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Viscosity is a parameter used to measure the fluidity of liquids and a key indicator in evaluating the states of body fluid in biological tissues and lesions. Most traditional detection methods have many drawbacks such as a short emission wavelength and interference by background fluorescence. Inspired by the multiple double bond structure of retinal, a novel pH and viscosity dual-response fluorescent probe (Rh-TR) was constructed in this study. Rh-TR exhibited two emission signals centered at 510 and 660 nm. As the pH of the phosphate-buffered saline increased, the fluorescence at 510 nm increased by about 124-fold, while the change in fluorescence at 660 nm was not obvious. When detecting the change in viscosity using the probe, the fluorescence at 510 nm decreased by about 85 %, while the fluorescence at 660 nm increased by over 20-fold. The probe also showed high selectivity and little toxicity. As demonstrated by the biological imaging experiment, the probe successfully imaged changes in the pH and viscosity of cells and in a live animal model of zebrafish. Considering the unique structure of Rh-TR with retinal and its pH- and viscosity-switchable spectral property, the probe may find further application in detecting viscosity-related diseases and industrial 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. Published by Elsevier B.V.)

N 2 H 4 is a common raw material used in the production of pesticides and has good water solubility, so it may contaminate water sources and eventually enter living organisms, causing serious health problems. Viscosity is an important indicator of the cellular microenvironment and an early warning signal for many diseases. The high reactivity of hydrazine depletes glutathione (GSH) in hepatocytes, causing oxidative stress ultimately leading to significant changes in intracellular viscosity and even death. Therefore, it is particularly important to develop an effective method to detect N 2 H 4 and viscosity in environmental and biological systems. On this basis, we developed two fluorescent probes, BDD and BHD, based on xanthene and 2-benzothiazole acetonitrile. The experimental results show that BHD and BDD have good imaging capabilities for N 2 H 4 in cells, zebrafish and Arabidopsis. BHD and BDD also showed sensitive detection and fluorescence enhancement in the near-infrared region when the intracellular viscosity was changed. Notably, the probe BDD has also successfully imaged N 2 H 4 in a variety of 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 © 2024 Elsevier B.V. All rights reserved.)

Hydrogen peroxide (H 2 O 2 ) is a reactive oxygen species (ROS) that can be used as a marker for the occurrence of oxidative stress in the organism. Lysosomes serve as intracellular digestive sites, and when the concentration of H 2 O 2 in them is abnormal, lysosomal function is often impaired, leading to the development of diseases. Hydrogen sulfide (H 2 S) acts as a gaseous signaling molecule that scavenges H 2 O 2 from cells and tissues, thereby maintaining the redox environment of the body. However, most of the reported hydrogen peroxide fluorescent probes so far can only detect H 2 O 2 , but cannot maintain the intracellular redox environment. In this paper, an H 2 O 2 fluorescent probe LN-HOD with lysosomal targeting properties was designed and synthesized by combining the H 2 O 2 recognition site with a naphthylamine fluorophore via a thiocarbamate moiety. The probe has the advantages of large Stokes shift (110 nm), high sensitivity and good H 2 S release capability. The probe LN-HOD can be used to detect H 2 O 2 in cells, zebrafish and plant roots. In addition, LN-HOD detects changes in the concentration of H 2 O 2 in plant roots when Arabidopsis is stressed by cadmium ion (Cd 2+ ). And through its ability to release H 2 S, it can help to remove excess H 2 O 2 and maintain the redox environment in cells, zebrafish and plant roots. The present work provides new ideas for the detection and assisted removal of H 2 O 2 , which contributes to the in-depth study of the cellular microenvironment in 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.)

A series of fluorescent dyes (NapPAs) based on 4-phenylacetylene-1,8-naphthalimide were synthesized and characterized, whose conjugated structures were extended by the introduction of phenylethynyl. Furthermore, changes in the photophysical properties of the dyes when substituents with varying electron richness were introduced at the p-position of phenylacetylene were studied. The theoretical calculation of the dye molecules was carried out by B3LYP functional and 6-31G(d,p) basis set, and the effects of different substituents at the p-position of phenylacetylene on the electronic structure and photophysical properties of the dyes were studied by theoretical calculation results. Theoretical calculations provided a reliable means of predicting the properties of dyes, which could help in the design of more efficient and novel dyes. To verify the practicability of the dyes, two dyes with excellent photophysical properties (large Stokes shift, high polarity-viscosity sensitivity, good biocompatibility) were selected as fluorescent probes for visualization of LDs and two-color imaging of LDs and lysosomes. Cell imaging showed that NapPA-LDs and NapPA-LDs-Lyso serve as excellent imaging tools to monitor the dynamic changes, movements, and behaviors of LDs and lysosomes in real time. Notably, NapPA-LDs-Lyso held promise as a potential tool to study the interaction between LDs and lysosomes., 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.)

