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[Display omitted] • We have developed a novel quercetin (a SARS-CoV-2 inhibitor) coupled benzyl ethers (QBE) chemosensor for selective detection of Hg2+. • To date, there are very few reports where quercetin itself have been used in sensing field (table 1) but the use of quercetin derivative in sensing field is almost nil. • To the best of our knowledge our chemosensor QBE is the first chemosensor based on quercetin derivative for the selective detection of Hg2+. • The binding phenomenon of QBE with Hg2+ has been proved by UV–vis, fluorescence, DFT and cyclic voltammograms study. • Lower LOD (Limit of Detection) at 8.47 µM and high binding constant value as 2 × 104 M−1 showed the strong binding affinity of Hg2+ towards QBE. • The intracellular activity of QBE with Hg2+ binding has been examined by using living plant tissue by using green gram seeds. Quercetin is an important antioxidant with high bioactivity and it has been used as SARS-CoV-2 inhibitor significantly. Quercetin, one of the most abundant flavonoids in nature, has been in the spot of numerous experimental and theoretical studies in the past decade due to its great biological and medicinal importance. But there have been limited instances of employing quercetin and its derivatives as a fluorescent framework for specific detection of various cations and anions in the chemosensing field. Therefore, we have developed a novel chemosensor based on q uercetin coupled b enzyl e thers (QBE) for selective detection of Hg2+ with "naked-eye" colorimetric and "turn-on" fluorometric response. Initially QBE itself exhibited very weak fluorescence with low quantum yield (Φ = 0.009) due to operating photoinduced electron transfer (PET) and inhibition of excited state intramolecular proton transfer (ESIPT) as well as intramolecular charge transfer (ICT) within the molecule. But in presence of Hg2+, QBE showed a sharp increase in fluorescence intensity by 18-fold at wavelength 444 nm with high quantum yield (Φ = 0.159) for the chelation-enhanced fluorescence (CHEF) with coordination of Hg2+, which hampers PET within the molecule. The strong binding affinity of QBE towards Hg2+ has been proved by lower detection limit at 8.47 µM and high binding constant value as 2 × 104 M−1. The binding mechanism has been verified by DFT study, Cyclic voltammograms and Jobs plot analysis. For the practical application, the binding selectivity of QBE with Hg2+ has been capitalized in physiological medium to detect intracellular Hg2+ levels in living plant tissue by using green gram seeds. Thus, employing QBE as a fluorescent chemosensor for the specific identification of Hg2+ will pave the way for a novel approach to simplifying the creation of various chemosensors based on quercetin backbone for the precise detection of various biologically significant analytes. [ABSTRACT FROM AUTHOR]

[Display omitted] • A dual-locked fluorescence probe (TPA-DNP) for LDs and HClO was designed. • TPA-DNP could detect LDs and HClO simultaneously by "turn-on" fluorescence singal. • TPA-DNP had successfully been applied in imaging HClO within LDs accumulation environments. • The real-time dynamic imaging of LDs and HClO by TPA-DNP under the LPS-induced inflammatory system. Inflammation is a key factor leading to the occurrence and development of many diseases, both lipid droplets (LDs) and hypochlorous acid (HClO/ClO-) are regarded as the important biomarkers of inflammation. Therefore, it is of great significance to develop an efficient single chemical sensor that can simultaneously detect these two biomarkers. To achieve the goal, we developed a dual-locked fluorescence probe (TPA-DNP) by fusing two targets activated reporting system, its implementation was achieved by turning-on the fluorescence of TPA-DNP through LDs and HClO/ClO- simultaneously. In simulated LDs environment, TPA-DNP displayed excellent selectivity to HClO/ClO-, high sensitivity (LOD = 0.527 μM) and strong anti-interference ability. In addition, cell and zebrafish imaging experiments showed that TPA-DNP could be utilized to visualize exogenous/endogenous HClO/ClO- in LDs environment, and could also be used to observe the impact of LDs changes on the HClO/ClO- detection. On the basis, TPA-DNP served as a favorable tool to achieve visualization of inflammatory dynamic changes. [ABSTRACT FROM AUTHOR]

[Display omitted] • A convenient approach to construct excimer emissive luminogens was established. • A double-bond linker between π-moiety and side-moiety is essential for AIE. • The structure-luminescence relationship was elucidated. • The high-resolution image of living Hela cells was observed. The excimer emission based on discrete π-stacked dimers of polycyclic π-systems has generated significant interest in the structure-luminescence relationship of excimers owing to their ultra-large Stokes shift. Herein, a series of excimer emissive luminogens were obtained by conjugating different polycyclic aromatic aldehydes (anthraldehyde, pyrenealdehyde and perylenealdehyde) with triphenylmethylamine. In crystalline states, all the molecules were arranged in the form of π-stacked arene dimers which were spatially isolated from each other by the bulky triphenylmethyl groups, and thus emitted bright excimer emission. The anthracene and pyrene derivatives showed fluorescence enhancement responses to grinding and the enhanced fluorescence could recover to the original state upon heating. The aggregation-induced emission (AIE) properties of them were dependent on the shapes and sizes of the polycyclic aromatic groups. The pyrene derivative showed the most excellent excimer-based AIE behavior among them. All of them were more apt to exhibit the excimer emission when formed nanoparticles with pluronic F-127 than that without pluronic F-127. Furthermore, PETP was utilized for bioimaging of living Hela cells and the high-resolution image was observed. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel rhodamine-based chemosensor RB-Gly-4-NAP (RGN) was prepared for multi-ion detection. • The sensor enables highly selective detection of Hg2+ and trivalent cations (Fe3+, Al3+, Cr3+) across different channels. • Theoretical calculations confirmed the efficacy of the sensor in coordinating with Fe3+, Al3+, Cr3+, and Hg2+. • The sensor shows excellent sensitivity to Fe3+, Al3+, Cr3+, and Hg2+, with LODs of 10.20, 14.66, 58.78, and 73.33 nM. • The sensor has been successfully applied to actual water samples and bioimaging (cell imaging and zebrafish imaging). A novel rhodamine-based multi-ion fluorescent sensor, RGN, was designed and synthesized for the highly selective detection of mercury ions (Hg2+) in ethanol and water systems, as well as trivalent cations (Fe3+, Al3+, and Cr3+) in acetonitrile and water systems using a two-step Schiff base reaction method. Nuclear magnetic titration experiments and theoretical calculations demonstrated that the sensor achieved the detection of the aforementioned metal ions through the fluorescence turn-on phenomenon induced by lactam ring-opening. Density functional theory (DFT) calculation results showed decreased HOMO-LUMO energy gaps and increased dipole moments, indicating the effective coordination of the sensor with the corresponding metal ions to form more stable complexes, thereby achieving detection objectives. Furthermore, the fluorescence turn-on sensor RGN exhibited relatively low detection limits, with limits of detection (LOD) for Fe3+, Al3+, Cr3+, and Hg2+ being 10.20 nM, 14.66 nM, 58.78 nM, and 73.33 nM, respectively. Finally, practical applications of sensor RGN in environmental water samples, L929 cells, and zebrafish were demonstrated, indicating its potential for detecting and tracking Fe3+, Al3+, Cr3+, and Hg2+ in environmental samples and biological systems, with prospects for biomedical applications in the diagnosis and treatment of heavy metal ion-induced diseases. [ABSTRACT FROM AUTHOR]

