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[Display omitted] • Two rhodamine dyes with 2-allyloxy- and 4-allyloxy- benzaldehyde were developed. • Both of them detected Al3+ ion with high selectivity. • Increment in fluorescence at 550 nm and absorbance at 530 nm occurred with Al3+. • LOD values (∼1.0 nM) for Al3+ lower compared to the reported values. • Both of these probes were used to image the cation in C6 cells. Selective detection of a metal ion with high selectivity is of great importance to understand its existence and its role in many chemical and biological processes. We report here the synthesis, characterization and Al3+ sensing properties of two rhodamine-based isomers, (E)-2-((2-(allyloxy)benzylidene)amino)ethyl)-3′,6′-bis(ethylamine)-2′,7′-dimethylspiro[isoindoline-1,9′-xanthen]-3-one (L-2-oxy) and (E)-2-((4-(allyloxy)benzylidene)amino)ethyl)-3′,6′-bis(ethylamine)-2′,7′-dimethylspiro[isoindoline-1,9′-xanthen]-3-one (L-4-oxy). L-2-oxyand L-4-oxy show pink coloration, significant enhancement in absorbance at 530 nm and fluorescence intensity at 553 nm in the presence of Al3+ among several cations. Quantum yield and lifetime of the probes increase in the presence of Al3+. LOD values have been determined as low as ∼1.0 nM for both the isomers. DFT study suggests that the cation induces opening of spirolactam ring resulting in the changes of the rhodamine dyes. Additional reason could be Chelation Enhanced Fluorescence (CHEF) effect due to the subsequent chelation of the metal ion. Between two isomers, L-2-oxy displays better sensing ability towards Al3+ in terms of fluorescence enhancement, limit of detection, lifetime enhancement. Both the probes have been utilized in cell imaging studies using rat skeletal myoblast cell line (L6 cell line). [ABSTRACT FROM AUTHOR]

[Display omitted] • The stronger the positive electricity of the probe, the more sensitive it is to detect cyanide. • The adsorption process of probe and cyanide was studied through theoretical calculation. • The probe PI-N has high sensing sensitivity. • The probe PI-N can be used in cell imaging and food analysis. As cyanide is a huge hazard to the environment and human health, the study of the method of detecting low concentrations of cyanide is of great significance. In general, materials with strong positive electrostatic properties can use electrostatic attraction to enrich anions in the water near the materials, then realize rapid detection of low concentration anions by fluorescent probes. In this paper, fluorescent probes PI-S, PI-I and PI-N with cyanide-specific recognition and different charges were synthesized to study the relationship between the charge effect of probes and the sensing sensitivity. Through the zeta potential test and the calculation of the surface electrostatic potential, the positive electricity of PI-S, PI-I and PI-N gradually increased, the ΔG < 0 of the adsorption process gradually decreased, CN– could be aggregated to the vicinity of probes. As a result, the detection limit of the probe was gradually reduced from 1.07 × 10−6 to 5.03 × 10−8 M, the sensitivity was significantly enhanced. Therefore, this is expected to be a new strategy to improve the sensitivity of anion probes by increasing the positive electricity of molecules. In addition, PI-N has good anti-interference ability, short response time and certain application value in cell imaging and identification of endogenous cyanide in food. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sulfur and nitrogen self-doped carbon dots were prepared hydrothermally from waste garlic peel. • The as-prepared GPSNCDs emit strong fluorescence without capping and passivation. • The GPSNCDs were highly sensitive to Fe3+ and Mn2+ with lower detection limits of 0.75 and 0.95 µM, respectively. • The novel fluorescent GPSNCDs can be used as high-performance sensors for environmental monitoring. • The GPSNCDs can be applied to imaging normal fibroblast cells without further modifications. Here, we prepared sulfur and nitrogen self-doped carbon dots derived from garlic peel extract (GPSNCDs) using a hydrothermal method. The as-synthesized GPSNCDs were confirmed using Fourier-transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. The analytical techniques indicate that the resulting GPSNCDs exhibit distinct emissive carbon-core with functionalities (owing to various ligands in the GPSNCDs). These functionalities are responsible for excellent hydrophilic and optical properties, including excitation-dependent emission and anti-photobleaching. Fluorescence intensities of GPSNCDs were quenched in the existence of Mn2+ and Fe3+ ions. This indicates that the GPSNCDs were sensitive to Fe3+ and Mn2+ ions with a limited range from 5 to 50 µM and showed lower recognition at ∼0.75 and 0.95 µM, respectively. In addition, the sensing results were generated in a short time (20 s). The cytotoxicity of GPSNCDs was tested to demonstrate that they are sufficiently safe to use for cellular imaging. The novel fluorescent GPSNCDs-based sensor can be used as a high-performance sensor for environmental monitoring. Further, GPSNCDs showed greater biocompatibility with normal fibroblast cells, and In Vitro fluorescent imaging of GPSNCDs revealed strong fluorescence signals in the two-dimensional (2D) and three-dimensional (3D) spheroids cultured fibroblast cells. The properties mentioned above demonstrate that the GPSNCDs can be applied to imaging normal cells without further modifications. [ABSTRACT FROM AUTHOR]

[Display omitted] • An "off–on" long-wavelength fluorescent probe is synthesized for Cys detection. • The probe has a large Stokes shift (211 nm) and reacted with Cys specifically. • The probe can monitor Cys fluctuations caused by redox imbalance in HepG2 cells. • The probe can be used for fluorescence imaging in cells and mice. In this research, an "off–on" long-wavelength fluorescent probe (DCMN-Cl) based on (E)-2-(3-(2-(6-hydroxynaphthalen-2-yl)vinyl)-5,5-dimethylcyclohex-2-en-1-ylidene) malononitrile (DCMN) is designed and synthesized for cysteine (Cys) detection. DCMN-Cl exhibits a large Stokes shift (211 nm) and shows rapid response and high specificity to Cys. The fluorescence initensity at 635 nm reveals a good linear relationship with Cys concentration in the 0 to 50 μM range, and the detection limit is as low as 159 nM. The probe is also used for fluorescence imaging of Cys in cells and mice. Moreover, the probe provided visual evidence of Cu2+ and curcumin-induced intracellular Cys fluctuations. [ABSTRACT FROM AUTHOR]

[Display omitted] • Chemosensor was configured by attaching responsive group, diaminomaleonitrile, to BODIPY scaffold. • Cu2+ can be selectively recognized on a 2-s time-scale. • The recognition mechanism is based on the Cu2+ induced intramolecular oxidative cyclization of γ-aminoimine. • The absolute fluorescence quantum yield of BD + Cu2+ is determined to be 98%, attributing to the formation of dicarbonitrile substituted imidazole ring. A highly fluorescent Cu2+-responsive sensor, 2-amino-3-(BODIPYmethyleneamino)maleonitrile (BD) was constructed by attaching diaminomaleonitrile to a BODIPY scaffold. Cu2+ can be selectively recognized on a 2-s time-scale by way of fluorescence emission. When Cu2+ and BD coexist in solution, typical BODIPY emission was observed and the emission intensity could be increased to 334 times that of the blank dye solution. The mechanism of fluorescence increase is based on the generation of highly fluorescent species by Cu2+-triggered oxidative cyclization of the attached diaminomaleonitrile. The absolute fluorescence quantum yield (AFQY) of the cyclization product is 98% determined by integrating sphere. The highly emissive character can be attributed to the imidazole ring and dicarbonitrile on the BODIPY scaffold. It surpasses the meso -phenyl substituted analogue in AFQY and detection limits (DL). The specific Cu2+ recognition behavior was also validated in Hela cells with high-contrast fluorescence images. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel yellow emission Y-CDs were prepared by a hydrothermal method using DHTA. • The Y-CDs as a sensitive sensor could detect Fe3+ and biothiols by dual signals. • This sensor was utilized to sense biothiols in actual samples and living cells. • The Y-CDs were applied for message encryption as solid sensor to detect analytes. The different levels of biothiols in cells can not only screen cancer cells but also play a selective role in killing cancer cells. Therefore, accurate monitoring of biothiol in cancer cells is of great research significance. Herein, novel yellow emission CDs (Y-CDs) were prepared by a simple hydrothermal method using 2, 5-dihydroxyterephthalic acid (DHTA) as precursors. The Y-CDs as a highly efficient dual-mode sensor could detect Fe3+ and biothiols by colorimetric and fluorescence signals. Especially, with the addition of L-Cysteine, the quenched fluorescence could be quickly restored within 2 min and the detection limit was as low as 31.65 nM. Additionally, this sensor was utilized to sense biothiols in actual samples and living cells due to its eminent biocompatibility. Finally, the Y-CDs were successfully applied not only as fluorescent ink for message encryption but also as a portable solid hydrogels sensor for the detection of Fe3+ and biothiols. Therefore, these results suggested that Y-CDs could serve as a promising sensor for Fe3+ and biothiol detection in early cancer screening. [ABSTRACT FROM AUTHOR]

