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The excessive formation of peroxynitrite (ONOO−) in mitochondria has been implicated in various pathophysiological processes and diseases. However, owing to short emission wavelengths and small Stokes shifts, previously reported fluorescent probes pose significant challenges for mitochondrial ONOO− imaging in biological systems. In this study, a near-infrared (NIR) fluorescent probe, denoted as DCO-POT, is designed for the visual monitoring of mitochondrial ONOO−, displaying a remarkable Stokes shift of 170 nm. The NIR fluorophore of DCO-CHO is released by DCO-POT upon the addition of ONOO−, resulting in off–on NIR fluorescence at 670 nm. This phenomenon facilitates the high-resolution confocal laser scanning imaging of ONOO− generated in biological systems. The practical applications of DCO-POT as an efficient fluorescence imaging tool are verified in this study. DCO-POT enables the fluorometric visualization of ONOO− in organelles, cells, and organisms. In particular, ONOO− generation is analyzed during cellular and organism-level (zebrafish) inflammation during ferroptosis and in an Alzheimer's disease mouse model. The excellent visual monitoring performance of DCO-POT in vivo makes it a promising tool for exploring the pathophysiological effects of ONOO−. [ABSTRACT FROM AUTHOR]

Alkaline phosphatase (ALP) is an essential hydrolase and widely distributed in living organisms. It plays important roles in various physiological and pathological processes. Herein, a turn-on near-infrared (NIR) fluorescent probe (DXMP) was developed for sensitive detection of ALP activity both in vitro and in vivo based on the intramolecular charge transfer (ICT) mechanism. Upon incubation with ALP, DXMP exhibited a strong fluorescence increment at 640 nm, which was attributed to the fact that ALP-catalyzed cleavage of the phosphate group in DXMP induced the transformation of DXMP into DXM-OH. The probe exhibited prominent features including outstanding selectivity, high sensitivity, and excellent biocompatibility. More importantly, it has been successfully used to detect and image endogenous ALP in living cells and zebrafish. [ABSTRACT FROM AUTHOR]

The authors describe a dual-signal colorimetric and ratiometric fluorescent probe for uric acid (UA). It is based on cascade catalysis and an inner filter effect. The method involves uricase-catalyzed oxidation of UA and iodide-catalyzed oxidation of the colorless peroxidase substrate o-phenylenediamine (OPD) to form yellow 2,3-diaminophenazine (oxOPD). This can be visually observed or monitored by measuring absorbance at 417 nm. Furthermore, oxOPD quenches the fluorescence of silicon nanoparticles (SiNPs) (with peaks at 450 and 565 nm) via an inner filter effect. The change in the ratio of emissions peaking 565 and 450 (at excitation wavelength of 380 nm) increases linearly in the 0.01–0.8 mM UA concentration range). The lower detection limits are 8.4 and 0.75 μM when using the colorimetric and ratiometric fluorometric method, respectively. The assay was successfully applied to the quantitation of UA in spiked serum samples. [ABSTRACT FROM AUTHOR]

Studying numerous biologically important species simultaneously is crucial to understanding cellular functions and the root causes of related diseases. Direct visualization of endogenous biothiols in biological systems is of great value to understanding their biological roles. Herein, a novel multi‐signal fluorescent probe was rationally designed and exploited for the simultaneous sensing of homocysteine (Hcy), cysteine (Cys), and glutathione (GSH) using different emission channels. This probe was successfully applied to the simultaneous discrimination between and visualization of endogenous Hcy, Cys, GSH, and their transformation in living cells. Multitasking: A multi‐signal fluorescent probe was exploited for simultaneously differentiating between and sensing of endogenous homocysteine, cysteine, glutathione, and their transformation in living cells. [ABSTRACT FROM AUTHOR]

In this work, a colorimetric and ratiometric fluorescent probe, 2,3-bis(((E)-4-(diethylamino)-2-hydroxybenzylidene)amino)maleonitrile (DHM), was developed based on N2H4-induced bond cleavage. Two cyanide groups of DHM were applied to sense hydrazine (N2H4) for the first time, which was demonstrated using 1H NMR and HRMS spectra. The specific ‘C-CN’ bond cleavage induced by N2H4 showed an excellent fluorescence ratiometric behavior and a visible colorimetric change from purple to yellow. Meanwhile, it showed a low detection limit of 58.1 nM (1.65 ppb), which is far below the safety level (10 ppb) set by the U.S. EPA. Moreover, the probe was successfully employed for the quantitative detection toward N2H4 in real water samples. [ABSTRACT FROM AUTHOR]

In this study, a facile and environment-friendly method for the preparation of bovine serum albumin (BSA) capped fluorescent Cu nanoclusters (BSA-CuNCs) was adopted. The as-prepared BSA-CuNCs were characterized by ultraviolet-visible spectroscopy (UV-Vis), fluorescent spectroscopy, Fourier transform infrared (FT-IR) spectroscopy and transmission electron microscopy (TEM). The fluorescence excitation and emission wavelength of BSA-CuNCs appeared at 325 and 406 nm, respectively. The as-synthesized BSA-CuNCs can be utilized as a bi-functional nanomaterial for pH sensing and dopamine (DA) detection with good performance. The fluorescence intensity decreased linearly with decrease in pH from 12 to 5 and increased linearly with increase in DA concentration from 0.5 to 50 μM. TEM measurements proved that the decrease in the pH value resulted in the aggregation of BSA-CuNCs, leading to color change and the quenching of fluorescence. The FT-IR spectra, fluorescent spectra, UV-Vis spectra and zeta potential measurements demonstrated that DA can be combined with Cu2+ and the Cu2+ would be removed from the surface of BSA-CuNCs. As a result, the fluorescence was recovered owing to the formation of the highly stable compound CuH2(DA)2. The pH value of five water samples was determined by the proposed method with relative errors of less than 0.91%. Furthermore, DA in human urine samples was also analyzed by BSA-CuNCs with good recoveries ranging from 90.4% to 104.7% using the standard addition method. It is believed that the bi-functional BSA-CuNCs will show great potential in bio-systems. [ABSTRACT FROM AUTHOR]

In this paper, we report a simple and sensitive fluorescent biosensor for the quantitative analysis of silver ions (Ag) by using NaYF:Yb, Tm upconversion nanoparticles (UCNPs). Ag could oxidize o-phenylenediamine (OPD) to the oxidized OPD (oxOPD) directly. The fluorescence of UCNPs can be significantly quenched by oxOPD through inner filter effects (IFE). Under the optimized conditions, the Ag concentration is proportional to the changes of the fluorescence intensity of UCNPs. The proposed method shows high selectivity and Ag could be quantitatively detected in the range of 0 to 0.5 mM with a low detection limit of 33 nM for Ag. The selectivity and sensitivity of the detection can also be satisfactory. More importantly, this method has potential in practical application to detect Ag in real samples without interference. [ABSTRACT FROM AUTHOR]

