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In recent years, the mechanism concerning fluorescence can be modulated by intramolecular charge transfer (ICT) effect has been widely used in the creation of ratiometric fluorescent probes. However, on this basis, further studies on the structure-activity relationship between molecular constitution of probes and their photophysical characteristics, as well as sensing performance remained less comprehensive. In this work, with triphenylamine (TPA) and methylthio as typical fluorophore and recognition groups respectively, an ICT-based hypochlorite (ClO - ) fluorescent probe named Probe A was initially constructed, and then through ingenious molecular design, the second probe defined as Probe B was successfully prepared by introducing methoxyls as electron donors. The subsequent results showed that, compared with Probe A, the Probe B can exhibit superior aggregation-induced emission (AIE) properties and significant ratiometric fluorescence color change from blue to green within 4 min upon the addition of ClO - in a 99 % water content system. Ultimately, the best performing Probe B was successfully applied to ClO - detection in real water samples, the creation of portable test strips for naked-eye identification, and live cell imaging., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Peroxynitrite (ONOO - ) is a transient and reactive oxidant with significant roles in numerous biological processes. Research has established a correlation between excessive mitochondrial ONOO - production and various diseases. As such we developed a mitochondria-targeting, fluorescence-based ratiometric probe using a boronate group for ONOO - recognition and coumarin as the fluorophore. The probe exhibited a 615 nm far-red emission, and a new fluorescence emission at 475 nm developed upon adding ONOO - .The probe possessed high sensitivity and selectivity for ONOO - detection with distinct ratiometric fluorescent output and a low detection limit of 11 nM. Significantly, Probe 1 could monitor ONOO - level fluctuations in biological systems due to its superior spectral properties and low toxicity. Notably, probe 1 has been effectively used for imaging in live HepG2 cells, zebrafish, Arabidopsis thaliana, and liver injury mouse tissues., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Phosgene is a suffocating toxic gas that seriously threatens human health and public security. With this research, we developed a simple ratiometric fluorescent probe (1) bearing indole and benzimidazole moieties as the sensing sites and employed it for the aggregation-induced emission-based (AIE-based) detection of phosgene. It was the first time that the probe could detect phosgene in an almost pure aqueous solution (f w  = 99.5 %). Probe 1 had AIE-activity, and the maximum emission peak was 392 nm with increasing water fraction (0-99.5 %). When reacting with phosgene, the emission peak at 392 nm gradually decreased, while a new peak appeared at 449 nm and continued to increase with increasing water fraction (0-99.5 %). Probe 1 exhibited a rapid response toward aqueous phosgene with high selectivity and sensitivity (limit of detection being 23.8 nM). Additionally, we fabricated 1-loaded test strips for gas phosgene detection, enabling dual-channel detection under 245 nm and 365 nm hand-held UV lamps. Finally, this probe was used to monitor phosgene in bionic samples., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Sulfur dioxide (SO 2 ), a toxic air pollutant, can have harmful effects on human health when inhaled or when it forms bisulfite in the body. In the present work, a ratiometric fluorescent probe, 2-(2'-hydroxyphenyl)benzothiazole-3-ethyl-1,1,2-trimethyl-1H-benzo[e]indolium (HBT-EMBI), was selected to study the mechanism of SO 2 derivatives detection. This study provides insights into the attributions of ratiometric fluorescence through hydrogen bond dynamics, electronic excitation properties, radiation rates, and excited state intramolecular proton transfer (ESIPT) processes using the density functional theory (DFT) and the time-dependent density functional theory (TDDFT) level. The results confirm that the large Stokes shifts and broad emission spectra of the HBT-EMBI probe are associated with its intramolecular charge transfer (ICT) characteristics and hydrogen bonding-driven ESIPT processes, respectively. After the addition reaction between the probe and HSO 3 - /SO 3 2- , the conformational populations of HBT-EMBI-HSO 3 - transfer abnormally from enol configurations to more stable keto configurations, which leads to a distinguished change in the visible color and the ratiometric fluorescence signal, and is not due to the blockage of the ICT process of HBT-EMBI-HSO 3 - , as previously reported. This work provides a new perspective on the mechanism of detection of SO 2 derivatives by ESIPT fluorescent probes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

A novel ratiometric fluorescent probe was constructed for sensitive assay of hydrogen peroxide (H2O2) and glucose, which utilized the synergistically enhanced effects of Ce3+ and Fe2+ on copper nanoclusters (CuNCs) and coumarin. In the CuNCs-Ce3+/Fe2+-coumarin system, Ce3+ triggered the aggregation-induced emission phenomenon of CuNCs, and Fe2+ catalyzed the Fenton reaction to efficiently yield hydroxyl radical (•OH). In the presence of H2O2, the 625-nm red fluorescence of CuNCs was sharply quenched owing to the oxidation of CuNCs to Cu(II) by •OH, but the 460-nm blue fluorescence of 7-hydroxycoumarin from the oxidation of coumarin by •OH dramatically increased. Based on the reversible changes in two fluorescence signals, a satisfactorily ratiometric probe was constructed for H2O2 assay with a detection limit (LOD) of 0.6 μM accompanied by a visual color variation from red to blue. For glucose assay, this ratiometric probe gave a linear range of 3.2–160 μM and LOD of 0.96 μM owing to the oxidization of glucose to yield H2O2 in the presence of glucose oxidase and O2. Overall, the newly developed ratiometric probe shows a great prospect in real applications for visual assay of H2O2 and glucose by our naked eyes.

Accurately detecting cysteine (Cys) in vivo is crucial for diagnosing Cys-related diseases. A novel ratiometric fluorescent probe featuring dual near-infrared emission is developed in this study for the in vivo ratio imaging of Cys. The probe comprises a hemicyanine organic small-molecule dye (HCy-CYS) with specific Cys recognition capabilities covalently coupled with carbon dots (CDs) synthesized using glutathione (GSH) as the carbon source (GCDs), forming a unique composite nanofluorescent probe (GCDs@CYS). The probe undergoes a specific reaction with acrylate upon the addition of Cys, converting HCy-CYS to HCy-OH. Consequently, the GCD fluorescence intensity at 685 nm gradually decreases, whereas that of HCy-OH at 720 nm progressively increases, yielding a ratiometric fluorescence signal. Notably, both emission wavelengths of the probe exceed 650 nm, thereby effectively mitigating the interference from background signals during cellular and in vivo imaging. Furthermore, the probe demonstrates high specificity for Cys, enabling its differentiation from homocysteine and GSH. The Cys concentration and fluorescence ratiometric intensity exhibit a strong linear correlation at 10-150 μM with a detection limit of 0.95 μM. These results indicate that the ratiometric fluorescent probe can serve as a valuable tool for monitoring Cys-related physiological or pathological processes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2025 Elsevier B.V. All rights reserved.)