[Display omitted] • Three novel fluorescence chemosensors were developed for Hg2+ determination based on dethioacetalization reaction. • Sensors displayed highly sensitive and selective to Hg2+ in aqueous system with low detection limit. • Sensor was successfully applied to detect Hg2+ in real water samples and herb extract samples. • Sensor is capable of monitoring Hg2+ in living cell. Mercury ion is one of the most harmful metal ions with significant hazards to the environment and human health. Thus, the development of innovative, sensitive, and selective sensors to help address the detrimental impacts of heavy metal contamination is necessary. In this work, we present three new chemosensors based on the deprotection reaction of the thioacetal group for distinguishing Hg2+ in environmental samples. These chemosensors show good photophysical properties with high quantum yield in aqueous medium. These prepared chemosensors were employed as fluorometric sensors for the determination of Hg2+ through the quenching of fluorescence emission due to the Hg2+-induced hydrolysis of the thioacetal to the aldehyde group. In the presence of Hg2+, chemosensors showed an emissive color transformation from blue fluorescence to non-fluorescence under UV light, which was readily seen by the visual eye. These chemosensors also exhibited highly distinctive selectivity toward Hg2+ over other interfering metal ions, with detection limits of 1.1 ppb, 13.4 ppb, and 12.7 ppb. Moreover, the practical applicability of chemosensor was successfully demonstrated in real water samples and herb extract samples. [ABSTRACT FROM AUTHOR]

[Display omitted] • We present a simplified fluorescent microscopy-surface plasmon resonance (FM-SPR) system. • Real-time simultaneous observation and acquisition of fluorescent carbon dots labeled silk fibroin kinetic processes using FM-SPR system. • The fluorescence image changes fitted well with the SPR signal changes. • The linear detection range was 2.5 μg/mL–100 μg/mL, and the real lowest detection limit reached 0.5 μg/mL. • The association rate and dissociation rate of N-CDs to SF which were 2.65 × 10−5/s and 1.52 × 10 −5/s, respectively. The use of fluorescent carbon dots (CDs) as highly precise biolabeling probes has been widespread in the fields of live cell imaging and protein labeling due to their small size and excellent photoluminescence ability to accurately target specific molecules with surface chemical properties. However, there was a lack of research on the interaction between CDs and labeled molecules. In this work, we presented a novel investigation strategy, the fluorescence microscopy-surface plasmon resonance (FM-SPR) system, which combined the use of fluorescence microscopy and wavelength modulation surface plasmon resonance to study the interaction between CDs and labeled molecules in real-time. Using this system, simultaneously recorded the SPR signals and the fluorescence images on the surface of the FM-SPR sensor chip. We observed the dynamic curve and fluorescence images of the interaction between green emissive nitrogen-doped carbon dots (N-CDs) and silk fibroin (SF) in real-time. The kinetic parameters, the quantitative analysis, and the investigation of the binding could be achieved. The results showed a strong linear relationship between the change in SPR signals and the concentration of N-CDs, with a linear coefficient of 0.99913. The linear detection range was 2.5 μg/mL–100 μg/mL, and the real lowest detection limit reached 0.5 μg/mL. Additionally, the green fluorescence points in the imaging region on the FM-SPR sensor chip increased with the concentration of N-CDs, which was consistent with the change in SPR signals. Using this system we also acquired the association rate and dissociation rate of N-CDs to SF which were 2.65 × 10−5/s and 1.52 × 10−5/s, respectively. This demonstrated the effectiveness of our method in quantitatively analyzing SF labeled with N-CDs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two spirobifluene-based turn-on fluorescent probes for Cysteine were synthesized. • The probes shows highly selectivity for Cysteine. • The probes had been applied to imaging Cysteine under two-photon excitation. • One probe displayed excellent detection limit for Cysteine. Two spirobifluene-based fluorescent probes SPF1 and SPF2 , were designed and synthesized. The probes displayed "turn-on" fluorescence response for Cysteine. One of the challenges in developing a Cysteine probe is to secure high selectivity. SPF1/SPF2 can discriminate Cysteine from GSH as well as Hcy, and showed high substrate selectivity. The detection limit of SPF1 is 36 nM, which is excellent comparing with other optical sensors for Cysteine. The sensing mechanism of SPF1/SPF2 was verified by experimental data and theoretical calculations. There was a good linear relationship between the fluorescence intensity of SPF1/SPF2 and the concentration of Cysteine. The MTT tests indicated that SPF1/SPF2 had low cytotoxicity and good biocompatibility. Theoretical calculations demonstrated that SPF1 , SPF2 , and their related reaction products with Cysteine exhibited good two-photon absorption properties. Finally, SPF1/SPF2 had been successfully applied to the imaging of Cysteine in living cells under two-photon excitation. [ABSTRACT FROM AUTHOR]

Under physiological conditions, K(TPE)EFYp is converted to K(TPE)EFY containing hydroxyl by dephosphorylation of ALP and fluorescence is turned on. [Display omitted] • An enzyme-responsive biosensor with AIE properties. • A peptide-based Fluorescent supramolecular hydrogel (FSH) material. • Sol-gel phases transformation to determine alkaline phosphatase (ALP) activity. • "Turn-on" strategy due to the AIE effect has a higher sensitivity and a lower LOD. Alkaline phosphatase is an important biomarker for medical diagnosis. An enzymatic fluorescence supramolecular hydrogel with AIE properties was developed and used for sensing alkaline phosphatase in vitro and in living cells. In the presence of ALP, K(TPE)EFYp was partially converted to the hydrogelator K(TPE)EFY and self-assembled into nanofibers to form Hydrogel. With the sol–gel transition and the AIE effect, the fluorescence emission was turned on. The linear concentration range of ALP activity in vitro quantified by this method was determined as 0–3 U/L with a LOD at 0.02 U/L. In addition, cell imaging and serum experiment showed that K(TPE)EFYp could also be used to detect ALP activity in living cells and biological samples. [ABSTRACT FROM AUTHOR]

