-MS and DFT calculations. • NR-BS4 is a powerful tool for detecting the H 2 S n in living cells and zebrafish. Hydrogen polysulfide (H 2 S n , n > 1) has a valuable function in various aspects of biological regulation. Therefore, it is of great significance to realize the visual monitoring of H 2 S n levels in vivo. Herein, a series of fluorescent probes NR-BS were constructed by changing types and positions of substituents on the benzene ring of benzenesulfonyl. Among them, probe NR-BS4 was optimized due to its wide linear range (0 ∼ 350 μM) and little interference from biothiols. In addition, NR-BS4 has a broad pH tolerance range (pH = 4 ∼ 10) and high sensitivity (0.140 μM). In addition, the PET mechanism of probe NR-BS4 and H 2 S n was demonstrated by DFT calculations and LC-MS. The intracellular imaging studies indicate that NR-BS4 can be successfully devoted to monitor the levels of exogenous and endogenous H 2 S n in vivo. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new benzo-bodipy based fluorescent probe for HClO has been designed and developed. • The probe has excellent sensitivity and a fast response to HClO. • The probe was applied to the fluorescence imaging of HClO in HeLa cells and zebrafish. Due to the highly significant biological activity of hypochlorous acid, the monitoring of its concentration in vivo has received extensive attention. In this work, a photoinduced electron transfer (PeT) based benzo-bodipy fluorescent probe BBy-T has been developed for the rapid, sensitive, and selective detection of HClO in an aqueous solution. Based on the HClO-specific oxidation reaction, BBy-T exhibited a distinct fluorescence turn-on response to HClO with a remarkable Stokes shift (84 nm), immediate response (less than 20 s), and low detection limit (13.7 nM). In addition, the bioimaging results indicated that the probe BBy-T could be applied to real-time fluorescence imaging of living HeLa cells as well as living zebrafish. [ABSTRACT FROM AUTHOR]

Human serum albumin (HSA) is considered to be a diagnostic index of numerous diseases, and detecting HSA in subcellular environments is of great importance. In this work, we successfully synthesized a fluorescent probe NDIC based on hydrazide Schiff base, which can self-assemble into nanospheres in aqueous solution and produce distinct fluorescence signal in the presence of HSA. NDIC showed advantages including good sensitivity (LOD = 8.44 nM), high selectivity and anti-interference (over different coexisting proteins, amino acids, cations and anions). Job's plot, CD spectra, HSA destruction, site binding replacement and molecular docking provided reliable evidence for the fact that NDIC could combine at drug site I of HSA. Non-toxic probe NDIC could be applied to quantitatively detect HSA contents in urine, and achieve cancer identification by HSA imaging in cancer cells. More importantly, successful confocal experiment proved that NDIC possessed the lysosome selective imaging ability with the aid of HSA. These results showed the probe NDIC met the requirements of biological applications and was expected to explore HSA at the subcellular levels. • Self-assembled nanoprobe NDIC showed advantages including good sensitivity, high selectivity and anti-interference. • NDIC could be applied to quantitatively detect HSA in urine samples. • Cancer identification was implemented by cell imaging of HSA with non-toxic NDIC. • NDIC possessed the lysosome selective imaging ability with the aid of HSA. [ABSTRACT FROM AUTHOR]

Abstract The detection of cysteine (Cys) is of great significance ascribed to its important role in physiological and psychological process. This paper reported a new fluorescent probe CBFA with red emission signal, which can be prepared through a simple method and exhibited potential application value. Solution experiments demonstrated that the probe revealed high selectivity towards Cys in spite of the interference of its two analogues, homocysteine (Hcy) and glutathione (GSH). And the sensitivity indicated that the probe was suitable for Cys detection in living cells. Furthermore, the recognition mechanism was confirmed to be a concerted reaction including Michael addition and intramolecular cyclization by high resolution mass spectrometer (HRMS) and high-performance liquid chromatography (HPLC). Besides, CBFA showed favorable pH adaptability in biological conditions and low cytotoxicity. Finally, CBFA was successfully applied to selectively imaging Cys in living MCF-7 cells with good cell permeability. We hope this probe will bring some help to the diagnosis of Cys-related diseases. Graphical abstract Image 1 Highlights • A new fluorescent probe for cysteine detection with red emission signal. • Preparing process of the probe was rather simple. • Sensitivity of the probe was satisfactory for Cys detection in living cells. • Endogenous Cys imaging in living cells with high selectivity and sensitivity. [ABSTRACT FROM AUTHOR]

