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Nitroreductase (NTR) is overexpressed in hypoxic tumor cells, which is closely related to inflammation, tumorigenesis, tumor invasion and metastasis. Therefore, developing fluorescence probes for detecting intracellular NTR sensitivity has great significance for diagnosis and treatment of tumors. Therefore, we designed a novel fluorescent probe (Pro-CN) based on julolidine skeleton for the detection of NTR. The probe could discriminate rapidly NTR from other biological species like sulfhydryl compounds and some ions. Meanwhile, a fine linear relationship between fluorescence intensity of the probe and NTR consistence has been observed with a very low detection limit of 4.4 ng/mL. In addition, Pro-CN was successfully applied in imaging endogenous NTR in Hela cells and living zebrafish. The excellent performance of the probe makes it have great potential for monitoring NTR in complex biological systems, and it also provides the possibility of its application in human health, disease diagnosis and treatment. [Display omitted] • Probe Pro-CN exhibits a turn-on fluorescence for sensing NTR. • Pro-CN is highly sensitive to sense NTR with a very low detection limit of 4.4 ng/mL. • Pro-CN was successfully applied for imaging endogenous NTR in living Hela cells and zebrafish. [ABSTRACT FROM AUTHOR]

Ammonia is a common toxic gas in industrial and agricultural production, which will cause harm to the environment and human health in certain extent. Here, a novel fluorescent probe (R)- 1 based on 1,1′-binaphthol (BINOL) was synthesized for real-time, on-site and quantitative detection of ammonia. The mechanism study shows that the functional groups of –CHO and –OH on (R)- 1 interact with ammonia, which changes the electronic state of the probe molecule and excites strong fluorescence. A test strip for rapid detection of ammonia was developed, which changed from light yellow to reddish brown under natural light after interacting with ammonia, thus realizing the rapid detection and easy visualization of ammonia. Meanwhile, bioimaging experiments shows that probe (R)- 1 can detect exogenous ammonia in cells. [Display omitted] • Specific selective fluorescence recognition of ammonia. • Fast response time (300 s) and high sensitivity (0.96 ppm). • A test strip for real-time and visual detection of ammonia. • Exogenous ammonia fluorescence imaging of cells. [ABSTRACT FROM AUTHOR]

Ratiometric probes are favored for their application in biological systems, and the signal ratio between two channels is a crucial indicator for evaluating the performance. Since changing the substituent group on the recognition group would significantly influence the response performance of a fluorescent probe, in this work, we modified the substituent group on the 7-position of a coumarin to give two Hg2+ probes based on through-bond energy transfer (TBET) strategy; the probes displayed a much higher detection capacity and emission ratio between the red and blue channels. The probes were successfully applied for Hg2+ imaging in cells and living mice and possess significant bacteriostatic activity, demonstrating potential application in biological science, but also present excellent stability and detection ability serving as solid-phase detection materials via fabricating into nanofiber using electrostatic spinning. [Display omitted] • TBET-based Hg2+ probes were constructed with LOD low to 2.7 nM. • Better response performance was achieved by modifying the recognition group. • Living cells and mice detection suggest good bioimaging ability. • The probes possess good bacteriostatic activity due to their lactam structure. • The probes were fabricated into nanofiber test strips via electrospinning. [ABSTRACT FROM AUTHOR]

The tertiary structures of HSA and BSA show a 76 % similarity, and the abnormal levels of HSA in body fluids can cause many diseases. Therefore, accurate quantification of HSA and effectively distinguishing HSA from BSA have significant application value in various fields. In this paper, a deep-red fluorescent probe, NITH , based on 1,8-naphthalimide, is demonstrated as a potential tool for accurately quantifying HSA and distinguishing HSA from BSA. The probe not only exhibits large stokes shift (100 nm) and low detection limit (4.61 μg/L, 0.0692 nM), but also effectively detects HSA by entering its hydrophobic cavity and emitting red fluorescence. Furthermore, NITH is capable of tracking the distribution levels of HSA within the cells through endogenous and exogenous cellular imaging. The application of NITH spans various environments such as cells, zebrafish, urine, and test strips, solidifying it as an effective tool for HSA detection. [Display omitted] • NITH has been synthesized by introducing benzothiazole sulfonate at the 3-position of 1,8-naphthalimide. • NITH can effectively distinguish HSA from BSA. • NITH can quickly identify, detect and track HSA in bioimaging. • NITH can be successfully applied in test strips, urine, cells and zebrafish imaging. [ABSTRACT FROM AUTHOR]

A new hemicyanine-based near-infrared "off-on" recognition Cu2+ fluorescent probe NRh-NP was designed and successfully synthesized. The structure of NRh-NP was characterized by NMR, ESI-HRMS and single crystal X-ray diffraction analysis. NRh-NP has high sensitivity, selectivity and a low limit of detection (33 nM as fluorescence sensor and 35 nM as UV sensor) to Cu2+. According to Job's plot and ESI-HRMS, the coordination ratio of NRh-NP to Cu2+ was 1:1. DFT theoretical calculations proved that the sensor mechanism was photo-induced electron transfer (PET). More importantly, NRh-NP has excellent membrane permeability and low cytotoxicity, which could be used not only for the detection of Cu2+ in human breast cancer cells (MCF-7), but also for imaging Cu2+ in living mice. [Display omitted] • The structure of NRh-NP was characterized by NMR, ESI-HRMS and single crystal X-ray diffraction analysis. • The responses of NRh-NP toward Cu2+ were fully proved by Job's plot, ESI-HRMS and DFT theoretical calculations. • NRh-NP has high sensitivity and selectivity with detection limit as low as 33 nM. • NRh-NP can be used for Cu2+ imaging in living cells and in vivo. [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]