A novel ratiometric fluorescent Hg2+ detecting system was rationally developed based on the typical excited state intramolecular proton transfer (ESIPT) characteristic of the latent fluorophore, 2-(1-(p-tolyl)-1H-phenanthro[9,10-d]imidazol-2-yl)phenol (Pol) and the Hg2+-mediated cleavage of the vinyl group. The probe responds selectively to Hg2+ over various other metal ions with a larger bathochromic shift (∼100 nm). The sensing mechanism was investigated in detail by fluorescence spectroscopy, NMR spectra and mass spectrometry. Taking advantage of the enhancement effect of dichloromethane on the ESIPT efficiency, a facile dichloromethane extraction was introduced in the process of detection of Hg2+, which affords a high sensitivity for the probe with a detection limit of 7.8 × 10−9 M for Hg2+. By using the new strategy, the novel probe can be used for the detection of Hg2+ in practical water samples with good recovery. Moreover, the probe was successfully applied to the fluorescence image of Hg2+ in living cells. These results indicated that the probe and the proposed method have promising applications for Hg2+ sensing in biological and environmental sciences. [ABSTRACT FROM AUTHOR]

In this study, we synthesized a new fluorescence probe which was used to detect melamine by coupling with gold nanoparticles (AuNPs). The new fluorescence probe has good optical stability and high fluorescence intensity, which can greatly improve the detection sensitivity. Compared to the traditional fluorophore, it is less dependent on the pH value. It has a very strong fluorescence emission peak at 550 nm, which has larger overlap with the absorption peak of AuNPs. When the probe incubates with the AuNPs, the fluorescence of the probe can be effectively quenched by AuNPs. Adding melamine into a probe–AuNPs mixture caused aggregation of AuNPs and released the adsorbed probe; the fluorescence intensity of the probe was recovered. By measuring the changes of the fluorescence intensity of the probe, the detection of melamine can be realized. Under optimized conditions, the linear response to melamine is in the range of 1.0 × 10−8–4.0 × 10−6 mol L−1 and lowers the detection limit down to 3.0 nmol L−1 with the sensor. This method can detect melamine in milk and milk-based productions. [ABSTRACT FROM AUTHOR]

The authors describe a fluorometric method for the turn-on determination of vitamin C (ascorbic acid). The blue fluorescence of silicon nanoparticles (SiNPs; with excitation/emission maxima at 350/450 nm) is found to be quenched by CoOOH nanoparticles (NPs). In the presence of vitamin C, the CoOOH NPs are decomposed by a redox reaction between the diol group of vitamin C and CoOOH NPs. As a result, fluorescence recovers. On the basis of this finding, a fluorometric method was designed for the turn-on detection of vitamin C. Under optimal conditions, the method has a low detection limit (0.47 μM) and a linear response in the 0.5 μM to 20 μM a concentration range. It was successfully applied to the determination of vitamin C in spiked red grape and orange juice, and in vitamin C tablets.A target-triggered dissociation of quencher-based strategy for the fluorescence "turn-on" detection of vitamin C was developed. It is based on surface energy transfer (SET) and an inner filter effect (IFE) between silicon nanoparticles and CoOOH nanoparticles as well as the redox reaction between vitamin C and CoOOH nanoparticles. [ABSTRACT FROM AUTHOR]

A novel colorimetric and ratiometric fluorescent fluoride ion detecting system was been constructed base on ICT-modulated characteristic of the latent fluorophore, 7-(diethylamino)-3-(2-(pyridin-4-yl)vinyl)-coumarin and triisopropylsilane ether. The probe exhibited high selectivity and sensitivity detection of fluoride ion over other anion with a large emission wavelength shift (100 nm), and it also showed a low detection limit of 12 nM ( S / N = 3). The sensing mechanism was investigated by NMR spectra, HRMS spectrometry and theoretical calculations. The results indicated the colorimetric and ratiometric response of the probe to fluoride ion was ascribed to the cleavage reaction of Si-O bond between triisopropylsilyl group and phenyl group by fluoride ion and induced the intermolecular charger transfer (ICT) process. By using the strategy, the probe has been successfully applied to detect mitochondrial fluoride ion in live cells by ratiometric fluorescence imaging, which demonstrated that the colorimetric and ratiometric fluorescence probe has promising applications for investigation of fluoride ion in biological samples. [ABSTRACT FROM AUTHOR]

A novel mitochondria-targeted fluorescent probe compound 1 for H 2 O 2 has constructed based on a coumarin as the fluorophore and a boronate moiety as the reaction site, which showed colorimetric and ratiometric fluorescence dual response to H 2 O 2 . This probe displayed a large blue-shifted in emission wavelength (105 nm) with two well-resolved emission bands toward hydrogen peroxide. The compound 1 can be quantitative, good selective and sensitive recognition to H 2 O 2 with low detection limit (10 nM). The sensing mechanism was confirmed by H NMR and HRMS spectroscopy. The mechanism regarding the optical responses of the compound 1 toward H 2 O 2 was also determined by density function theory (DFT) calculations. Moreover, the probe could be used for determining H 2 O 2 in living cells by ratiometric fluorescence imaging with excellent mitochondrial targeting. [ABSTRACT FROM AUTHOR]

A new turn-on phthalimide fluorescent probe has designed and synthesized for sensing cysteine (Cys) based on excited state intramolecular proton transfer (ESIPT) process. It is consisted of a 3-hydroxyphthalimide derivative moiety as the fluorophore and an acrylic ester group as a recognition receptor. The acrylic ester acts as an ESIPT blocking agent. Upon addition of cystein, intermolecular nucleophilic attack of cysteine on acrylic ester releases the fluorescent 3-hydroxyphthalimide derivative, thereby enabling the ESIPT process and leading to enhancement of fluorescence. The probe displays high sensitivity, excellent selectivity and with large Stokes shift toward cysteine. The linear interval range of the fluorescence titration ranged from 0 to 1.0 × 10 − 5 M and detection limit is low (6 × 10 − 8 M). In addition, the probe could be used for bio-imaging in living cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • A high selectivity fluorescent probe DNO-HC for glutathione (GSH) was developed. • The probe exhibited fast response speed (1 min) and low detection limits (45 nM) toward GSH. • DNO-HC can readily evaluate GSH levels in different gut-derived bacteria and assess the antimicrobial sensitivity of different antibiotics. The human gut microbiota plays an integral role in the management of human health. Effective detection of gut-derived bacteria and their metabolites, as well as assessing antibiotic susceptibility, are crucial for the treatment of intestinal bacteria-related diseases. Herein, we designed and developed a dual-site (nitrophenyl sulfide group and aldehyde group) fluorescent probe DNO-HC , which could rapidly (∼1 min) respond to glutathione (GSH) with low background fluorescence, high selectivity, and low detection limits (45 nM). Moreover, the probe can be used to evaluate the metabolic levels (GSH) in different gut-derived bacteria and discriminate their Gram status. Remarkably, the assessment of antimicrobial susceptibility to a variety of antibiotics has been successfully accomplished utilizing this probe. It offers a promising strategy for the treatment of diseases associated with bacterial infections. [ABSTRACT FROM AUTHOR]