• Development of a novel red-emitting fluorescent probe (HSA) for the detection of Cys. • The probe can high sensitivity detect Cys with a low LOD. • Successfully verified the experimental results by the theoretical calculation study. • The probe can be used for exogenous Cys monitoring and endogenous Cys cell imaging experiments. Herein, we synthesized a red-emitting fluorescence turn-on probe (HSA) for specific detection of cysteine (Cys) over other biothiols (glutathione (GSH) and homocysteine (Hcy)). The acrylate group was chosen as the recognition site for specific discrimination of Cys. Absorption and emission spectra display a high selectivity towards Cys over GSH/Hcy, organic small-molecule interfering substances and anions, with a high sensitivity towards Cys (0.12 μM) in 1% ethanol-containing PBS buffer solution (25 mM, pH = 7.4). Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations were conducted to clarify the luminescence mechanism of the probe. Furthermore, the probe was successfully applied to the determination of free Cys in human serum and the fluorescence imaging of endogenous Cys in living cells. [ABSTRACT FROM AUTHOR]

Abstract In this study, we report a sequential and reversibility fluorescent probe (DP5) based on pentapeptide conjugated with dansyl groups using the solid phase peptide synthesis (SPPS) technology. DP5 showed immediate "turn off" response toward Cu2+ ions at an excitation wavelength of 330 nm with detection limits of 23.5 nM. The 2:1 binding ratio between DP5 and Cu2+ were confirmed using Job's plot method and fluorescence titration study, and DP5 -Cu complex was observed with an association constant of 6.76 × 108 M−2. As designed, DP5 -Cu complex as a promising analytical probe exhibited highly selective for H 2 S detection in aqueous solutions. The detection limit for H 2 S was obtained to be 17.2 nM, and lower than EPA and WHO guidelines. In addition, the reversibility and cyclicity were imparted to the DP5 during the detection of Cu2+ and H 2 S, and cycle effect is very good. Furthermore, DP5 displayed better biocompatibility and low biotoxicity, and sequential fluorescence "on-off-on" responses of DP5 to Cu2+ and H 2 S were successfully applied in two different living cells. Graphical abstract Unlabelled Image Highlights • A novel peptide fluorescent probe DP5 was synthesized. • DP5 exhibited selective fluorescent "on-off-on" response toward Cu2+and H 2 S. • The detection limits of Cu2+ and H 2 S were 23.5 nM and 17.2 nM respectively. • The reversibility process of DP5 with Cu2+ and H 2 S were confirmed. • DP5 could detect Cu2+ and H 2 S in two different living cells. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A new N-oxide based and turn on fluorescent probe for Fe2+ was developed. • The probe possessed a high selectivity for Fe2+ among various biologically relevant species and fast rapid response. • Monitoring Fe2+ with TPM fluorescence imaging for the first time. Abstract Iron is an essential element for human body, involved in important biochemical processes in the body, especially in biological oxidation. Misregulation of iron levels in the cell is concerned with serious diseases. Here, a novel two photon and turn on NIR-fluorescent probe based ICT for detection of Fe2+ is first reported. The probe exhibited brilliant selectivity and excellent sensitivity (DL = 4.5 μM), rapid response (15 min) and "naked-eye colorimetric sensor" for monitoring of Fe2+. More importantly, the probe was successfully applied to real-time monitor Fe2+ in living cell through two-photon microscopy fluorescence imaging with excitation 680 nm. [ABSTRACT FROM AUTHOR]

