Two Ratiometric Fluorescent Probes Based on the Hydroxyl Coumarin Chalcone Unit with Large Fluorescent Peak Shift for the Detection of Hydrazine in Living Cells

Application of a fluorescent probe exhibiting a large stokes shift after the precise detection of hydrazine in plants, foods and living cells

As a strongly reducing agent and highly reactive alkaline substance, hydrazine is widely used in various industrial productions. Excessive hydrazine may pose a significant risk to the environment and human health. Here, a new fluorescent probe, (E)-6-(2-(3-(dicyanomethylene)-5,5-dimethylcyclohex-1-en-1-yl)vinyl) naphthalen-2-yl-7-(diethylamino)-2-oxo-2H-chromene-3-carboxylate (abbreviated as MNC) for detecting hydrazine in environmental and biological samples was introduced. The probe not only shows a good photostability, a turn-on red fluorescent response with a low detection limit (0.40 μM), but also exhibits a large Stokes shift (215 nm) after reacting with hydrazine. In practical applications, this probe has been effectively used for the detection of hydrazine in environmental, plant, and food samples. It has also been applied to identify the presence of hydrazine in the roots of Arabidopsis thaliana, as well as in zebrafish and living cells. This research introduces a potent and versatile tool for the environmental and biological monitoring of hydrazine.

A cellulose based fluorescent microsphere for sensitive detection and efficient removal of hydrazine and its versatile applications in environmental samples and live plants

Hydrazine (N2H4) is being extensively utilized in various industrial fields, yet its high toxicity can cause enormous adverse effects on human health and the ecological environment. Herein, an aggregation-induced emission (AIE) fluorescent probe FNA-B-CA (naphthalimide small molecule (FNA-B) grafting onto cellulose acetate (CA)) for sensitive detection and high effective removal of N2H4 was synthesized. Probe FNA-B-CA can recognize N2H4 across a wide pH range (5 -12) with a low detection limit (84 nM), high selectivity, and strong anti-interference ability. It enabled quantitative detection of N₂H₄ concentrations in actual water and soil samples quantitatively and functioned as an efficient tool for tracking N2H4 in plant tissue (bean sprouts). More importantly, probe FNA-B-CA was hereby successfully prepared into fluorescent microspheres using the favorable processing properties of CA, further facilitating the simultaneous detection and adsorption of N2H4 in aqueous solutions.

Ultra-sensitive, versatile and portable detection of hydrazine in eco-environmental systems using a smartphone-integrated ratiometric fluorescent sensor

Hydrazine (N2H4), a highly reactive specie widely used in industrial processes, poses significant ecological risks. Accurate detection of N2H4 is essential for safeguarding public health, yet developing a robust tool for its global detection remains a significant challenge. Herein, we developed a ratiometric fluorescent sensor, DIPOT, designed for ultra-sensitive and portable detection of N2H4 in eco-environmental systems. DIPOT exhibited excellent ratiometric fluorescence performance for N2H4 in aqueous solution, with a detection limit as low as 4.5 nM and a substantial 156 nm blue shift, transitioning from red to green fluorescence. We integrated it into portable test strips for on-site quantitative detection and analysis of N2H4 vapor and solution via a smartphone application. DIPOT and its portable platform have been successfully applied to monitor ultra-trace levels of N2H4 in 20 diverse eco-environmental samples, including water, soil, crops, food and living organisms, showcasing its versatility. Furthermore, DIPOT facilitates real-time ratiometric bioimaging of N2H4 in living plants, cells and zebrafish. Our findings provide a robust and eco-friendly approach for global tracking of N2H4, representing a significant advancement in environmental sensing technology.

A novel boronic acid-based fluorescent sensor for the selective detection of l-lysine in food samples and cells

A novel probe DFC (2-(dicyanomethylene)-2,5-dihydro-5,5-dimethyl-4-((E)-2-(5-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)furan-2-yl)vinyl)furan-3-carbonitrile) was successfully designed and synthesized for the detection of l-lysine (l-Lys). The sensing behavior was characterized using absorption and fluorescence emission spectra. Upon addition of l-Lys to DFC, a rapid response time of 5 seconds was observed, accompanied by a significant 4-fold enhancement in fluorescence intensity. Additionally, DFC exhibits an impressively low detection limit of 0.14 μMol L-1. Furthermore, the applicability of DFC was demonstrated through successful detection of l-Lys in water samples, food samples, and imaging of l-lys in live HeLa cells.