The excessive use of pesticides is an urgent issue facing environmental sustainability and human health. In this study, a uniform dispersion size, good fluorescence performance and mesoporous structure of a ratiometric fluorescent probe were constructed for nicosulfuron detection. A solvent-free in situ solid-phase synthesis method was used to encapsulate biomass carbon dots within mesoporous silica (CDs@mSiO₂), followed by the modification of l-cysteine-modified manganese-doped zinc sulfide quantum dots (ZnS:Mn QDs), to construct a ratiometric fluorescent probe for highly sensitive and selective detection of nicosulfuron. This design effectively prevents the aggregation of CDs and reduces interference between the two fluorescent signals. Nicosulfuron detection had a low detection limit of 0.082 μM. Density functional theory calculations were carried out to uncover the specific interactions between nicosulfuron and ZnS:Mn QDs. The process of fluorescence quenching is ascribed to photoinduced electron transfer. This work offers a special strategy to produce a ratiometric fluorescent probe and illustrate the mechanism, which is crucial for sensing and environmental engineering., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2025 Elsevier B.V. All rights reserved.)

As a heavy metal contaminant, mercury ion (Hg 2+ ) has caused great harm to environment and life. Mercury ions will migrate and transform in the environment and eventually accumulate in the human body, thus causing human poisoning. Therefore, it is of great significance to detect Hg 2+ in the environment and living bodies. Based on this, we constructed an example of reactive near-infrared ratiometric fluorescent probe NIRPC-Hg based on the ICT-ESIPT mechanism. The probe could not only effectively overcome the effects of environmental changes, thus realizing the accurate detection of Hg 2+ in the environment, but also possessed the advantages of large emission wavelength shift (130 nm red shift). In addition, the probe NIRPC-Hg was constructed with the classical recognition structure of Hg 2+ and NIR fluorophore, which could detect Hg 2+ sensitively with a low detection limit (9.21 nM). The satisfactory experimental results of environmental water samples proved that the probe had high application potential in the environment. At the same time, the probe NIRPC-Hg had the characteristics of smaller photo-toxicity and lower autofluorescence interference in the bioimaging applications, which could conveniently realize the sensitive detection of Hg 2+ in cells and zebrafish. Therefore, the construction of probe NIRPC-Hg provided an effective tool to detect Hg 2+ in the environment and living organisms., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Nitroxyl (HNO) is an important reactive nitrogen that is associated with various states in physiology and pathology and plays a unique function in living systems. So, it is important to exploit fluorescent probes with high sensitivity and selectivity for sensing HNO. In this paper, a novel ratiometric fluorescent probe for HNO was developed utilizing intramolecular charge transfer (ICT) and fluorescence resonance energy transfer (FRET) mechanisms. The probe selected coumarin as energy donor, naphthalimide as energy receptor and 2-(diphenylphosphino)benzoate as the sensing site for detecting HNO. When HNO was not present, the 2-(diphenylphosphino)benzoate unit of the probe restricted electron transfer and the ICT process could not occur, leading to the inhibition of FRET process as well. Thus, in the absence of HNO the probe displayed the intrinsic blue fluorescence of coumarin. When HNO was added, the HNO reacted with the 2-(diphenylphosphino)benzoate unit of the probe to yield a hydroxyl group which resulting in the opening of ICT process and the occurring of FRET process. Thus, after providing HNO the probe displayed yellow fluorescence. In addition, the probe showed good linearity in the ratio of fluorescence intensity at 545 nm and 472 nm (I 545 nm /I 472 nm ) with a concentration of HNO (0.1-20 μM). The probe processed a detection limit of 0.014 μM and a response time of 4 min. The probe also specifically identified HNO over a wide pH scope (pH = 4.00-10.00), including physiological conditions. Cellular experiments had shown that this fluorescent probe was virtually non-cytotoxic and could be applied for ratiometric sensing of HNO in A549 cells., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

A desirable ratiometric fluorescent probe was designed by using 3-carboxyphenylboronic acid functionalized polyethyleneimine ethoxylated modified copper nanoclusters (CPBA@PEI-CuNCs) for detecting luteolin (LTL, cis-diols structure) with sensitivity and selectivity. Characterization techniques were carried out with the TEM, PSD, FT-IR, XPS and XRD, confirming its successful formation with a quantum yield of 40.49 %. As the optimal excitation wavelength at 386 nm, the fluorescence intensity was detected by fluorophotometer. Meanwhile, the nanoprobe has two emission wavelengths 396 and 473 nm. According to the fluorescence quenching intensity ratio (F 473 /F 396 ), the LOD reached as low as 1.22 nM within the range from 0.11 to 600 μM. The CPBA@PEI-CuNCs exhibited pH-controlled, covalent, and reversible binding properties. Using PEI capped by CuNCs, cytotoxicity is reduced for potential treatment purposes. Additionally, the developed probe was used for LTL detection, HepG2 cell imaging and pH-responsive drug delivery in real samples with carrot leaves, peanut shells, and perilla leaves samples. CPBA@PEI-CuNCs demonstrated repeatability and reproducibility, making it a cost-effective and practical tool for fluorescence analysis in detection., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