Nonalcoholic fatty liver disease (NAFLD) poses a significant global health concern, necessitating precise diagnostic tools and effective treatment strategies. Peroxynitrite (ONOO−), a reactive oxygen species, plays a pivotal role in NAFLD pathogenesis, highlighting its potential as a biomarker for disease diagnosis and therapeutic evaluation. This study reports on the development of a near-infrared (NIR) fluorescent probe, designated DRP-O, for the selective detection of ONOO− with high sensitivity and photostability. DRP-O exhibits rapid response kinetics (within 2 min) and an impressive detection limit of 2.3 nM, enabling real-time monitoring of ONOO− dynamics in living cells. Notably, DRP-O demonstrates excellent photostability under continuous laser irradiation, ensuring reliable long-term monitoring in complex biological systems. We apply DRP-O to visualize endogenous ONOO− in living cells, demonstrating its potential for diagnosing and monitoring NAFLD-related oxidative stress. Furthermore, DRP-O effectively evaluates the efficacy of therapeutic drugs in NAFLD cell models, underscoring its potential utility in drug screening studies. Moreover, we confirm DRP-O to enable selective identification of fatty liver tissues in a mouse model of NAFLD, indicating its potential for the early diagnosis of NAFLD. Collectively, DRP-O represents a valuable tool for studying ONOO− dynamics, evaluating drug efficacy, and diagnosing NAFLD, offering insights into novel therapeutic strategies for this prevalent liver disorder. [Display omitted] • Development of a near-infrared fluorescent probe peroxynitrite detection. • The probe has high selectivity, good photostability, and rapid response kinetics. • The probe can diagnose and monitor NAFLD-related oxidative stress. • The probe can evaluate the efficacy of therapeutic drugs for treating NAFLD. [ABSTRACT FROM AUTHOR]

A novel probe based on the fluorescence off–on strategy was prepared to optically detect hydrogen sulfide (H 2 S) via an excited state intramolecular proton transfer (ESIPT) mechanism. The probe shows high sensitivity and excellent selectivity to H 2 S. It also displays a large Stokes shift (∼140 nm) and a remarkable quantum yield enhancement (Ф = 0.412) after interaction with H 2 S. Moreover, the cellular imaging experiment demonstrated that it has potential utility for H 2 S sensing in biological sciences. [ABSTRACT FROM AUTHOR]

β-Galactosidase (β-gal), an enzyme related to cell wall degradation, plays an important role in regulating cell wall metabolism and reconstruction. However, activatable fluorescence probes for the detection and imaging of β-gal fluctuations in plants have been less exploited. Herein, we report an activatable fluorescent probe based on intramolecular charge transfer (ICT), benzothiazole coumarin-bearing β-galactoside (BC-βgal), to achieve distinct in situ imaging of β-gal in plant cells. It exhibits high sensitivity and selectivity to β-gal with a fast response (8 min). BC-βgal can be used to efficiently detect the alternations of intracellular β-gal levels in cabbage root cells with considerable imaging integrity and imaging contrast. Significantly, BC-βgal can assess β-gal activity in cabbage roots under heavy metal stress (Cd2+, Cu2+, and Pb2+), revealing that β-gal activity is negatively correlated with the severity of heavy metal stress. Our work thus facilitates the study of β-gal biological mechanisms. [Display omitted] • An activatable fluorescence probe (BC-βgal) for detecting β-galactosidase was designed. • BC-βgal was high sensitivity and selectivity towards β-gal with fast response (8 min). • BC-βgal imaged the β-gal fluctuation in situ in cabbage roots. • BC-βgal evaluated the β-gal activity under heavy metal stress for the first time. [ABSTRACT FROM AUTHOR]

The typical neurodegenerative Alzheimer's disease (AD) poses an increasing threat to human health as the population ages. Though increasing attention has been drawn for the etiology of AD over decades, regretfully, the exact pathogenesis of AD is not fully elucidated. The elevated levels of ROS are among the major pathological alterations in AD. Among them, peroxynitrite (ONOO-) exhibits a greater impact compared to other reactive oxygen species and plays an important role in AD, but the role ONOO- plays in AD progression remains unclear. In this work, the near-infrared (NIR) fluorophore (benzopyran derivative) was optimized by molecular skeleton modification, and a fluorophore DCM-Cl-OH with better spectral properties was obtained. On this basis, a NIR fluorescence probe DCM-Cl-P with excellent detection performance was obtained. Based on the high selectivity and fast response of the probe to ONOO-, DCM-Cl-P was used to visual detection of ONOO- in living cells and zebrafish, and further demonstrated the excessive accumulation of ONOO- in AD model mice. More importantly, through analysis of the correlation between ONOO- and amyloid- β protein (A β), ONOO- and the aggregation of A β were closely related and mutually reinforcing was demonstrated and ONOO- underwent significant changes in the early stage of the change of A β aggregation, indicating that ONOO- may serve as an early marker of AD. These findings have greatly promoted the research on the intrinsic relationship between ONOO- and AD, and provides a powerful means for pathological research of AD. [Display omitted] • A NIR fluorescent probe with excellent spectral properties for rapid detecting ONOO- with high selectivity was constructed. • The probe was successfully applied to imaging of ONOO- in cells, zebrafish and brain tissues of mice with AD. • This work confirmed that accumulation ONOO- underwent significant changes in the early stage of A β aggregation. [ABSTRACT FROM AUTHOR]

Thiophenol has a broad application in agriculture and industry. However, thiophenol can harm to the environment and health for its high toxicity. Developing an effective method for detection of thiophenol in the field of environmental and biology is valuable. In this work, we construct a reaction-based ratiometric fluorescent probe (E)-4-(2-(7-(diethylamino)-2-oxo-2H-chromen-3-yl)vinyl)-1-(4-(2,4-dinitrophenoxy)benzyl)pyridin-1-ium bromide (DCVP-DNP) for probing thiophenol in environment and cells by employing (E)-7-(diethylamino)-3-(2-(pyridin-4-yl)vinyl)-2H-chromen-2-one (DCVP) as the fluorophore and 2,4-dinitrophenyl (DNP) ether as the recognition group for the first time. The probe has high selectivity for thiophenol though thiophenol-triggered nucleophilic substitution reaction. In addition, the ratio of emission intensities of the probe has linearly with thiophenol concentration in the range of 0–65 μM and the detection limit of thiophenol is as low as 4.8 × 10−8 M. Moreover, the probe can not only be applied for detection of thiophenol in water samples, but also image thiophenol in living cells, suggesting its potential application in environment and biological system. Unlabelled Image • A coumarin fluorescent probe for detection of thiophenol was synthesized. • The probe exhibited ratiometric emission and a large pseudo-Stokes shift with a low detection limit. • The probe has been successfully used for thiophenol detection in real water samples and in living cells. [ABSTRACT FROM AUTHOR]