In this paper, several novel nitrogen-containing heterocycle dyes 1a-c with large conjugated planar structures based on naphthyridine derivatives were designed and synthesized, which had excellent optical properties and biological applications. Optical test showed the maximum absorption wavelengths of 1a-c were in the range of 443–485 nm, while the maximum emission wavelengths located at 523–610 nm in difference solvents. Furthermore, they exhibited polarity related fluorescence intensity changes with high fluorescence quantum yields, even up to 88% (1a in THF). Moreover, the transient absorption spectra revealed the excited-state lifetime of dye 1a became shorter with the increase of solvent polarity. Density functional theory calculations are also used to help explain the effect of the polarity of solvents on their fluorescence properties. Interestingly, the dyes 1a-c were somewhat toxic to cancer cells, while had an obvious growth-promoting effect on normal cells. Additionally, 1a-c with excellent lipid droplet (LD) targeting could be used for long-term observation of targeted cellular lis) hysiological activity and further applied to dynamic monitoring of changes in LDs polarity stimulated by TLR4 activator (LPS) in living cells. Overall, the excellent optical properties and biocompatibility of 1a-c indicate that they can serve as fluorescent probes for biological applications, and the results have important implications for understanding the physiological functions of LDs, especially in terms of morphological and polar changes. [Display omitted] • The dibenzo[c,f] [2,7]naphthyridine skeleton have been first applied in the field of cell imaging. • Dyes 1a-c possess high fluorescence quantum yield and excellent polarity response. • Dyes 1a-c are somewhat toxic to cancer cells, while have a growth-promoting effect on normal cells. • Dyes 1a-c can sensitively target lipid droplets with a low concentration, and dynamically monitor their polarity changes. [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]

Hydrogen sulfide (H 2 S) is a vital gas signaling molecule that performs crucial physiological functions in biological systems, and it can also cause food safety problems. In this study, we developed a cyanine derivative-based mitochondrial-targeted near-infrared fluorescent probe PC-H 2 S for detecting H 2 S. When PC-H 2 S reacted with H 2 S, it reached maximum fluorescence intensity at 656 nm and detection limit as low as 34 nM, and exhibited strong chromogenic response from green to red for H 2 S. Moreover, PC-H 2 S could be utilized to identify H 2 S generated during food spoilage and thus monitored the process of food spoilage. More significantly, PC-H 2 S showed excellent mitochondrial targeting capabilities and endogenous/exogenous H 2 S imaging of living cells and zebrafish could be performed. As a result, this research provides an attractive method for detecting H 2 S in food and biological systems and has potential value in physiopathological research. [Display omitted] • A cyanine derivative-based mitochondrial-targeted NIR fluorescent probe PC-H 2 S for detecting H 2 S was developed. • PC-H 2 S had a low detection limit and exhibited strong chromogenic response from green to red for H 2 S in naked eyes and UV light. • PC-H 2 S test strips was capable of monitoring H 2 S produced by food spoilage. • PC-H 2 S could be used for living cells and zebrafish imaging. [ABSTRACT FROM AUTHOR]

Developing fluoran dyes for fluorescent material is significant but challenging because they are notorious for terrible luminescent efficiency. In this manuscript, two fluoran dyes (F3 and F4) were synthesized by the introduction of thiazole and indazole into the fluoran skeleton, which showed colored and fluorescent spirolactone opening form in a wide pH range (F3 : 1–10, F4 : 1–13). In addition, the absorption and emission spectra of methyl esterification products F3Me and F4Me showed large Stokes shifts (over 75 nm) in water and achieved an improved fluorescence quantum yield of 30.1% in CHCl 3. Based on the dye F4Me, a new fluorescent probe F4HP was developed, which showed high selectivity and high sensitivity (LOD of 2.0 nM) to copper ions in H 2 O/CH 3 CN (v/v, 3/2) system. Moreover, the sensing experiment was allowed in the pH range of 4.0–7.5. Furthermore, the F4HP exhibits suitable cell cytotoxicity and can be applied for imaging intracellular copper ions by confocal fluorescence imaging technology. Thiazole and indazole functionalized fluoran dyes were prepared with improved fluorescence and application in the construction of a novel copper-selective and sensitive fluorescent probe. [Display omitted] • Two modified fluoran dyes were prepared with stable fluorescence in water. • F4Me achieved a fluorescence quantum yield of 30.1% in CHCl 3. • A novel probe F4HP for Cu2+ was prepared with high selectivity and sensitivity. • F4HP could be employed as a tool for imaging intracellular Cu2+. [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]

The fluorescent probe with both aggregation-induced emission (AIE) and excited-state intramolecular proton transfer (ESIPT) shows significant advantages, such as no self-quenching at high concentration, large Stokes shift, high selectivity towards analyte etc. Based on tetraphenylethene and ESIPT structural modules, three AIE-ESIPT molecules containing one different atom (S, O, N) have been constructed in this paper. The effects of three atoms on the optical properties of fluorescent molecules have been investigated by fluorescence spectroscopy and X-ray crystallographic analyses. Interestingly, the cyclic detection of HCl and NH 3 gases can be achieved with the BTY-TPE -based portable test paper. In addition, BOY-TPE and HBIY-TPE can detect ClO− by naked eye with low detection limit, good biocompatibility. Three AIE-ESIPT fluorescent probes respectively containing S, O, N atoms have been synthesized. The effects of S, O, and N atoms on the optical properties of fluorescent molecules have been investigated by fluorescence spectroscopy and X-ray crystallographic analyses and DFT calculation. The results indicate that all three exhibit AIE and ESIPT properties, X-ray crystallographic analysis indicate a significant difference in molecular packing, which should be the dominant factor in the polymorph dependence of ESIPT luminescence. It is interesting to note that BTY-TPE -based test paper can be used for cyclic detection of HCl and NH 3 gases. In addition, BOY-TPE and HBIY-TPE can be used as intracellular probes for detecting ClO−.[ [Display omitted] ] • Three AIE-ESIPT double-mechanism fluorescent crystals have been synthesized. • Effects of S, O, and N on the properties of three fluorescent crystals were discussed. • BTY-TPE -based test strip could repeatable detect HCl and NH 3 gases. • Both BOY-TPE and HBIY-TPE with extremely low detection limit for detecting ClO−. • Both BOY-TPE and HBIY-TPE could detect ClO− in living cells. [ABSTRACT FROM AUTHOR]