[Display omitted] • The first coumarin-based HNO donor (CD1) was developed. • HNO-releasing has a t 1/2 ∼90 min under physiological conditions. • The fluorescence intensity increased by about 4.9-fold. • HNO release can be visualized by cellar images. Nitroxyl (HNO), the single-electron reduction product of nitric oxide (NO), has attracted great interest in the treatment of congestive heart failure in clinical trials. In this paper, we describe the first coumarin-based compound N -hydroxy-2-oxo-2H-chromene-6-sulfonamide (CD1) as a dualfunctional HNO donor, which can release both an HNO signaling molecule and a fluorescent reporter. Under physiological conditions (pH 7.4 and 37 °C), the CD1 HNO donor can readily decompose with a half-life of ∼90 min. The corresponding stoichiometry HNO from the CD1 donor was confirmed using both Vitamin B 12 and phosphine compound traps. In addition to HNO releasing, specifically, the degradation product 2-oxo-2H-chromene-6-sulfinate (CS1) was generated as a fluorescent marker during the decomposition. Therefore, the HNO amount released in situ can be accurately monitored through fluorescence generation. As compared to the CD1 donor, the fluorescence intensity increased by about 4.9-fold. The concentration limit of detection of HNO releasing was determined to be ∼0.13 μM according to the fluorescence generation of CS1 at physiological conditions. Moreover, the bioimaging of the CD1 donor was demonstrated in the cell culture of HeLa cells, where the intracellular fluorescence signals were observed, inferring the site of HNO release. Finally, we anticipate that this novel coumarin-based CD1 donor opens a new platform for exploring the biology of HNO. [ABSTRACT FROM AUTHOR]

[Display omitted] • A simple single step multicomponent ugi type reaction was carried out to yield N-(tert-butyl)-2-(furan-2-yl)imidazo[1,2- a ]pyridine-3-amine (TBFIPA). • The synthesized TBFIPA was characterized using 1H NMR, 13C NMR and HRMS spectroscopic methods. • The selective & sensitive detection was identified using hypsochromic shift (lab : 335nm → 285nm) & fluorescence quenching. • The proposed mechanism is evident from Job plot, 1H NMR titration, ESI-MS data and theoretical DFT calculation. • The Cr3+ ion-selective TBFIPA was successfully applied in the design of a user-friendly silica-based portable test kits. • Also, the fluorescence quenching ability of TBFIPA in presence of Cr3+ ions are validated by imaging onion epidermal cells. • Real samples contaminated with Cr3+ ions were identified using TBFIPA with an appropriated relative error percentage. A simple single step one pot multicomponent reaction was performed to synthesize N-(tert -butyl)-2-(furan-2-yl)imidazo[1,2- a ]pyridine-3-amine (TBFIPA). The synthesized TBFIPA was subjected to library of cations to study its ability for selective and sensitive detection of specific metal ions. Selective detection of chromium ions by TBFIPA were found from the significant hypsochromic shift (335 nm → 285 nm) in the UV–Visible spectra. The fluorescent TBFIPA displays complete quenching of fluorescence under UV lamp (365 nm) only in the presence of chromium without the interference of common metal ions. Binding constant (k a) obtained from Benesi-Hildebrand plot is 0.21 × 105 M−1, limit of detection (LOD) and limit of quantification (LOQ) of TBFIPA toward Cr3+ ions are 4.70 × 10−7 M and 1.56 × 10−7 M, respectively. The mechanism proposed during complex formation were supported by stoichiometric Job continuous variation plot, 1H NMR titration and ESI-MS spectroscopic data. All the experimental confirmation for complex formation were corroborated with theoretical DFT studies optimized using RB3LYP/6-31G(d) basis set. The selectivity and sensitivity of TBFIPA toward Cr3+ ions are found suitable to design a user-friendly silica based portable test kit. Alongside, TBFIPA was successfully utilized for imaging onion epidermal cells. Furthermore, the results obtained for biological, environmental, and industrial samples provided solid evidence to estimate chromium ions using TBFIPA in these real samples. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel Al3+ Schiff base probe JHK was designed and synthesized. • JHK has high selectivity, high fluorescence quantum yield and low detection limit for Al3+. • JHK was successfully applied to living cells and zebrafish. A novel fluorescent probe N'-(2-hydroxybenzylidene)-indole-3-formylhydrazine (JHK) was designed and synthesized based on the condensation reaction of indole-3-formylhydrazine and salicylaldehyde. The probe JHK solution could highly selectively recognize Al3+ by the obvious fluorescence enhancement (288-fold) after adding Al3+. And the probe solution with Al3+ had a very high fluorescence quantum yield (89.29 %). The detection limit was calculated to be 1.135 nM, which was significantly lower than many reported detection limits, indicating that the probe JHK had pretty good sensitivity. The ratio of JHK to Al3+ (1:1) and the sensing mechanism were determined by Job's plot, 1H NMR spectra, FTIR spectra, ESI-MS and Gaussian calculation. The probe solution and medium-speed filter paper were successfully used to make test papers for more convenient detection of Al3+. Furthermore, the probe JHK had been successfully applied to the detection of Al3+ in real water, zebrafish and living cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • The probe EDPH specializes in the detection of H 2 S with high selectivity, high sensitivity and good detection limits. • The probe EDPH has been shown to have applications in intracellular fluorescence imaging. • Purine-based fluorescent probes for the detection of H 2 S are a new direction. Hydrogen sulfide (H 2 S) is a gas with a toxic odor that plays an irreplaceable role in physiological activities within the mammalian body. Therefore, it is important to do the distribution and quantitative detection of H 2 S in mammalian cells. In this paper, a fluorescence probe (EDPH) based on purine scaffold was designed and synthesized with high sensitivity and good selectivity. H 2 S induced ether bond breakage in EDPH , resulting in a significant redshift of the absorption band (from 370 nm to 500 nm) with a Stokes shift of 130 nm. After the addition of H 2 S, the fluorescence intensity of EDPH showed a good linear correlation with the concentration of H 2 S, which enabled the quantitative detection of H 2 S with a low limit of detection (41 nM). Finally, the EDPH was applied to the cellular Hele, and the probe has good cellularity imaging capability for the detection of H 2 S in living systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • A mitochondria-targeting fluorescence probe NIR1 for H 2 S visualization. • NIR1 has excellent detection limits as low as 30.2 nM. • NIR1 was successfully applied for H 2 S imaging analysis in living inflammatory mice. The mechanism of the interaction between the signaling molecule hydrogen sulfide (H 2 S) and mitochondria and its related diseases is difficult to elusive. Thus it is urgent to develop effective methods and tools to visualize H 2 S in mitochondria and in vivo. In this work, a robust mitochondrial-targeting NIR fluorescence "turn-on" fluorescent probe, NIR1, was reported, by adopting a Changsha-OH near-infrared (NIR) dye as the NIR fluorophore, a 2,4-dinitrophenyl (DNB) moiety as both the responsive site of the H 2 S and the fluorescence quenching group of the NIR fluorophore, and an oxygen onium ion site as the mitochondria-targeting group, for the detection and analysis of H 2 S in living Raw 264.7 cells and drug-induced inflammatory mice models. NIR1 exhibited a much smaller background fluorescence signal in lack of H 2 S, whereas strong enhanced NIR fluorescence "turn-on" was detected in the presence of H 2 S, these results showed a low detection limit (30.2 nM) for quantitative detection of H 2 S in aqueous solutions with concentrations ranging from 0 to 1 μM H 2 S. These characteristics were beneficial to direct detection and imaging analysis of H 2 S in complicated biosystems. Therefore, first, NIR1 was applied for the NIR detection of mitochondrial H 2 S in living inflammatory cells with satisfactory results. Finally, NIR1 was applied to detect H 2 S in drug-induced inflammatory mice models with agreeable results, demonstrating that NIR1 as a molecular tool has an excellent practical application in the study of the interaction between inflammatory and H 2 S. [ABSTRACT FROM AUTHOR]