Hydrazine (N 2 H 4 ) plays an important role in industrial production, but it is highly toxic, leaking or exposing it will pollute the environment and cause serious harm to human beings. Therefore, it is necessary to use a simple and effective method to detect N 2 H 4 in environmental systems and organisms. Herein, a novel water-soluble fluorescent probe based on coumarin fluorophore, 2-(7-(diethylamino)-2-oxo-2H-chromen-3-yl)isoindoline-1,3-dione (C-Z1), is reported. The fluorescence intensity of the probe at 530 nm was enhanced gradually with the addition of N 2 H 4 , and the maximum enhancement was about 28 times. The probe has good selectivity and sensitivity, the detection limit of hydrazine hydrate is 1.48 × 10 -7  M, and the response mechanism of the probe is proved by theoretical calculation and experiment. C-Z1 has been shown to detect N 2 H 4 in a variety of environmental samples, including water, soil, air, cells, zebrafish and plants. In addition, C-Z1 can be made into test strips for easy portability and used for rapid quantitative detection of N 2 H 4 in the field by its distinct change in fluorescence color. Thus, C-Z1 has great potential for the analysis and detection of environmental contaminants., 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.)

H 2 S is one of the signal molecules in live organisms and a poisonous gas, which is closely related to our life. The traditional synthetic small molecular organic probes often have the disadvantages of low biocompatibility. In this paper, a fluorescent nanoprobe for detecting H 2 S in live organisms was constructed based on chitosan. The structure of CH-CN was characterized by infrared spectroscopy, nuclear magnetic resonance, x-ray photoelectron spectroscopy (XPS), XRD and scanning electron microscope (SEM). In the presence of Na 2 S, the fluorescence intensity at 560 nm was significantly enhanced, and showed high selectivity and sensitivity toward H 2 S. Based on the good fluorescence response of CH-CN, the probe was also successfully applied to H 2 S imaging in HepG2 cells and zebrafish. These experimental results indicate that the probe has lower cytotoxicity and excellent stability. The present research shows a typical example of construction of chitosan-based macromolecular fluorescent materials and their bio-imaging application., Competing Interests: Declaration of competing interest The authors declare no conflicts of interest., (Copyright © 2023. Published by Elsevier B.V.)

The AIE bio-probes have attracted extensive attention because of their good brightness, long-term in situ retention ability, photostability and low cytotoxicity. Recently, the transformation of ACQ to AIE has become very popular, which is very important for the further development of AIE probes. Herein, a series of novel dyes (NR-Lyso-Ⅰ, NR-Lyso-Ⅱ, NR-Lyso-III, NR-Lyso-IV) were designed and synthesized. It was found that alkylation of 4-aminonaphthalimide could achieve the transformation of the dye from ACQ to AIE effect due to the growth of carbon chain. Moreover, the AIE probe NR-Lyso-IV exhibited dual-state emission (DSE) and large Stokes shift (＞100 nm), excellent selectivity, photostability, and low cytotoxicity, which was able to simultaneous visualize the lipid droplets (LDs) and lysosomes 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 B.V. All rights reserved.)