Herein, we designed a potent ClO− probe named ETMC , which exhibited aggregation-induced emission (AIE) characteristic in solid state and water/EtOH binary solvent. Probe ETMC exhibited an colormetric from yellow to blue and ratiometric response to ClO− with high selectivity and sensitivity, and a low detection limit of 3.66 × 10−7 M. Moreover, probe ETMC could be applied to visibly and quantitatively detect the different concentraction of ClO− in test paper. Importantly, probe ETMC could effectively detect endogenous and exogenous ClO− in living A549 cells by an outstanding ratio signal change. Also, the sensing mechanism of probe ETMC for ClO− was confirmed by FT-IR, 1H NMR, HRMS, DLS, TEM and DFT calculation. In this work, probe ETMC, which exhibited aggregation-induced emission (AIE) characteristic in solid state and water/EtOH binary solvent was developed and could effectively detect endogenous and exogenous ClO− in living A549 cells by an outstanding ratio signal change. Also, the probe ETMC has been successfully applied in visibly and quantitatively detection the different concentraction of ClO−. [Display omitted] • A fluorescent probe ETMC with AIE effect was developed, which exhibited an colormetric and ratiometric response to ClO−. • The probe ETMC could be applied to visibly and quantitatively detect the different concentraction of ClO− in test paper. • The probe ETMC could detect endogenous and exogenous ClO− in living A549 cells by an outstanding ratio signal change. [ABSTRACT FROM AUTHOR]

Strategically modified4-(diethylamino)-2-(pyridin-2-ylmethoxy)benzaldehyde appended BODIPY-based probe N,N-SP-BPY detects aspartic acid (Asp) and glutamic acid (Glu) by inhibition of Photoinduced electron transfer (PET) process in water. The probe shows considerable and rapid fluorescence enhancement upon addition of Asp and Glu. Additionally, a distinct colorimetric change from pink to a colorless solution can be observed to recognize traces of Asp and Glu. The probe detects Asp and Glu as low as 1 μM and 5 μM respectively. Furthermore, the probe can efficiently detect intracellular Asp and Glu in live HeLa, A549, MDA-MB-468 and HEK-293T cells under fluorescence microscope without showing any cytotoxic effect. Two model BODIPY derivatives are also synthesized to establish strategic modification. 1H NMR titration and theoretical calculations strongly supports experimental findings. Image 1 • A highly selective BODIPY probe, N,N-SP-BPY detects aspartic acid (Asp) and glutamic acid (Glu) in water. • 'Turn On' fluorescence can be observed by inhibition of Photoinduced Electron Transfer (PET) process. • A distinct colorimetric change from pink to colourless solution can be observed to recognize Asp and Glu. • N,N-SP-BPY efficiently images intracellular Asp and Glu in live cells under fluorescence microscope. [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]

In this study, a pH-sensitive fluorescent probe was created through the host-guest assembly of an amphiphilic hydroxyphenyl benzotriazole derivative (HBT-11) and cucurbit[7]uril (CB7). The fluorescence of HBT-11 is highly dependent on the molar ratio (r) of CB7 to HBT-11. If r < 1, the peak positions remain unchanged while the intensity increases with r. If r > 1, the emission peaks shift to longer wavelengths. The complexation also results in a shift in the p K a of HBT-11. The 1:1 mixture of CB7 and HBT-11 has a p K a close to neutral pH. The supramolecular probe allows for discrimination of malignant A549 and benign HEK 293T cells owing to a pronounced 8-fold light-up effect in malignant A549 cells attributed to the pH-responsive fluorescence. Given that the selective light-up mechanism is based on the pH-sensitive fluorescence of the supramolecular probe, this approach is expected to be applicable to other cancer cells. [Display omitted] • A pH-sensitive supramolecular fluorescence probe was constructed. • The fluorescent intensity of the probe was greatly enhanced as pH < p K a. • The probe was applied to discriminate malignant and benign cells. [ABSTRACT FROM AUTHOR]

Mitochondria and lysosomes play important roles in maintaining normal cellular metabolism; thus, visualizing their morphology, structure, and interactions in living cells at the nanometer scale is essential for further understanding their functions. However, this remains challenging because of the current limitations of fluorescent probes, including poor photobleaching resistance, low biocompatibility, and lack of multi-organelle targeting. Herein, we report the development of biocompatible nitrogen-doped carbon dots (CNDs) with long excitation wavelengths, stable fluorescence, and dual-organelle targeting capabilities. The CNDs enter cells predominantly via energy-dependent transport (including clathrin- and caveolae-mediated endocytosis) and free diffusion and subsequently target the interior mitochondria and lysosomes; furthermore, they enable the stimulated emission depletion imaging of these organelles in living cells with resolutions of up to 134 and 55 nm, respectively. This study provides practical guidance for designing dual-organelle targeting fluorescent probes for the dynamic super-resolution imaging of cellular systems. The nitrogen-doped carbon dots (CNDs) with Long-wavelength excitation for the visualization of lysosomes and mitochondria in the stimulated emission depletion imaging (STED) of live HeLa cells. [Display omitted] • N co-doped CNDs with green fluorescence are successfully synthesized. • CNDs have high fluorescence stability and long-wavelength excitation. • CNDs can target the both the mitochondria and lysosomes in the living cell. • CNDs were suitable as probes for STED imaging of mitochondria and lysosomes. [ABSTRACT FROM AUTHOR]

Fluorescent probes sensitive to microenvironments have constantly been attractive, due to their significant benefits in monitoring changes in the pathophysiological microenvironment and their use in the early detection of associated disorders. In this work, we explored three new molecular rotors that could be potential candidates for detecting lipid droplets (LDs) in cancer cells based on coumarin derivatives connected with electron-donating polycyclic units including, tetraphenylethylene (LD-TPE), pyrene (LD-PYR), and 4,5-diphenylimidazole (LD-DIP). Gratifyingly, LD-PYR showed exceptional polarity and viscosity sensitivity and demonstrated bright fluorescence in highly viscous environments due to the suppression of the twisted intramolecular charge transfer (TICT) phenomenon and intramolecular rotation. Moreover, microenvironment-guided specific LD bioimaging by LD-PYR exhibited a reasonable ability to distinguish between cancer and noncancer cells. These data suggested that LD-PYR has interesting clinical diagnostic and microenvironment-related biological applications. [Display omitted] • Highly polarity and viscosity-sensitive fluorescence probes have been introduced. • LD-PYR probe shows bright fluorescence in a lipophilic environment due to TICT suppression. • LD-PYR demonstrates good biocompatibility in both cancer cell and normal cell lines. • LD-PYR can selectively image lipid droplet in cancer cells. [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]

