A novel coumarin-based fluorescent probe with fine selectivity and sensitivity for hypochlorite and its application in cell imaging

Ratiometric fluorescent probe with AIE characteristics for hypochlorite detection and biological imaging

It is very important and highly valuable to detect ClO- in samples and living cells with accuracy and speed. In this work, a novel fluorescent probe NA was prepared from 4-bromo-1,8-naphthalic anhydride by acylation reaction and Suzuki coupling reaction and used for the detection of ClO-. Thiomethyl serves as the recognition group for probe NA, while naphthalimide serves as fluorescent chromophore. The probe exhibited an extremely pronounced blue shift from yellow to blue fluorescence within 1 min after the addition of hypochlorite (ClO-). The probe demonstrates high sensitivity to ClO- with a limit of detection (LOD) of 1.22 µM. Also, probe NA demonstrates excellent selectivity and immunity to interference. Additionally, simple fluorescent test strips containing probe NA were prepared in this study, enabling rapid detection of ClO- in water samples. And NA had been effectively used to image endogenous and exogenous ClO-fluorescence in living cells. The results suggest that probe NA has significant potential for portable detection and biological applications.

A new FRET-based fluorescent probe: Colorimetric and ratiometric detection of hypochlorite and anti-counterfeiting applications

Hypochlorite (ClO-), as the main component of widely used disinfectants in daily life, comes into closer contact with the human body, which can lead to a number of diseases. The high-performance method is increasingly needed to detect ClO- in our daily life. In this report, we successfully synthesized a FRET ratiometric fluorescent probe (NDAC) containing benzoxadiazole moieties and coumarin moieties bound via ethylenediamine. As expected, NDAC has excellent selectivity and anti-interference ability toward ClO-, and the ratio of fluorescence intensity (I471 nm/I533 nm) has a very good linear relationship with the concentration of ClO-, with a wide linear range (2.5-1750 μM) and low detection limit (0.887 μM). Furthermore, we have successfully applied it for the quantitative detection of ClO- in water samples in daily life. At the same time, there is a very clear change in the fluorescence color after the reaction of the NDAC with ClO-. The blue/green value (B/G) of this color change also shows a very good linear relationship to ClO- (5.0-1000 μM). Therefore, the NDAC has also been successfully used for test strip detection and quantitative detection of ClO- in actual samples through smartphone-based fluorescence image analysis, and this method can provide faster, more convenient and more accessible detection. In addition, NDAC sensors also have potential applications in the field of information anti-counterfeiting.

Ex Tenebris Lux: Illuminating Reactive Oxygen and Nitrogen Species with Small Molecule Probes

Reactive oxygen and nitrogen species are small reactive molecules derived from elements in the air─oxygen and nitrogen. They are produced in biological systems to mediate fundamental aspects of cellular signaling but must be very tightly balanced to prevent indiscriminate damage to biological molecules. Small molecule probes can transmute the specific nature of each reactive oxygen and nitrogen species into an observable luminescent signal (or even an acoustic wave) to offer sensitive and selective imaging in living cells and whole animals. This review focuses specifically on small molecule probes for superoxide, hydrogen peroxide, hypochlorite, nitric oxide, and peroxynitrite that provide a luminescent or photoacoustic signal. Important background information on general photophysical phenomena, common probe designs, mechanisms, and imaging modalities will be provided, and then, probes for each analyte will be thoroughly evaluated. A discussion of the successes of the field will be presented, followed by recommendations for improvement and a future outlook of emerging trends. Our objectives are to provide an informative, useful, and thorough field guide to small molecule probes for reactive oxygen and nitrogen species as well as important context to compare the ecosystem of chemistries and molecular scaffolds that has manifested within the field.

A novel thienothiophene-based "dual-responsive" probe for rapid, selective and sensitive detection of hypochlorite

BACKGROUND

Hypochlorite/hypochlorous acid (ClO-/HOCl) is a biologically crucial reactive oxygen species (ROS), produced in living organisms and has a critical role as an antimicrobial agent in the natural defense system. However, when ClO- is produced excessively, it can lead to the oxidative damage of biomolecules, resulting in organ damage and various diseases. Therefore, it is imperative to have a straightforward, quick and reliable method for over watching the minimum amount of ClO- in different environments.