[Display omitted] • A fluorescent probe ( CyNa-N 3 ) based on naphthalimide and cyanine dyes was synthesized. • CyNa-N 3 can detect HClO and H 2 S with different fluorescence signals. • The sensing mechanism of CyNa-N 3 to HClO and H 2 S was confirmed by ESI–MS and 1H NMR. • CyNa-N 3 was adapted to visualize HClO and H 2 S in cell imaging. Hypochlorous acid (HClO) and hydrogen sulfide (H 2 S) play very important roles in both physiological and pathological processes, however, the methods for simultaneously detecting HClO and H 2 S were rarely reported. Here, a dual–responsive fluorescent probe ( CyNa-N 3 ) based on cyanine and naphthalimide dyes was synthesized and investigated. The fluorescence probe showed better sensitivity, high selectivity response to HClO and H 2 S by red emission and green emission bands, and the limits of detection were 0.17 µM and 0.15 µM respectively. MS (Mass Spectrum) and 1H NMR (Nuclear Magnetic Resonance) confirmed the sensing mechanism of CyNa-N 3 detected HClO and H 2 S, the calculation of density functional theory (DFT) further explained the internal mechanism of spectral change of CyNa-N 3 . Moreover, CyNa-N 3 was successfully applied to image HClO and H 2 S in living cells, which is beneficial for more efficient application in biological imaging. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel near-infrared fluorescent probe, TTPB, for the detection of mitochondrial viscosity was fabricated. • TTPB had an AIE effect and mitochondrial targeting function. • TTPB could track autophagy in addition to detecting the mitochondrial viscosity. The development of fluorescent probes capable of detecting abnormal changes in cellular mitochondrial viscosity is of great significance, as these changes have been connected to many diseases. In this study, the conventional tetraphenylethylene (TPE) molecule was modified to fabricate a novel near-infrared fluorescent, TTPB, which was then used to measure the mitochondrial viscosity. Due to the introduction of TPE and pyridine groups, TTPB had an AIE effect and mitochondrial targeting function. Meanwhile, TTPB was extremely sensitive to variations in viscosity for the twisted intramolecular charge transfer (TICT) phenomenon. The logarithm of fluorescence intensity (log I 620) of the probe demonstrated an excellent linear connection with the logarithm of viscosity (log η) in the viscosity range of 1.2 ∼ 956.0 cP, indicating the probe could quantitatively detect viscosity. Moreover, TTPB was able to visually track autophagy in addition to detecting the mitochondrial viscosity in the inflammatory cell model. These results showed that the probe was anticipated to be employed for the early diagnosis of related diseases. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two novel near-infrared emissive probes were designed and synthesized for mercury ions detection. • CyHg-Cl probe exhibited high photostability, low background fluorescence and biotoxicity. • Mercury ions in living cells and real water samples were successfully monitored. Mercury sensing and imaging in the bio-system is essential for comprehending its toxicity and therapies. Based on the merocyanine scaffold, we designed and synthesized two novel near-infrared (NIR) fluorescent probes for detecting Hg2+. The release of chloro-substituted merocyanine structure on the probe CyHg-Cl enables fluorescence enhancement rapidly by introducing Hg2+. In addition, the probe CyHg-Cl exhibits NIR emission and a low detection limit of 0.59 µM. Finally, the probe CyHg-Cl was used to detect Hg2+ in live cells and real water samples. [ABSTRACT FROM AUTHOR]

In this work, probe EHMC with AIE characteristics in solid state and aqueous ethanol solution was developed. EHMC displayed "turn on" response to Erythromycin in pure water with high selectivity and sensitivity and the sensing mechanism was confirmed by FT-IR, 1H NMR, HRMS, DLS and TEM, DFT calculation. Moreover, probe EHMC could as a portable test strips for highly selective detection of Erythromycin and identification of different concentrations of Erythromycin. [Display omitted] • Probe EHMC with AIE effect was developed for sensing Erythromycin in pure water. • Probe EHMC could serve as a portable test strips for detection of Erythromycin. • Probe EHMC could detect Erythromycin in A549 cells and BEAS-2B cells successfully. Erythromycin could be used to treat various bacterial infection, but it was harmful to the colonic microflora. Therefore, it is highly desirable to develop a fluorescence probe that could selectively and sensitively detect Erythromycin in pure water. In this work, a fluorescent probe named EHMC , which exhibited aggregation-induced emission (AIE) characteristic in solid state and water/EtOH binary solvent was developed for "turn on" sensing Erythromycin in pure water with high selectivity and sensitivity (detection limit: 1.78 × 10−8 M). Also, there are fewer interference from other antibiotics in the detection process of probe EHMC for Erythromycin. Moreover, probe EHMC could as a portable test strips for highly selective detection of Erythromycin and identification of different concentrations of Erythromycin. In addition, living cells imaging experiments displayed that probe EHMC could detect Erythromycin in A549 cells and BEAS-2B cells successfully. Combined with the theoretical calculation results The sensing mechanisms that the C O in Erythromycin and OH in EHMC formed intermolecular hydrogen bond and further formed new aggregates were confirmed by job' plot, 1H NMR, FT-IR, ESI-MS, DLS and TEM and DFT calculation. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel nicotinic hydrazone-based turn-on fluorescence probe 3 has been synthesized for the detection of carbonate ions in an aqueous medium. • The probe showed excellent selectivity, sensitivity, and good reversibility toward CO 3 2– ions. • The deprotonation mechanism of sensing was elucidated by 1H NMR, ESI-MS spectra, and DFT calculations. • An INHIBIT-type molecular logic gate was successfully constructed using probe 3- CO 3 2– and CH 3 COOH. • Probe 3 effectively senses CO 3 2– ions in the real water samples and live cells. A novel turn-on fluorescent probe 3 was synthesized by condensing salicylaldehyde and nicotinic hydrazide for the selective detection of CO 3 2– in aqueous medium. Probe 3 exhibited a turn-on fluorescence response toward CO 3 2– with excellent selectivity, sensitivity (DL = 2.76 μM), and good reversibility. The binding constant (K) of probe 3 with CO 3 2– was calculated to be 5 × 103 M−1 (log K 3.69). The 1:1 stoichiometry of the complex between probe 3 and CO 3 2– ions was confirmed by Job's plot and ESI-MS spectra. Deprotonation and hydrogen-bonding interactions are involved in the recognition of CO 3 2– ion, which was also suggested by 1H NMR, ESI-MS spectra, and Density Functional Theory (DFT) calculations. Moreover, an INHIBIT type molecular logic gate was constructed by using 3:CO 3 2– and CH 3 COOH as inputs and current signal as output. Owing to the practical applications, probe 3 demonstrated its efficiency in quantifying CO 3 2– ion in real water samples through standard addition method, thus showcasing its potential in real environment. Further, the MTT assay indicated very low cytotoxicity (IC 50 = 1 mM) of probe 3 and also the cell imaging experiments demonstrated the effective sensing of CO 3 2– ions with probe 3 in the biological systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • An intermolecular ESPT-based fluorescent probe (DQN) for N 2 H 4 was synthesized. • DQN exhibits high selectivity, large Stoke shift (200 nm) and low cytotoxicity. • The sensing strategy for N 2 H 4 detection is based on the hydrogen bonding recognition of DQN to N 2 H 4 , lighting up ESIPT fluorescence. • DQN was also successfully applied in cell imaging. The broad occurrence of the hydrazine (N 2 H 4) residues in aqueous environment is a potential threat to human health. Currently, the mainstream strategy for designing N 2 H 4 -specific probes is to functionalize a fluorophore with nucleophilic sites for the reduction reaction with N 2 H 4. In this work, we designed and synthesized an excited-state intermolecular proton transfer (inter-ESPT) fluorescent dye(2-amino-4-(4-methoxyphenyl)-7,8-dihydro-5H-spiro[quinoline-6,2′- [1,3] dioxolane]-3-carbonitrilem, DQN) and used it as a probe to sense N 2 H 4. DQN exhibits blue fluorescence in conventional solvents, which is assigned to its normal emission. In the presence of N 2 H 4 , the probe DQN can anchor the N 2 H 4 molecule via hydrogen binding, enabling DQN to undergo inter-ESPT process and light up its tautomeric fluorescence. From this basis, an inter-ESPT-based method for N 2 H 4 detection was established, offering high selectivity and sensitivity (11.5 nM). Furthermore, we demonstrated that the probe DQN can recognize the proteins in living cells, affording cell-imaging. This research provides a promising sensing strategy for monitoring N 2 H 4 in water environments and this inter-ESPT dye is a powerful tool for cell-imaging. [ABSTRACT FROM AUTHOR]