The extensive use of fluoride in agriculture, industry, medicine, and daily necessities has raised growing concerns about fluoride residue. To date, real-time visual detection and efficient removal of fluoride ions from water remain greatly desirable. Herein, nano-CAU-10-NH 2 @RhB is introduced as a ratiometric fluorescent probe and efficient scavenger for the intelligent detection and removal of fluoride ions. CAU-10-NH 2 @RhB is readily obtained through one-pot synthesis and exhibits high sensitivity and selectivity for real-time fluoride ion detection, with a naked-eye distinguishable color change from pink to blue. A portable device for point-of-care testing was developed based on color hue analysis readout using a smartphone. A quantitative response was achieved across a wide concentration range, with a detection limit of 54.2 nM. Adsorption experiments suggest that nano-CAU-10-NH 2 @RhB serves as an efficient fluoride ion scavenger, with a fluoride adsorption capacity of 49.3 mg/g. Moreover, the mechanistic study revealed that hydrogen bonds formed between fluoride ions and amino groups of CAU-10-NH 2 @RhB are crucial for the detection and adsorption of fluoride ions. This analysis platform was also used for point-of-care quantitative visual detection of fluoride ions in food, water, and toothpaste., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Malononitrile is a very important chemical material and has wide application fields in production of medicines, pesticides, and extraction of gold. However, its nonnegligible hypertoxicity inspired researchers to develop more efficient analysis techniques to sensitively and selectively detect malononitrile. Nopinone derivatives initiated by our research group have been developed as a class of organic fluorescent chemosensors for identifying multiple analytes in recent years. Different heterocyclic compounds based on nopinone were designed and synthesized to be applied in the fields of environmental analysis, food detection and bioimaging. Nevertheless, the comparison research on the optical properties of fluorescent compounds containing the nopinyl matrix with other structural analogs including alkyl, cyclohexyl and phenyl groups was deficient. Herein, four 4-(1H-imidazol-2-yl)benzaldehyde-based ratiometric fluorescent chemosensors based on o-dimethyl cyclohexyl, phenyl and nopinyl units for recognizing malononitrile were designed and developed, and their differences in the optical properties and detection performances were investigated by using spectral analysis combined with theoretical calculations. Moreover, the nopinone-based 4-(1H-imidazol-2-yl)benzaldehyde fluorescent chemosensor NMZQ was successfully applied in the dual channel fluorescence bioimaging of malononitrile in living HeLa cells and zebrafish, which attributed to its outstanding spectral property and detection performance., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Hypochloric acid (HClO) is a reactive oxygen species (ROS). ROS is an important component that has antibacterial effects on the biological immune defense system. Therefore, the detection of HClO has become an unavoidable issue. This paper reports a cellulose-based fluorescent probe. Naphthalimide serves as the fluorescent group, and the methylthio group serves as the recognition site. The principle is that HClO can oxidise the methyl sulphide group to a sulphoxide. Under a 365 nm UV lamp, this ratiometric fluorescent probe emits a bright yellow green fluorescence, which turns blue after adding HClO. This probe uses more environmentally friendly and sustainable biomass resources, and has significant fluorescence characteristics compared to most reported probes. Its detection limit (LOD) is as low as 4.34 μM. The equilibrium constant K = 3.54 × 10 2  M -1 for the probe plus HClO. The response time is 30 s, and it has good specificity recognition and anti-interference ability. In addition, the probe has been successfully prepared into a fluorescent film, providing potential applications for the convenient detection of HClO. Finally, the probe will be combined with smartphone technology as a portable signal processing device to further achieve visual detection of HClO., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Polarity is a vital element in endoplasmic reticulum (ER) microenvironment, and its variation is closely related to many physiological and pathological activities of ER, so it is necessary to trace fluctuations of polarity in ER. However, most of fluorescent probes for detecting polarity dependent on the changes of single emission, which could be affected by many factors and cause false signals. Ratiometric fluorescent probe with "built-in calibration" can effectively avoid detection errors. Here, we have designed a ratiometric fluorescent probe HM for monitoring the ER polarity based on the intramolecular reaction of spiro-oxazolidine. It forms ring open/closed isomers driven by polarity to afford ratiometric sensing. Probe HM have manifested its ratiometric responses to polarity in spectroscopic results, which could offer much more precise information for the changes of polarity in living cells with the internal built-in correction. It also showed large emission shift ( 133 nm), high selectivity and photo-stability. In biological imaging, HM could selectively accumulate in ER with high photo-stability. Importantly, HM has ability for in situ tracing the changes of ER polarity with ratiometric behavior during the ER stress process with the stimulation of tunicamycin, dithiothreitol and hypoxia, suggesting that HM is an effective molecule tool for monitoring the variations of ER polarity., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

The detection of trace antibiotic residues holds significant importance because it's related to food safety and human health. In this study, we developed a new high-yield red-emitting carbon dots (R-CDs) with aggregation-induced emission properties for ratiometric sensing of norfloxacin. R-CDs were prepared in 30 min using an economical and efficient microwave-assisted method with tartaric acid and o-phenylenediamine as precursors, achieving a high yield of 34.4 %. R-CDs showed concentration-dependent fluorescence and aggregation-induced-emission properties. A ratiometric fluorescent probe for detecting the norfloxacin was developed. In the range of 0-40 μM, the intensity ratio of two emission peaks (I 445 nm /I 395 nm ) towards norfloxacin show good linear relationship with its concentrations and a low detection limit was obtained (36.78 nM). In addition, complex patterns were developed for anti-counterfeiting based on different emission phenomenon at different concentrations. In summary, this study designed a novel ratiometric fluorescent probe for detection of norfloxacin, which greatly shortens the detection time and improves efficiency compared with high-performance liquid chromatography and other methods. The study will promote the application of carbon dots in anti-counterfeiting and other related fields, laying the foundation for the preparation of low-cost photosensitive anti-counterfeiting materials., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: ei Liu reports financial support was provided by National Natural Science Foundation of China, Department of Chemical Sciences, Division of Environmental Chemistry. Lei Liu reports financial support was provided by Key Project of Biomedicine Joint Fund of Hebei Natural Science Foundation (B2020208043). Lei Liu reports financial support was provided by Hebei innovation center of pharmaceutical and chemical engineering (225676121H). If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Peroxynitrite (ONOO - ) is a highly reactive oxygen species that plays a critical role in many physiological and pathological processes of cell function. This study aimed to propose a ratiometric fluorescent probe BDHCA derived from coumarin for determining the ONOO - level. ONOO - could specifically induce oxidative cleavage of the conjugated C = C double bond in probe BDHCA, providing a fluorescent ratiometric output. The response of probe BDHCA to ONOO - was selective, fast, and highly sensitive, with a detection limit of 50.3 nM. Biological imaging experiments suggested that probe BDHCA could be used to image ONOO - in living RAW264.7 cells and zebrafish., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)