AIE and ICT Synergistic Lysosome-Targeted Ratiometric Fluorescence Sensor for the Detection and Imaging of Th4+ in the Liver of Zebrafish and Mice

The sensitive detection of the radioactive thorium (Th) ion with an oxidation state of +4 (Th4+) is of great significance for environmental protection and life safety. In this study, five fluorescence sensors with regulated donor-acceptor (D-A) interactions were constructed for Th4+ detection based on intramolecular charge transfer and aggregation-induced emission mechanisms. Among the developed sensors, TPE-D bearing electron-deficient π-bridge and weak D-A interactions presented ratiometric fluorescence detection behavior toward Th4+ in aqueous solution due to its aggregation-induced emission characteristics and unique D-A-D structures. Moreover, TPE-D showed excellent selectivity and sensitivity for Th4+ detection, and the detection limit was as low as 8.1 × 10-8 M. The sensing mechanism observation revealed that Th4+ could coordinate with the hydroxyl, imine, and carbonyl groups of TPE-D accompanied by an electron transfer process. In addition, TPE-D could selectively be enriched in the lysosome. Both the detection of Th4+ in the lysosome and liver of mice and zebrafish were realized based on this strategy, and a mobile-assisted detection approach toward Th4+ in actual water samples was also established with high sensitivity. This is the first report for Th4+ detection in organelles and organs, which provides a great significance and reliable strategy for radionuclide toxicology detection and analysis applications.

An interesting aggregation induced red shifted emissive and ESIPT active hydroxycoumarin tagged symmetrical azine: Colorimetric and fluorescent turn on-off-on response towards Cu2+ and Cysteine, real sample analysis and logic gate application

We report a newly synthesized 7-diethylamino-4-hydroxycoumarin tagged symmetrical azine derivative (SHC), with an interesting color transformation from yellowish green to orange via aggregation induced red shifted emissive (117 nm) feature in THF-H2O mixture. Interestingly, the single crystal X-ray analysis of this molecule demonstrates that two hydroxycoumarin moieties were present in azine unit, among them one of the coumarin units was exist as enol form and another one transferred to keto form via ground state proton transfer reaction. The optical responses of the compound in different solvents exposed the observation of dual emissive bands which corresponds to the presence of ESIPT phenomenon in SHC molecule. Further, this characteristic was confirmed by absorption, emission, solid state structure and time resolved fluorescence decay measurements. Furthermore, the fluorophore, SHC was exploited as a colorimetric and turn on-off-on fluorescent probe for detection of Cu2+ ions and Cysteine (Cys). The 1:1 binding ratio of the probe with Cu2+ and Cys with SHC-Cu2+, was established via Job plot analysis, mass spectral technique and the DFT calculations. The probe, SHC was employed for the detection of copper ions in the environmental real water samples. Finally, the reversible fluorescent turn on-off-on character of the probe, SHC was established to construct the IMPLICATION logic gate application.

Live cell imaging of lipid droplets: fluorescent chalcones as probes for lipophagy and lipid-mitochondria interactions

Lipid droplets are crucial organelles involved in cellular energy storage and metabolism, which is key in maintaining energy homeostasis through lipophagy. In this work, we successfully synthesized donor-acceptor chalcone derivatives (M1-M3) with improved photophysical characteristics, such as significant Stokes shifts and strong emission features. DFT and TDDFT calculations have been employed to evaluate the structure-property relationship of the chalcone derivatives. The molecules show excellent selectivity in staining lipid droplets in COS-7 cells and other cell lines. The molecule M1 was also further utilized to monitor verapamil-induced lipophagy. Using M1, we also demonstrate the link between lipid droplets and mitochondria during stress, emphasizing the significance of lipophagy in cellular energy balance and metabolism. These results not only shed light on the lipid metabolism but also have profound implications for researching and potentially treating metabolic diseases, underscoring the importance of our work in the field.