Abstract A red emissive fluorescent probe 1,7-dimethyl-3,5-bis(4-methoxyphenyl-vinyl)-8-(10-n-butyl-10H-phenothiazine-3-yl)BODIPY 1,7-dimethyl-3,5-bis(4-methoxyphenyl-vinyl)-8-(10- n -butyl-10 H -phenothiazine-3-yl)BODIPY (avyl-BODIPY-PTZ) with a special orthogonal donor-acceptor structure was designed and synthesized for rapid, sensitive, and selective discrimination of ClO−, over other reactive oxygen species and anions. The probe displays a linear ratiometric absorption (A 578 /A 640) and fluorescence (F 599 /F 660) response toward ClO− with a fast response velocity (~10 s). The limit of detection (LOD) for ClO− was obtained as 22.6 nM from the fluorescence titration experiment. The fluorescence enhancement of the probe can be observed from the 32-fold enhancement in ratiometric value (F 599 /F 660) and the increasement of quantum yield from 0.01 at 660 nm to 0.28 at 599 nm. The oxidation of S atom in phenothiazine by ClO− to form the sulfoxide-type structure was proposed as the recognizing mechanism according to the Mass spectral analysis. The ratiometric enhancement of fluorescence was rationalized by the theoretical calculations. The orthogonal donor-acceptor structure according to optimized calculation and solvent effects of avyl-BODIPY-PTZ illustrated that the ClO− oxidation induced conversion from the nonradiative TICT process to the radiative LE process and caused the fluorescence ratiometric enhancement. The probe with low cytotoxity can successfully permeate into living cells and the cell images can be achieved in single channel. Moreover, after addition of ClO−, another bright red emission channel of the probe switched on and the probe displayed two-channel emission in living cells. Graphical abstract fx1 [ABSTRACT FROM AUTHOR]

Abstract Hydrogen polysulfides (H 2 S n , n > 1) influence a variety of important biological functions and activities associated with hydrogen sulfide (H 2 S). The development of probes for rapid, selective, and sensitive detection of H 2 S n still remains a great challenge. Lysosome plays crucial roles in various physiological processes among living cells, which arouse high interest in detecting endogenous lysosome-targetable H 2 S n. To the best of our knowledge, there is no lysosome-targetable probe for H 2 S n has been reported. In this work, a new lysosome-targetable probe NIPY NF , based on the scaffold of imidazo [1,5-]pyridine, with a large Stokes shift (215 nm), low detection limit (84 nM), fast response time (6 min) and low cytotoxicity was designed and synthesized. Furthermore, NIPY NF was successfully applied into the cell imaging for detection of endogenous lysosome-targetable H 2 S n. Graphical abstract Image 1 Highlights • A novel lysosome-targetable probe NIPY NF was reported. • NIPY NF could discriminate H 2 S n over other analytes with high sensitivity, a low detection limit and a large Stokes shift. • NIPY NF could detect the endogenous H 2 S n in lysosome of living cells. [ABSTRACT FROM AUTHOR]

Abstract A novel dansyl-tetrapeptide fluorescent probe (L) for the continuous fluorescent "off-on-off" response detection of Cd2+ ions and Cysteine (Cys) has been designed and synthesized. In our approach, L exhibited very high selectivity to Cd2+ ions over other common metal ions in buffer aqueous solution at natural pH. The resulting L -Cd binding motif system could continuously detect Cys among Glutathione (GSH), Homocysteine (HCy) and 20 natural amino acids. The excellent reversibility and cyclicity of L were also confirmed during the detection of Cd2+ ions and Cys. The detection limit of Cd2+ ions and Cys were obtained to be 93 nM and 35 nM, and lower than EPA and WHO guidelines. What's more, L showed low cytotoxicity and exciting cell infiltration toward living cells, which successfully fluorescent "off-on-off" biological imaged Cd2+ ions and Cys effectively in HeLa cells and renal tubule epithelium (HK2) cells by confocal fluorescence imaging. This study will promote the development of novel multifunctional peptide-based fluorescent probe for Cd2+ ions and Cys in environmental and biological systems. Graphical abstract Unlabelled Image Highlights • A novel peptide fluorescent probe L was synthesized. • L displayed high sensitivity for Cd(II) with a low detection limit of 93 nM. • L -Cd binding motif system could continuously detected Cys with detection limits of 35 nM, and cycle effect were very good. • As a potential probe, L could continuously detected Cd2+ ions and Cys in living HeLa cells. [ABSTRACT FROM AUTHOR]