[Display omitted] • A robust probe Bptp-RD was developed to identify DNA and RNA. • Bptp-RD was successfully applied to image DNA and RNA in cells. • Bptp-RD was successfully used to detect different types of DNA. • Recognition rule of probes to different types of DNA was revealed with Bptp-RD. The roles of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) in cells are closely related. However, the absence of molecular tools for simultaneous imaging of the two nucleic acids has prevented scientists from elucidating the regulatory mechanisms of nucleic acid interaction. The nucleic acid probes developed in recent years have ignored the regulatory relationship between DNA and RNA. Simultaneously imaging RNA and DNA in cells through a single small-molecule fluorescent probe is important. In this study, we propose a strategy for developing fluorescent probes localized to DNA and RNA to investigate their detection and imaging characteristics. The novel probe Bptp-RD has been successfully used for DNA and RNA imaging in cells. We investigated the detection and imaging characteristics of this nucleic acid probe and discovered the following: 1) the differences in the detection results of this nucleic acid probe for DNA and RNA come from the structural differences of the nucleic acids rather than chemical composition differences; 2) through using small-molecule probes to image a nucleic acid in cells, another nucleic acid can be visualized by reducing the fluorescence signal caused by DNA or RNA; 3) the order of response of the small-molecule fluorescent probe with intercalation and binding mechanisms to the type of nucleic acid structure is single chain, double chain, and ring. This work will help improve the understanding of RNA and DNA probes, and the novel probe has high potential to explore the interaction between RNA and DNA in cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel fluorescence proe for Hg2+ was developed based on aggregation induced emission. • The probe exhibited a limit of detection of 22 nM and a fast response time. • The mechanism of the probe is based on the Hg2+ reaction induced solubility decrease, resulting in activated fluorescence due to aggregation induced emission. • The probe can be used for imaging of Hg2+ in live cells with fast response. Mercury ions (Hg2+), as one of heavy transition metals (HTM), is a highly toxic metal that is hazardous to human health. Here an aggregation-induced emission (AIE) fluorescent probe is designed for the highly sensitive and selective detection of Hg2+. The probe is engineered with a tetraphenylethene (TPE) derivative as the fluorophore and thiopropionic acid as the site of recognition for Hg2+. Due to the different solubilities of the probe AIE-COOH and its corresponding product after reaction with Hg2+. The probe demonstrates a maximum detection limit of 22 nM and a fast response time of ∼100 s. Simultaneously, AIE-COOH exhibits outstanding detectivity and hypersensitivity for the detection of Hg2+ in aqueous solutions. These characteristics demonstrate that AIE-COOH hold a great potential in environmental, food and biological systems. Moreover, we have also successfully applied it to Hg2+ fluorescence imaging in in living cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • The conjugated structures of fluorescent dyes (NapPAs) were extended by the introduction of phenylethynyl, and the effects of different substituents at the p -position of phenylacetylene on the geometry, frontier orbital electron distribution, energy gap and photophysical properties of the dyes were studied. • Correlating the theoretical calculation results with the experimentally measured spectra, it was found the dyes exhibited the characteristics predicted by theoretical calculations, and various properties of the dyes could be regulated through structural modification during molecular design. • Two dyes (NapPA-LDs and NapPA-LDs-Lyso) with excellent photophysical properties (large Stokes shift, high polarity-viscosity sensitivity, good biocompatibility) were selected as fluorescent probes for bioimaging. • NapPA-LDs exhibited remarkable affinity towards LDs with excellent imaging effect, and enabled monitor the dynamic changes and movements of LDs in real time, helping to uncover previously unexplored cellular mechanisms. • NapPA-LDs-Lyso enabled simultaneous two-color imaging of LDs and lysosomes, which could monitor the dynamic changes, movements and dynamic behavior (aggregation, dissociation and fusion) of LDs and lysosomes in real time, and could serve as a potential tool to study the interactions and potential functions between LDs and lysosomes. A series of fluorescent dyes (NapPAs) based on 4-phenylacetylene-1,8-naphthalimide were synthesized and characterized, whose conjugated structures were extended by the introduction of phenylethynyl. Furthermore, changes in the photophysical properties of the dyes when substituents with varying electron richness were introduced at the p -position of phenylacetylene were studied. The theoretical calculation of the dye molecules was carried out by B3LYP functional and 6-31G(d,p) basis set, and the effects of different substituents at the p -position of phenylacetylene on the electronic structure and photophysical properties of the dyes were studied by theoretical calculation results. Theoretical calculations provided a reliable means of predicting the properties of dyes, which could help in the design of more efficient and novel dyes. To verify the practicability of the dyes, two dyes with excellent photophysical properties (large Stokes shift, high polarity-viscosity sensitivity, good biocompatibility) were selected as fluorescent probes for visualization of LDs and two-color imaging of LDs and lysosomes. Cell imaging showed that NapPA-LDs and NapPA-LDs-Lyso serve as excellent imaging tools to monitor the dynamic changes, movements, and behaviors of LDs and lysosomes in real time. Notably, NapPA-LDs-Lyso held promise as a potential tool to study the interaction between LDs and lysosomes. [ABSTRACT FROM AUTHOR]

In this review, we first summarized the recent progress of multifunctional probes towards small-molecular since 2018, focusing on the molecular structures, response mechanism, optical properties and biological imaging in the detection and imaging of cellular ONOO– and analytes. [Display omitted] • There is the first review of multifunctional fluorescent probes for cellular ONOO- and other analytes. • The development of multifunctional fluorescent probes helps to study the relationship between ONOO and analytes. • The molecular structure, response mechanism and biological imaging of ONOO- multifunctional fluorescent probes are reviewed. Although peroxynitrite (ONOO–) plays an essential role in cellular redox homeostasis, its excess ONOO– will affect the normal physiological function of cells. Therefore, real-time monitoring of changes in local ONOO– will contribute to further revealing the biological functions. Reliable and accurate detection of biogenic ONOO– will definitely benefit for disentangling its complex functions in living systems. In the past few years, more fluorescent probes have been developed to help understand and reveal cellular ONOO– changes. However, there has been no comprehensive and critical review of multifunctional fluorescent probes for cellular ONOO– and other analytes. To highlight the recent advances, this review first summarized the recent progress of multifunctional fluorescent probes since 2018, focusing on molecular structures, response mechanisms, optical properties, and biological imaging in the detection and imaging of cellular ONOO– and analytes. We classified and discussed in detail the limitations of existing multifunctional probes, and proposed new ideas to overcome these limitations. Finally, the challenges and future development trends of ONOO– fluorescence probes were discussed. We hoped this review will provide new research directions for developing of multifunctional fluorescent probes and contribute to the early diagnosis and treatment of diseases. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel mitochondria-targeted red-emitting fluorescent probe (VP) was synthesized. • The probe VP was used to detect viscosity with high selectivity and sensitivity. • The probe VP could visualize the mitochondrial viscosity change in living cells. • The probe VP was a potential tool for monitoring viscosity and phagocytosis. Mitochondrial viscosity is a critical factor affecting numerous physiological processes, including phagocytosis. Abnormal viscosity in mitochondria is related to some pathological activities and diseases. Evaluating and detecting the changes in mitochondrial viscosity in vivo is crucial. Thus, a mitochondria-targeted red-emitting fluorescent probe (VP) was prepared, and can be used to detect viscosity with high selectivity and sensitivity. The synthesis of probe VP was as simple as two steps and the cost was low. In addition, the fluorescence intensity (log I 615) exhibited an excellent relationship with viscosity (log η) in the range of 0.5 – 2.5 (R2 = 0.9985) in water/glycerol mixture. It is noteworthy that the probe VP displayed the highest signal-to-noise ratio (about 50-fold) for viscosity in water and glycerol system. The probe VP can visualize the mitochondrial viscosity change in living cells. More importantly, phagocytic test for BV2 cells further demonstrated that phagocytosis decreased with increased viscosity. Furthermore, VP was successfully used for monitoring the mitophagy process induced by starvation, and mitochondrial viscosity exhibited enhancement during mitophagy. The probe was a potential tool for studying viscosity and phagocytosis. [ABSTRACT FROM AUTHOR]