Coumarin-aurone based fluorescence probes for cysteine sensitive in-situ identification in living cells

The quantification of cysteine (Cys) levels in the organisms holds paramount significance in biological research and disease diagnosis, which can give the correlation between abnormal Cys levels and diseases. In this study, two fluorescent probes, designated as DEA-OH and DEA-AC, featuring a coumarin-aurone backbone specifically engineered for Cys detection, were meticulously designed and synthesized. The diethylamino coumarin-aurone probe DEA-OH and the acrylate-substituted probe DEA-AC demonstrated remarkable sensitivity in detecting cysteine by means of copper displacement (DEA-OH) and acrylate hydrolysis mechanisms (DEA-AC) with fluorescence detection limits of 7.25 μM and 1.65 μM, respectively. Moreover, the fluorescence peak wavelength of the two probes displayed a linear relationship with solvent polarity in the ET (30) range of 30-65 kcal•mol-1, indicating the potential for monitoring changes in environmental polarity within this ET (30) range. The outstanding attributes exhibited by DEA-AC including superior photostability, remarkable selectivity, and swift response (kinetic rate constant: 0.00747 s-1), coupled with the exceptional anti-interference ability, have significantly broadened its scope of applications, for example detecting alterations in Cys within biological systems.

Fluorescent probe for imaging N2H4 in plants, food, and living cells and for quantitative detection of N2H4 in soil and water using a smartphone

Hydrazine is volatile and highly toxic, causing severe harm to water, soil, air, and organisms. Therefore, real-time detection and long-term monitoring of hydrazine are crucial for environmental protection and human health. Herein, an "OFF-ON" fluorescent probe 5-((10-ethyl-2-methoxy-10 H-phenothiazin-3-yl)methylene)-2,2-dimethyl-1,3-dioxane-4,6-dione (MPD) for hydrazine detection through a nucleophilic addition reaction was developed. MPD could exclusively identify hydrazine through colorimetric and fluorescent dual-channel responses within 30 s, which also demonstrated high sensitivity (detection limit, 12 nM) and a wide pH range (6 -12). The sensing mechanism of MPD was confirmed using theoretical calculations, where fluorescence was emitted following the recognition of hydrazine because of the disappearance of the photoinduced electron transfer (PET) process. Using a smartphone, MPD enabled the quantitative detection of hydrazine in real water samples and sandy soil. Notably, in the process of detecting hydrazine in actual water samples, the establishment of analytical methods and the completion of rapid quantitative detection only required a smartphone and built-in apps. Additionally, we showed that MPD could recognize hydrazine in various environmental samples, including plants, food, hydrazine vapors, and cells. We believe that the fluorescent probe MPD developed in this study and the established smartphone visualization platform will provide a convenient and effective tool for detecting hydrazine in environmental monitoring, food safety assessment, biological system safety, and other fields.

A versatile fluorescent probe for the ratiometric detection of hydrazine (N2H4) in water, soil, plant, and food samples

Hydrazine (N2H4) is a crucial chemical raw material extensively utilized in chemical production. However, due to its volatility, water solubility, and high toxicity, both the gaseous form and aqueous solution of N2H4 pose significant environmental risks by causing severe pollution that can adversely impact plants, microorganisms, and human health. Therefore, accurate detection of N2H4 in the environment is imperative for safeguarding public health. In this study, we synthesized a ratiometric fluorescent probe (BCaz-Cy2) based on Carbazole and Hemicyanine groups. This probe exhibits simple synthesis procedure, rapid response time, high sensitivity and selectivity as well as remarkable detection signals. It enables effective detection of N2H4 in various matrices such as water, food, soil and plant samples thereby significantly expanding the scope of applications for N2H4 probes.