As a signal molecule, SO 2 plays an important role in the process of cell metabolism. The abnormal level of sulfur dioxide will induce many diseases of human body. Viscosity is an important index of lysosome. Abnormal lysosome viscosity can also lead to many diseases. Therefore, we have developed a new fluorescence probe PAPD for simultaneous imaging of sulfur dioxide derivatives and lysosomal viscosity. The probe realizes rapid detection of HSO 3 − based on Michael addition reaction mechanism. At the same time, with the increase of viscosity, intramolecular rotation is inhibited, thus the probe shows sensitive fluorescence enhancement. In addition, the results of the co-localization experiments show that PAPD has good lysosomal targeting ability. Further studies show that PAPD can be used as a dual-responsive fluorescence probe for SO 2 and viscosity in lysosomes. PAPD can monitor the changes of sulfur dioxide derivatives and viscosity sensitively at the same time, and can well locate in lysosomes. [Display omitted] • A NIR fluorescent probe PAPD was developed for detecting the SO 2 derivatives and viscosity in lysosomes. • PAPD towards HSO 3 − represented excellent selectivity, anti-interference, photostability, and thermal stability. • PAPD was applied for sensing viscosity, endogenous and exogenous HSO 3 − in cells. [ABSTRACT FROM AUTHOR]

Abstract Fluoride recognition and sensing via artificial receptors have attracted a great deal of attention since it plays an important and indispensable role in biological and environmental processes. Herein, a novel colorimetric and fluorescent chemodosimeter (3-triisopropylsilylflavone 1) based on 3-hydroxyflavone framework has been rationally designed and synthesized for selective recognition towards fluoride. As confirmed by UV–vis and fluorescence techniques, the fluorescent probe 1 exhibited a highly sensitive and selective as well as rapidly responsive (20 s) recognition towards fluoride with a large Stokes shift of 180 nm. The detection limit was deduced to be 0.68 μM, which is much lower than the limit concentration level in drinking water specified by USEPA. The distinctive sensing mechanism is attributed to fluoride-triggered desilylation reaction on the cleavage of Si O bonds, leading to the strong excited-state intramolecular proton transfer emission of 3-hydroxyflavone. In addition, test strips experiment based on the sensor demonstrated the excellently practical feasibility of 1 to sense fluoride even in ppm level. Moreover, the probe is cell permeable and can be capable of reliably detecting fluoride in living cells. Graphical abstract The first colorimetric and fluorescent chemodosimeter based on 3-hydroxyflavone framework has been rationally designed and synthesized for selective recognition towards fluoride in the field of flavone chemistry. Image 1 Highlights • A novel fluorescent chemodosimeter 1 for selective recognition towards fluoride has been designed and synthesized. • It presents the first chemodosimeter for selectiverecognition towards fluoride in the field of flavone chemistry. • The probe 1 exhibited a highly sensitive and selective as well as a rapidly responsive recognition towards fluoride. • The probe 1 is cell permeable and can be capable of reliably detecting fluoride in living cells. [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]

Abstract Cysteine (Cys) plays a vital role in many physiological processes, and also is closely related to various diseases, thus the development of novel high selectivity and sensitivity fluorescent probes for in situ monitoring of biothiol (Cys) is crucial. Herein, we present a fluorogenic method to detect Cys in vitro and live cells based on fluorescent protein chromophores, which have been modulated by chemical reaction. Probe (RFP) is a fluorescence turn on probe with red emission wavelength and large Stokes shift (127 nm). This Michael-addition reaction-based probe exhibits low detection limit (18.7 μM), fast response time, and low cytotoxicity. RFP can differentiate the Cys and Hcy, using the difference of reaction time between probe and Cys or Hcy. Together, this probe exhibited excellent cell permeability, and can be successfully applied to detect the endogenous Cys in living cells. Highlights • Provide a fluorogenic method to detect Cys based on fluorescent protein chromophores. • Realize the red emission and large Stokes shift using chemical modulation method. • Differentiate the Cys and Hcy using the difference of reaction time. • Detection endogenous or exogenous Cys in living cells and served as bioimaging reagent. [ABSTRACT FROM AUTHOR]

Abstract Recently, the fluorescence detection of H 2 S in biological systems has attracted the attention of many analytical chemists. However, most of H 2 S probes showed shorter fluorescence emission (<600 nm) with fluorescence intensity change induced by H 2 S, which has some disadvantages of shallower tissue penetration and bigger autofluorescence interference. Herein, we have rationally designed a near-infrared and ratiometric fluorescent probe (YC−1) for the detection of H 2 S based on isophorone. The detection process can be monitored by naked-eye. Addition of H 2 S, YC−1 showed that the emission ratios of fluorescence intensity at 540 and 660 nm (I540/I660) with an obvious enhancement from 0.05 to 13.3. Besides, the color of YC−1 changes from pink to yellow. As a probe for H 2 S, YC−1 exhibited better selectivity, better sensitivity and lower detection limits (0.17 μM). Moreover, YC−1 showed lower toxicity to HepG−2 cells and can be used for cell imaging. Graphical abstract Image 1 Highlights • 1. A novel ratiometric and near-infrared fluorescent probe for detecting H2S was developed. • 2. The probe showed higher selectivity and lower detection limit (0.17 μM) for H2S monitored by naked-eye. • 3. The probe can be used for monitoring exogenous and endogenous H2S in HepG-2 cells. [ABSTRACT FROM AUTHOR]

Abstract Hydrogen sulfide (H 2 S) is a powerful toxin which has a strong stimulating effect on the eye, respiratory system and central nervous system. Therefore, it is essential to detect H 2 S in biological samples. Fluorescence imaging technology has the advantages of real-time and non-invasive, so it is very advantageous to detect H 2 S in living cells. In this work, we designed and synthesized a fluorescent probe (named ND-N 3) based on naphthalimide derivative with symmetric structure and double recognition sites. The fluorescence intensity at 532 nm of ND-N 3 obviously increased with the increase of H 2 S concentration. Apart from this, the probe showed excellent selectivity and rapid response time. More importantly, ND-N 3 can be used to detect endogenous/exogenous H 2 S in living cells. Graphical abstract Image 1 Highlights • A novel H 2 S fluorescent probe (named ND-N 3) with dual-sites based on naphthalimide derivative. • The application of the probe for selective detection H 2 S in HepG-2 cells has been successfully demonstrated. • The probe has a good linear relation and limit of detection is only 0.02 μM. [ABSTRACT FROM AUTHOR]