Mitochondrial copper signaling pathway plays a role in Alzheimer's disease (AD), especially in relevant Amyloid-β oligomers (AβOs) neurotoxicity and mitochondrial dysfunction. Clarifying the relationship between mitochondrial copper homeostasis and both of mitochondrial dysfunction and AβOs neurotoxicity is important for understanding AD pathogenesis. Herein, we designed and synthesized a ratiometric fluorescent probe CHC-NS4 for Cu(I). CHC-NS4 possesses excellent ratiometric response, high selectivity to Cu(I) and specific ability to target mitochondria. Under mitochondrial dysfunction induced by oligomycin, mitochondrial Cu(I) levels gradually increased, which may be related to inhibition of ATP7A-mediated Cu(I) exportation and/or high expression of COX. On this basis, CHC-NS4 was further utilized to visualize the fluctuations of mitochondrial Cu(I) levels during progression of AD model cells induced by AβOs. It was found that mitochondrial Cu(I) levels were gradually elevated during the AD progression, which depended on not only AβOs concentration but also incubation time. Moreover, endocytosis maybe served as a prime pathway mode for mitochondrial Cu(I) dyshomeostasis induced by AβOs during AD progression. These results have provided a novel inspiration into mitochondrial copper biology in AD pathogenesis., Competing Interests: Declaration of competing interest The authors declare no competing financial interest., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Nitric oxide (NO) plays critical roles in both physiology and pathology, serving as a significant signaling molecule. Recent investigations have uncovered the pivotal role of lysosome as a critical organelle where intracellular NO exists and takes function. In this study, we developed a novel ratiometric fluorescent probe called XL-NO and modified it with a morpholine unit, which followed the intramolecular charge transfer (ICT) mechanism. The probe could detect lysosomal nitric oxide with high selectivity and sensitivity. The probe XL-NO contained a secondary amine moiety that could readily react with NO in lysosomes, leading to the formation of the N-nitrosation product. The N-nitroso structure enhanced the capability in push-pull electron, which obviously led to the change of fluorescence from 621 nm to 521 nm. In addition, XL-NO was discovered to have some evident advantages, such as significant ratiometric signal (I 521 /I 621 ) change, strong anti-interference ability, good biocompatibility, and a low detection limit (LOD = 44.3 nM), which were crucial for the detection of lysosomal NO. To evaluate the practical application of XL-NO, NO imaging experiments were performed in both living cells and zebrafish. The results from these experiments confirmed the feasibility and reliability of XL-NO for exogenous/endogenous NO imaging and lysosome targeting., Competing Interests: Declaration of competing interest The authors declare that there is no conflict of economic interests., (Copyright © 2024. Published by Elsevier B.V.)

2,6-pyridinedicarboxylic acid (DPA) is an excellent biomarker of Bacillus anthracis (B. anthracis). The sensitive detection of DPA, especially through visual point-of-care testing, was significant for accurate and rapid diagnosis of anthrax to timely prevent anthrax disease or biological terrorist attack. Herein, a ratiometric fluorescent (R-FL) and electrochemiluminescent (ECL) dual-mode detection platform with a lanthanide ion-based metal-organic framework (Ln-MOF, i.e., M/Y-X: M = Eu, Y = Tb, and X = 4,4',4″-s-triazine-1,3,5-triyltri-m-aminobenzoic acid) was developed. Eu/Tb-TATAB nanoparticles were constructed to identify DPA. The R-FL detection platform quantitatively detected DPA by monitoring the I 545 /I 617 ratio of the characteristic fluorescence peak intensities of Tb 3+ ions and Eu 3+ ions. The ECL sensing platform successfully quantified DPA by exploiting the burst effect of DPA on the ECL signal. The above methods had highly sensitive and rapid detection of DPA in water and serum samples. The results showed that this dual-mode detection platform may be projected to be a powerful instrument for preventing related biological warfare and bio-terrorism., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Copper ion (Cu 2+ ) is not only a transition metal ion but also a significant environmental pollutant. The imbalance of Cu 2+ content will threaten the safety of the environment and even life. The portable detection devices based on ratiometric fluorescent probes have garnered increasing attention and acclaim because of their reliable analysis parameters. Therefore, two Cu 2+ ratiometric fluorescent probes (RH-1 and RH-2) were developed, which exhibit pronounced fluorescence changes, high sensitivity, excellent selectivity, and large Stokes shift. Both probes are capable of detecting Cu 2+ in water and milk samples. It is worth noting that a 3D-printed fluorescence sensing device was constructed using RH-1, and a new 3D-printed copper ion detection kit was developed based on RH-2, enabling on-the-spot estimation of Cu 2+ concentration. These devices significantly facilitate Cu 2+ detection in daily life. RH-2 has been successfully employed for imaging Cu 2+ in living cells and zebrafish. In conclusion, this work provides, for the first time, the 3D-printed ideal tools for detecting Cu 2+ . It also provides valuable insights for the establishment of on-site portable detection methods for other important substances., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

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., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

A novel core-shell structure ratiometric fluorescent probe was developed, which can selectively and sensitively detect 2,6-dipicolinic acid (DPA) as an anthrax biomarker. Carbon dots (CDs) was embedded into SiO 2 nanoparticles, which was acted as an internal reference signal. Tb 3+ with green emission was connected to the carboxyl functionalized SiO 2 , which was acted as a responsive signal. With the addition of DPA, the emission of CDs at 340 nm was unchanged, while the fluorescence of Tb 3+ at 544 nm was enhanced by the antenna effect. In the concentration range of 0.1-2 μM, the fluorescence intensity ratio of I 544 /I 340 showed a good linear relationship with the concentration of DPA, and the limit of detection (LOD) was 10.2 nM. In addition, the dual-emission probe showed an obvious fluorescence color change from colourless to green with increasing DPA under UV light, which enabled visual detection., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Carbonate ion (CO 3 ) is an anion essential for the maintenance of life activities and is of great importance to human health. Here, a novel ratiometric fluorescent probe Eu/CDs@UiO-66-(COOH) 2- ) is an anion essential for the maintenance of life activities and is of great importance to human health. Here, a novel ratiometric fluorescent probe Eu/CDs@UiO-66-(COOH) 2 (ECU) was prepared by introducing europium ions (Eu 3+ ) and carbon dots (CDs) into the UiO-66-(COOH) 2 parent framework under the guidance of a post-synthetic modification strategy and used for the detection of CO 3 2- ion in the aqueous environment. Interestingly, when CO 3 2- ions were added to the ECU suspension, the characteristic emission of carbon dots at 439 nm was significantly enhanced, while the characteristic emission of Eu 3+ ions at 613 nm was reduced. Therefore, the detection of CO 3 2- ions can be realized through the peak height ratio of the two emissions. The probe had a low detection limit (about 1.08 μM) and a wide linear range (0-350 μM) for the detection of carbonate. In addition, the presence of CO 3 2- ions can cause a significant ratiometric luminescence response and resulted obvious red-to-blue color shift of the ECU under UV light, which will facilitate visual analysis by the naked eye., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Abnormal levels of SO 2 in organisms can cause cardiovascular disease and respiratory allergies. In addition, the amount of SO 2 derivatives used as food preservatives is strictly controlled, and excessive addition can also be harmful to health. Therefore, it is essential to develop a highly sensitive method for the detection of SO 2 and its derivatives in biological systems and real food samples. In this work, a new fluorescent probe (TCMs) with high selectivity and sensitivity for the detection of SO 2 derivatives was reported. The TCMs could quickly identify SO 2 derivatives. It has been successfully used to detect exogenous and endogenous SO 2 derivatives. Furthermore, the TCMs has high sensitivity to SO 2 derivatives in food samples. Moreover, the prepared test strips could be evaluated for the content of SO 2 derivatives in aqueous solutions. This work provides a potential chemical tool to detect SO 2 derivatives in living cells and real food samples., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