Peroxynitrite (ONOO−) is a primary kind of reactive oxygen species. Excessive ONOO− can induce oxidative damage to biomolecules and further results in various diseases. So, quantitative monitoring ONOO− with excellent selectivity and sensitivity is imperative for elucidating its role in biological processes. In this study, a novel pyridinium fluorescent ONOO− probe (CPC) has been constructed base on ICT-modulated by combining coumarin fluorophore and diphenylphosphinate recognition group. The fluorescence response of CPC for ONOO− is realized via the removal of diphenylphosphinate group. The probe CPC shows prominent features for detection of ONOO− including fast response rate (within 3 min), excellent selectivity and sensitivity, distinct colorimetric (red to green), and a large emission wavelength shift (105 nm). The emission intensity ration (I 538 /I 643) exhibits 153-fold enhancement along with the increasing ONOO− and the detection limit is as low as 1.60 × 10−8 M. These good response properties make CPC possible to quantitative detection of ONOO− concentration. By using the strategy, the ratiometric CPC has been employed to detection of mitochondrial ONOO− in live cell successfully. Unlabelled Image • A novel ratiometric pyridinium fluorescent ONOO− probe was synthesized. • The probe exhibited fast response, ratiometric, excellent selectivity and sensitivity detection of ONOO−. • The probe could be used to employ to ratiometric detection of mitochondrial ONOO− in live cell. [ABSTRACT FROM AUTHOR]

A novel nanosensor is developed for selective and highly sensitive detection of phytic acid (PA) based on small-sized conjugated polyelectrolyte dots (Pdots) fabricated from a new conjugated polymer (P1) by a modified reprecipitation method. P1 featuring a π -delocalized backbone bearing meta -substituted pyridyl groups can be endowed with enhanced flexibility and hence is beneficial for the synthesis of ultrasmall Pdots (i.e. Pdot-1, ∼3.8 nm in average diameter) as well as for the binding of Fe3+, thus leading to the obvious fluorescence quenching of Pdot-1 (∼444 nm) in the presence of Fe3+ via an electron transfer (ET) process. In addition, phytic acid with six phosphate groups exhibits strong chelating ability. When phytic acid is added, phytic acid readily binds to Fe3+ and the fluorescence of Pdot-1 around 444 nm can be recovered, rendering the supersensitive and selective sensing of PA. Under the optimum conditions, this ultra-small Pdot-based nanoprobe favors the fluorescent determination of PA with the detection limit as low as 10 nM. Particularly, Pdot-1 with bright blue fluorescence exhibits low cytotoxicity. Furthermore, the small-sized and biocompatible Pdot-1 can be applied to the sensitive fluorescence assay for PA in cell extracts and the efficient imaging of PA in live cells. Image 1 • A novel nanosensor is designed based on small Pdot-1 (∼3.8 nm) using P1. • This fluorescent probe favors the ultrasensitive detection of PA (LOD 10 nM). • Pdot-1 with bright blue fluorescence exhibits low cytotoxicity. • Pdot-1 facilitates the sensing and imaging of PA in cell extracts or live cells. [ABSTRACT FROM AUTHOR]

Phosgene is a highly toxic gas that poses a serious threat to public health and safety. Herein, we describe the preparation of a ratiometric fluorescence probe (Pi) bearing hydroxyl and imidazole moieties as recognition sites, and employ it for the excited-state intramolecular proton transfer-based (ESIPT-based) detection of phosgene. It is the first time that hydroxyl and imidazole have been exploited as recognition sites for phosgene. In the presence of phosgene, Pi undergoes sequential nucleophilic substitution and cyclization reactions that facilitate a rapid response, high selectivity, and excellent sensitivity (detection limit = 0.14 μM). The sensing mechanism was verified by 1H NMR spectroscopy and high-resolution mass spectrometry. Furthermore, we fabricated a fluorescent test strip (FTS-Pi) for the detection of phosgene in the gas phase that undergoes a fluorescence color change, from green to blue, under 365 nm UV light in the presence of phosgene, which is easily observed with the naked eye. fx1 • Ratiometric fluorescent probe for phosgene detection in solution and gas phase was prepared. • The above detection was based on excited-state intramolecular proton transfer. • Hydroxyl and imidazole moieties were utilized as phosgene recognition sites. • Rapid response, high selectivity, and excellent sensitivity were achieved. [ABSTRACT FROM AUTHOR]

Abstract Thiophenol is widely known as a highly toxic substance that can cause serious harm to the environment and health. Rapid and non-destructive detection of thiophenol is of great significance for environmental management. In this work, we designed and synthesized a near-infrared (NIR) fluorescent probe, (E)−4-(2-(4-(dicyanomethylene)−4 H -chromen-2-yl)vinyl)−2-formylphenyl-2,4-dinitrobenzenesulfonate (DCM-CHO-D), that can respond to thiophenol rapidly (less than 3 min) based on intramolecular charge transfer (ICT) mechanism. DCM-CHO-D has high selectivity and sensitivity to the detection of thiophenol. And there is a linear relationship between the fluorescence intensity of DCM-CHO-D and thiophenol concentration in the range of 0–10 μM, the limit of detection (LOD) is as low as 0.22 μM. What′s more, DCM-CHO-D can not only be used as an ideal colorimetric tool for detecting thiophenol in water samples, but also image thiophenol in living cells, indicating its potential utility for thiophenol sensing in environmental and biological samples. Graphical abstract fx1 Highlights • The emission wavelength of the probe is in the near infrared region. • The obvious change in color could be used for "naked-eye" detection. • The response time of the probe to thiophenol is as low as 3 min. • The probe could be applied for thiophenol detection in real water samples and living cells. [ABSTRACT FROM AUTHOR]