[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] • 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] • 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 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 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] • 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] • 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]

Abstract In this work, we have designed and synthesized a dinitrobenzene-sulfonate tetrahydro[5]helicene (H-DNP) as an effective fluorescent probe for detection of hydrogen sulfide (H 2 S). Upon the addition of H 2 S, a significant fluorescence enhancement (75-fold) at 495 nm can be observed with a distinct color change from colorless to yellow. Additionally, H-DNP shows low background spectroscopic signal, large Stokes Shift up to ~140 nm, good sensitivity, rapid response time less than 2 min, low detection limit (48 nM) and high selectivity toward common bio-thiols (Cysteine, Homocysteine and Glutathione). Compared with the previous dinitrophenoxy tetrahydro[5]helicene, this probe has shorter response time and lower detection limit. Most importantly, this probe H-DNP has low toxicity to cells and excellent cell permeability, which can be applied to visualize H 2 S in living cells. Graphical abstract Unlabelled Image Highlights • A tetrahydro[5]helicene based fluorescence probe displayed a rapid, sensitive and selective in response to H 2 S. • The probe has very low detection limit and fast response time. • The response mechanism is confirmed to be thiolysis reaction induced by H 2 S. • The detection of intracellular H 2 S was successfully demonstrated in living cells. [ABSTRACT FROM AUTHOR]

Abstract Developing near-infrared (NIR) fluorescence probes for detection of intracellular viscosity is still sufficiently challenging. In this work, three kinds of D-A-D type naphthyl and 2,1,3‑benzoxadiazol hybrid NIR dyes functionalized with amino (NY1), N ‑methylamino (NY2) and N , N ‑dimethylamino (NY3) groups for intracellular micro-viscosity detection were designed and synthesized. All the probes exhibited very weak NIR emission in low viscosity environment and obvious fluorescence enhancement with the increased viscosity. Different substituent groups had a high impact on the photophysical properties and response sensitive of the probes to viscosity. The structure-property relationships were systematic investigated. The results showed that stronger electron-donating ability and larger steric effect of N , N ‑dimethylamino led to a narrower energy gap and more sensitive to viscosity environment. Therefore, NY3 exhibited higher signal noise ratio for viscosity detection and was successfully applied for imaging the changes of intracellular micro-viscosity. This work provides an efficient way to design powerful NIR fluorescence probes for viscosity detection. Graphical abstract A series of D-A-D type naphthyl and 2,1,3‑benzoxadiazol hybrid NIR dyes functionalized with amino (NY1), N -methylamino (NY2) and N , N ‑dimethylamino (NY3) groups for intracellular micro-viscosity detection have been designed and synthesized. Unlabelled Image Highlights • A series of NIR probes with large Stokes shift were designed and synthesized. • The dyes were sensitive and selective to the change of viscosity. • Structure-property relationships are systematic investigated in detail. • The probe was successfully applied for imaging the changes in intracellular micro-viscosity. [ABSTRACT FROM AUTHOR]

Abstract Carbon dots (CDs) synthesized from natural products have drawn numerous attentions due to some unique properties. Here, Prunus cerasifera fruits were used as carbon source to synthesize high luminescent CDs by hydrothermal method. The obtained CDs were characterized by TEM, FTIR and XPS methods, founding the CDs were near-spherical and contained abundant nitrogen element. The CDs aqueous solution exhibited bright blue fluorescence under ultraviolet illumination, with the maximum emission at 450 nm. They could be potentially used as invisible fluorescent ink by written on the paper and irradiated by UV light, due to their fluorescent properties. Moreover, the CDs were found being selectively quenched by Fe3+ ion. The quench of CDs was linearly related to the concentration of Fe3+ ion in the range of 0–0.5 mM, meaning they could be developed as fluorescent probe of Fe3+ ion. At last, the CDs were used for cell imaging, founding they were low toxicity to HepG2 cells and exhibited blue and green fluorescence under a fluorescence microscope. In summary, the CDs prepared from Prunus cerasifera fruits exhibited excellent fluorescence properties, and could be potentially applied in the field of fluorescent ink, Fe3+ ion detection and cell imaging. Graphical Abstract Unlabelled Image Highlights • Carbon dots were synthesized using Prunus cerasifera fruits as carbon source. • They exhibited bright blue fluorescence and can be used as invisible fluorescent ink. • They were selectively quenched by Fe3+ ion and can be used as the fluorescent probe. • They were low toxicity to HepG2 cells and can be used to label cells for imaging. [ABSTRACT FROM AUTHOR]

Abstract A selective diaminomaleonitrile-based fluorescent probe for Al3+(L) has been synthesized and characterized. The sensing behavior of L towards different metal ions was investigated by fluorescent spectra and competition experiment. The results showed that L exhibited a dual channel emission (λ em 522 & 558 nm) with yellow fluorescence in the presence of Al3+ over other metal ions in EtOH solution. The probe L was bound to Al3+ in a 1:2 stoichiometric manner as supported by Job's plot analysis. The binding constant was 9.55 × 108 M−2 with the detection limit of 10.3 nM. The turn-on response was attributed to the inhibition of PET and C N isomerization after binding with Al3+ while the dual emissions were due to ESIPT and ICT processes. In addition, the application of L for imaging Al3+ in living Hela cells was achieved. Graphical Abstract A selective diaminomaleonitrile-based dual channel emissive probe for Al3+(L) has been fabricated. L exhibited a dual channel emission, good selectivity and low LOD value towards Al3+. Importantly, it is suitable for fluorescence imaging in living Hela cells. Unlabelled Image Highlights • A new diaminomaleonitrile-based fluorescent probe for Al3+(L) has been synthesized and characterized. • L has a dual channel emission with yellow fluorescence in the presence of Al3+ in EtOH solution. • The limit of detection of L for Al3+ was estimated to be as low as 10.3 nM. • L was applied in Hela cells to detect intracellular Al3+ successfully. [ABSTRACT FROM AUTHOR]