Hypochlorous acid (HClO) plays a critical role in physiological activities of maintaining the stable oxidation balance of organisms, which was proved to relate to some serious diseases. In this work, 4-nitrobenzenesulfonylhydrazide based fast-responsive two-photon fluorescent probe CoPh-ClO was designed and synthesized reasonably, which possessed low cytotoxicity, good anti-interference characteristics, a large Stokes shift (85 nm), and good two-photon performance. In addition, probe CoPh-ClO was successfully applied to detect exogenous HClO in living HeLa cells and endogenous HClO in living RAW264.7 cells respectively. Moreover, we successfully achieved tissues imaging with a deep penetration depth of 65 µm and zebrafish imaging accompanied with a high contrast (about 45-fold). Interestingly, the introduce of benzene ring between fluorophore and reaction site made probe CoPh-ClO more sensitive (only 20 s) with a large turn-on signal. The probe CoPh-ClO was modified and possessed better stability (more than 10 mins) even in excessive HClO. All of mentioned above merits demonstrated that CoPh-ClO could be a promising imaging tool for monitoring HClO in various physiological processes, and the introduction of benzene ring would provide a new perspective for the development of multi-function probes., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Carbon monoxide (CO) is one of the most significant signal molecules and plays an important role in regulating human physiological and pathological processes. In this study, a novel Pd-based complex (Pd-BNP-OH) was developed for endogenous CO detection. The structure and morphology of Pd-BNP-OH was characterized by SEM, XPS, and NMR analyses. When Pd-BNP-OH was reacted with CO, a strong fluorescence enhancement at 510 nm was observed. In addition, Pd-BNP-OH exhibited high stability and selectivity toward CO in PBS buffer. In biological experiments, Pd-BNP-OH exhibited little cytotoxicity in cellular environment, and a bright fluorescence turn on was observed in the presence of exogenous CO and endogenous generated CO. The probe was then applied for CO detection in live zebrafish by both one-photon and two-photon excitation. Significantly, Pd-BNP-OH has excellent two-photon property, controllable structure and high biocompatibility. These features enable the probe to detect endogenously generated carbon monoxide in live organisms successfully., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Recently, cellulose-based stimuli-responsive nanomaterials have received significant attention because of its natural source and biocompatibility. In this study, cellulose-graft-poly(nisopropylacrylamide)-co-2-methyl-acrylic acid 2-carbazol-9-yl-ethyl ester (cellulose-g-(PNIPAAm&PCz)) block polymers were successfully synthesized by homogeneous atom transfer radical polymerization (ATRP) in LiCl/N,N-dimethylacetamide (DMAc) dissolution system. The block polymers showed different properties due to the different PCz content. The block polymer with low PCz content (cellulose-g-(PNIPAAm&PCz)1) was dispersed in water at 25 °C and self-assembled into micelles at 37 °C. On the other hand, the block polymer with high PCz content (cellulose-g-(PNIPAAm&PCz)2) was dissolved in DMF, THF, DMSO firstly, and dialyzed at 25 °C, 37 °C and 60 °C respectively to obtain the micelles. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) indicated that the distribution range of micelles formed by cellulose-g-(PNIPAAm&PCz)1 was narrower than cellulose-g-(PNIPAAm&PCz)2. And the sizes of the micelles formed by cellulose-g-(PNIPAAm&PCz)2 had little difference under different solvents, but became bigger with the temperature increased. The micelles displayed thermo-enhanced fluorescence due to the thermal-driven chain dehydration of the grafted PNIPAAm brushes, which is contrary to the decrease of the fluorescence of the monomer when the temperature increased. The results provided a potential for the application of cellulose-based stimuli-responsive micelles in the field of drug delivery and fluorescent probes., Competing Interests: Declaration of competing interest The authors declare that they have no competing interests., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Multiple types of metal ions and active small molecules (reactive nitrogen species, reactive oxygen species, reactive sulfur species, etc.) exist in living organisms. They have connections to each other and can interact and/or interfere with each other. To investigate the relationship of metal ions and active small molecules in living cells, it is necessary and critical to develop molecular tools that can track two kinds of associated certain metal ions and reactive molecules with multiple fluorescence signals. However, this is a challenging task that requires an ingenious molecular design to achieve this goal. Here, we present a fluorescent probe (D-CN) that can offer fluorescence imaging of H 2 S and copper (II) ions with different response signals. Recognition of H 2 S and Cu (II) by the new probe can result in green and red emissions, respectively, providing different signal responses to the two substances in living cells and zebrafish. In addition, we used this probe to visually prove that the cytotoxicity of copper ions in living cells increases in the presence of hydrogen sulfide and could lead to cell apoptosis., 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.)

As one type of the solid wastes, the increasing contamination of waste cellulose diacetate (CDA) from discarded cigarette filters is a growing problem worldwide. Finding a facile and suitable approach to convert the CDA into value-added materials is of significance. Herein, we reported a green, simple and effective method to reuse CDA as precursor for preparing fluorescence N-doped carbon dots (N-CDs) via one-pot hydrothermal carbonization in aqueous solution with low-cost ammonium hydroxide as the passivation agent. The N-CDs showed a quantum yield up to 22.4% with a maximum emission at 415 nm and excitation at 320 nm. Interestingly, the N-CDs exhibited high selectivity toward tetracycline (TC) as their fluorescence was obviously quenched by TC as a result of inner-filter effect. A linear relationship was fabricated over concentration range of 0-80 μM with a detection limit of 0.06 μM. Moreover, the N-CDs could also be applied as fluorescent ink for anti-forgery., Competing Interests: Declaration of competing interest The authors declare that they have no conflict of interest., (Copyright © 2020 Elsevier B.V. All rights reserved.)