Abstract A novel mitochondria-targeted fluorescent probe for sensing SO 2 derivatives was constructed by integrating phenanthroimidazole and cyanine moieties. Excited by different channels, this probe exhibited unique dual-channel fluorescence-enhanced emissions and colorimetric response to HSO 3 - quickly (less than 20 s). The sensing process was confirmed to undergo nucleophilic addition of HSO 3 - to C˭C double bond in the probe Mito-PTB via NMR and HRMS analyses. Furthermore, fluorescence co-localization studies demonstrated that the probe Mito-PTB was a mitochondria-targetable fluorescent probe for SO 2 derivatives with good cell membrane permeability. Thus, probe Mito-PTB has the potential applications to explore the role played by SO 2 derivatives in biology. Graphical abstract fx1 Highlights • A novel mitochondria-targeted fluorescent probe for detecting SO 2 derivatives was developed. • The probe showed several advantages, such as low cost, ease of operation, high sensitivity and selectivity. • Two different emission channels were applied to sense SO 3 2-/HSO 3 - via dual excited channels. • The probe was successfully applied to the detection of mitochondria SO 3 2-/HSO 3 - in BEL-7402 cells. [ABSTRACT FROM AUTHOR]

A simple benzothiazole fluorescent chemosensor was developed for the fast sequential detection of Cu 2 + and biothiols through modulating the excited-state intramolecular proton transfer (ESIPT) process. The compound 1 exhibits highly selective and sensitive fluorescence “ on - off ” recognition to Cu 2 + with a 1:1 binding stoichiometry by ESIPT hinder. The in situ generated 1 -Cu 2 + complex can serve as an “ on - off ” fluorescent probe for high selectivity toward biothiols via Cu 2 + displacement approach, which exerts ESIPT recovery. It is worth pointing out that the 1 -Cu 2 + complex shows faster for cysteins (within 1 min) than other biothiols such as homocysteine (25 min) and glutathione (25 min). Moreover, the compound 1 displays 160 nm Stoke-shift for reversibly monitoring Cu 2 + and biothiols. In addition, the probe is successfully used for fluorescent cellular imaging. This strategy via modulation the ESIPT state has been used for determination of Cu 2 + and Cys with satisfactory results, which further demonstrates its value of practical applications. [ABSTRACT FROM AUTHOR]

A novel fluorescent probe ( E )-3-ethyl-2-(4-hydroxystyryl)-1,1-di-methyl-1 H -benzo-[ e ]indolium iodide (probe EDB) based on benzo[ e ]indolium was synthesized, which provided the simultaneous detection of SO 3 2- /HSO 3 - and HSO 4 - ion with different emission channels. Based on the principle of ion-induced rotation-displaced H-aggregates, when treated with NaHSO 4 , a fluorescence enhancement at 580 nm was observed with the excitation wavelength at 420 nm. While, in the advantage of the nucleophilic addition of SO 3 2- to the vinyl group, strong fluorescence was obtained at 455 nm when treated with Na 2 SO 3 with the excitation wavelength at 320 nm, along with obvious color change by naked eyes. So the probe could be applied to sense SO 3 2- /HSO 3 - and HSO 4 - ion via different excited and emission channels simultaneously. The probe was also applicable for fluorescence imagings of bisulfite and hydrosulfate in HeLa cells. [ABSTRACT FROM AUTHOR]

Herein we report a novel switch-off fluorescent probe for highly selective determination of uric acid (UA) based on the inner filter effect (IFE), by using poly-(vinylpyrrolidone)-protected gold nanoparticles (PVP-AuNPs) and chondroitin sulfate-stabilized gold nanoclusters (CS-AuNCs) as the IFE absorber/fluorophore pair. In this IFE-based fluorometric assay, the newly designed CS-AuNCs were explored as an original fluorophore and the hydrogen peroxide (H 2 O 2 ) -driven formed PVP-AuNPs can be a powerful absorber to influence the excitation of the fluorophore, due to the complementary overlap between the absorption band of PVP-AuNPs and the emission band of CS-AuNCs. Under the optimized conditions, the extent of the signal quenching depends linearly on the H 2 O 2 concentration in the range of 1–100 μM ( R 2 =0.995) with a detection limit down to 0.3 μM. Based on the H 2 O 2 -dependent fluorescence IFE principle, we further developed a new assay strategy to enable selective sensing of UA by using a specific uricase-catalyzed UA oxidation as the in situ H 2 O 2 generator. The proposed uricase-linked IFE-based assay exhibited excellent analytical performance for measuring UA over the concentration ranging from 5 to 100 μM ( R 2 =0.991), and can be successfully applied to detection of UA as low as 1.7 μM (3σ) in diluted human serum samples. [ABSTRACT FROM AUTHOR]

Oxidative stress is closely related to the crop health status under stress conditions. H 2 O 2 is an important signaling molecule in plants under stress. Therefore, monitoring H 2 O 2 fluctuations is of great significance when risk-assessing oxidative stress. However, few fluorescent probes have been reported for the in situ tracking of H 2 O 2 fluctuations in crops. Herein, we designed a "turn-on" NIR fluorescent probe (DRP-B) to detect and in situ -image H 2 O 2 in living cells and crops. DRP-B exhibited good detection performance for H 2 O 2 and could image endogenous H 2 O 2 in living cells. More importantly, it could semi-quantitatively visualize H 2 O 2 in cabbage roots under abiotic stress. Visualization of H 2 O 2 in cabbage roots revealed H 2 O 2 upregulation in response to adverse environments (metals, flood, and drought). This study provides a new method for risk-assessing oxidative stress in plants under abiotic stress and is expected to provide guidance for the development of new antioxidant defense strategies to enhance plant resistance and crop productivity. [Display omitted] • A NIR fluorescent probe (DRP-B) for detecting and imaging H 2 O 2 was designed. • DRP-B was highly sensitive, H 2 O 2 -selective, colorimetric, and dual-signaling. • DRP-B visualized and monitored H 2 O 2 levels in living cells and cabbage roots. • DRP-B risk-assessed oxidative stress in cabbage roots subjected to various stresses. [ABSTRACT FROM AUTHOR]

Viscosity changes in mitochondria are closely associated with numerous cellular processes and diseases. Currently available fluorescence probes used in mitochondrial viscosity imaging are not very photostable or sufficiently permeable. Herein, a highly photostable and permeable mitochondria-targeting red fluorescent probe (Mito-DDP) was designed and synthesized for viscosity sensing. Viscosity was imaged in living cells using a confocal laser scanning microscope, and the results suggested that Mito-DDP penetrated the membrane and stained the living cells. Importantly, practical applications of Mito-DDP were demonstrated: viscosity visualization was realized for mitochondrial malfunction, cellular and zebrafish inflammation, and Drosophila Alzheimer's disease models, i.e., for subcellular organelles, cells, and organisms. The excellent analytical and bioimaging performance of Mito-DDP in vivo makes it an effective tool for exploring the physiological and pathological effects of viscosity. [Display omitted] • Development of a mitochondria-targeting red fluorescent probe (Mito-DDP). • The probe exhibited excellent photostability and permeability. • The probe is highly sensitive and selective to viscosity. • Mito-DDP was used to visualize viscosity changes caused by various factors. • LO2 cells, HepG2 cells, zebrafish, and AD Drosophila brains were all imaged. [ABSTRACT FROM AUTHOR]