A novel ratiometric fluorescent tyrosinase assay is developed based on hybrid nano-assembly of gold nanocluster and tyrosine-containing peptides. The AuNCs@YCY nano-probe (AYNP) is fabricated through the hydrophobic interactions and π-π stacking between the tyrosine residues of the Tyr-Cys-Tyr tripeptide (YCY) and the ligands on the surfaces of AuNCs under the near-isoelectric pH value. The resulted AYNP shows distinct fluorescence responses, spontaneous turn-on of the blue emission and turn-off of the near-infrared emission, with a single wavelength excitation. It is demonstrated that the enhancement and quenching are due to the production of pheomelanin and dopaquinone structures, respectively, induced by tyrosinase oxidation. The internal referencing system provides the tyrosinase assay with superior sensitivity and a detection limit as low as 6.3 U L -1 could be achieved. The experimental results also demonstrate the excellent selectivity, good photo-stability, and both in vitro and cellular applications of AYNP. This assay technique is low-cost, easy to prepare, and shows excellent potential as a novel melanoma clinical diagnostic platform and a tyrosinase inhibitor screening tool., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

In this work, pH-sensitive blue fluorescent carbon dots (CDs) with high fluorescence quantum yield (17.24%) were synthesized by hydrothermal method using Toona sinensis leaves and ethylenediamine (EDA) as raw materials. The CDs can detect urea with a limit of detection (LOD) of 6.700 mmol L -1 . For more sensitive detection of urea, we constructed a ratiometric fluorescent probe (CDs@5-FAM) using CDs and 5-carboxyfluorescein (5-FAM). The CDs@5-FAM probe can rapidly and sensitively detect urea according to the changes of I 514 /I 405 , with LOD as low as 0.014 mmol L -1 . Furthermore, with the help of a smartphone and RGB analysis software, urea's visual intelligent detection was realized using a CDs@5-FAM probe. The method proposed in this paper is consistent with the standard method, which indicates that the pH-sensitive ratiometric fluorescent probe CDs@5-FAM is accurate and reliable for practical application. It provides a new way for rapid and visual detection of urea., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Hypochlorite (ClO - ) plays an important role in the human immune defense system, but high concentrations of ClO - in the endoplasmic reticulum (ER) damage cellular proteins, causing ER stress, cell death, and various diseases. Herein, we developed a simple hydrazone probe (1) featuring aggregation-induced ratiometric emission, which would quickly (within 20 s) and sensitively (detection limit of 15.4 μM) respond to ClO - in an almost pure aqueous solution via a fluorescent ratiometric output. Furthermore, the probe was employed to track the level of ClO - in the ER of HeLa cells and zebrafish., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

The concentration of copper ions (Cu 2+ ) in the environment is closely related to water quality, food, and biological health. As an indispensable metal element for the human body, its content is closely related to many diseases. However, the current detection methods for Cu 2+ have some limitations, such as complicated operations and unfavorable on-site analysis. Therefore, this work constructs a novel ratiometric fluorescent probe (QLP), which has the advantages of rapid response, good anti-interference ability and high sensitivity. It has been successfully used for the detection of Cu 2+ in water samples, soil, and food. In addition, low cytotoxicity and strong tissue penetration make it suitable for the detection of Cu 2+ in living cells and zebrafish, offering a chemical tool for exploring the physiological and pathological processes related to Cu 2+ . It is important to use probe QLP and portable UV lamp to create an easy-to-operate Cu 2+ detection platform, which can quickly detect Cu 2+ on-site by combining with a smartphone. This work not only provides a detection tool for on-site analysis of Cu 2+ , but also provides a reference strategy for the development of on-site detection methods for other environmental pollutants., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Monitoring intracellular pH using ratiometric fluorescent probes can provide further insights into various biological processes including many diseases. Although ratiometric fluorescent probes with dual emission can efficiently exclude interferences (probe concentration, instrumental efficiency, and environmental conditions) compared with traditional off-on fluorescent probes, development of pH-responsive fluorescent probes with dual emission remains relatively unexplored and challenging. Herein we reported a new hemicyanine-based ratiometric fluorescent probe 1 with a hydroxyl group. The probe 1 exhibits dual emission and shows a real-time and selective fluorescence response to micro-environmental pH conditions in a range of 6.0 ∼ 8.0. Further studies revealed that 1 could exclusively enter and accumulate into mitochondria and monitor the pH micro-environmental conditions through fluorescence imaging in HepG2 cells. We suggest that this probe might be used as a probe to elucidate the role of pH in many physiological processes., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

We developed a new core-shell ratiometric fluorescent nanoprobe simply prepared by a seeded growth method. The strong luminescence arising from the shell formed by coordination self-assembly of an alkaline phosphatase (ALP) substrate, l-ascorbic acid 2-phosphate (AAP), and Tb 3+ , together with the weak fluorescence of the core-a metal-organic framework, UiO-66-NH 2 , constitutes an ideal dual-emission characteristic. Since AAP can be specifically cleaved by ALP, the well-formulated core-shell nanostructure was destroyed upon exposure to ALP. In this case, the luminescence of Tb 3+ was quenched due to the inefficient antenna effect, while the fluorescence of UiO-66-NH 2 was strengthened by the synergistical enhancement of dual hydrolysates to inhibit the ligand-to-metal charge transfer (LMCT) process. Using the dual signal response, this nanoprobe was employed for ratiometric fluorescence detection of ALP activity in the range of 0.05-0.6 U mL -1 with a detection limit of 0.018 U mL -1 , accompanied by a discernible fluorescence color evolution from turquoise to blue. In virtue of good properties in accuracy, sensitivity, selectivity and simplicity, this assay enabled quantitative detection of ALP activity in human serum and efficient screening of ALP inhibitors. More Importantly, a smartphone-assisted paper-based sensing platform was designed for on-site visual analysis of ALP activity in human serum, which may be very promising as a facile, portable, and robust format to facilitate relevant biological and clinical applications., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Ascorbate oxidase (AAO) and ascorbic acid (AA) play an important role in delaying lives senescence and metabolism. In this study, a sensitive ratiometric fluorescence sensing system based on the inner filter effect (IFE) between persistent luminescent particles (PLPs) and 2, 3-diaminophenazine (DAP), was designed for the detection of AA and AAO activity. Wherein, PLPs emit blue fluorescence at 475 nm with an excitation wavelength of 370 nm. CoOOH nanosheets with oxidase-like activity can oxidize o-phenylenediamine (OPD) to produce 2, 3-diaminophenazine (DAP) with orange fluorescence at 558 nm. The generated DAP quenched the fluorescence of PLPs by an inner filter effect (IFE). When AA was introduced to the system, CoOOH nanosheets were destroyed and reduced to Co 2+ , thereby inhibiting the oxidization of OPD and effectively preserving the blue fluorescence of PLPs at 475 nm. Besides, AAO can catalyse AA to produce the oxided dehydroascorbic acid (DHA). The dissipative AA can recover orange fluorescence of DAP with weakening the blue fluorescence of PLPs. Therefore, a sensitive ratio fluorescence sensing strategy was established by using PLPs as the reference signal and DAP as a reported signal for the detection of AA and AAO activity. Under optimal conditions, the obtained linear ranges were 1-45 μM and 1-20 mU/mL, and detection limits were 0.2 μM and 0.25 mU/mL, respectively. Finally, this proposed ratiometric fluorescent analytical strategy was used to detect AA in real samples (lemon, orange, tomato), which exhibited satisfactory results comparing with commercial kit., (Copyright © 2022. Published by Elsevier B.V.)