Abstract Thiols such as amino acids Cys/Hcy and peptides GSH play vital roles in biological systems. Due to their similar structures and reaction activities, it is still desirable to develop new probes to simultaneously detect and discriminate Cys/Hcy and GSH. Taking advantage of the reductive activity of SH in these thiols, we combined two fluorophores coumarin and 7-nitrobenzofurazan with an ether bond to form the CA-NBD sensor to detect and discriminate Cys/Hcy and GSH simultaneously. CA-NBD showed high selectivity towards Cys/Hcy and GSH over other analytes with apparent colorimetric and fluorescent signals. At the excitation wavelength of 460 nm, CA-NBD could be used to discriminate Cys/Hcy from GSH with different fluorescence response. Furthermore, CA-NBD was successfully used to detect thiols in living Hela cells with low cytotoxicity. Graphical abstract A structurally simple and versatile fluorescent probe CA-NBD was synthesized, which could be used as a dual emission fluorescent probe for the detection and discrimination of Cys/Hcy and GSH in aqueous solution under mild conditions. Furthermore, the probe was successfully used to simultaneously detect Cys and GSH in living cells with low cytotoxicity. Image 1 Highlights • Coumarin and 7-nitrobenzofurazan were combined by an ether bond to form CA-NBD. • CA-NBD can be used as a naked-eye detector for biothiols over other amino acids. • CA-NBD can detect and discriminate Cys/Hcy and GSH simultaneously. • CA-NBD can be used to detect Cys in living cells with low cytotoxicity. [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 series of compounds (W1 - W8) based on triphenylamine with -C=N- or -NH- group, were designed and studied by fluorescence emission spectra and DFT/TDDFT calculations. Probes W1 - W4 were selectively leveraged to sensitively detect glutathione by two distinct reaction mechanisms, thereinto, W1 - W2 featured a convenient detection for glutathione using hydrolysis and W3 - W4 utilized displacement to probe glutathione possessing sensitivity and practicability. Compound W5 - W8 here provided an avenue for understanding structure-property relationship. Taken considerations for toxicity and biocompatibility together, W1 - W4 showed great advance for endogenously and exogenously imaging GSH in living cells. Graphical abstract Image 1 Highlights • A series of fluorescent probes for monitoring glutathione were synthesized. • Structural relation adjustment introduced two distinct reaction mechanisms: hydrolysis and replacement. • The probes had a good advantage for further endogenously and exogenously monitoring glutathione in vivo. [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 The development of organic dye-based fluorescent probes for detection of H 2 S in living systems has attracted considerable attention in recent years. In this work, a novel tetrahydroquinoxaline iminocoumarin-based red to near-infrared (red-to-NIR) fluorescent probe was developed for detection of H 2 S. This probe shows a rapid and distinct red-to-NIR fluorescent turn-on detection process for H 2 S with high selectivity and sensitivity (the detection limit was determined to be as low as 10 nM at physiological pH). In addition, this probe exhibits a remarkable large Stokes shift (128 nm) and low cytotoxicity, and can be applied for imaging H 2 S in living cells and animals. All these results demonstrated that this new probe is promising for detection of H 2 S both in vitro and in vivo. Graphical abstract Image 1 Highlights • A new iminocoumarin-based NIR fluorescent probe for H 2 S was reported. • This probe shows a rapid NIR fluorescent turn-on response for H 2 S with high selectivity and sensitivity. • This probe features a large Stokes shift (128 nm). • This probe can be used to image H 2 S in living cells and in vivo. [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]

Abstract Peroxynitrite (ONOO−) is an important kind of reactive oxygen species (ROS), played an essential role in physiology and pathology. To date, various fluorescent probes for ONOO− have been constructed successfully, but these probes exhibit turn-on fluorescence signal in single channel. While, ratiometric fluorescent probes, especially those probes with large emission shift, are suitable for bioimage in two channels. Herein, a hemicyanine-based fluorescent probe named Cy-NH 2 was designed and synthesized for ratiometric detection of ONOO−. The characteristics of Cy-NH 2 are as follows: (1) The probe possesses a simple structure, which can be obtained by easy synthetic steps; (2) The ratiometric fluorescent probe owns large emission shift (248 nm) due to the disruption of π-conjugation system caused by strong oxidizing ability of ONOO−; (3) The probe exhibits high sensitivity to ONOO− with 1728-fold enhancement of fluorescence intensity ratio and superior selectivity for ONOO− over various potentially interfering biological analytes; (4) The ratiometric fluorescent probe is applied for the image detection of exogenous and endogenous ONOO− in living cells successfully. Graphical abstract Image 1 Highlights • A ratiometric fluorescent probe (Cy-NH 2) is developed for detecting ONOO−. • The probe possesses a simple structure and can be obtained by easy synthetic steps. • The probe owns large emission shift due to the disruption of conjugation system. • The ratiometric fluorescent probe shows high sensitivity and selectivity to ONOO−. • The probe has been applied for the detection of ONOO− in living cells successfully. [ABSTRACT FROM AUTHOR]

Abstract A novel colorimetric fluorescent chemosensor TP1 with a D-π-A structure for the detection of (cyanide) CN− has been developed. TP1 is capable of showing high selectivity and sensitivity towards CN− over a wide range of other interfering anions. After reaction with CN−, TP1 shows a significant blue-shift of absorption peak from 514 to 437 nm, which induces color changes from amaranth to yellow. Non-fluorescent TP1 upon interaction with CN− exhibits a ca. 17-fold fluorescence enhancement at 551 nm, resulting in strong orange emission. The sensing mechanism of TP1 recognizes CN− which undergoes a nucleophilic addition reaction. Moreover, the detection limit of the probe TP1 towards CN− is 1.4 × 10−8 M, which is far lower than the WHO guideline of 1.9 μM cyanide for drinking water. In addition, the cell imaging experiments certify that TP1 can be successfully applied as a bioimaging agent for monitoring CN− in pheochromocytoma cell (PC12). Graphical abstract Image 1 Highlights • Probe TP1 with D-π-A featured structure for CN− was developed. • TP1 can detect cyanide with high sensitivity and selectivity. • The detection limit of TP1 towards CN− was 1.4 × 10−8 M. • TP1 can be applied in cell imaging with turn-on emission and low cytotoxicity. [ABSTRACT FROM AUTHOR]