As a natural fluorescent material, the fluorescent property and mechanism of lignin were elusive until now, which hindered the high value application of lignin fluorescence. Herein, we firstly probed the previous studies on lignin fluorescence and the results indicated that lignin microstructure was an important factor for its complex fluorescence property because of fluorophore interaction and aggregation behavior. Following the rules, lignin fluorescence was explored by analyzing its aggregation fluorescence behaviors and basic fluorescence properties based on the theory of traditional conjugated luminescence and aggregation-induced emission. It was demonstrated that intermicellar aggregation of loose lignin micelle made no substantial effect on lignin fluorescence, while intramicellar aggregation could induce the enhancement of lignin fluorescence before the micellar compactness exceeded a critical value. Combined with the physicochemical structures and fluorescence properties of lignin, aggregation-induced conjugation from phenylpropane units was believed as the main sources of the visible emission of lignin and different phenylpropane aggregates consequently formed the multi-fluorophore system in lignin micelle. Furthermore, lignin aggregation fluorescence behavior has great potential in its microstructure analysis and a case study of pH/ionic strength-induced solution behavior analysis was presented. This work provided a totally new prospective for lignin fluorescence., (Copyright © 2020. Published by Elsevier B.V.)

Fluorescent nanoprobe with good water dispersibility was synthesized by the coupling of fluorescent 1,8-naphthalimide dye (NANI) as well as biocompatible poly (ethylene glycol) (PEG) to cellulose nanocrystals (CNC). FTIR, TGA and XPS analysis confirmed the successful covalent conjugation of NANI and PEG. The rod-like morphology of CNC was generally retained after two-step successive grafting of NANI and PEG. The contact angle and transmittance measurements showed that the grafted PEG brushes improve the hydrophilicity of fluorescent CNC probes and their dispersibility in high-concentration NaCl solutions. The fluorescent CNC probe had good biocompatibility and was successfully used for the bioimaging of Hela cells in physiological environment at high salt concentration. Laser confocal microscopy showed that the fluorescent CNC probe can penetrate the cell membrane and disperse uniformly in the cell with good biocompatibility. The fluorescent CNC probe with nanometer size, strong fluorescence emission and high salt-tolerance possess potential application in biomedical field., Competing Interests: Declaration of competing interest The authors declare no competing financial interest., (Copyright © 2020 Elsevier B.V. All rights reserved.)

A two-photon fluorescent probe for Cu 2+ and S 2- has been strategically prepared with naphthalimide derivative platform (NPE) covalently grafted onto the surface of magnetic core-shell Fe 3 O 4 @SiO 2 nanoparticles. The probe (NPE-Fe 3 O 4 @SiO 2 ) exhibits selective response to Cu 2+ with enhanced fluorescence and efficient separation of Cu 2+ with external magnetic field. The consequent product NPE-Fe 3 O 4 @SiO 2 -Cu of NPE-Fe 3 O 4 @SiO 2 and Cu 2+ can work as an excellent sensor for S 2- by removing Cu 2+ from the complex with fluorescence decreased, recovering the fluorescence of the probe. Therefore, the constituted Off-On-Off type fluorescence monitoring system means the probe is resumable. Moreover, the probe has been used to quantitatively detect Cu 2+ and S 2- with low detection limits, which are 0.28 μM and 0.12 μM, respectively. Furthermore, the probe shows low cytotoxicity and excellent membrane permeability, which has been successfully applied for monitoring Cu 2+ and S 2- in living cells and imaging Cu 2+ in deep-tissue with two-photon excited fluorescence., (Copyright © 2018. Published by Elsevier B.V.)

A novel dicyanoisophorone based fluorescent probe HP was developed to detect hydrazine. Upon the addition of hydrazine, probe HP displayed turn-on fluorescence in the red region with a large Stokes shift (180nm). This probe exhibited high selectivity and high sensitivity to hydrazine in solution. The detection limit of HP was found to be 3.26ppb, which was lower than the threshold limit value set by USEPA (10ppb). Moreover, the probe was successfully applied to detect hydrazine in different water samples and living cells., (Copyright © 2018 Elsevier B.V. All rights reserved.)