Thiophenol (PhSH) is widely used in industry, however, it is extremely harmful to the environment and human health due to its high toxicity. In this work, we developed a new FRET-ICT-based ratiometric fluorescent and colorimetric probe (DMNP) for detecting PhSH. DMNP had an ultrahigh energy transfer efficiency (99.7%) and clear spacing of two emission peaks (133 nm). DMNP achieved a fast response to PhSH and exhibited drastic enhancement (over 2100 folds) of the fluorescence intensity ratio upon addition of PhSH. DMNP showed good linear response in the PhSH concentration ranges of 0.5-13 μM and 17.0-22.0 μM. Meanwhile, DMNP could also be applied to monitor PhSH in a variety of real water samples., (Copyright © 2022 Elsevier B.V. All rights reserved.)

γ-Glutamyl transpeptidase (GGT) is one of the biomarker of cancer, hepatitis, and numerous other diseases. The accurate analysis of GGT is useful for the early diagnosis of these diseases. In this work, Probe 1, a ratiometric fluorescent probe based on 2,3,5,6-tetrafluoroterephthalonitrile, was designed for GGT detection. The results indicated that Probe 1 can sensitively and selectively detect GGT in phosphate buffered solution and complex biological systems (e.g., blood serum). Furthermore, Probe 1 has been successfully applied for ratiometric imaging of GGT in cancer cells and normal cells., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Nickel resources are abundant in the world, and the application of nickel in production and life is more and more extensive. However, excessive nickel entering the environment will not only cause environmental pollution but also seriously endanger plants, animals and human health. Nickel compounds are carcinogenic and have been classified as a class 1 carcinogen. Nickel mainly exists in the form of divalent ions in the environment. However, there are few simple and effective methods for the detection of nickel ions, and these methods still have certain limitations. At present, the mechanisms of nickel influence in organisms are also unclear. Therefore, we constructed a ratiometric fluorescent probe Ra-Ni, which can achieve its own self-calibration and avoid the interference of other factors, thereby realizing the specific identification of nickel ions. The probe can detect nickel ions sensitively with a detection limit as low as 26.2 nM and can respond in a short time (< 2 min), which proves the great potential of the probe in the detection of nickel ions. At the same time, Ra-Ni has also been successfully used for imaging nickel ions in living cells and zebrafish, providing an effective tool for the study of physiological and pathological processes. The detection effect of nickel ions in actual water sample is also satisfactory, which further demonstrates the practicability of Ra-Ni in environmental applications., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

A lysosome-targeting ratiometric fluorescent probe was synthesized for detecting sulfite based on sulfite-triggered nucleophilic addition reaction. Due to the specific reaction, the fluorescence intensity ratio (I 530 /I 390 ) of the probe in an almost aqueous solution (0.5% DMSO) changed significantly after the addition of HSO 3 - , corresponding to the change in the fluorescence color of the solution from green to blue. The recognition was conducted using high-resolution mass spectrometry, proton nuclear magnetic resonance, and density functional theory calculations. The fluorescent probe could be utilized to quantitatively monitor HSO 3 - in lysosomes of living C6 glioma cells and real-water samples., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Sulfur dioxide derivatives (HSO 3 - and SO 3 2- ) play an important role in food preservative, antibacterial, antioxidant and other aspects, so it is urgent for us to develop more efficient detection methods to broaden their application in biochemical research and related disease diagnosis. Fluorescent probes are of particular interest because of their simplicity and high temporal and spatial resolution. Herein, we constructed a new near-infrared (NIR) fluorescence probe, CQC, composed of coumarin fluorophore and quinoline fluorophore, for detecting SO 2 derivatives. The near-infrared emission probe CQC with a large Stokes shift (260 nm) not only kept the distance between the two emission peaks large enough (165 nm), but also had a particularly high energy transfer efficiency (99.5%), and was particularly sensitive to the detection of HSO 3 - /SO 3 2- (LOD: 0.1 μM). The powerful probe CQC succeeded in real-time visualizing endogenous HSO 3 - /SO 3 2- in living cells., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Hydrogen sulfide (H 2 S) has been recently regarded as one of the most important gasotransmitters in the metabolic system, while abnormal H 2 S concentration is associated with various diseases. Although numerous fluorescent probes have been developed for the detection of cellular H 2 S, only a few of them can monitor lysosomal H 2 S with ratiometric fluorescent output. Here, we developed a water-soluble probe 1 toward H 2 S by introducing 2,4-dinitrophenyl ether into a novel merocyanine-based dye. As expected, H 2 S induced an obvious red-shift of the probe from 520 nm to 580 nm in neat aqueous solution, and this fluorescent ratiometric response is highly selective and sensitive (with the detection limit of 0.81 nM), rapid (within 10 s), and effective in a wide pH range (2.0-10.0). In particular, the probe was successfully applied for tracing H 2 S in the lysosomes of living cells and in zebrafish., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Herein, a facile self-assembly through adenosine monophosphate (AMP) and luminol with Tb 3+ was employed to construct a dual-ligand coordinated AMP-Tb-luminol coordination polymers (CPs), which emitted the typical fluorescence of luminol. Based on the sensitization effect of ciprofloxacin (CIP) on the luminescence of Tb 3+ , a ratiometric sensor was fabricated using the fluorescence of luminol as an inert reference. The fluorescent intensity ratios of Tb 3+ to that of luminol enhanced linearly with the CIP concentration in the range from 5 nM to 2.5 μM with a lower limit of detection of 2 nM. In addition, the proposed ratiometric fluorescent sensor exhibited high selectivity for CIP, which could also be used to detect CIP in human blood serum (HBS) with satisfactory results. To our knowledge, this is the first demonstration of using dual-ligand coordination lanthanide (Ln)-based CPs for ratio-metric CIP assay, and this straightforward strategy may open up a new platform for designing the ratio-metric sensors based on the Ln CPs., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