Abstract A simple asymmetric hydrazone 1 based on salicylaldehyde was designed and prepared, and exhibited an evident aggregation-induced emission (AIE) at a long wavelength of 570 nm in aqueous medium. Probe 1 can selectively sense Al3+ in CH 3 OH solution through the chelation-enhanced fluorescence mechanism and also recognize Cu2+ via fluorescence quenching in H 2 O solution through the Cu2+-induced assembly of aggregates. In addition, the probe can be applied for detecting Cu2+ in biological samples. Graphical Abstract Unlabelled Image Highlights • A simple Schiff base-based fluorescent sensor for Cu2+ in aggregation states has been developed. • The sensor could also detect Al3+ in CH 3 OH solution with fluorescence enhancement. • The sensor is an aggregation induced emission active compound with emission at a long wavelength of 570 nm. • The sensor has been used for imaging of Cu2+ in living cells. [ABSTRACT FROM AUTHOR]

Abstract A rhodamine hydrazone 1 bearing coumarin moiety was designed and prepared. Compound 1 exhibited high selectivity toward Co2+ and trivalent metal ions with fluorescence enhancement in CH 3 OH solution. However, 1 selectively responded to Al3+ in nearly pure H 2 O media and was further applied to monitor Al3+ in live cells. Moreover, 1 could also act as a colorimetric probe toward Cu2+ in either CH 3 OH or H 2 O solution. In addition, sensor 1 displayed aggregation-induced ratiometric emission (AIRE) activities in mixed H 2 O/CH 3 OH solution. Graphical Abstract Unlabelled Image Highlights • A rhodamine hydrazone sensor bearing coumarin moiety with aggregation induced ratiometric emission has been developed. • The sensor could detect Al3+ in H 2 O solution with fluorescence enhancement. • The sensor has been used for imaging of Al3+ in living cells. • The sensor could recognize Co2+ and trivalent metal ions based on different 'turn-on' emission. • The sensor is a colorimetric probe toward Cu2+ in either CH 3 OH or aqueous solution. [ABSTRACT FROM AUTHOR]

Abstract As an efficient turn-on fluorescent chemosensor for Al3+, a new coumarin derivative (CND) has been designed and synthesized by the condensation of 8-formyl-7-hydroxycoumarin with niacin hydrazide. The spectroscopic studies revealed that the sensor CND exhibited a remarkable fluorescence enhancement towards Al3+ with high selectivity and sensitivity in EtOH-HEPES (95:5, v/v, pH = 7.40), which was attributed to the photoinduced electron transfer (PET) and C N isomerization mechanism. Fluorescence titration calculations data showed that the detection limit and the association constants of CND for Al3+ were found to be 2.51 × 10−7 M and 9.64 × 104 M−1, respectively. The results of experiments, including Job's plot, 1H NMR titration and ESI-MS, revealed that the stoichiometric binding between CND and Al3+ was 1:1. The investigations of the pH dependency of CND for Al3+ detection, and the cell imaging suggested the sensor CND could be promisingly applied for the recognition of Al3+ in biological cells. Graphical Abstract Unlabelled Image Highlights • A novel coumarin-based fluorescence sensor for Al3+ was designed and synthesized. • This sensor has good selectivity and sensitivity for Al3+. • This sensor can be applied in live cells. [ABSTRACT FROM AUTHOR]

Abstract Single crystal X-ray structurally characterized benzimidazole-naphthalene hybrid (NABI) functions as a unique dual analyte sensor that can detect Zn2+ cation and N 3 − anion independently. The NABI forms chelate with Zn2+ to inhibit internal charge transfer (ICT) and CH N isomerisation resulting chelation enhanced fluorescence (CHEF). On the other hand, the sensing of N 3 − is based on formation of supramolecular H-bonded rigid assembly. The association constant of NABI for Zn2+ and N 3 − ions are 19 × 104 M−1 and 11 × 102 M−1, respectively. Corresponding limit of detections (LOD) are 6.85 × 10−8 and 1.82 × 10−7 M, respectively. NABI efficiently detects intracellular Zn2+ and N 3 − ions with no cytotoxicity on J774A.1cells under fluorescence microscope. DFT studies unlock underlying spectroscopic properties of free NABI and Zn2+/N 3 − bound forms. Graphical Abstract A benzimidazole-naphthalene hybrid (NABI) acts as a dual analyte sensor and detects Zn2+ and N 3 − independently. The sensing of Zn2+ occurs through inhibition of internal charge transfer (ICT) and CH N isomerisation along with chelation enhanced fluorescence (CHEF) whereas N 3 − sensing proceeds through formation of supramolecular H-bonded rigid assembly. Single crystal X-ray structurally characterized NABI has association constant for Zn2+ and N 3 − ions, 19 × 104 M−1 and 11 × 102 M−1 respectively. Corresponding limit of detections (LOD) are 6.85 × 10−8 and 1.82 × 10−7 M. NABI efficiently detects intracellular Zn2+ and N 3 − ions with no cytotoxicity on J774A.1cells under fluorescence microscope. DFT studies unlock underlying spectroscopic properties of free NABI and its Zn2+/N 3 − bound forms. Unlabelled Image Highlights • A benzimidazole–naphthalene (NABI) fluorescence probe selectively and independently detects Zn2+ and N 3 − ions. • The CHEF assisted Zn2+ sensing involves inhibition of ICT and CH N isomerization while N 3 − sensing proceeds through supramolecular H-bond assisted rigid structure formation. • The association constants of NABI for Zn2+ and N 3 − ions are 19 × 104 M−1 and 11 × 102 M−1 while corresponding LODs are 6.85 × 10−8 and 1.82 × 10−7 M. • X-ray structurally characterized, non- cytotoxic NABI efficiently detects Zn2+ and N 3 − ions within J774A.1cells. • DFT studies unfold underlying spectroscopic properties of free NABI and its Zn2+ and N 3 − adducts. [ABSTRACT FROM AUTHOR]

Abstract A highly sensitive fluorescent probe, 2‑butyl‑6‑(2‑ethylidenehydrazinyl)‑1H‑benzo[ de ]isoquinoline‑1,3(2H)‑dione (P) has been designed and synthesized to detect Cu2+ in CH 3 CN-HEPES (4:1, v/v, pH = 7.4) solution. This probe functions via a distinctive hydrolysis mechanism through Cu2+-promoted accompany by extinction of the fluorescent and other competing metal ions did not showed any interference. The limit of detection toward Cu2+ was calculated of 320 nM. Probe P was not only successfully used for the determination of trace level Cu2+ in the CH 3 CN-HEPES (4:1, v/v, pH = 7.4) solution, but also valid for fluorescence imaging of Cu2+ in lysosomes of 293T cells and it was applied in real water samples. This work indicated that P would be of great application prospect in environmental monitoring and medical diagnosis. Graphical Abstract Unlabelled Image Highlights • High sensitivity and selectivity for Cu2+ detection in CH 3 CN/HEPES (4:1 v/v, pH = 7.4) solution • Feasible "naked-eye" sensor for Cu2+ detection • The probe was evaluated by the determination of spiked Cu2+ in real water samples. • The probe could be used to monitor copper ion in living cells by fluorescence imaging. [ABSTRACT FROM AUTHOR]