An AIE-active tetra-aryl imidazole-derived chemodosimeter for turn-on recognition of hydrazine and its bioimaging in living cells

A new chemodosimeter SWJT-31 with an aggregation-induced emission (AIE) effect was designed and constructed. Upon increasing the water fraction in the solution, it exhibited typical AIE, which showed bright red fluorescence at 610 nm. SWJT-31 could sensitively and specifically recognize hydrazine by the TICT effect with an LOD of 33.8 nM, which was much lower than the standard of the USEPA. A portable test strip prepared using SWJT-31 was also developed for the visual detection of hydrazine. Eventually, it was successfully used for the detection of hydrazine in water samples and HeLa cells.

Fluorescence Recognition of Hydrazine Driven by Neighboring Group Participation

Hydrazine (N2H4) has toxic effects on the environment. Although a variety of reactive probes have been used to identify hydrazine, practical applications required continuous development of hydrazine fluorescent probes with improved performance. Here, we applied the neighboring group participation (NGP) to the design of a fluorescent probe for hydrazine. The probe exhibited a rapid response to N2H4 and strong anti-interference ability, with detection limited to 0.031 μmol/L. Theoretical calculation showed that the energy barrier could be reduced by NGP. The cyclic intermediate formed by the indole ring and the α-ester carbonyl group significantly reduced the activation energy of the reaction. Practically, the probe could detect hydrazine in actual water samples.

A fluorescent probe based on cyclochalcone for detecting peroxynitrite

A novel cyclic chalcone fluorescent probe C-PN was synthesized to detect ONOO-. After reaction with peroxynitrite, the double bond of C-PN in the cyclic chalcone structure was disconnected, which caused the change of intramolecular charge transfer (ICT) effect, emitting blue fluorescence and quenching orange red fluorescence. Visible to the naked eye, the color of the probe solution changed. The probe showed low sensitivity (detection limit = 20.2 nm), short response time (less than 60 s) at low concentration of ONOO-, good visibility, and good selectivity and stability for ONOO-.

A near-infrared fluorescent ratiometric probe with large Stokes shift for multi-mode sensing of Pb2+ and bioimaging

Pb2+ is a heavy metal ion pollutant that poses a serious threat to human health and ecosystems. The conventional methods for detecting Pb2+ have several limitations. In this study, we introduce a novel fluorescent probe that enables the detection of Pb2+ in the near-infrared region, free from interference from other common ions. A unique characteristic of this probe is its ability to rapidly and accurately identify Pb2+ through ratiometric measurements accompanied by a large Stokes shift of 201 nm. The limit of detection achieved by probe was remarkably low, surpassing the standards set by the World Health Organization, and outperforming previously reported probes. To the best of our knowledge, this is the first organic small-molecule fluorescent probe with both near-infrared emission and ratiometric properties for the detection of Pb2+. We present a triple-mode sensing platform constructed using a probe that allows for the sensitive and selective recognition of Pb2+ in common food items. Furthermore, we successfully conducted high-quality fluorescence imaging of Pb2+ in various samples from common edible plants, HeLa cells, Caenorhabditis elegans, and mice. Importantly, the probe-Pb2+ complex exhibited tumour-targeting capabilities. Overall, this study presents a novel approach for the development of fluorescent probes for Pb2+ detection.

Converging optical and electrochemical detection strategies for multimodal hydrazine sensing: insights into substituent-driven diverse response

A pair of pyrene-based chalcogen derivatives have been developed, which demonstrate multimodal ratiometric response towards hydrazine. Although these probes share a common pyrene core and differ primarily in the electronic nature of their terminal side arms, they display distinct photophysical properties. Notably, both probes undergo significant spectral changes upon the addition of hydrazine, but probe 1 exhibits a more pronounced interaction (∼5-fold fluorescence enhancement) than probe 2, attributed to the higher level of aggregation in probe 2, rendering the binding site less accessible to the incoming analyte. Additionally, we have explored electrochemical techniques, including cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), for hydrazine detection. Our molecular design strategy relies on ratiometric-responsive specific cyclization triggered by hydrazine, leading to the disruption of the π-conjugated system and the subsequent suppression of intramolecular charge transfer (ICT) processes, along with dis-assembly of the aggregated probe molecules. These probes enable the nakеd-eye detection of hydrazine, with a low detection limit of 7.33 ppb and 7.58 ppb for probe 1 and 2, respectively. Furthermore, we have investigated cost-effective probe-coatеd paper strips for the detection of hydrazine in water.