A terpyridyl-rhodamine based probe has been designed and prepared for the sensitive and discriminative detection of Hg2+ and Cu2+ in water by dual/single emission change and applications in constructing a combinatorial logic gate and cell imaging. [Display omitted] • A new terpyridyl-rhodamine hybrid dye TR and sensor TRH have been facilely prepared. • TRH can discriminatively sense Hg2+ and Cu2+ in water with high sensitivity. • TRH can be employed for the construction of a combinatorial logic gate. • TRH can be applied for the discriminative sensing of Hg2+ and Cu2+ in living cells. Sensitive and discriminative sensing of more than one analyte with a single fluorescent probe is significant and challenging. Herein a new terpyridyl-rhodamine hybrid, namely TRH, has been rationally designed and prepared with two responsive groups in the molecular structure, which facilitate the discriminative detection of Hg2+ and Cu2+ ions in water with detection limits of 4.9 and 53.3 nM by ratiometric fluorescence change (F 595 /F 485) and fluorescence quenching, respectively. Investigations show that the selectivity to Hg2+ ions can be attributed to Hg2+-promoted spirolactam ring opening and further hydrolysis, followed by a through-bond energy transfer (TBET) process. The selective fluorescence quenching to Cu2+ ions probably can be ascribed to the binding Cu2+ to terpyridyl that triggers a ligand-to-metal charge transfer (LMCT) process, which can also efficiently inhibit the TBET process induced by Hg2+ ions and promotes the discriminative sensing of Cu (II) and Hg (II). In addition, the fluorescent responses to Hg2+ and Cu2+ ions cover a wide pH range. Moreover, a combinatorial logic gate with the functions of NOR and INHIBIT has been fabricated by using Hg2+ and Cu2+ ions as chemical input signals, and fluorescence at 485 and 595 nm as output signals. Besides, TRH also exhibits sensitive and discriminative sensing ability to Hg2+ and Cu2+ ions by the fluorescence of rhodamine fluorophore. Significantly, based on the fluorescence signal output of rhodamine moiety, TRH can be used as a tracer for the discriminative sensing of Hg2+ and Cu2+ ions by using living cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • S, N-co-doped carbon dots are synthesized from reactive red 2 and L-cysteine or L-methionine. • The maximum fluorescent of N, S-CDs-A is 565 nm with 14.0 % fluorescence intensity. • The maximum fluorescent of N, S-CDs-B is 615 nm with 6.3 % fluorescence intensity. • Both N, S-CDs-A and N, S-CDs-B showed high sensitive and selective to Fe3+. • N, S-CDs-A can also detect Al3+ ion with high sensitivity and selectivity. Turning waste into wealth, herein, two highly fluorescent N and S co-doped carbon dots (N, S-CDs-A and N, S-CDs-B) were synthesized by the hydrothermal reaction of contaminant reactive red 2 (RR2) and L-cysteine or L-methionine, respectively. The detailed morphology and structure of N, S-CDs were characterized by XRD, Raman spectrum, FTIR spectra, TEM, HRTEM, AFM and XPS. The maximum fluorescent of N, S-CDs-A and N, S-CDs-B are 565 and 615 nm under different excitation wavelengths with moderate fluorescence intensity of 14.0 % and 6.3 %, respectively. The microstructure models of N, S-CDs-A and N, S-CDs-B, which were induced by FT-IR, XPS and element analysis, had been applied in DFT calculation. The result indicated that the doping of S and N is beneficial to obtain the red-shift of fluorescent spectra. Both N, S-CDs-A and N, S-CDs-B showed highly sensitive and selective to Fe3+. N, S-CDs-A can also detect Al3+ ion with high sensitivity and selectivity. Finally, N, S-CDs-B was successfully applied in cell imaging. [ABSTRACT FROM AUTHOR]

The article highlights a quinoline-based probe for the detection of Cd2+ over other metal ions with a nanomolar level detection limit. Both DFT and TD-DFT studies were carried out to explore the sensing mechanism as well as the theoretical electronic spectra. The utilization of the probe in real-life applications has been investigated in live cells. [Display omitted] • A quinoline-based probe for the detection of Cd2+ in near-aqueous medium. • Binding mode is confirmed by single crystal XRD analysis. • Nanomolar detection limits of Cd2+. • DFT and TD-DFT analysis of both ligand and its Cd2+ complex. • Positive response towards bioimaging in live RAW 264.7 cell line. The present investigation highlights a quinoline-based small molecule probe (DEQ) for the detection of Cd2+ among other metal ions in near-aqueous media. The probe DEQ and its Cd2+ complex (DEQ-Cd) have been synthesized and characterized by all possible spectroscopic methods. The weakly emissive DEQ showed its strong emission in the presence of Cd2+, which is attributed to the photoinduced electron transfer (PET) along with the chelation-enhanced fluorescence (CHEF) mechanism. The 1:1 binding mode between ligand and Cd2+ is confirmed by single crystal XRD analysis, which is further supported by Job's plot and HRMS. The detection limit of the probe to recognize Cd2+ was found to be as low as 89 nM. Furthermore, DEQ can act as a reversible fluorescence probe with the off-on-off mechanism by the alternative addition of Cd2+ and EDTA. DFT and TD-DFT studies exposed the proposed mechanism after Cd2+ insertion and the obtained results for electronic spectra are in line with the experimental results. The response towards pH was quite interesting and allowed us to study its application in live cell imaging. With all the positive results, the proposed ligand DEQ can be used as a potential probe for the detection of Cd2+ in real-life applications. [ABSTRACT FROM AUTHOR]

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

[Display omitted] • Heteroatom-doped photoluminescent CDs was prepared by hydrothermal method. • NSB-CDs exhibited good water solubility, stability, biocompatibility, and less toxic. • NSB-CDs presented high sensitivity and selectivity towards Fe3+ ions and cysteine. • The limit of detection of the sensor NSB-CDs is 54.4 nM/Fe3+ and 4.9 nM/Cys. • NSB-CDs/Fe3+ ion and cysteine were promising multicolor imaging with HCT-116 cells. Herein, a simple hydrothermal synthesis is used to prepare multiple heteroatom-doped photoluminescent carbon dots (CDs) from thiourea (N and S source) and boric acid (B source) as precursors. The optical and physicochemical properties of the as-synthesized NSB-CDs were studied using UV–Vis, photoluminescence, TEM, FT-IR, XRD, Raman, and XPS analyses. The NSB-CDs exhibited excellent stability, high photostability, pH, and ionic strength tolerance; they retained their excellent stability independent of excitation. The NSB-CDs featured small sizes of approximately 3.2 ± 0.4 nm (range: 2.0–5.0 nm) as evidenced using TEM measurements. The NSB-CDs were used as a photoluminescent sensing platform to detect Fe3+ as well as cysteine (Cys) molecules. The competitive binding of Cys to Fe3+ resulted in NSB-CDs that retained their photoluminescence. For the rapid identification and quantification of Fe3+ and Cys, NSB-CDs were developed as a "switch-on" dual-function sensing platform. The linear detection range of Fe3+ was 0–20 μM (limit of detection [LOD]: 54.4 nM) and that of Cys was 0–50 μM (LOD: 4.9 nM). We also introduced a smartphone RGB analysis method for detecting low-concentration solutions based on digital images. The NSB-CDs showed no toxicity at 100 μg/mL. Photoluminescent probes for multicolor live-cell imaging can be used with NSB-CDs at this concentration, suggesting that NSB-CDs may be promising photoluminescent probes. [ABSTRACT FROM AUTHOR]