Abstract Hydrogen sulfide (H 2 S) can undergo dual nucleophilic reaction, which is a wise and effective way to distinguish biothiols and H 2 S. A novel H 2 S fluorescence probe, 4-{2-[4-(2-disulfide pyridyl-benzoyloxy)-phenyl]-vinyl}-1-methyl-pyridinium[ e ]iodide (DSPBP), with two nucleophilic reaction sites has been developed. The spectra results showed that DSPBP could detect H 2 S in ratiometric and colorimetric signals and has excellent selectivity and sensitivity. The fluorescence ratiometric signals (F 520 /F 450) displayed a prominent increase from 0.74 to 7.08, the fluorescence color turned to yellow form blue simultaneously. The linear range was 2–14 μM and its detection limit was 25.7 nM. Moreover, the biocompatibility of DSPBP was fine and its toxicity was very low. It has been successfully used for imaging H 2 S in cells. Graphical Abstract Unlabelled Image Highlights • A ratiometric fluorescence probe (DSPBP) for H 2 S with bis-nucleophilic center was developed. • DSPBP showed rapid response time, high selectivity and sensitivity for H 2 S over biothiol. • DSPBP would used to detect H 2 S in living cells. [ABSTRACT FROM AUTHOR]

Abstract We reported a novel and readily synthesized fluorescent "turn-on" probe L (Dansyl-Glu-Pro-Gly-Cys) based on dansyl group combine tetrapeptide. The probe L exhibited highly sensitive fluorescent recognition to Cd2+ ions in HEPES buffer solutions (10.0 mM, pH 7.4). The 2:1 binding stoichiometry of L with Cd2+ were determined based on fluorescence titration and the Job's plot investigation. The competitive experiments were found to be highly selective for the Cd2+ ions even in the existence of excess competing metal ions including Zn2+, Pb2+, Hg2+ and Cu2+ ions. The binding constant of the complex L -Cd was calculated to be 5.18 × 1010 M−2, and showed great affinity compared to other probes. In addition, the detection limit of the probe L for Cd2+ ions was calculated to be 45 nM, which presented a pronounced sensitivity toward Cd2+ ions. Most importantly, the probe L had wide range of pH and good biocompatibility, and were successfully applied to selectively detected Cd2+ ions within pH range of 7–12 and bioimaging studies in live cells. Graphical Abstract Unlabelled Image Highlights • A novel fluorescent peptide-based probe (L) was synthesized. • L exhibited exclusively selective fluorescent "turn-on" response toward Cd2+ ions. • L displayed high sensitivity for Cd(II) with a low detection limit of 45 nM. • L could serve as a potential probe to detect Cd2+ ions in living cells. [ABSTRACT FROM AUTHOR]

Abstract Hydrazino-carbothioamide, 1 , serves as a turn-on fluorescent chemosensor to Zn2+ and the mixture shows green emission (λ em 492) in presence of large number of ions with impressive limit of detection (LOD), 0.59 nM. Intense fluorescence of Zn-complex is selectively turn-off upon adding H 2 PO 4 − only to the limit of detection, 26 μM, while other anions remain silent. The sensing mechanism of 1 is established by suppressing the ESIPT of 1 and complexation with Zn2+ (CHEF) is supported by Job's plot, 1H NMR, and HR-MS data. Turn-on-off sequential detection of Zn2+ and H 2 PO 4 − also have successfully been employed for the engineering of INHIBIT molecular logic gate. The sensor is non-toxic and has been used in identifying Zn2+ in the intracellular region of African green monkey kidney cells (Vero cells). Graphical Abstract Very low detection limit (0.59 nM) is shown by green emission (492 nm) of hydrazino-carbothioamide probe on binding selectively with Zn2+ at pH, 7.2 which is specifically quenched by H 2 PO 4 − with LOD, 26 μM. This probe uses detection of Zn2+ in Vero cells and INHIBIT logic gate is constituted. Unlabelled Image Highlights • Hydrazino-carbothioamide sensor shows green emission with Zn2+. • Highly selective turn-on Zn2+ sensor shows LOD 0.59 nM. • Emission of the complex is quenched specifically upon addition of H 2 PO 4 − and LOD is 26 μM. • The sensor is non-toxic and identifies Zn2+ in the intracellular region of Vero cells. • Emission change at 492 nm with Zn2+ and H 2 PO 4 − can be described to INHIBIT logic gate. [ABSTRACT FROM AUTHOR]

Abstract A new naphthalene-quinoline based chemosensor L was prepared and structurally characterized. L exhibited excellent selectivity and sensitivity to Al3+ through distinct fluorescence enhancement (335-fold) and ratiometric detection in DMF/H 2 O (v/v, 1/9) based on the combined mechanisms of ESIPT and CHEF. The recognizing behavior of L toward Al3+ had been investigated in detail through Job's Plot, FT-IR, HNMR, and HRMS analysis. The limit of detection (LOD) for Al3+ was as low as and 3.67 × 10−8 M. L was successfully applied in real sample detection and construction of molecular logic gate. Moreover, L was verified to be of low cytotoxicity and good imaging characteristics for the detection of Al3+ in cells HSC. Graphical abstract Unlabelled Image Highlights • A naphthalene-quinoline based chemosensor L was prepared and structurally characterized. • L exhibited excellent selectivity and sensitivity to Al3+ through fluorescence enhancement (335-fold) and ratiometric detection. • The limit of detection (LOD) for Al3+ was determined as 3.67 × 10−8 M. • L was successfully applied in the detection of Al3+ in cells HSC. [ABSTRACT FROM AUTHOR]

The zinc ions (Zn 2+ ) play extremely irreplaceable role in the organism and the environment, the design and synthesis of a biomolecule-based fluorescence chemosensor for the detection of Zn 2+ with high sensitivity is very important. Herein, a novel tetrapeptide-based dansyl fluorescent “turn-on” response chemosensor ( L ) has been designed and synthesized by solid phase peptide synthesis (SPPS). As designed, L can detect Zn 2+ ions with specifically and sensitively based on photo-induced electron transfer (PET) mechanism in 100% aqueous solutions, and other metal ions do not interfere with Zn 2+ ions recognition. The stoichiometric ratio of L with Zn 2+ ions was 2:1, which matches with fluorescence titration and Job-plot assay. In addition, the reversibility and circularly process of the detection of L was confirmed by adding bonding agent Na 2 EDTA. Moreover, L exhibits excellent biocompatibility and low biotoxicity with the limit of detection (LOD) for Zn 2+ about 18 nM, and has been successfully utilized for fluorescence imaging of Zn 2+ ions in living HeLa cells under physiological conditions. [ABSTRACT FROM AUTHOR]