RESULTS

Herein, a new probe TTM, containing thienothiophene and malononitrile units, was developed for exceptionally selective and sensitive hypochlorite (ClO-) detection. TTM demonstrated a rapid "turn-on" fluorescence response (<30 s), naked-eye detection (colorimetric), voltammetric read-out with anodic scan, low detection limit (LOD = 0.58 μM and 1.43 μM for optical and electrochemical methods, respectively) and applicability in detecting ClO- in real water samples and living cells.

SIGNIFICANCE AND NOVELTY

This study represents one of the rare examples of a small thienothiophene-based molecule for both optical and electrochemical detections of ClO- in an aqueous medium.

A new turn-on fluorescent probe for fast detection of diabetic biomarker beta-hydroxybutyrate in vitro

Beta-hydroxybutyrate (β-HB) serve as a valuable diagnostic biomarker for Diabetic Ketoacidosis (DKA). Here, a new Schiff base fluorescent probe T was designed and synthesized to detect β-HB level in aqueous solution in vitro. The probe T can detect β-HB sensitively and selectively in DMF solution (5.0 × 10-5 M) among other interfering species (cations, anions, amino acids, biomarkers). The detection limit of probe T for β-HB was calculated to be 0.154 μM. These results demonstrate that the probe T may provide a convenient method for rapid detection of β-HB to diagnose diabetic ketoacidosis.

A deep-red xanthene-based highly sensitive fluorescent probe for detection of hypochlorite

As an oxidant, deodorant and bleaching agent, the hypochlorous acid (HClO) and hypochlorite (ClO- ) are widely used in corrosion inhibitors, textile dyes, pharmaceutical intermediates and in our daily lives. However, excess usage or aberrant accumulation of ClO- leads to tissue damage or some diseases and even cancer. Therefore, it is necessary to develop a fluorescent probe that specifically identifies ClO- . In this article, we synthesized a deep-red xanthene-based fluorescent probe (XA-CN). The strong electron deficient group dicyano endows the probe XA-CN deep-red fluorescent emission with high solubility, selectivity and sensitivity for ClO- detection. Studies showed that the probe demonstrated turn-off fluorescence (643 nm) at the presence of ClO- in dimethylsulfoxide/phosphate-buffered saline 1:1 (pH 9) solution with a limit of detection of 1.64 μM. Detection mechanism investigation revealed that the electron deficient group -CN and the hydroxyl group was oxidized into aldehyde or carbonyl groups at the presence of ClO- , resulting ultraviolet-visible absorption of the probe blue shifted and turned-off fluorescence. Furthermore, XA-CN was successfully used for the detection of ClO- in tap water samples.

Two smart coumarin-based fluorescent probes with AIE effect for sensing ClO- and imaging in living cells

It's worth noting that detect effective methods for tracking ClO^- could help us uncover the function of ClO^- in living systems. Here, two coumarin-based probes, named (E)-3-(1-hydrazonoethyl)-2H-chromen-2-one (1A) and 3-((E)-1-(((E)-(2,3-dihydro-1H-imidazol-4-yl)methylene)-hydrazono)ethyl)- 2H-chromen-2-one (1B) with aggregation-induced emission (AIE) effect in Tris-HCl (pH = 7.2) buffer solution were synthesized and used for sensing ClO^- selectivity. 1A and 1B responded to ClO^- through the oxidation hydrolysis effect. The mechanism was further verified by HR-MS and DFT calculation. Cell imaging indicated that 1A and 1B were good membrane permeability with low toxicity to HEK293T, and expected to be used to detect ClO^- in cells.