[Display omitted] • An ICT-FRET-based fluorescent probe for the ratiometric detection of H 2 S n has been reported. • The probe displays high sensitivity and high selectivity for H 2 S n. • The probe had been applied for the ratiometric detection of H 2 S n in A549 cells. Hydrogen polysulfide (H 2 S n , n > 1), as one of the important members of reactive sulfur species (RSS), plays a vital part in the processes of both their physiology and pathology. In this work, a ratiometric fluorescent probe for H 2 S n had been designed and prepared based on the combination mechanism of intramolecular charge transfer (ICT) and fluorescence resonance energy transfer (FRET). The probe chose a coumarin derivative as the energy donor, a naphthalimide derivative as the energy acceptor and 2-fluoro-5-nitrobenzoate as the H 2 S n recognition group. When H 2 S n was not present in the system, the ICT process of the naphthalimide acceptor was inhibited and the FRET process from the coumarin donor to the naphthalimide acceptor was turned off. When H 2 S n was added, both ICT and FRET occurred due to the nucleophilic substitution-cyclization reactions between the probe and hydrogen polysulfide. In addition, the ratio value of the emission intensities at 550 nm and 473 nm (I 550 nm/I 473 nm) of this probe had a good linear relationship with H 2 S n concentration in the range of 6.0 × 10-7-5.0 × 10-5 mol·L-1, and a detection limit of 1.8 × 10-7 mol·L-1 was obtained. The developed probe had high selectivity and sensitivity, as well as good biocompatibility. Additionally, the probe had been used to successfully image both indigenous and exogenous hydrogen polysulfide in A549 cells using confocal microscope. [ABSTRACT FROM AUTHOR]

[Display omitted] • Probes 1a-b for detection of thiophenols by ESIPT mechanism were constructed with diethylcoumarin–salicylaldehyde units. • They showed large Stokes shift (greater than100 nm) and one of them displayed NIR-emitting (670 nm) when detecting thiophenols. • Probes 1a-b could form inclusion complexes with M-β-CD. • The presence of M-β-CD reduced the detection limits of probes 1a - b towards thiophenols. Thiophenol and its derivatives are compounds with high toxicity to organisms and environmental pollution, so it is necessary to detect the level of thiophenols in the environment and biological samples. The probes 1a-b were obtained by introducing the 2,4-dinitrophenyl ether group into diethylcoumarin–salicylaldehyde based compounds. And they can form host-guest compounds with methylated β-cyclodextrin (M-β-CD), the association constants of inclusion complexes are 49.2 M−1, 125 M−1 respectively. The fluorescence intensities of probes 1a-b at 600 nm (1a) and 670 nm (1b) increased significantly in thiophenols detection. Meanwhile, with the addition of M-β-CD, the hydrophobic cavity of M-β-CD significantly increased the fluorescence intensity of probes 1a-b , thus the detection limits of probes 1a-b to thiophenols were reduced from 410 nM, 365 nM to 62 nM, 33 nM respectively. Whereas, the good selectivity and short response time of probes 1a-b towards thiophenols was not affected in the presence of M-β-CD. Moreover, probes 1a-b were used for further water sample detection and HeLa cell imaging experiments due to their good response to thiophenols and the results suggested that probes 1a-b had the potential to detect the content of thiophenols in water samples and living cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel dual-functional probe FAM-SSH was fabricated for fluorescence and colorimetric detection of Cu2+ and S2− ions. • FAM-SSH exhibited a wide linear range and a lower detection limit towards Cu2+ (55.5 nM) and S2− (31.1 nM). • FAM-SSH was successfully used to determine Cu2+ and S2− in real samples with good recovery rate and accuracy. • FAM-SSH was successfully applied for semi-quantitative detection of Cu2+ and S2− with the aid of smartphone APP and test strips. • FAM-SSH was found useful for imaging of Cu2+ and S2− in living cells. A new dual-mode probe FAM-SSH with fluorescence and colorimetric properties was developed by solid-phase peptide synthesis, comprising 5-carboxy fluorescein (5-FAM) as a fluorophore, and tripeptide (Ser-Ser-His) as a recognition group. FAM-SSH not only displayed highly selective detection of Cu2+ based on fluorescence quenching mode, but also achieved colorimetric recognition of Cu2+ in solution, wherein a color change was observable to the naked eye. Additionally, the FAM-SSH -Cu2+ ensemble was highly selective for S2− over a wide pH range (7.0–12.0), characterized by a fluorescence enhanced response and colorimetric recognition, which was caused by the release of FAM-SSH and the precipitation of CuS. Moreover, the limit of detection (LOD) values for Cu2+ and S2− were 55.5 nM and 31.1 nM, respectively. Results of sample analyses and cell imaging experiments indicated that FAM-SSH has exciting field practicability and good cell permeability, and would be further useful for detection and imaging in environmental systems and living cells. Finally, test strips were produced by immersing them in FAM-SSH solution, thereby creating a method for portable visual detection. More importantly, a smartphone-assisted visual sensing platform was also developed for semi-quantitative Cu2+ and S2− detection with LOD values of 0.48 μM and 1.22 μM, respectively. [ABSTRACT FROM AUTHOR]

A sulfone based chemosensor, namely 2,2′-(1E)-(5,5′-sulfonylbis(2-hydroxy-5,1-phenylene))bis(azan-1-yl-1-ylidene)bis(methan-1-yl-1-ylidene)dinaphthalen-1-ol (H 4 L-naph), with two coordination pockets has been found to be highly selective for Al3+. Its properties have been modified significantly by introducing naphthyl ring in place of phenyl ring. [Display omitted] • A sulfone based chemosensor, 2,2′-(1E)-(5,5′-sulfonylbis(2-hydroxy-5,1-phenylene))bis(azan-1-yl-1-ylidene)bis(methan-1-yl-1-ylidene)dinaphthalen-1-ol (H 4 L-naph), was synthesized. • H 4 L-naph with two binding pockets explored for selective Al3+ sensing in DMF- HEPES buffer (1:4, v/v, pH 7.4). • In comparison to an analogous probe having phenyl, it showed fluorescence in longer wavelength. • It was applied in living cell imaging studies. A chemosensor with two binding pockets facilitates binding of one metal ion in either of the pockets providing a better chance for the interaction and hence recognition of the cation. We report here a chemosensor, namely 2,2′-(1E)-(5,5′-sulfonylbis(2-hydroxy-5,1-phenylene))bis(azan-1-yl-1-ylidene)bis(methan-1-yl-1-ylidene)dinaphthalen-1-ol (H 4 L-naph), for selective sensing of Al3+ in DMF- HEPES buffer (1:4, v/v, pH 7.4). It shows almost 100-fold fluorescence enhancement at 532 nm (λ ex = 482 nm) in the presence of Al3+. Its quantum yield and excited state lifetime enhances significantly with the cations. H 4 L-naph forms a 1:2 complex with Al3+ with an association constant value of 2.18 × 104 M−2. Fluorescence enhancement may be attributed to CHEFF mechanism and restriction of >C N isomerization. Effect of the presence of naphthyl rings instead phenyl ring of a previously reported probe has resulted shifting of excitation/emission peak towards longer wavelength. The probe has been applied to image Al3+ in L6 cells with no significant cytotoxicity. [ABSTRACT FROM AUTHOR]