In this communication, we have developed an optical chemosensor 2-amino N-(6-bromo-1,3-dioxo-1H-benzo[ de ]isoquinolin-2(3H)-yl)benzamide ( NAPH ) for selective detection of Al 3+ by reacting 4-bromo-1,8-naphthalic anhydride with 2-aminobenzohydrazide. In (DMSO:H 2 O, 1:1, v/v) medium, the selective and specific nature of NAPH towards Al 3+ was observed by the quenching along with a blue-shift in the absorption of NAPH at 465 nm that resulted in the distinct colour change from light brown to colourless. The selective complexation that occurred between NAPH and Al 3+ was investigated by 1 H NMR and DFT methods. Under similar conditions, the weakly fluorescent receptor NAPH showed a distinct fluorescence enhancement at 555 nm in the presence of Al 3+ among the other tested metal ions and anions. The NAPH ·Al 3+ complex formation is reversible upon addition of strong chelating agent EDTA. The receptor NAPH can be applied to detect Al 3+ down to 2.9 μM without any interference from other tested metal ions. In addition, the receptor NAPH was successfully applied to detect Al 3+ in live HeLa cells. [ABSTRACT FROM AUTHOR]

On base of the good optical properties of coumarin and fluorescein, we designed and synthesized two coumarin/fluorescein-fused fluorescent dyes ( CF dyes), which enlarged the emission wavelength and increased the Stokes shift of fluorescein moiety. The corresponding optical properties of CF dyes were investigated in detail. CF dyes could easily introduce other groups to design different functional molecules. CF dyes also exhibited rapid and sensitive responses to pH values in the range of 4.0–7.4 through the characterization of absorption and fluorescence spectra in buffer solution. More importantly, CF ethyl ester dye ( CFE dye) not only showed good cell membrane permeability and low cytotoxicity, but also had the ability to rapidly monitor mitochondrial pH changes in living cells. [ABSTRACT FROM AUTHOR]

Cysteine (Cys), homocysteine (Hcy), and glutathione (GSH) are interconnected and play essential roles in many biological processes. It is significant importance to detect these thiols for investigating their functions in cells and disease diagnosis. In this work, we have designed and synthesized two novel BODIPY-based turn-on fluorescent probes ( BDP-Ph and BDP-R-Ph ) carrying 4-methoxythiophenol moiety at meso position as good leaving group for highly selective detection of Cys and Hcy. Furthermore, the probes have been successfully applied to detect intracellular Cys and Hcy by fluorescent imaging in living cells. [ABSTRACT FROM AUTHOR]

A new benzimidazole base turn-on fluorescent and ratiometric absorption chemosensor (L) bearing bidentate ligand for detection of Cu 2+ was designed and synthesized. Fluorescence and UV–vis spectra studies demonstrated that L can detect Cu 2+ ions in aqueous solution using fluorescence enhancement and ratiometric absorption sensing over a wide pH range. Both fluorescent and ratiometric absorption sensing of L for Cu 2+ possessed high selectivity and sensitivity over other competitive metal ions and had low detection limit. Job's plot, mass spectra and DFT calculation indicated the sensing mechanism is the complex formation between L and Cu 2+ with 1:2 stoichiometry. Fluorescence images of HepG2 in the absence and presence of Cu 2+ displayed L had cell permeability and detection ability for Cu 2+ in live cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • Blue emissive pyridinic- N -rich carbon dots (NCDs) were synthesized from l -malic acid and urea. • Selective and sensitive detection of diethyl chlorophosphate (DCP), a nerve agent mimic. • Inner filter effect (IFE) mediated fluorescence quenching. • Multicolor cell imaging. Fluorometric sensors for the detection of nerve agent mimics have received a lot of interest nowadays due to their high sensitivity and selectivity, ease of operation, and real-time monitoring. Pyridinic- N -rich carbon dots (NCDs) prepared through microwave-assisted pyrolysis of l -Malic acid and urea have been explored first time in this work as a novel turn-off fluorescent probe for the sensitive and selective detection of diethyl chlorophosphate (DCP), a nerve agent mimic. The as-prepared carbon dots contained a large amount of pyridinic nitrogen on their surface, which can modulate the photoluminescence properties of the NCDs. The blue emissive NCDs possessed both excitation wavelength-dependent and independent emission behavior. The detection of DCP was premised on quenching of the fluorescence emission intensity of NCDs in the presence of similar chemical reagents (e.g., trimethyl phosphate, triethyl phosphate, triethyl phosphonoacetate, triphenyl phosphate, diphenyl phosphate, tributyl phosphate). Fluorescence quenching of the NCDs in the presence of DCP has been attributed to the inner filter effect (IFE). From the linear Stern-Volmer plot (R2 = 0.9992), the limit of detection (LOD) was found to be 84 μM for sensing DCP for the concentration ranging between 3 and 15 mM. The biocompatibility of NCDs was assessed through cytotoxicity assay on MDA-MB-231 breast cancer cells. Fluorescence imaging demonstrated that NCDs have low cytotoxicity and can be employed successfully in cell imaging. [ABSTRACT FROM AUTHOR]

[Display omitted] • Near-infrared "turn-on" H 2 S fluorescence probe NIR-H 2 S constructed by novel fluorophore dye NIR-OH , excited at 686 nm and emitted at 736 nm. • Easily acquisitive (3 steps synthesis), Naked-eye visible colour change (from purple to green), high selectivity, high sensitivity (0.353 μM H 2 S), satisfactory response and low cytotoxicity. • Successfully imaged exogenous and endogenous H 2 S in living cells. Hydrogen sulfide (H 2 S) plays a substantial role as a messenger in the physiological and pathological processes of many diseases. Recently, the fluorescence probe of H 2 S based on organic dye has attracted great attention. However, the emission of many probes is in the UV–vis region (400–600 nm), so it has the disadvantages of shallow tissue penetration and more vulnerable to spontaneous fluorescence interference. Although several H 2 S probes have been developed that emit more than 650 nm, there is a complex structure difficult to synthesize or unstable in storage. Aimed at simply structural and easily synthesized H 2 S fluorescent probes with emission wavelength more than 650 nm, a novel near-infrared (NIR) probe (NIR-H 2 S) here was rationally designed with 4-(2-carboxyphenyl)-7-(diethylamino)-2-(4-hydroxystyryl)chromenylium (NIR-OH) as a fluorescent dye and 2,4-dinitrophenyl moiety as a recognition group. Addition of H 2 S, the "turn-on" NIR fluorescence response at 736 nm of NIR-H 2 S was displayed, accompanied by a visual colour change from purple to green when excited at 686 nm. As an easily acquisitive H 2 S probe, NIR-H 2 S has been successfully applied to cell imaging for H 2 S detection with the advantages such as long fluorescence emission, low toxicity, high sensitivity and strong selectivity. [ABSTRACT FROM AUTHOR]