Near-Infrared Catalytic Chemiluminescence System based on Zinc Gallate Nanoprobe for Hydrazine Sensing

To the deep tissue penetration and ultra-low background, developing near-infrared (NIR) chemiluminescence probes for human health and environmental safety has attracted more and more attention, but it remains a huge challenge. Herein, a novel NIR chemiluminescence (CL) system was rationally designed and developed, utilizing Cr3+-activated ZnGa2O4 (ZGC) nanoparticles as a catalytic luminophore via hypochlorite (NaClO) activation for poisonous target (hydrazine, N2H4) detection. With superior optical performance and unique catalytic structure of ZGC nanoparticles, the fabricated ZGC-NaClO-N2H4 CL system successfully demonstrated excellent NIR emission centered at 700 nm, fast response, and high sensibility (limit of detection down to 0.0126 μM). Further experimental studies and theoretical calculations found the cooperative catalytic chemiluminescence resonance energy transfer mechanism in the ZGC-NaClO-N2H4 system. Remarkably, the ZGC-based NIR CL system was further employed for N2H4 detection in a complicated matrix involving bioimaging and real water samples, thereby opening a new way as a highly reliable and accurate tool in biomedical and environmental monitoring applications.

Phenothiazine-based fluorescent probes for the detection of hydrazine in environment and living cells

As an important chemical raw material, hydrazine brings convenience to people's lives and provides opportunities for human development. However, the misuse or leakage of hydrazine has brought pollution to the environment, including water, soil and living organisms. At the same time, hydrazine poses a potential threat to human health as a carcinogen. Despite the enormous challenges, it is crucial to develop an effective method to detect hydrazine in environmental samples. In this work, we have synthesized a series of probes based on phenothiazine fluorophore by the introduction of different substituents and developed a novel probe for the detection of hydrazine. The probe is capable of detecting hydrazine in aqueous solutions with high sensitivity and selectivity, and can be easily fabricated into paper test strips for use in in situ samples. In addition, the probe is effective in detecting hydrazine in water, soil, cells, and zebrafish, providing an excellent tool for detecting hydrazine in the environment.

Development of Human Serum Albumin Fluorescent Probes in Detection, Imaging, and Disease Therapy

Human serum albumin (HSA) acts as a repository and transporter of substances in the blood. An abnormal concentration may indicate the occurrence of liver- and kidney-related diseases, which has attracted people to investigate the precise quantification of HSA in body fluids. Fluorescent probes can combine with HSA covalently or noncovalently to quantify HSA in urine and plasma. Moreover, probes combined with HSA can improve its photophysical properties; probe-HSA has been applied in real-time monitoring and photothermal and photodynamic therapy in vivo. This Review will introduce fluorescent probes for quantitative HSA according to the three reaction mechanisms of spatial structure, enzymatic reaction, and self-assembly and systematically introduce the application of probes combined with HSA in disease imaging and phototherapy. It will help develop multifunctional applications for HSA probes and provide assistance in the early diagnosis and treatment of diseases.

A Ratiometric Fluorescent Probe for N2H4 Having a Large Detection Range Based upon Coumarin with Multiple Applications

Although hydrazine (N2H4) is a versatile chemical used in many applications, it is toxic, and its leakage may pose a threat to both human health and environments. Consequently, the monitoring of N2H4 is significant. This study reports a one-step synthesis for coumarin-based ratiometric fluorescent probe (FP) CHAC, with acetyl as the recognition group. Selected deprotection of the acetyl group via N2H4 released the coumarin fluorophore, which recovered the intramolecular charge transfer process, which caused a prominent fluorescent, ratiometric response. CHAC demonstrated the advantages of high selectivity, a strong capacity for anti-interference, a low limit of detection (LOD) (0.16 μM), a large linear detection range (0-500 μM), and a wide effective pH interval (6-12) in N2H4 detection. Furthermore, the probe enabled quantitative N2H4 verifications in environmental water specimens in addition to qualitative detection of N2H4 in various soils and of gaseous N2H4. Finally, the probe ratiometrically monitored N2H4 in living cells having low cytotoxicity.