[Display omitted] • BQBH with quinoline fluorophore was synthesized and characterized. • BQBH exhibits highly sensitivity fluorescence enhancement to Cd2+ along with significant color change. • Limit of detection (LOD) for Cd2+ was reached the level of μM. • BQBH was successfully applied in the detection of Cd2+ on test paper and cell imaging. A facile fluorescence probe BQBH was synthesized and investigated on its spectrum property. The result showed that the BQBH had high sensitivity and selectivity for Cd2+ with lowest detection determined as 0.14 μM by fluorescence response. The 1: 1 binding ratio between BQBH and Cd2+ was determined by Job's plot, and the binding details were further confirmed by 1H NMR titration, FT-IR spectrum and HRMS analysis. The applications including on test paper, smart phone and cell image were all also investigated. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel open-type NIR fluorescent probe was reported for the detection of PhSH. • The probe shows high sensitivity and selectivity to thiophenol. • Probe shows a large Stoke shift and significant fluorescence enhancement. • Probe has been applied to the detection of PhSH in living cells and water samples. In this study, a NIR fluorescent probe based on ICT principles was developed for the detection of phenylthiophenol. An excellent fluorescent mother nucleus is constructed with tricyano groups, and benzenesulfonate was introduced as a specific recognition site for thiophene, which can be used for rapid detection of thiophenol. The probe has a significant Stokes shift (220 nm). Meanwhile, it had rapid response to thiophene and high specificity. The fluorescence intensity of the probe at 700 nm showed a good linear relationship with thiophene concentration in the range of 0 to 100 μM, and the detection limit was as low as 45 nM. The probe had also been successfully applied to the detection of thiophene in real water samples. MTT assay showed low cytotoxicity and excellent fluorescence imaging in live cells. [ABSTRACT FROM AUTHOR]

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

A multifunctional fluorescent probe with "ESIPT+AIE" properties were synthesized. Three mental ions including Pb2+, Ag+ and Fe3+ could be selectively recognized and distinguished and remarkable fluorescence enhancement was observed. [Display omitted] • 1. A multifunctional fluorescent probe with "ESIPT + AIE" properties was synthesized. • 2. Pb2+, Ag+ and Fe3+ ions could be selectively recognized and distinguished with remarkable fluorescence enhancement. • 3. The probe had been successfully applied to water sample detection, test paper experiment and biological cell imaging. In this work, three Schiff-based fluorescent probes with aggregation-induced emission (AIE) and excited intramolecular proton transfer (ESIPT) characters were synthesized by grafting 2-aminobenzothiazole group onto 4-substituted salicylaldehydes. More important, a rare tri-responsive fluorescent probe (SN-Cl) was developed by purposeful variation of substituents in the molecule. It could selectively identify Pb2+, Ag+ and Fe3+ in different solvent systems or with the help of masking agent and show complete fluorescence enhancement without interference of other ions. Meanwhile, the other two probes (SN-ON and SN-N) could only recognize Pb2+ in DMSO/Tris-HCl buffer (3: 7, v/v, pH = 7.4). According to Job's plot, density functional theory (DFT) calculations and NMR analysis, coordination between SN-Cl and Pb2+/Ag+/Fe3+ was determined. The LOD values for three ions were as low as 0.059 μM, 0.012 μM and 8.92 μM, respectively. Ideally, SN-Cl showed satisfactory performance in real water samples detection and test paper experiments for three ions. Also, SN-Cl could be used as an excellent imaging agent for Fe3+ in HeLa cells. Therefore, SN-Cl has the ability to be a "single fluorescent probe for three targets". [ABSTRACT FROM AUTHOR]

Ratiometric fluorescent probes based on FRET mechanism have attracted great attention due to their large pseudo-Stokes shifts and built-in correction for environmental effects. However, most donors failed to meet the requirement that the emission of the donor must overlap well with the absorption of the acceptor. Therefore, searching for new fluorophore to construct FRET system is in great need. In this paper, a new fluorescent dye pyrazolo[1,5- a ]pyridine was synthesized and used as a donor in the FRET system for ratiometric sensing of Cu2+. The probe is based on FRET and PET mechanism. It shows high selectivity and sensitivity toward Cu2+ (detection limit 30 nM). Furthermore, it was successfully used to detect Cu2+ in Glioma cells. Unlabelled Image • A ratiometric fluorescent probe for sensing Cu2+ based on new fluorophore pyrazolo[1,5- a ]pyridine has been synthesized. • The probe exhibits highly sensitivity and selectivity toward Cu2+ (detection limit: 23 nM). • The ratiometric fluorescent probe displays a remarkable emission shift (about 200 nm). • The probe can be applied to image in cells. [ABSTRACT FROM AUTHOR]

A bifunctional organic compound 2-butyl-6-hydroxy-1,3-dioxo-2,3-dihydro-1H-benzo[ de ] isoquinoline-5-carbaldehyde (BHC) with photochromic properties in solid state and probe detection for ClO− in complete water solution was synthesized and fully characterized. A 'white–yellow–white' reversible photochromic behavior could be observed when alternating UV/vis light irradiation on the solid BHC powder. Good fatigue resistance and adjustable bleaching rate were shown when heating conditions changes. In addition, BHC displayed a high selectivity and low detection limit (1.16 × 10−8 M) for ClO−. The photoluminescent fluorescence "on-off" recognition result can be easily identified and BHC has been tested for safely imaging living cells and detecting hypochlorite anion in vitro and vivo. A better water solubility of BHC effectively reduces damage caused by organic solvent in cell imaging progress. Unlabelled Image • This is an interesting bifunctional material with reversible photochromic behavior and ClO− recognition effect. • BHC exhibits a rare naphthalimide-based ESIPT mechanism for photochromic properties and fatigue resistance. • This is a completely water soluble fluorescent probe. • BHC is capable of simultaneously detecting ClO− in aqueous solution and living cells • Probe BHC exhibits ideal properties including high sensitive, good selectivity and short response time. [ABSTRACT FROM AUTHOR]

A quinoline-based fluorescence sensor QDTD was developed for Zn2+. QDTD can detect Zn2+ by fluorescence turn-on. Detecting limit (0.27 μM) of QDTD for Zn2+ was far below WHO standard (76.0 μM). For the practical application, compound QDTD could be used to determine Zn2+ in real samples and applied to the test kit. More importantly, QDTD was expertly applied for Zn2+ imaging in HeLa cells and zebrafish with good membrane-permeability. Detection mechanism of Zn2+ ion by compound QDTD was suggested through the analytical tools like 1H NMR titration, ESI-MS, Job plot, fluorescent and UV–vis titration, and theoretical calculations, and through the synthesis and applications of a model compound AAQA. Unlabelled Image • A highly selective fluorescent chemosensor QDTD for Zn2+ was designed and synthesized. • QDTD could detect Zn2+ by fluorescence turn-on with the low detection limit (0.27 μM). • Sensor QDTD was applied to the real water samples and test strip. • Sensor QDTD could successfully quantify Zn2+ in HeLa cells and zebrafish. [ABSTRACT FROM AUTHOR]