Abstract A long-wavelength fluorescent probe NR-CY was developed for simultaneous identification of cysteine/glutathione and sulphide by combining the derivative of Nile red with 7-nitrobenzofurazan. The response of NR-CY to thiols is regulated by intramolecular charge transfer and photoinduced electron transfer mechanisms. For sulphide at 560 nm, cysteine at 475 nm and glutathione at 425 nm, different absorbance increases can be observed. NR-CY can detect cysteine at fluorescence emission 543 nm and distinguish sulphide from other analytes by kinetic experiments at 636 nm. The probe showed a rapid response to these thiols (cysteine was 90 s and sulphide was 30 s). In addition, NR-CY has been successfully applied to live MCF-7 cell imaging. Graphical abstract A long-wavelength fluorescent probe NR-CY was developed for simultaneous identification of cysteine/glutathione and sulphide by combining the derivative of Nile red with 7-nitrobenzofurazan. The response of NR-CY to thiols is regulated by intramolecular charge transfer and photoinduced electron transfer mechanisms. For sulphide at 560 nm, cysteine at 475 nm and glutathione at 425 nm, different absorbance increases can be observed. NR-CY can detect cysteine at fluorescence emission 543 nm and distinguish sulphide from other analytes by kinetic experiments at 636 nm. The probe showed a rapid response to these thiols (cysteine was 90 s and sulphide was 30 s). In addition, NR-CY has been successfully applied to live MCF-7 cell imaging. fx1 Highlights • A new long-wavelength-emitting fluorescent turn-on probe NR-CY for simultaneous determination of biothiols was developed. • This probe is easily prepared from readily available inexpensive reagents. • Probe shows rapid response (90 s for Cys, 30 s for H 2 S) to these thiols. • The first PET and ICT-based fluorescent probe is suitable for biological imaging applications. [ABSTRACT FROM AUTHOR]

Abstract Novel cyanine-based fluorescent probes for the detection of H 2 S were developed. The probes developed are stable under physiological conditions. The water soluble fluorescent probe 2 displayed ultrafast and specific response to H 2 S displaying NIR fluorescence of 115-fold turn-on with the detection limit of 11 nM without assistance of organic solvent or surfactant. Cell imaging experiments indicated that probe 2 was cell-permeable and was able to detect H 2 S sensitively in lysosomes. Moreover, our probe was able to detect H 2 S intrinsically produced H 2 S through enzymatic/non-enzymatic biosynthetic pathway from Cys/GSH. Moreover, we applied probe 2 to detect H 2 S in living mice and demonstrated the fast metabolism of H 2 S. Thus, probe 2 shows great promise as a reporter for H 2 S. Graphical abstract Unlabelled Image Highlights • A novel water soluble cyanine-based NIR fluorescent probe for H 2 S. • Ultrafast and specific response to H2S with low detection limit in PBS buffer. • Lysosome-targeted and capable of detecting H 2 S (both enzymatic/non-enzymatic biosynthesized). • Visualization of H 2 S in living mice and demonstrated fast metabolism of H 2 S. [ABSTRACT FROM AUTHOR]

Abstract Hydrazine and its derivatives are one of the most important raw chemical materials that have extensive utilization in many areas. It is also widely applied as pharmaceutical derivatives, such as the antipsychotic drug, anti-infective drug, and antitumor drug. However, hydrazine is a highly toxic reagent which can bring severe damage to human and animals. Herein, we have reported a new benzothiazole substituted naphthalene based probe for hydrazine with huge fluorescence change ratio. The fluorescence change ratio at F 390 /F 509 is up to 200-fold in the presence of hydrazine in 60 min. The probe exhibited negligible cytotoxicity toward HeLa cells and was applied for hydrazine detection successfully in HeLa cells. Graphical Abstract Unlabelled Image Highlights • A ratiometric fluorescent probe highly sensitive to hydrazine has been designed and developed. • The fluorescence change ratio could be up to 200-fold in the presence of hydrazine. • The fluorescent probe exhibited negligible cytotoxicity and was successfully applied for hydrazine detection in HeLa cells. [ABSTRACT FROM AUTHOR]