Abstract Three novel fluorescent probes (L1, L2 and L3) derived from 2-hydroxyphenyl-4-chloromethyloxazole 8-ydroxyquinaldine were designed and synthesized. The probes showed highly selectively and sensitivity towards Cu2+ ion through "turn off" response in DMF/H 2 O solution (v/v = 1/1, 0.01 M, Tris-HCl buffer, pH 7.30). The detection limits of probes were up to 8.24 × 10−8 M for Cu2+ ion, which were much lower than drinking water permission concentrations by the United States Environmental Protection Agency. Sequentially, the L1-Cu2+, L2-Cu2+ and L3-Cu2+ complexes detected citrate anion (CA) through "turn on" response. The probes, were also found to be reversible and recyclable toward Cu2+ ion and CA controlled "On–Off–On" fluorescent switch and acted as molecular logic gates. Furthermore, the in vivo sensitivity experiments of Cu2+ ion and CA were demonstrated through fluorescence imaging in living cells. Graphical abstract In this study, we reported three novel probes L1, L2 and L3 for highly selectively and sensitivity detected Cu2+ ion through "turn off" response in DMF/H 2 O solution (v/v = 1/1, 0.01 M, Tris-HCl buffer, pH 7.30). Sequentially, the L1-Cu2+, L2-Cu2+ and L3-Cu2+ complexes detected citrate anion through "turn on" response, which could be applying as molecular logic gate. Furthermore, the in vivo sensitivity experiments of Cu2+ ion and citrate anion were demonstrated through fluorescence imaging in living cells. Image 1 Highlights • Three novel fluorescent probes L1, L2 and L3 exhibited excellent selectivity and sensitivity for the sequential detection of Cu2+ ion and citrate anions (CA). • The binding modes of probes L1, L2 and L3 with Cu2+ ion had been well demonstrated by UV–vis, fluorescence, IR and DFT calculation. • The detection limit of probe L3 for Cu2+ ion was 8.24 × 10−8 M which lower than the U.S. EPA limits and WHO of Cu2+ ion detection in drinking water. • The probes could act as INHIBIT logic gates and applied for Cu2+ ion and CA fluorescence imaging in living cells. [ABSTRACT FROM AUTHOR]

Abstract A new imidazo [1,5- a ]pyridine-based fluorescent probe, named MZC-AC, is developed for the detection of cysteine (Cys) based on an excited state intramolecular proton transfer (ESIPT) mechanism. The probe MZC-AC uses an acrylate moiety as the ESIPT blocking group as well as the recognition site. Upon the treatment with Cys, MZC-AC exhibits a dramatic fluorescence enhancement (85-fold) and a large Stokes shift (166 nm). The limit of detection obtained from fluorescent titration was as low as 0.07 μM. MZC-AC displays highly sensitive and selective response to Cys over homocysteine (Hcy) and glutathione (GSH). Significantly, MZC-AC could be used to detect Cys in living cells. Graphical abstract Image 1 Highlights • An imidazo [1,5- a ]pyridine-based fluorescent probe MZC-AC was developed. • MZC-AC can detect cysteine with high sensitivity and selectivity. • MZC-AC shows a large Stokes shift. • The limit of detection was as low as 0.07 μM. • MZC-AC can be applied in imaging intracellular cysteine in living cells. [ABSTRACT FROM AUTHOR]

Abstract Herein we pay attention to the design, synthesis and sensor activity of a novel biocompatible perylene-3,4,9,10-tetracarboxylic diimide (PDI) pH-probe in water. The synthesized compound shows selective fluorescence signalling properties as a function of pH (p K a value of 6.35 ± 0.02) which makes the probe suitable for pH determination in the physiological range. Thus prepared water soluble fluorescent system demonstrate low cytotoxicity to L929 cell lines from 330 μM to 1.3 μM and cell permeability in the lower concentration range. That findings show the high potential of the newly prepared PDI probe for monitoring of pH variations in bio-samples. Graphical abstract Image 1 Highlights • Fluorescent water-soluble perylene diimide pH probe is synthesized. • Probe is configured on the " fluorophore-spacer-receptor " model. • Probe operates via photoinduced electron transfer. • Probe shows low cytotoxicity towards L929 cell line. • Nano sized probe is cell-permeable at 0.001 mg/mL concentration. [ABSTRACT FROM AUTHOR]

A mitochondria-targetable ratiometric fluorescent probe, HBTPB , has been developed for the detection of H 2 O 2 with a near infrared (NIR) emission and a large Stokes shift (357 nm). Probe HBTPB displays high selectivity toward H 2 O 2 over other reactive oxygen/nitrogen species (ROS/RNS), biological thiols and anions. The detection limit of this probe is as low as 5.9 × 10 −7  M. The sensing process confirmed by NMR and mass spectral analysis shows that the addition of H 2 O 2 to the solution of HBTPB triggers an oxidative hydrolysis and a subsequent elimination reaction undergoes to release an ESIPT (excited-state intramolecular proton transfer) featured fluorescent dye. Probe HBTPB is cell permeable and has been applied to sense exogenous and endogenous H 2 O 2 in living A549 cells. [ABSTRACT FROM AUTHOR]