A simple julolidine based chemosensor (JT) was designed and synthesized by single condensation step. JT displayed excellent selectivity and sensitivity with on-off responses towards Zn2+ and Cu2+ over other biologically relevant metal ions in aqueous media. Upon addition of Zn2+ ions, JT exhibited a significant blue shift in emission followed by turn- on enhancement while with Cu2+, the fluorescence intensity of JT was completely vanished. The 1:1 binding affinity between JT and Zn2+/Cu2+ was proposed by Job's plot analysis. The detection limit for Zn2+ and Cu2+ ions reached at 3.5 × 10−8 M and 1.46 × 10−6 M, respectively. The sensing mechanism of JT with Zn2+/Cu2+ was supported by DFT calculations. Based on photophysical studies and its reversibility environment with EDTA, molecular logic gates were fabricated. Furthermore, JT was successfully established to detect intracellular Zn2+ ions in live cells by turn-on response. A bifunctional chemosensor JT was synthesized to distinguish Zn2+ and Cu2+ ions based on emission on-off response. Unlabelled Image • New julolidine based Schiff base derivative (JT) was designed and synthesized and JT served as a selective emission on-off response towards Zn2+ and Cu2+ ions. • The sensor shows excellent sensitivity for Zn2+ and Cu2+ ions with an LOD at 3.5 × 10 -8 M and 1.46 × 10 -6 M, respectively. • The 1:1 binding model of the sensor JT with Zn2+/Cu2+ was established and reversibility of the chemosensor JT was proved by experiments with EDTA. • JT was successfully established to track intracellular Zn2+ ions in HeLa cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • A red-emissive fluorescent probe HBTI for reversible recognition of HSO 3 − and H 2 O 2 has been developed. • HBTI showed fluorescence on–off-on variations upon sequential addition of HSO 3 − and H 2 O 2. • HBTI is applicable to detect HSO 3 − in real food samples. • HBTI is mitochondria-targetable and can be used in cell imaging. Reducing agent SO 2 and oxidant H 2 O 2 are two essential substances in cells, and the balance between them is closely related to the survival of cells. SO 2 derivative HSO 3 − is often used as food additive. Therefore, simultaneous detection of SO 2 and H 2 O 2 is of great significance in biology and food safety. In this work, we successfully developed a mitochondria-targeted red fluorescent probe (HBTI), which has excellent selectivity, high sensitivity and large Stokes shift (202 nm). HBTI and HSO 3 −/SO 3 2− undergo Michael addition on the unsaturated C=C bond, and the addition product (HBTI-HSO 3 −) can react with H 2 O 2 to restore the conjugated structure. Fluorescence changes from red to non-emissive and then restores to red, and can be detected quickly and visually. In addition, HBTI has been successfully targeted mitochondria, and achieved dynamic reversible response to SO 2 /H 2 O 2 in living cells, and has been successfully applied to detect SO 2 in food samples. [ABSTRACT FROM AUTHOR]

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

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

[Display omitted] • ESIPT probe (E)-N'-(5-bromo-2-hydroxybenzylidene)-4-hydroxybenzohydrazide (BHHB) • Al3+ ion sensor in the sub-nano molar scale by fluorescence enhancement in aqueous medium. • Imaging of nucleus of live cells by fluorescence confocal microscopy. The molecule (E)-N'-(5-bromo-2-hydroxybenzylidene)-4-hydroxybenzohydrazide (BHHB) has been synthesized and its photophysical properties have been investigated by using steady state absorption, emission and time resolved emission spectroscopy. The molecule shows excited state intramolecular proton transfer (ESIPT) process with characteristics large Stoke shifted emission. Fluorescence enhancement of BHHB only in presence of Al3+ ion is used as selective aluminium ion sensor in the sub-nano molar scale in aqueous solution. BHHB-Al3+ ion complex can penetrate through live Hepatocellular Carcinoma (HepG2) cell membranes and is capable for imaging of nucleus of live cells by fluorescence confocal microscopy. [ABSTRACT FROM AUTHOR]

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

[Display omitted] • A turn-on fluorescent nanosensor XNP1 was constructed for H 2 S imaging in vitro and in vivo. • Compared to other competing species, the detection limit of XNP1 was as low as 32.3 nM. • XNP1 has been successfully used for H 2 S detecting and imaging in inflammatory cells and mice. Hydrogen sulfide (H 2 S) is an endogenously generated gaseous signaling molecule and is known to be involved in the occurrence and development of inflammation. To better understand its physiological and pathological process of inflammation, reliable tools for H 2 S detection in living inflammatory models are desired. Although a number of fluorescent sensors have been reported for H 2 S detection and imaging, water-soluble and biocompatibility nanosensors are more useful for imaging in vivo. Herein, we developed a novel biological imaging nanosensor, XNP1 , for inflammation-targeted imaging of H 2 S. XNP1 was obtained by self-assembly of amphiphilic XNP1 , which was constructed by the condensation reaction of the hydrophobic, H 2 S response and deep red-emitting fluorophore with hydrophilic biopolymer glycol chitosan (GC). Without H 2 S, XNP1 showed very low background fluorescence, while a significant enhancement in the fluorescence intensity of XNP1 was observed in the presence of H 2 S, resulting in a high sensitivity toward H 2 S in aqueous solution with a practical detection limit as low as 32.3 nM, which could be meet the detection of H 2 S in vivo. XNP1 also has a good linear response concentration range (0–1 μM) toward H 2 S with high selectivity over other competing species. These characteristics facilitate direct H 2 S detection of the complex living inflammatory cells and drug-induced inflammatory mice, demonstrating its practical application in biosystems. [ABSTRACT FROM AUTHOR]

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

A naphthalimide functionalized fluoran sensor with AIE effect has been prepared for ratiometric sensing Hg2+ and application in living cell imaging. [Display omitted] • A novel naphthalimide functionalized fluoran sensor NAF has been synthesized with AIE effect. • NAF shows ratiometric fluorescence to Hg2+ with high selectivity and real-time. • The LOD to Hg2+ is low down to 5.5 nM. • NAF can be used for tracing intracellular Hg2+ by ratiometric fluorescence imaging. The pollution caused by mercury ions (Hg2+) poses a potential threat to public health. Therefore, monitoring Hg2+ concentration in the environment is necessary and significant. In this work, a naphthalimide functionalized fluoran dye NAF has been prepared, which shows a new red-shift in emission at 550 nm with the maximum intensity in a mixture of water-CH 3 CN (v/v = 7/3) due to aggregating induced emission (AIE) effect. Meanwhile, NAF can be employed as a Hg2+ ions sensor, which displays a selective and sensitive response to Hg2+ ions by the reduced fluorescence of naphthalimide fluorophore and increased fluorescence of fluoran group, respectively, showing ratiometric fluorescence signal changes with more than 65-fold emission intensity ratio increase and naked eyes visible color change. In addition, the response time is fast (within 1 min) and the sensing can be conducted in a wide pH range (4.0–9.0). Moreover, the detection limit has been evaluated to be 5.5 nM. The sensing mechanism may be attributed to the formation of a π-extended conjugated system due to the Hg2+ ions-induced conversion of spironolactone to the ring-opened form, partially accompanied by the fluorescence resonance energy transfer (FRET) process. Significantly, NAF exhibits suitable cytotoxicity to living HeLa cells, which allows it to be utilized for ratiometric imaging of Hg2+ ions assisted by confocal fluorescence imaging. [ABSTRACT FROM AUTHOR]

In this study, we designed and synthesized a NIR probe, named W-1a derivatives for specific detection of ClO−. The probe exhibited dual fluorescence and colorimetric sensing with a response time of <1 min and a detection limit of 0.15 μM. Additionally, the probe was successfully applied for fluorescence imaging of ClO− at the cellular level and its endogenous/exogenous detection in zebrafish and dairy products. [Display omitted] • Development of a near-infrared fluorescent probe for hypochlorite detection. • Highly selective and sensitive responses with a low limit of detection. • The ClO− probe mediated for fluorescence imaging of HeLa cells and zebrafish and evaluating the toxicity of dairy products. Oxidative stress has been reported to be closely associated with many diseases, and an excessive overdose of hypochlorite (ClO−) can also induce stress-related diseases. In this study, we designed and synthesized a NIR probe, named W-1a based on computational analysis of DCM (4-(Dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran) derivatives for specific detection of ClO−. The probe exhibited dual fluorescence and colorimetric sensing with a response time of <1 min and a detection limit of 0.15 μM. Additionally, the probe was successfully applied for fluorescence imaging of ClO− at the cellular level and ebrafish endogenous/exogenous ClO− assay and dairy toxicity assessment. Thus, we present a potential method for developing an efficient and reliable detection of ClO− in early stage using near-infrared dyes. [ABSTRACT FROM AUTHOR]