A Hydroxytricyanopyrrole-Based Fluorescent Probe for Sensitive and Selective Detection of Hypochlorous Acid

Hypochlorous acid (HOCl) is a reactive substance that reacts with most biomolecules and is essential in physiological and pathological processes. Abnormally elevated HOCl levels may cause inflammation and other disease responses. To further understand its key role in inflammation, HOCl must be detected in situ. Here, we designed a hydroxytricyanopyrrole-based small-molecule fluorescent probe (HTCP-NTC) to monitor and identify trace amounts of HOCl in biological systems. In the presence of HOCl, HTCP-NTC released hydroxyl groups that emit strong fluorescence covering a wide wavelength range from the visible to near-infrared region owing to the resumption of the intramolecular charge transfer process. Additionally, HTCP-NTC demonstrated a 202-fold fluorescence enhancement accompanied by a large Stokes shift and a low detection limit (21.7 nM). Furthermore, HTCP-NTC provided a rapid response to HOCl within 18 s, allowing real-time monitoring of intracellular HOCl. HTCP-NTC exhibited rapid kinetics and biocompatibility, allowing effective monitoring of the exogenous and endogenous HOCl fluctuations in living cells. Finally, based on fluorescence imaging, HTCP-NTC is a potential method for understanding the relationship between inflammation and HOCl.

A novel and fast-responsive two-photon fluorescent probe with modified group for monitoring endogenous HClO accompanied by a large turn-on signal and its application in zebrafish imaging

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.

An AIE based fluorescent chemosensor for ratiometric detection of hypochlorous acid and its application

Detecting and imaging intracellular hypochlorous acid (HClO) is of great importance owning to its prominent role in numerous pathological and physiological processes. In this contribution, a novel AIE-based fluorescent chemosensor has been developed by employing a benzothiazole derivative. The synthesized probe displayed remarkable ratiometric fluorescent response to HClO with a large emission shift (139 nm), resulting in naked-eye fluorescence changes from red to blue. Under the optimal conditions, this probe was capable of quantitatively detecting HClO within 10 s, and possessed good sensitivity and high selectivity toward HClO over other biologically relevant species. Moreover, it has been successfully utilized to image the exogenous and endogenous HClO in living cells through dual channels, and conveniently detect hypochlorous acid solution on test strips with better accuracy, demonstrating its potential for monitoring HClO in biological and environment fields.

Comparative studies on the absorption and fluorescence responses of hemicyanine to HSO3-, CN-, HS- and ClO. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2022;269:120781. [PMID: 34968839 DOI: 10.1016/j.saa.2021.120781]

A fluorescent probe Hcy-Im bearing an indolium-hemicyanine structure was designed and synthesized to compare its responses to four anions, namely HSO₃^-, CN^-, HS^- and ClO^-. The results disclosed that Hcy-Im reacted with all these four anions in 5% DMSO-PBS buffer with different speeds and spectral changes. Hcy-Im responded to HSO₃^- markedly quicker than CN^- and HS^-, and it responded to CN^- a little quicker than HS^- while the response to ClO^- was much slower than the other three anions. The detection limits for these four anions were calculated to be 0.15 μM, 1.32 μM, 2.07 μM and 2.29 μM, respectively. The characteristic conjugated CN⁺ and CC bonds in Hcy-Im were responsible for the responses towards these four anions via a Michael addition-rearrangement reaction, a 1, 2-addition reaction or an oxidation reaction. These different sensing mechanisms were verified by ¹HNMR and HRMS. Thus, it could be inferred that hemicyanine-based fluorescent probe could detect HSO₃^- sensitively and selectively while the interference of HSO₃^- should not be neglected when it was used for the detection of CN^-, HS^- and ClO^-. Moreover, as HSO₃^-, HS^- and ClO^- are anions endogenously generated in human bodies, enough attention should be paid to the presence of physiological level of these three anions in certain tissues when hemicyanine-based fluorescent probe is applied for the detection of biorelevant analytes in biological samples.

A simple sensitive ratiometric fluorescent probe for the detection of mercury ions in living cells and zebrafish

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 Hg²⁺ (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.

The development of a highly selective fluorescent probe for the rapid detection of HClO in living cells and zebrafish

A new turn-on fluorescent probe, BM-HA, for the rapid detection of HClO in living cells and zebrafish is proposed, and DFT/TDDFT calculations provide insights into the optical properties of the BM-HA probe.