G-quadruplex (G4) is a noncanonical nucleic acid secondary structure that has been demonstrated to have an impact on many physiological and pathological processes. To facilitate the development of small molecule drugs targeting G4, it is critical to develop functional G4 fluorescent probes that selectively reflect the unknown physiological functions of G4 and enrich the library of G4 ligand molecules. In this study, trimethine cyanine with a p -hydroxybenzyl substituent at the α -position on the polymethine chain ( α -HBCy3.5) was used as a fluorescent probe for G4. By introducing bulky benzyl substituent on the polymethine chain, α -HBCy3.5 showed excellent G4 selectivity and could identify G4s from single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA) by fluorescence turn-on. Thus, red fluorescence is emitted by α -HBCy3.5 in the presence of G4s (606 nm). In addition, the ability of α-HBCy3.5 to stain DNA in mitochondria in a short time (internalization in 6 min) is expected to be developed for real-time detection and monitoring of endogenous G4 DNA in living cells. [Display omitted] • Polymethine chain modified cyanine dye is used as G4 fluorescent probe. • α -HBCy3.5 is highly specific in identifying G4. • α -HBCy3.5 emits red fluorescence (606 nm) upon bounding to G4. • α -HBCy3.5 localizes in mitochondria and stains DNA. [ABSTRACT FROM AUTHOR]

In this work, a novel FRET-based fluorescent probe (named CBC) was developed to detect bisulfite with outstanding selectivity by ratiometric method. Probe CBC exhibited excellent sensitivity toward HSO 3 − within 1 equivalent. The cell imaging of CBC indicated that it could detect exogenous and endogenous bisulfite with excellent photostability and low cytotoxicity. What's more, probe CBC realized the lipid droplet targeting. Therefore, probe CBC has the capacity to be used as a biological tool to monitor the bisulfite changes in vivo. [Display omitted] • A novel ratiometric fluorescent probe CBC was developed to detect sulfur dioxide derivatives. • CBC had a large Stokes shift of 230 nm and 95.7% energy transfer efficiency. • CBC possessed good selectivity and sensitivity toward sulfur dioxide derivatives. • CBC achieved detection sulfur dioxide derivatives in living cells and targeted lipid droplets. [ABSTRACT FROM AUTHOR]

The development of long-wavelength fluorescent probes with a pH working range from weakly acidic to neutral is important for cell-imaging studies. In this study, quinoline-malononitrile (QM)-based fluorescent probes without and with iodine substitution surrounding its phenolic ring are synthesized. The iodine substitution manner was found to compromise the aggregation-induced emission of QM whilst resulting in a significantly enhanced sensitivity for biothiols including l -cystine (L-Cys) detection in weakly acidic to neutral aqueous buffer solutions through reducing the pKa of the QM fluorogen. The probe also effectively achieved the fluorescence visualization of the fluctuation in L-Cys levels in cells. [Display omitted] • Iodine substitution compromises the AIE property of QM dye. • pKa of QM dye is reduced by iodine substitution. • Iodine-substituted QM dye works at weakly acidic and neutral pH. • Visualization of fluctuations in biothiol level in cells is achieved. [ABSTRACT FROM AUTHOR]

A dual-responsive fluorescent probe FDOCl-N-Na was designed and synthesized for the detection of two reactive oxygen species (ROSs) H 2 O 2 and HClO. FDOCl-N-Na displayed individual response toward H 2 O 2 and HClO presenting green and red fluorescence, respectively. FDOCl-N-Na was able to simultaneously monitor the cellular variations of H 2 O 2 and HClO with high selectivity, and high sensitivity under a wide application range of pH. The cell imaging experiments demonstrated that FDOCl-N-Na could successfully distinguish cancer cells from normal cells base on abnormal expression of H 2 O 2 and HClO. Moreover, FDOCl-N-Na also could be applied to tracing the fluctuation of H 2 O 2 and HClO in Caenorhabditis elegans. In this paper, a dual-responsive fluorescent probe (FDOCl-N-Na) was designed and synthesized for revealing cellular levels of H 2 O 2 and HClO in normal and cancer cells. FDOCl-N-Na displayed individual response toward H 2 O 2 and HClO presenting green and red fluorescence, respectively. FDOCl-N-Na could successfully distinguish cancer cells from normal cells base on abnormal expression of H 2 O 2 and HClO, and could be applied to tracing the fluctuation of H 2 O 2 and HClO in Caenorhabditis elegans. [Display omitted] • A H 2 O 2 and HClO dual-responsive fluorescent probe (FDOCl-N-Na) was designed and synthesized. • FDOCl-N-Na displayed individual response toward H 2 O 2 and HClO. • FDOCl-N-Na could distinguish cancer cells and could tracing H 2 O 2 and HClO in Caenorhabditis elegans. [ABSTRACT FROM AUTHOR]

Abnormal SO 2 derivatives level induces mitochondrial and lysosomal dysfunction, which is associated with a variety of diseases. Therefore, it is imperative to develop fluorescent probes which are suitable for detection of SO 2 derivatives in biological systems. Herein, we developed two new ratiometric fluorescent probes, MByn and HByn, which can respond to HSO 3 − in PBS buffer solution accurately and rapidly on basis of Michael addition reaction. After addition of HSO 3 −, ratiometric response signal increases by 5 folds, accompanied by a macroscopic change of fluorescence color. What's more, the two novel fluorescent probes MByn and HByn exhibited low detection limit (LOD = 0.96/0.79 μM), good photostability and low cytotoxicity. Cell imaging experiments showed that MByn and HByn were able to localize mitochondria and lysosomes accurately and detect both exogenous and endogenous SO 2 derivatives in living cells. [Display omitted] • Beyond fluorescence ratio changed of the probes toward addition of HSO 3 − (0−20.0 μM). • The probes showed relatively high fluorescence quantum yields. • Two probes can achieve dual targeting of mitochondria and lysosomes. • The probes could be used to monitor exogenous and endogenous HSO 3 − . [ABSTRACT FROM AUTHOR]

The abnormal expression of cytochrome P450 2J2 (CYP2J2) is closely related to the proliferation of human cancer cells. In this study, a red-emitting probe with an aggregation-induced emission (AIE) effect for the quantification of CYP2J2 was developed by modifying the typical AIE fluorescent group tetraphenylethylene (TPE) through two-step synthesis. Upon addition of CYP2J2, the probe underwent O-demethylation and spontaneously 1,6-elimination reactions of p-hydroxybenzyl that allowed it to alter its photophysical properties, thus realizing light-up detection of CYP2J2 with extremely large Stokes shift (236 nm), excellent sensitivity and selectivity, low detection limit (1.09 nM). Moreover, this new AIE-active probe with good biocompatibility was admirably employed to tracking endogenous CYP2J2 in living cells. • An AIE-based fluorescent probe (TPE-Bn) was designed to detect CYP2J2. • This probe showed significant Stokes shift (236 nm), good photostability, excellent sensitivity and selectivity, and low cytotoxicity. • This probe can be used to visualize endogenous CYP2J2 in living cells and tissues. [ABSTRACT FROM AUTHOR]