Abstract An abnormal level of bisulfite can induce toxicological effects associated with lung cancer, cardiovascular and neurological disorders. Therefore, it is of significance to develop an effective fluorescent probe to detect bisulfite in living cells. Herein, a novel fluorescent probe QPCT , based on a 1,4-addition mechanism, was constructed for the colorimetric and ratiometric detection of bisulfite. QPCT displayed high selectivity and anti-interference ability to bisulfite over other anions and biothiols. The probe renders a sensitive ratiometric response to bisulfite with a remarkable fluorescence blue shift from 590 to 537 nm and the fluorescence ratio was linear with bisulfite concentration over the range of 0–120 μM. More importantly, QPCT has been successfully applied to detect bisulfite in sugars and living A549 cells, which indicated that QPCT had a great capability for monitoring bisulfite in complex systems. Graphical abstract A novel fluorescent probe QPCT for the colorimetric and ratiometric detection of HSO 3 − was constructed and successfully applied for sugar analysis as well as imaging in living A549 cells. Image 1 Highlights • QPCT displays a colorimetric and ratiometric response towards HSO 3 −. • QPCT exhibits good selectivity to HSO 3 − among various anions and biothiols. • QPCT has been successfully applied to detect HSO 3 − in real samples and living cells. [ABSTRACT FROM AUTHOR]

Abstract A new coumarin-derived hydrazone (1) has been developed as a "turn-on" fluorescent probe for the detection of Cu2+ in two different sensing mechanisms. In anhydrous acetonitrile, the strong fluorescence response of 1 to Cu2+ was mainly attributed to the chelation-controlled C=N isomerization. Besides, S-donor is indispensable in protecting from the Cu2+-induced fluorescence quenching. In aqueous acetonitrile, 1 as a chemodosimeter can highly selectively sense of Cu2+, which was ascribed to the Cu2+-promoted cyclization reaction affording the strong fluorescent cyclization product (2). The proposed cyclization reaction was confirmed by the single-crystal structure of 2. Furthermore, 1 was utilized for imaging intracellular Cu2+ with good performance. Graphical abstract Image 1 Highlights • A fluorescent chemodosimeter for Cu2+ based on Cu2+-promoted cyclization reaction was developed. • The fluorescent product of the Cu2+-promoted reaction was characterized by single-crystal X-ray analysis. • The aza-michael addition based mechanism of the Cu2+-promoted cyclization reaction was proposed. • The chemodosimeter was utilized for imaging intracellular Cu2+ with good performance. • The fluorescent probe can sense Cu2+ in two different sensing mechanisms. [ABSTRACT FROM AUTHOR]

Abstract A multisite-binding fluorescence turn-on probe of Rh6G NH PBA has been prepared in this study. The probe selectively responds to mitochondrion adenosine triphosphate (ATP) concentrations. The fluorescence intensity of Rh6G NH PBA toward ATP was enhanced by approximately 51-fold in water at 1.0 mM. In particular, Rh6G NH PBA exhibited good selectivity to ATP, surpassing other anions due to a cooperative effect from multisite-binding recognition. Live-cell imaging indicates that Rh6G NH PBA locates mainly into mitochondria with good biocompatibility. The results demonstrate that Rh6G NH PBA is a useful probe for the monitoring of mitochondria ATP-relevant processes. Highlights • A multisite-binding switchable fluorescent probe of Rh6G NH PBA. • Rh6G NH PBA exhibits good selectivity to ATP, surpassing other anions. • Rh6G NH PBA can be specifically localized in mitochondrion. • Real-time detection of mitochondrial ATP concentration changes. [ABSTRACT FROM AUTHOR]