Sulfur, nitrogen co-doped carbon dots (S, N co-doped C-dots) as highly selective fluorescent probe for uric acid (UA) detection were designed. The S, N co-doped C-dots with high quantum yield of 73.1% were prepared by hydrothermal method. It was found that the fluorescence of S, N co-doped C-dots was quenched apparently by hydroxyl radicals from Fenton reaction between H 2 O 2 and Fe 2+ . The production of H 2 O 2 originated from the oxidization of UA by uricase. Therefore, an optical biosensor was developed for the detection of UA based on Fenton reaction and enzymatic reaction. Under the optimized conditions, two linear relationships between the ratio of fluorescence quenching of the C-dots and UA concentration were found in the range of 0.08–10 µM and 10–50 µM, respectively. The detection limit was down to 0.07 µM. Moreover, the proposed biosensor was successfully applied to the detection of uric acid in human serum samples. [ABSTRACT FROM AUTHOR]

Endogenous H 2 S and HClO play vital roles in regulating the redox status in vivo, and are involved in many pathophysiological events. Accordingly, accurate sensing and imaging of intracellular H 2 S and HClO have become greatly in demand. However, conventional double-response fluorescent probes for these two substances suffered from the notorious aggregation-caused quenching effect and required multiple excitations to achieve discrimination determination. In this study, we firstly constructed an AIE-active fluorescent probe with three potential reaction sites for individual and continuous detection of H 2 S and HClO using a single excitation wavelength. The multiple-site probe exhibited distinctive fluorescence behaviors to H 2 S and HClO with fast response (H 2 S: 12 min; HClO: 1.8 min), well-separated emission peaks (88 nm), high sensitivity and good selectivity due to H 2 S-induced thiolysis of 2,4-dinitrophenyl ether assisted by an adjacent aldehyde and HClO-triggered sulfur oxidation. The corresponding recognition mechanisms were fully confirmed by HRMS, 1H NMR and control experiments. Moreover, the probe was successfully utilized for separate and continuous imaging of intracellular H 2 S and HClO in different fluorescent channels, indicating its potential for further study the biological functions of H 2 S and HClO in living systems. [Display omitted] • An AIE-active multiple-site probe for H 2 S and HClO was firstly developed. • It can individually and continuously detect H 2 S and HClO using a single wave excitation. • It showed rapid response to H 2 S and HClO with high sensitivity and selectivity. • It was used for individual and continuous imaging of intracellular H 2 S and HClO. [ABSTRACT FROM AUTHOR]

β- Galactosidase is closely related to primary ovarian cancer and highly expressed in metastatic ovarian cancer. Therefore, the development of effective tool for in situ detecting β -gal is urgently needed for further studies in ovarian cancer. Inspired by the advantages of near-infrared (NIR) fluorescence imaging, a NIR fluorescent probe (DCM-CHO-βgal) with improved near-infrared fluorescence emission and detection performance was reasonably designed for the quantification and visualization of β -gal, employing structurally modified dicyanobenzopyran derivative (DCM-CHO-OH) as fluorophore. DCM-CHO-βgal showed a rapid response (<20 min) towards β -gal accompanied by nearly 40-fold fluorescence enhancement at 665 nm. DCM-CHO-βgal can quantitatively detect β -gal ranging from 0.2 to 3 U/mL with a low detection limit (3.15 × 10−5 U/mL), and can selectively detect β -gal in the presence of other possible interferences. In view of excellent optical, analytical performance and good biocompatibility, DCM-CHO-βgal was applied to the visualization of endogenous β -gal in ovarian cancer cells and zebrafish, which provided a powerful tool for the in-depth study of the role of β-gal in β-gal-related diseases. [Display omitted] • A near-infrared fluorescent probe with improved performance is constructed. • The probe featured low detection limit to β -gal with high sensitivity. • The probe can visualize β -gal in living cells and zebrafish. • The probe can distinguish ovarian cancer cells from other cancer cells. [ABSTRACT FROM AUTHOR]

Sudan dyes are banned as food additives due to the carcinogenicity of their metabolites in the human body. Therefore, it is of great significance for sensitive detection of Sudan dyes. This paper reports a novel nanosensor for Sudan dyes detection based on fluorescence (FL) quenching of hexadecyl trimethyl ammonium bromide (CTAB) stabilized upconversion nanoparticles (UCNPs) through the inner filter effect (IFE). In the presence of Sudan I–IV, the fluorescence emission of UCNPs was effectively quenched due to the absorption bands of Sudan I–IV largely covered the emission bands of UCNPs. Under the optimized conditions, the FL was quenched with Sudan concentration over the range of 0.05–40, 0.01–20, 0.01–40 and 0.05–40 μg/mL for Sudan I–IV, respectively. The corresponding limit of detection is 15.1, 2.83, 3.52 and 16.7 ng/mL (at 3 σ /slope) respectively. Meanwhile, the nanosensor shows good selectivity, sensitivity and can be successfully applied to detection of Sudan in chili powder samples. [ABSTRACT FROM AUTHOR]

A highly sensitive and selective fluorescence method for the detection of acetylcholine (ACh) based on enzyme-generated hydrogen peroxide (H 2 O 2 ) and a new boronate intramolecular charge transfer (ICT) fluorescence probe, 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)- N -butyl-1,8-naphthalimide (BN), was developed. This strategy involves the reaction of ACh with acetylcholinesterase (AChE) to produce choline, which is further oxidized by choline oxidase (ChOx) to obtain betaine and H 2 O 2 . The enzyme-generated H 2 O 2 reacts with BN and results in hydrolytic deprotection of BN to generate fluorescent product (4-hydroxyl- N -butyl-1,8-naphthalimide, ON). Two consecutive linear response ranges allow determining ACh in a wide concentration range with a low detection limit of 2.7 nM (signal/noise = 3). Compared with other fluorescent probes based on the mechanism of nonspecific oxidation, this reported boronate probe has the advantage of no interference from other biologically relevant reactive oxygen species (ROS) on the detection of ACh. This study provides a new method for the detection of ACh with high selectivity and sensitivity. [ABSTRACT FROM AUTHOR]