Two novel acridine-based fluorescence chemosensors (L1 and L2) were prepared and their metal ions sensing properties were investigated. L1 (L2) exhibited an excellent selective fluorescence response toward Fe 3+ (Ni 2+ ) and the stoichiometry ratio of L1-Fe 3+ and L2-Ni 2+ were 1:1. The detection limits of L1 and L2 were calculated by the fluorescence titration to be 4.13 μM and 1.52 μM, respectively, which were below the maximum permissive level of Fe 3+ and Ni 2+ ions in drinking water set by the EPA. The possible mechanism of the fluorescence detection of Fe 3+ and Ni 2+ had been proposed according to the analysis of Job's plot, IR spectra and ESI-MS. The determination of Fe 3+ and Ni 2+ ions in living cells had been applied successfully. [ABSTRACT FROM AUTHOR]

A quinoline-based fluorescence probe has been prepared and characterized. Probe 1 showed a selective sensing ability for Al 3 + and Fe 3 + ions through fluorescence enhancement response at 515 nm when it was excited at 360 nm. In the presence of Fe 3 + ion, probe 1 exhibited a detection limit of 2.10 × 10 − 6 M. As for Al 3 + , its detection limit of 3.58 × 10 − 7 M was significantly lower than the highest limit of Al 3 + in drinking water recommended by the WHO (7.41 μM), representing a rare example in reported fluorescent probe for Al 3 + ion. The fluorescence microscopy experiments have demonstrated that probe 1 could be used in live cells for the detection of Al 3 + and Fe 3 + ions. [ABSTRACT FROM AUTHOR]

A simple relay identification fluorescence probe for Fe 3 + and phosphate anion with “on-off-on” switching was designed and synthesized based on the phenylthiazole and biphenylcarbonitrile. Probe 1 displayed highly selective and sensitive recognition to Fe 3 + in HEPES aqueous buffer (EtOH/H 2 O = 2:8, v/v, pH = 7.4) solutions. The optimized structures and HOMO and LUMO of probe 1 and [1-Fe 3 + ] complex were obtained by the density functional theory (DFT) calculations with B3LYP as the exchange and correlation functional using a suite of Gaussian 09 programs. The [1-Fe 3 + ] complex solution also showed a high selectivity toward PO 4 3 − . The lower limits of detection of probe 1 to Fe 3 + and [1-Fe 3 + ] complex to PO 4 3 − were estimated to 1.09 × 10 − 7 M and 1.86 × 10 − 7 M. Besides, the probe 1 also was used to detected the target ions in real water sample and living cells successfully. [ABSTRACT FROM AUTHOR]

A simple and cost effective unsymmetrical azine based Schiff base, 5-diethylamino-2-[(2-hydroxy-benzylidene)hydrazonomethyl]-phenol (1) was synthesized which selectively detect Cu 2 + ions in the presence of other competitive ions through “naked eye” in physiological conditions (EtOH–buffer (1:1, v/v, HEPES 10 mM, pH = 7.4)). The presence of Cu 2 + induce color change from light yellow green to yellow with the appearance of a new band at 450 nm in UV–Vis spectra of Schiff base 1. The fluorescence of Schiff base 1 (10 μM) was quenched completely in the presence of 2.7 equiv. of Cu 2 + ions. Sub-micromolar limit of detection (LOD = 3.4 × 10 − 7 M), efficient Stern–Volmer quenching constant (K SV = 1.8 × 10 5 L mol − 1 ) and strong binding constant (log K b = 5.92) has been determined with the help of fluorescence titration profile. Further, 1 − Cu 2 + complex was employed for the detection of phosphate ions (PO 4 3 − , HPO 4 2 − and H 2 PO 4 − ) at micromolar concentrations in EtOH–buffer of pH 7.4 based on fluorescence recovery due to the binding of Cu 2 + with phosphate ions. Solubility at low concentration in aqueous medium, longer excitation (406 nm) and emission wavelength (537 nm), and biocompatibility of Schiff base 1 formulates its use in live cell imaging. [ABSTRACT FROM AUTHOR]

Colloidal semiconductor quantum dots (QDs) are light-emitting ultra-small nanoparticles, which have emerged as a new class of nanoprobes with unique optical properties for bioimaging and biomedical diagnostic. However, to be used for most biomedical applications the biocompatibility and water-solubility are mandatory that can achieved through surface modification forming QD-nanoconjugates. In this study, semiconductor II–VI quantum dots of type MX (M = Cd, Pb, Zn, X = S) were directly synthesized in aqueous media and at room temperature using carboxymethylcellulose sodium salt (CMC) behaving simultaneously as stabilizing and surface biofunctional ligand. These nanoconjugates were extensively characterized using UV–visible spectroscopy, photoluminescence spectroscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, dynamic light scattering and zeta potential. The results demonstrated that the biopolymer was effective on nucleating and stabilizing the colloidal nanocrystals of CdS, ZnS, and PbS with the average diameter ranging from 2.0 to 5.0 nm depending on the composition of the semiconductor core, which showed quantum-size confinement effect. These QD/polysaccharide conjugates showed luminescent activity from UV–visible to near-infrared range of the spectra under violet laser excitation. Moreover, the bioassays performed proved that these novel nanoconjugates were biocompatible and behaved as composition-dependent fluorescent nanoprobes for in vitro live cell bioimaging with very promising perspectives to be used in numerous biomedical applications and nanomedicine. [ABSTRACT FROM AUTHOR]

A novel coumarin chemosensor, 7-hydroxy-2-oxo-N-(pyridin-2-ylmethyl)chromene-3-carboxamide (Probe 1) , demonstrated significant selectivity towards Fe 3+ ions. Probe 1 exhibited high fluorescence emission profile at 447 nm, excellent selectivity towards Fe 3+ over other biologically important metal ions (Al 3+ , Ba 2+ , Co 2+ , Cu 2+ , Zn 2+ , Cd 2+ , Hg 2+ , Pb 2+ and Sn 2+ ). Interestingly, there was ~ 30-fold decrease in fluorescence intensity upon Fe 3+ binding. The limit of detection of Fe 3+ was found to be 0.76 μM (~ 40 ppb). Probe 1 also exhibited high potential as an intracellular chemosensor for Fe 3+ . [ABSTRACT FROM AUTHOR]