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

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

[Display omitted] • A novel"turn-on" chemosensor MTRH was developed by a simple two-step reaction. • MTRH exhibited excellent sensitivity and selectivity for Hg2+ in pure aqueous media. • MTRH can realize naked-eye recognition of Hg2+. • MTRH demonstrated low cytotoxicity, good biocompatibility, and potency in the bioimaging of Hg2+. The deleterious toxicity of Hg2+ on ecological and biological system makes it crucial for the precise monitoring of Hg2+. Herein, we prepared a novel "turn-on" chemosensor N'-(4-(methylthio)butan-2-ylidene) rhodamine B hydrazide (denoted as MTRH) by a simple two-step reaction. MTRH exhibited an ultra-low detection limit (LOD) in fluorescence measurement of Hg2+ in pure aqueous media, which was estimated to be 1.3 × 10-9 mol·L-1. Moreover, the proposed chemosensor holds the ability of visualizing Hg2+ by the distinct color change of the solution. The corresponding recognition mechanism was investigated by Job's plots, mass spectrometry and DFT calculation analysis. Importantly, the characteristics such as high sensitivity, low cytotoxicity and good biocompatibility of MTRH exhibited in the application of detecting Hg2+ in real water sample and bioimaging of intracellular Hg2+ prove that MTRH is a promising tool to evaluate the levels of Hg2+ in complex biological systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nitrogen and bromine co-doped red fluorescence carbon dots (N,Br-CDs) with high QY were synthesized. • The multifunctional fluorescent sensors for off–on detection of Ag+ and glutathione were constructed based on N,Br-CDs. • The fluorescence sensor has been applied to the determination of Ag+ in environmental water samples. • Cellular imaging of Ag+ and glutathione was performed in HeLa cells by the N,Br-CDs. Carbon dots (CDs) with red fluorescence emission have excellent advantages in cell imaging. Herein, novel nitrogen and bromine doped CDs (N,Br-CDs) were prepared with 4-bromo-1,2-phenylenediamine as precursor. The N, Br-CDs present the optimal emission wavelength at 582 nm (λ ex = 510 nm) at pH 7.0 and 648 nm (λ ex = 580 nm) at pH 3.0 ∼ 5.0, respectively. The fluorescence intensity of N,Br-CDs at 648 nm versus Ag+ concentration shows a good relationship from 0 to 60 μM with the limit of detection (LOD) of 0.14 μM. Furthermore, the fluorescence of N,Br-CDs/Ag+ is efficiently restored via the combination of glutathione (GSH) and Ag+ and linearly changes with GSH concentration from 0 ∼ 6.0 μM with LOD of 49 nM. This method has been successfully employed to monitor intracellular Ag+ and GSH with fluorescence imaging. The results suggest that the N,Br-CDs has application potential in the sensing of Ag+ and visual monitoring of GSH in cells. [ABSTRACT FROM AUTHOR]

Hydrogen sulfide (H 2 S) is a kind of gaseous signal molecule in many physiological processes. In order to detect H 2 S, a novel "turn on" fluorescent probe 6,12-dihydroxyperylene-1,7-dione (DPD) was designed and synthesized. The probe DPD is fluorescence silence, while the addition of H 2 S induces an obvious green fluorescence with an obvious color change from dark blue to yellow-green. The probe shows excellent selectivity, fast response (2.5 min) and linear curve (0–90 μM) in wide effective pH range (4–10). Competition experiments are also revealed in corresponding studies and the detection limit is 3.6 μM. The response mechanism is proved to be the reduction of the probe by H 2 S, which is confirmed by 1H NMR. Furthermore, through the fluorescence turn-on signal toward H 2 S in Hela cells, probe DPD was successfully applied to monitor H 2 S in living Hela cells. Unlabelled Image • A "turn-on" probe DPD for hydrogen sulfide was developed. • DPD shows highly selective and sensitive response to hydrogen sulfide. • DPD shows rapid response and high sensitivity toward hydrogen sulfide. • The response mechanism of the probe DPD with H 2 S was confirmed to be reduction of carbonyl groups to hydroxyl groups. • DPD can monitor the exogenous cysteine in solution and living cells. [ABSTRACT FROM AUTHOR]

A near-infrared turn-on two-photon fluorescent probe ST-BODIPY for glutathione-specific detection was designed and synthesized by attaching triphenylamine to BODIPY skeleton through the Knoevenagel condensation to prolong the maximum emission wavelength to the NIR region. And 2,4-dinitrobenzenesulfonyl group (DNBS), as the fluorescence quencher and thiol recognition moiety, was modified in 8 position of BODIPY. In the presence of GSH, the probe afforded an "off-on" signal response with a significant NIR fluorescence enhancement centered at 719 nm accompanying by quantum yield increased to 0.44, which was ascribed to the glutathione-induced S N Ar (aromatic substitution) reaction. Surprisingly, we found that the probe could discriminate GSH from other biothiols including Cys and Hcy upon the addition of intracellular concentrations of them. Time-dependence also demonstrated that the probe could distinguish GSH from Cys and Hcy under physiological environment. The limit of detection (LOD) for GSH was calculated as 25.46 nM from the titration experiments, which is lower than most previously reported GSH-selective probes. Under the Ti:sapphire pulsed laser's 800 nm irradiation, ST-BODIPY toward GSH generated an "off-on" signal response with a significant enhancement of fluorescence emission at 719 nm after treatment with GSH. Besides, the 2PA cross section value (σ 2) was calculated to be 410 GM, suggesting that it could not only function well as an excellent two-photon fluorescent probe for the detection of intracellular GSH, but also be applied for two-photon imaging with high sensitivity in living cells. Moreover, ST-BODIPY probe has been successfully employed for monitoring exogenous and endogenous GSH in MCF-7 cells with satisfying results, perhaps it was feasible for detecting abnormal contents of GSH in a biological system and accomplishing the goal of maintaining normal human activities. Unlabelled Image • ST-BODIPY was designed by attaching triphenylamine to BODIPY skeleton through Knoevenagel condensation to afford the NIR dye. • Emission wavelength of ST-BODIPY reached NIR region which was at 719 nm. • ST-BODIPY was served as two-photon fluorescent probe with large 2PA cross section value (σ 2) of 410 GM. • ST-BODIPY was applied for endogenous and exogenous cell imaging. [ABSTRACT FROM AUTHOR]

Abstract Considering the excellent photochemical properties of ruthenium(II) complexes, two new ruthenium(II) complexes, RuL 1 -DNBS and RuL 2 -DNBS , have been developed as phosphorescence probes for detection of biothiols in 100:1 (v/v) Hepes buffer (20 mM, pH = 7.2)/CH 3 CN solution. The response rate was highly improved of these two probes toward biothiols because the steric interactions between 1 H -imidazo [4, 5- f ] [ 1 , 10 ] phenanthroline group and ortho-2, 4-dinitrobenzensulfonate resulted in a relatively rapid thiol-induced S N Ar substitution reaction. RuL 1 -DNBS and RuL 2 -DNBS were weakly phosphorescent owing to the effectual photoinduced electron transfer from ruthenium(II) luminophore to the sensing group, 2,4-dinitrobenzenesulfonyl. After reacting with biothiols, the 2,4-dinitrobenzenesulfonyl group of RuL 1 -DNBS and RuL 2 -DNBS were cleavaged and the RuL 1 and RuL 2 were obtained. Meanwhile, the phosphorescence were "turn-on". Both of these two probes can detect biothiols sensitively and selectively under physiological conditions with submicromolar detection limits. Furthermore, application of RuL 2 -DNBS for detecting of intracellular biothiols has been successfully performed in living Glioma cells. Graphical abstract Two 2,4-dinitrobenzenesulfonyl appended ruthenium(II) complexes acts as efficient "turn on" phosphorescence sensors for biothiols in 99% aqueous solutions was successfully demonstrated. Both of them showed a fast response time, a large turn-on phosphorescence intensity enhancement, and an excellent limit of detection toward biothiols. Unlabelled Image Highlights • Two 2,4-dinitrobenzenesulfonyl appended ruthenium complexes (RuL 1- DNBS and RuL 2- DNBS) were synthesized and characterized. • Sensing ability of RuL 1- DNBS and RuL 2- DNBS for biothiols were successfully carried out in in nearly pure aqueous system. • RuL 1- DNBS and RuL 2- DNBS showed fast response time, large turn-on ratio, and low detection limits towards biothiols. • Probe RuL 2- DNBS is succesfully used for imaging intracellular biothiols in living cells. [ABSTRACT FROM AUTHOR]