Abstract: In this work, label-free silicon quantum dots (SiQDs) were used as a novel fluorescence probe for the sensitive and selective detection of Cu2+. The fluorescence of the SiQDs was effectively quenched by H2O2 from the reaction of ascorbic acid with O2, and hydroxyl radicals from Fenton reaction between H2O2 and Cu+. The fluorescence intensity of SiQDs was quenched about 25% in 15min after the addition of H2O2 (1mM). While the SiQDs was incubated with AA (1mM) and Cu2+ (1µM) under the same conditions, the fluorescence intensity of SiQDs decreased about 55%. Obviously, the recycling of Cu2+ in the test system may lead to a dramatical decrease in the fluorescence of SiQDs. Under the optimized experimental conditions, the rate of fluorescence quenching of SiQDs was linearly dependent on the Cu2+ concentration ranging from 25 to 600nM with the limit of detection as low as 8nM, which was much lower than that of existing methods. Moreover, the probe was successfully applied to the determination of Cu2+ in different environmental water samples and human hair. [Copyright &y& Elsevier]

A rhodamine-based fluorescent probe (Rho-GSH) was rationally designed and synthesized, using nitrobenzene as recognition group for monitoring and imaging GSH in vitro and in vivo. In the presence of GSH, Rho-GSH undergoes sequential nucleophilic substitution and spiro-ring-opening reaction, resulting the fluorescence increase of probe, which enables quantitative detection of GSH with "off-on" fluorescence. The cascade reaction also enables Rho-GSH to rapidly detect GSH (3 s). In addition, Rho-GSH exhibited outstanding selectivity in detecting GSH vs cysteine (Cys) and homocysteine (Hcy). Based on the outstanding detection performance and superior biocompatibility of Rho-GSH , it was used to visualize GSH in vitro and in vivo , demonstrating its highly selectivity for GSH detection (with respect to Cys and Hcy). Rho-GSH can help visually distinguishing cancer cells from normal cells by fluorescence imaging, demonstrating the overexpression of GSH in cancer cells. Because of the outstanding analytical capabilities of Rho-GSH for GSH detection, Rho-GSH may be useful for cancer diagnosis and clinical evaluation. [Display omitted] • Rho-GSH is a rhodamine-based fluorescent probe based on cascade reactions. • Rho-GSH can quantitatively detect GSH with high selectivity and rapidity (3 s). • Rho-GSH can visualize GSH in vitro and in vivo. • Rho-GSH distinguishes cancer cells from normal cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel colorimetric fluorescence probe for NO was developed. • The probe is of excellent selectivity and high anti-interference detection of NO. • It could not only detect NO in human serum and living cells, but also image NO in zebrafish inflammation models. Nitric oxide (NO), an essential biological messenger molecule, participates in various physiological and pathological processes. The sensitive and specific detection of NO is of great significance for understanding the biological function of NO. Here, we synthesized a fluorescent probe (Rho-NO) for highly selective detection of NO both in vitro and in vivo. The high selectivity of Rho-NO is attributed to the fact that NO is easily replaced by electron donor amino group to form N -nitrosation products, causing rhodamine spiro ring open and fluorescence emit. Rho-NO showed a good linear response to NO (0–100 µM) with a low detection limit (0.06 µM). Importantly, it exhibited excellent specificity for NO detection in human serum and was also applied for imaging NO in living cells and inflammatory model of zebrafish. This work proves the potential of Rho-NO in pathological research and disease diagnosis. [ABSTRACT FROM AUTHOR]

• A red-emitting fluorescent probe was developed for the detection of Cu2+ based on Cu2+-induced specific reactions. • The probe can detect Cu2+ with excellent sensitivity and high selectivity (LOD = 4 mM) in PBS buffer (1% DMSO). • It cloud not only detect Cu2+in real samples, but also visualize Cu2+ in living plant tissues and zebrafish. Herein, we developed a turn-on red-emitting fluorescent probe for the sensitive and selective detection of copper ions (Cu2+) in food samples and living zebrafish. The probe employs a hemicyanine scaffold as the fluorophore and a 2-pyridinecarbonyl group as the recognition receptor and quenching moiety. The 2-pyridinecarbonyl moiety can be specifically cleaved by Cu2+ and results in an approximately 18-fold fluorescence enhancement of the probe, thereby providing a fluorescence turn-on assay for Cu2+. Additionally, the probe exhibited excellent selectivity, high sensitivity, a broad linear relationship (0.020 to 8.0 μM), and a low limit of detection (4.0 nM, S/N = 3) for Cu2+. Concomitantly, the probe exhibited satisfactory analytical performance when used with actual food samples. Moreover, the probe could be used for in situ determination of Cu2+ in both living plant tissues and in living zebrafish. [ABSTRACT FROM AUTHOR]

Understanding cellular metabolism holds immense potential for developing new drugs that regulate metabolic pathways. Two gas signal molecules, SO 2 and H 2 S, are the main metabolites from cysteine (Cys) via oxidation and desulfurization pathways, respectively. However, a few fluorescent probes for real-time monitor of the metabolic pathways of cysteine have been reported. To understand metabolic alterations of cysteine, we have rationally designed and prepared a dual-signal fluorescent probe HN , which could differentiate SO 2 and H 2 S through two different fluorescence channels simultaneously, along with similar reaction kinetics and both "off-on" fluorescence responses. Probe HN exhibits the potential to monitor the metabolism pathways of cysteine, and the distinguishment of cancer cells from normal cells could be realized. This methodology will promote further understanding of the physiological and pathological roles of cysteine. Unlabelled Image • A novel fluorescent probe for simultaneously monitoring metabolisms of cysteine was developed. • The probe could simultaneously differentiate SO 2 and H 2 S through two different fluorescence channels. • The probe was applied to monitor and visualize the metabolism pathways of cysteine in living cells and zebrafishes. [ABSTRACT FROM AUTHOR]

β-Galactosidase (β-gal) which is overexpressed in primary ovarian cancer can be employed as a valuable biomarker for ovarian cancer. Thus, monitoring and imaging endogenous β-gal in living cells is of great importance. Herein, a dicyanoisophorone-based near-infrared (NIR) fluorescent probe 2-(5,5-dimethyl-3-((E)-4-(((2R,3S,4R,5S,6S)-3,4,5-trihydroxy-6-(hydroxymethyl)tetrahydro-2 H -pyran-2-yl)oxy)styryl)cyclohex-2-en-1-ylidene)malononitrile named DP-βgal , was rationally designed and synthesized for the monitoring of β-gal activity in living cells. In the presence of β-gal, with the breaking of the glycosidic bond, the NIR fluorescence of the dicyanoisophorone derivative gradually recovered, enabling the fluorescence "off-on" quantitative determination of β-gal activity. DP-βgal has the advantages of good selectivity and high sensitivity for the detection of β-gal, with the limit of detection (LOD) of 3.2 × 10−3 U. Furthermore, based on its advantages of long-wavelength emission and excellent biocompatibility, the practical applications of DP-βgal in NIR imaging of β-gal in living ovarian cancer cells (SKOV-3) were demonstrated. Image 1 • An "off-on" NIR fluorescent probe (DP-βgal) was rationally constructed for the detection of β-galactosidase (β-gal). • DP-βgal shows high sensitivity, compatibility and selectivity toward β-gal with large Stokes shift and NIR emission. • A method for diagnosis by imaging of endogenous β-gal in living ovarian cancer cells was developed. [ABSTRACT FROM AUTHOR]