HClO/ClO - , as one of important reactive oxygen species, is a highly reactive unavoidable by-product generated from normal cell metabolism. In recent years, efficient method for detectiing HClO/ClO - is of great important to research its pathological or physiological function in bio-systems. In this work, we have constructed a fluorescent probe (P-Hc) with ratiometric signal for sensing HClO/ClO - in aqueous solution, physiological saline and different serums based on 2-(benzo[d]thiazol-2-yl)phenol dye. The structure of P-Hc was characterized by NMR and HRMS spectrum. The sensing mechanism has also been verified by 1 H NMR spectrum. The P-Hc displays good sensitivity and selectivity for HClO/ClO - with a limit of detection (LOD) of 2.03 × 10 -6 M. Furthermore, P-Hc has been applied for sensing HClO/ClO - in physiological saline and different serums. Thus, P-Hc may provide a novel method for ratiometric fluorescent sensing HClO/ClO - in bio-samples., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

A water-soluble, stable, simple and dual ligands (bovine serum albumin and L-histidine)-enhanced copper nanoclusters (BSA-CuNCs@L-His) was synthesized by one-step wet chemical method. Interestingly, the introduction of L-His ligand could improve evidently the quantum yields (QYs, 3.47%) and stability of BSA-CuNCs due to forming the stronger interaction of L-His and Cu and producing bigger diameter CuNCs by coordination-induced aggregation. Thus, a new ratiometric fluorescent probe (RF-probe) was successfully exploited for sensitively and selectively mensurating doxycycline (DOX) because DOX could simultaneously regulate the fluorescence (FL) intensities of BSA-CuNCs@L-His at 410 and 520 nm. The FL quenching of BSA-CuNCs@L-His at 410 nm by DOX was mainly originated from the static quenching process, while DOX could bind to Trp-212 in BSA from the skeleton of BSA-CuNCs@L-His by electrostatic interaction causing the appearance of new emission peak at 520 nm. The content of DOX was monitored by the RF-probe with a linear range of 0.05-14.0 μM and a LOD (limit of detection) and LOQ (limit of quantification) of 6.4 and 21.3 nM (at 3σ/slope and 10σ/slope). Moreover, compared to the standard HPLC method, the proposed RF-probe was extended to the detection of DOX in doxycycline hydrochloride (DOXH) tablets, DOXH injections and DOXH capsules with satisfactory results., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Sulfur dioxide (SO 2 ) is an important signal molecule in living systems, and plays a wide range of physiological functions. Real-time and in situ detection of the dynamic balance of SO 2 in mitochondria is of great significance to in-depth study its biological roles. Herein, we have developed a mitochondria-targeted fluorescent probe Nap-L based on the FRET mechanism to detect SO 2 in living cells. The probe Nap-L employed naphthalimide and positively charged benzopyridine as the donor and acceptor in the FRET system, and emitted green and red fluorescence under excitation. In respond to SO 2 , the nucleophilic addition of bisulfite to benzopyridine and then interrupted the FRET process from naphthalimide to benzopyridine fluorophore, thereby triggering an obvious change in the fluorescence ratio. The probe Nap-L showed high selectivity to SO 2 over the biothiols (Hcy, GSH, Cys) and other biologically related species. Biological experiments suggested that the probe Nap-L mainly distributed in mitochondria, and can be successfully used to detect mitochondrial endogenous SO 2 in living cells., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