Hydrazone-Based Amphiphilic Brush Polymer for Fast Endocytosis and ROS-Active Drug Release

Due to the high reactivity of reactive oxygen species (ROS), it is essential to sweep them away in time. In this study, ClO--responsible amphiphilic brush polymers were prepared by free radical polymerization using two monomers consisting of polyethylene glycol as the hydrophilic part, and an alkyl chain connected by hydrazone as the hydrophobic part. The macromolecules assemble into particles with nanoscaled dimensions in a neutral buffer, which ensures quick cellular internalization. The polymer has a low critical micellization concentration and can encapsulate hydrophobic drug molecules up to 19% wt. The micelles formed by the polymer disassemble in a ClO--rich environment and release 80% of their cargo within 2 h, which possesses a faster release rate compared to the previous systems. The relatively small size and the quick response of hydrazone toward ClO- ensure a quick uptake and elimination of ROS in vitro and in vivo.

Broad-Specificity Screening of Pyrethroids Enabled by the Catalytic Function of Human Serum Albumin on Coumarin Hydrolysis

Sensing systems based on cholinesterase and carboxylesterase coupled with different transduction technologies have emerged for pesticide screening owing to their simple operation, fast response, and suitability for on-site analysis. However, the broad spectrum and specificity screening of pyrethroids over organophosphates and carbamates remains an unmet challenge for current enzymatic sensors. Human serum albumin (HSA), a multifunctional protein, can promote various chemical transformations and show a high affinity for pyrethroids, which offer a route for specific and broad-spectrum pyrethroid screening. Herein, for the first time, we evaluated the catalytic hydrolysis function of human serum albumin (HSA) on the coumarin lactone bond and revealed that HSA can act as an enzyme to catalyze the hydrolysis of the coumarin lactone bond. Molecular docking and chemical modifications indicate that lysine 199 and tyrosine 411 serve as the catalytic general base and contribute to most of the catalytic activity. Utilizing this enzymatic activity, a broad specific ratiometric fluorescence pyrethroids sensing system was developed. The binding energetics and binding constants of pesticides and HSA show that pyrethroids bind to HSA more easily than organophosphates and carbamates, which is responsible for the specificity of the sensing system. This study provides a general sensor platform and strategy for screening pesticides and reveals the catalytic activity of HSA on the hydrolysis of the coumarin lactone bond, which may open innovative horizons for the chemical sensing and biomedical applications of HSA.

A dual-responsive fluorescent turn-on sensor for sensitively detecting and bioimaging of hydrazine and hypochlorite in biofluids, live-cells, and plants

Hydrazine (N₂H₄) and hypochlorite (ClO^-) are extremely harmful to the public health, so it is vitally necessary to detect them in living system. Herein, we developed a new phenthiazine-thiobarbituric acid based dual-analyte responsive fluorescent sensor PT for visually distinguishing and detecting N₂H₄ and ClO^-. PT underwent N₂H₄/ClO^--induced CC breakage, achieving olive-drab/brilliant green fluorescence lighting-up response towards N₂H₄/ClO^- with superb specifity, ultra-sensitivity (detection limit: 15.4 nM for N₂H₄, 13.7 nM for ClO^-), and ultra-fast response (N₂H₄: <15 s, ClO^-: <20 s). The mechanisms for sensing N₂H₄ and ClO^- were investigated with support of spectral measurements and DFT investigation. Sensor based paper-strip/silica-gel device was developed for in-field supervision and on-site monitoring of gaseous and aqueous N₂H₄ and ClO^- solution. In addition, the PT was also applied for quantitatively detecting N₂H₄ and ClO^- in soil, food, plants and bio-fluids. Moreover, PT was utilized to visualize exogenous N₂H₄ and ClO^- in living plants and live-cells, demonstrating this sensor utilized as a powerful tool to detect N₂H₄ and ClO^- in biological fields.