Hypochlorous acid (HOCl) acts as crucial roles in pathologica processes and relevant diseases. Thus, it is meaningful to explore a reliable method for monitoring HClO in biosystem. In this work, a ratiometric fluorescent probe 2-(benzo d thiazol-2-yl)-4-(methylthio)phenol (BTMSP) has been constructed for HClO by adopting ICT-ESIPT strategy. The probe possessed itself red fluorescence due to the electron-donating capability of sulfur atom and showed remarkable blue fluorescence response to HClO by oxidizes the sulfur atom to a sulfoxide. The ratiometric probe exhibited highly specific, rapid response and excellent sensitivity toward HClO as well as a low detection limit (4.2 × 10−7 M). Moreover, the ratiometric probe showed well-separated dual emission (450/580), and a large pseudo Stokes shift (190 nm). In addition, the probe was used for the imaging of HClO with satisfying results. Unlabelled Image • A simple fluorescent probe for HOCl has been synthesized by on step reaction. • Ratiometric detection of HOCl through modulation of ICT-ESIPT dual mechanisms • Well-separated dual emission (450/580 nm) and large pseudo Stokes shift (190 nm) • The probe could be used to monitor HOCl in live cell. [ABSTRACT FROM AUTHOR]

β-Galactosidase (β -gal) is an important biomarker for primary ovarian cancers. Developing noninvasive bioimaging probes for studying the activity of β -gal is highly desirable for cancer diagnosis. Herein, a turn-on near-infrared (NIR) fluorescent probe， 2-((6-(((2 S , 3 R , 4 S , 5 R , 6 R)-3,4,5-trihydroxy-6-(hydroxymethyl)tetrahydro-2 H -pyran -2-yl)oxy)-2,3-dihydro-1 H -xanthen-4-yl)methylene)malononitrile named DXM- β gal, was rationally designed based on enzymatic reaction for the detection of β -gal activity both in vitro and in vivo. Upon incubating with β -gal, DXM- β gal displayed a significant fluorescence enhancement at 640 nm, accompanying by a color change of solution color from red to purple. DXM- β gal exhibited high selectivity and sensitively to β -gal with low limit of detection (2.92 × 10−4 U mL−1). Besides, based on its advantages of long-wavelength emission and excellent biocompatibility, DXM- β gal was successfully applied to imaging β -gal in living cells and zebrafish. Given these prominent properties, we believe that DXM- β gal will be a potential tool for investigating β -gal activity in biomedical research. Image 1 • A near-infrared (NIR) fluorescent probe, DXM- β gal, was developed for the detection of β -galactosidase (β -gal) activity via rapid response. • DXM- β gal showed a remarkable turn-on fluorescence signal and an obvious color change from pink to purple. • DXM- β gal showed high sensitivity and selectivity toward β -gal. • DXM- β gal has excellent biocompatibility, which can detect endogenous β -gal in living ovarian cancer cells and zebrafish. [ABSTRACT FROM AUTHOR]

A new strategy endowing probe with large Stokes shift, high quantum yield and red emission was developed by incorporating tetrahydroquinoxaline unit and five-membered pyrrolidine ring on fluorophore. As demonstrated, a novel probe was rationally designed and synthesized for sensitive monitor of cellular cysteine (Cys) and endogenous aminoacylase with large Stokes shift and high quantum yield. Image 1 • A novel fluorescent probe with large Stokes shift, high quantum yield and red emission was rationally designed and synthesized. • The probe was exhibited fast-response, high sensitivity and high selectivity towards cysteine. • The probe was successfully applied to real-time monitor and visualize endogenous cysteine and intracelluar aminoacylase in living cells. [ABSTRACT FROM AUTHOR]

Alkaline phosphatase (ALP) is a non-specific phosphate monoesterase and often regarded as an important biomarker of hypothyroidism and hepatobiliary diseases in medical diagnosis. In-situ detection of endogenous ALP and exploration of the distribution of ALP in cells are of great importance for the diagnosis of diseases associated with ALP. In this work, we designed and synthesized an aggregation-induced emission (AIE) fluorescent probe, (E)-2-(((9 H -fluoren-9-ylidene) hydrazono)methyl)phenyl dihydrogen phosphate (FAS-P), that can respond to ALP with a remarkable large Stokes shift (>200 nm) based on excited state intramolecular proton transfer (ESIPT) mechanism. The probe FAS-P has high selectivity and sensitivity to the detection of ALP. And there is a linear relationship between the fluorescence intensity of FAS-P and ALP activity in the range of 1–100 U L−1, the limit of detection (LOD) is as low as 0.6 U L−1. More importantly, we successfully applied FAS-P to detect ALP in living cells and the monitoring of ALP in real time. Image 1 • An aggregation-induced emission (AIE) fluorescent probe (FAS-P) has been synthesized with a few simple steps. • FAS-P showed a remarkable large Stokes shift (>200 nm) toward ALP. • FAS-P showed high sensitivity and selectivity toward ALP. • FAS-P has good water solubility and excellent cell permeability, which can detect endogenous ALP in real time. [ABSTRACT FROM AUTHOR]

Developing specific and sensitive method for endogenous peroxynitrite (ONOO−) in living systems is valuable to understand its various pathological events. In this work, a simple and novel fluorescent probe (HPP) based on aggregation induced emission (AIE) as well as excited state intramolecular proton transfer (ESIPT) processes for endogenous ONOO− detection was constructed containing a diphenylphosphinate as the reactive site and a salicylaldehyde azine as the fluorophore. The probe showed specific fluorescence turn-on response toward ONOO− owing to the diphenylphosphinate group of HPP reacted with ONOO−, releasing the salicylaldehyde azine with both AIE and ESIPT characteristics. In addition, the probe exhibited a large Stokes shift, an excellent light-up ratio, high selectivity and excellent sensitivity with a low detection limit of 8 × 10−8 M for endogenous ONOO−. Moreover, the probe could be applied to bioimaging of endogenous ONOO− in live cell, which demonstrated the probe can be used as effective tool for investigation of ONOO− in biological systems. Unlabelled Image • A novel and simple AIE-ESIPT fluorescent probe was designed and synthesized. • The probe exhibited a large Stokes shift, excellent selectivity and sensitivity for ONOO−. • The probe could be applied to bioimaging of endogenous ONOO− in live cell. [ABSTRACT FROM AUTHOR]