As a tremendously noxious and extensively utilized chemical reagent, hydrazine (N 2 H 4 ) has become a serious threat to ecosystem and human health. Thus, it is desirable to exploit an efficient method for real-time tracking of hydrazine. Here, a novel ratiometric fluorescent probe PBQ-AB for hydrazine was rationally constructed from isolongifolanone. This probe displayed an extremely large Stokes shift of 230 nm and could selectively recognize hydrazine in the presence of other competitive species within an extremely short time ( 40 s). PBQ-AB also displayed some fascinating merits in the detection of hydrazine, including low detection limit (48 nM), wide pH range (5-12), excellent photostability (>240 min), and well-resolved emission wavelength shift (148 nm). Moreover, this probe was utilized to fabricate a ready-to-use electrospinning nanofibrous membrane for convenient detection of hydrazine vapor by virtue of smartphone. Furthermore, PBQ-AB was capable of determining hydrazine contaminant in environmental soil and water samples. Additionally, its favorable performance for detecting hydrazine was successfully demonstrated in live HeLa cells as well as in live Arabidopsis thaliana tissues, manifesting its promising application for labeling hydrazine in living systems. Therefore, we believed that this probe has great potential in environmental analysis and health supervision., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Rapid, accurate and efficient detection of acidic pH and citric acid (CA) changes is of great significance for predicting environmental and food safety problems by fluorescence analysis technique. Herein, a small molecule ratiometric fluorescent probe (BICL) based on benzoindole derivatives is successfully synthesized and characterized and used for quantitatively and qualitatively "turn-on" detection acid pH and CA changes in solution and environment by ultraviolet spectrum and fluorescence emission spectrum. On the one hand, the probe has a good linear relation to acidic pH in the pH range 3.1-4.5 (I 604 /I 550  = 13.088-2.3878pH, R 2  = 0.9986). On the other hand, the probe has a good linear relationship in the range of CA concentration of 14.0-23.0 μM (I 604 /I 550  = 0.5324 [CA]-5.2628, R 2  = 0.9993) and a low detection limit of 2.967 μM. BICL has a good recovery rate in the range of 114.6 ~ 101.0% and a low relative standard deviation (RSD) (0.0011 ~ 0.0092) in the determination of CA in real samples (water, drinks and fruits), which holds great potential for application in determination of CA in real samples. Importantly, the probe has good blood compatibility, and it has been successfully applied to detect exogenously induced changes in acidic pH and CA in zebrafish with great time-stability by using fluorescence imaging technology, respectively., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Herein, a multifunctional ratiometric fluorescent (RF) probe Fe-MIL-88NH 2 @RhB was fabricated for individual detection of Cu 2+/ Glu and continuous sensing of Glu based on unique coordination principle by encapsulating RhB into the porous of metal-organic-framework-Fe-MIL-88NH 2 . Designed Fe-MIL-88NH 2 @RhB platform could selectively identify Cu(II)/Glu accompanying a turn-off/turn-on fluorescent behavior with good linearity. Moreover, if the Fe-MIL-88NH 2 @RhB/Cu 2+ is treated with Glu continuously, the quenching fluorescence of this platform (after Cu 2+ sensing at blue emission) would be further in turn restored. Utilizing Fe-MIL-88NH 2 @RhB probe, the imaging of intracellular Cu(II) and Glu in living A549 cells was successful conducted through divisional channels with a satisfactory low cytotoxicity, meanwhile, the sensing results of Glu in serum by the molecular logic gate was also superior, which may use for development of an medical occupational tool for amyotrophic lateral sclerosis tentative diagnosis. In addition, the MOF shows di-modal response (color and lumescence) to Cu 2+ and Glu with excellent selectivity against a wide range of other interference analytes, and the corresponding portable low-toxicity on-line test strips for Cu 2+ and Glu recognize has exhibited a remarkable visually chromogenic phenomena, which may utilize for monitoring these contaminants in real water sample. Finally, the feasibility of probe to monitor Cu 2+ and Glu in foodstuffs was also evaluated., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Peroxynitrite (ONOO - ) is a series of basic biological oxidants involved in physiological and pathological processes. The detection of ONOO - in biological systems has been challenging due to its extremely short half-life and low steady-state concentration. In this work, a ratiometric fluorescent nanoprobe for ONOO - was constructed by coupling covalently of graphene quantum dots (GQDs) with cyanine 5.5 (Cy5.5). This nanoprobe (GQD-Cy5.5) could selectively accumulate in mitochondrial, appears two strong fluorescence emission peaks at 520 and 694 nm. In the presence of ONOO - , the intensity of fluorescence emission peak at 520 nm increased and the intensity of fluorescence emission peak at 694 nm decreased. The ratio (F 520 nm /F 694 nm ) of fluorescence intensity at two emission peaks had a good linear relationship with the concentration of ONOO - in the range of 0-6.0 μM, and the detection limit was 0.03 μM. The excellent properties of the nanoprobe enable its applications in the ratiometric fluorescence imaging of endogenous ONOO - in cell mitochondria., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Detection of anthrax biomarker dipicolinic acid (DPA) is of great importance upon the crisis of bioterrorism. Development of fluorescent materials for DPA detection, particularly one that fully depends on single luminescent response, faces the challenge of being susceptible to interferences. The accompanying accuracy problems offer great opportunities for the establishment of more reliable ratiometric analysis method. Herein, a ratiometric fluorescent probe based on terbium functionalized graphitic carbon nitride nanosheets (Tb-g-C 3 N 4 NS) is attempted for quantitative detection of DPA to address the distinct function of g-C 3 N 4 NS as both carrier and reference fluorophore, which is a so-far unexplored option in fluorescent detection approaches. We achieve the incorporation of Tb 3+ into framework of g-C 3 N 4 NS by using a simple synthetic strategy comprised of thermal pyrolysis and ultrasonic exfoliation. Combining the reference signal over g-C 3 N 4 NS at 440 nm (I 440 ) with the response signal of Tb 3+ at 546 nm (I 546 ), concentration of DPA can be easily calculated via its linear correlation with the intensity ratio (I 546 /I 440 ), giving a precise measurement towards DPA with a detection limit as low as 9.9 nM. Besides enabling an excellent self-calibrating detection of DPA, this work also inspires broader use of g-C 3 N 4 NS for relevant process., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Mercury, as a highly toxic heavy metal, can cause very serious harm to human health and even death in severe cases. Therefore, we synthesized a novel ratiometric fluorescent probe for detecting mercury ions, with mercaptoethanol as the recognition receptor. Probe CMER could determine mercury ions in 0-1.6 μM and the detection limit is 7.6 nM. Moreover, CMER manifested a fast response for Hg 2+ (within 5 s) and simultaneously observed that the color changed from light yellow to orange by naked eye. In addition to these preeminent spectral properties, the probe also had satisfactory bioimaging results in RAW 264.7 macrophage cells and zebrafish., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

A novel dual-emission ratiometric fluorescent sensor (CDs@Eu-MOFs) has been synthesized successfully by encapsulating water-soluble fluorescent CDs into the chambers of Eu-MOFs via a simple one-pot hydrothermal method, which can be used for the detection of Hg 2+ in environmental water samples. The synthesized CDs@Eu-MOFs inherited simultaneously the excellent luminescence performance of Eu 3+ and CDs and exhibited good structural and fluorescence stability in aqueous solution. The presence of Hg 2+ changed the fluorescence intensity of CDs, while the fluorescence intensity of Eu-MOFs hardly changed, which could be used as the recognition part and the reference part respectively to construct the ratiometric fluorescence sensor. The obtained Hg 2+ fluorescent probe showed a wide linear range (0-300 μM) and a low detection limit (0.12 nM). The developed method can be used as a multi-functional fluorescent sensor with high sensitivity and good selectivity for the determination of Hg 2+ in actual water samples., Competing Interests: Declaration of competing interest About this paper, no any interest conflict exists., (Copyright © 2020 Elsevier B.V. All rights reserved.)

The profiling of bacterial metabolism is of great significance in practical applications. Therefore, the development of ultrasensitive and highly selective probe for bacterial metabolism detection and imaging is extremely desirable. Herein, a novel dual-emission pH-response bacterial metabolism detection and imaging probe is successfully developed. This probe consists of large-sized and easily separated SiO 2 microspheres, copper nanoclusters (Cu NCs) with red emission, and carbon dots (CDs) with blue emission through in-situ self-assembly. In this system, the fluorescence of Cu NCs is sensitive to pH change due to their obvious aggregation-induced emission enhancement (AIEE) property, while the blue fluorescence of CDs remained almost stable. Therefore, red fluorescence and blue fluorescence are compounded with different fluorescence intensity at different pH values, and their fluorescence ratio is also different. By observation of composite fluorescence color, the visual colorimetric pH detection can be realized with the change of pH value of 0.2 units. Utilizing this system, we are able to detect bacterial metabolism with high signal-to-noise ratio, and it can also be used for bacterial metabolic imaging. Therefore, the pH-responsive Cu NCs-based dual-emission ratiometric fluorescent probe we constructed can provide new ideas for bacterial detection, antimicrobial sterilization, and biological imaging., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Hydrazine (N 2 H 4 ) is extensively used in industry but highly toxic; hence, highly sensitive detection of N 2 H 4 is extremely meaningful. Herein, a colorimetric and near-infrared (NIR) ratiometric fluorescent probe named DXM-OH was rationally designed and synthesized based on oxanthrene malononitrile derivative for the specific detection of N 2 H 4 . The dicyanovinyl group in DXM-OH was served as the recognition unit for N 2 H 4 . DXM-OH showed high sensitivity to N 2 H 4 in the range of 1-900 μM, with the limit of detection (LOD) of 0.09 μM (2.87 ppb), which is much lower than the U.S. Environmental Protection Agency standard (10 ppb). Furthermore, the practical applications of DXM-OH in detecting N 2 H 4 in real water samples and imaging of N 2 H 4 in living cells were demonstrated, indicating its potential utility for N 2 H 4 sensing in environmental and biological samples., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)