Hydrazine is widely used as a wide range of industrial chemical reagents. Because of its toxicity and explosiveness, it poses a serious threat to human health and ecological security. Therefore, it is of great significance to develop a real-time tracing method for hydrazine. Here, a novel turn-on fluorescent probe SXNU-1 for the detection of hydrazine was synthesized based on phenothiazine. SXNU-1 showed excellent selectivity toward hydrazine over various competitive species. Vinyl group with cyano and ethylacetate groups in SXNU-1 could react with hydrazine to form Schiff's base, showing bright green fluorescence. The response mechanism was verified by theoretical calculation, 1H NMR titration and HRMS. In addition, SXNU-1 can determine hydrazine in soil, water samples and test strip. Because SXNU-1 has good cell membrane permeability, it can monitor different concentrations of hydrazine in HeLa cells. Therefore, we believe that SXNU-1 has great potential in the analysis and monitoring of environmental pollutants. [Display omitted] • Phenothiazine-based multifunctional fluorescent probe was synthesized by a simple condensation reaction. • The probe showed high selectivity and fast response to hydrazine in DMSO/PBS (1/1, v/v, pH = 7.4) system. • The probe with excellent performance showed good applications in cells, soil, water samples and test strip detection. [ABSTRACT FROM AUTHOR]

Endogenous hydrogen sulfide (H 2 S) has been acknowledged as the third important gasotransmitter and plays a vital role to human health and diseases. A "turn-on" near-infrared fluorescent probe DCM-PBA based on nucleophilic substitution–cyclization has been developed for the detection of hydrogen sulfide. The probe showed high selectivity and sensitivity toward H 2 S and was successfully applied to imaging H 2 S in HeLa cells. [ABSTRACT FROM AUTHOR]

Reactive oxygen species (ROS) are connected to aging and human diseases. The controlled generation of ROS, particularly H 2 O 2 , is necessary to maintain cellular fitness. Fluorescent probe based imaging is the most popular approach for H 2 O 2 detection. The photobleaching of the fluorophores is the significant limitation towards better signal-to-noise ratio and imaging resolution. We design and synthesize a highly sensitive and photo-stable fluorescent probe for detecting H 2 O 2 by using the 2-dicyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran (TCF) as an electron acceptor. After reacting with H 2 O 2 , the borate ester group in the probe was transformed into phenol group to form red emitted fluorophore that is highly photo-stable under the irradiation of UV light and excitation laser. A good linear relationship (R 2  = 0.9930) in the range of 1–20 μM of H 2 O 2 was obtained. The limit of detection (3σ/slope) of our probe was 61 nM, which make our probe one of the most sensitive fluorescent probes for H 2 O 2 detection. And the probe doesn't response to common other ROS species. The probe was successfully applied to endogenous intracellular H 2 O 2 imaging in live A549 lung cancer cells. More importantly, the imaging signal just had less than 10% difference in fluorescence intensity after 25 min continuous irradiation of excitation laser. Thus, we believe the proposed TCF-PB is very practical for sensing and imaging of trace amount of H 2 O 2 that endogenously generated in the live cancer cells, which is essential for the study of H 2 O 2 related cell signaling and human diseases. [ABSTRACT FROM AUTHOR]

A ratiometric fluorescent probe (L-HF3) based on an efficient FRET platform constructed by 2-dicyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran (TCF) and 3-hydroxyflavone (HF) fluorophores for detection of sulfur dioxide derivatives (HSO 3 − /SO 3 2− ) was developed. The probe featured very large (pseudo) Stokes shifts, good selectivity and high sensitivity, high FRET efficiency and high resolution of the emission bands. The probe was also mitochondria-targeted and could detect exogenous and endogenous bisulfite in living cells. [ABSTRACT FROM AUTHOR]

Hypochlorous acid (HOCl)/hypochlorite (ClO − ), an endogenous reactive oxygen species (ROS), plays an important role in a variety of physiological and pathological processes. Herein, a ratiometric fluorescent probe ( BIP ) for ClO − was prepared, which exhibited a noticeable color change from purple-red to colorless along with a remarkable fluorescence change from bright red to blue in response to ClO − . The probe could quantitatively determine the concentrations of ClO − with large Stokes shift (107 nm), excellent selectivity, fast response, as well as low limit of detection (182 nM). NMR and mass spectral analysis demonstrated that ClO − triggered the oxidative cleavage of the bridge double bond in BIP , resulting in significant changes in color and fluorescence. In particular, BIP was a specific mitochondria-targeted fluorescent probe with excellent photostability, biocompatibility and cell membrane permeability. BIP was successfully used to image intracellular ClO − and its fluctuation in living HeLa cells (human cervical cancer). Furthermore, the probe was employed to visualize the ClO − mediated redox equilibrium within living cells by a ratiometric fluorescence imaging manner. Therefore, BIP has a great potential application for the detecting HOCl, which also offers an effective tool for the investigation of some HOCl related biological processes. [ABSTRACT FROM AUTHOR]

A new ratiometric fluorescent probe ( RPM ) was developed based on through-bond energy transfer (TBET) mechanism for detecting hypochlorous acid. The probe was constructed from imidazo[1,5- a ]pyridine as the energy donor and the rhodamine as the energy acceptor. The probe could be used to determine the concentration of HOCl with high selectivity and sensitivity (the detection limit = 2.08 × 10 −6 M). In addition, RPM had a good time resolution for measuring HOCl with the response time of less than 30 s. Upon addition of HOCl, the fluorescence colors of probe RPM solution changed from green to red. Moreover, the probe has been successfully utilized for sensing HOCl in living cells. [ABSTRACT FROM AUTHOR]