Recent development of synthetic probes for detection of hypochlorous acid/hypochlorite

Hypochlorous acid/hypochlorite (HOCl/OCl^-), as one of the most important reactive oxygen species (ROS), plays an important role in various physiological and pathological processes. Nonproperly located or abnormal concentration of OCl^-, however, is associated with many diseases. Thus, developing the fluorescent probe for detecting OCl^- is of great significance. To this end, in last decade, many fluorescent probes have been developed and applied for detecting HOCl/OCl^- in vitro and in vivo. Despite a great progress has achieved, the development and application of near-infrared fluorescent HOCl/OCl^- probe still have some challenges. For example, highly specific and sensitive NIR fluorescent HOCl/OCl^- probes applied in endogenous OCl^- detection and subcellular organelle bioimaging. In this review, we summarized the representative cases of HOCl/OCl^- probes with properties that mentioned above. The discussion contains design strategies, detection mechanisms, as well as applications in bioimaging.

A mitochondria-specific fluorescent probe for rapidly assessing cell viability

Rapid detection of cell viability is of importance for various aspects of basic and applied research. However, the most commonly used MTT assay suffers from some disadvantages of time-consuming, poor solubility of formazan crystals, and interference of cell extracts, resulting in either delayed results or inconsistent cell viability. Accumulating evidences show that mitochondrial activity is closely associated with cell proliferation and apoptosis, making it valuable for real-time monitoring of cell fates. Herein, we present a novel type of cell-permeant mitochondrial dyes, composed of coumarin-quinoline conjugates (CQCs), for assessing cell viability through monitoring mitochondrial dynamic changes. CQCs exhibited superior preference for mitochondria, and could sensitively monitor their fissions under pathological conditions. Particularly, CQCs could accurately assess the cell viability within 10 min, allowing for rapidly evaluating therapeutic effects with high sensitivity and accuracy, in comparison of MTT assay. Therefore, CQCs provide a proof-of-concept assay that is appropriately practical either independently or in complementation with other assays for the analysis of cellular viability in broad range of biomedical applications.

Ultrasensitive and specific two-photon fluorescence detection of hypochlorous acid by a lysosome-targeting fluorescent probe for cell imaging

Hypochlorous acid (HOCl) is involved in numerous cellular processes, such as pathogen response, immune regulation, and anti-inflammation. Consequently, the development of HOCl detection at the cellular level has been an important issue in investigating the dynamic distributions of HOCl. Herein, a fluorescent probe, Lyso-NA, containing a HOCl-reactive aminophenol group and a lysosomal-targeting morpholine group, has been effectively designed for detecting lysosomal HOCl. The reaction of Lyso-NA with HOCl induces the oxidation of aminophenol and accompanied by a 136-fold fluorescence enhancement. The detection limit is found at 13 nM. The fluorescence enhancement is accomplished through the suppression of twisted intramolecular charge transfer (TICT). With morpholine, the probe Lyso-NA shows the great lysosomal targetable ability for imaging endogenous lysosomal HOCl in living cells and tissues by two-photon microscopy, providing an opportunity to monitor HOCl in the lysosomes for understanding its biological functions.

Overview on developed synthesis procedures of coumarin heterocycles

Considering highly valuable biological and pharmaceutical properties of coumarins, the synthesis of these heterocycles has been considered for many organic and pharmaceutical chemists. This review includes the recent research in synthesis methods of coumarin systems, investigating their biological properties and describing the literature reports for the period of 2016 to the middle of 2020. In this review, we have classified the contents based on co-groups of coumarin ring. These reported methods are carried out in the classical and non-classical conditions particularly under green condition such as using green solvent, catalyst and other procedures.

Developed a novel quinazolinone based turn-on fluorescence probe for highly selective monitoring hypochlorite and its bioimaging applications

A novel quinazolinone based turn-on fluorescence probe for sensitive monitoring hypochlorite was prepared using the mild condensation reaction between 2-(2'-hydroxyphenyl)-4(3H)-quinazolinone derivative and 4-methylbenzenesulfonyl hydrazide. The probe exhibited specific selectivity to ClO^- with obvious optical signal changes from weak fluorescence at 560 nm to a strong fluorescence emission at 520 nm and color changes from colorless to yellow, which could be noticed by the naked eye. The detection limit toward hypochlorite is as low as 11.4 nM. Moreover, the probe could sensitively response to ClO^- in living cells with satisfying imaging effect and has been successfully applied to the determination of ClO^- in practical water samples, which indicated that the probe has certain application potential for hypochlorite monitoring.

A mitochondria-targeted fluorescent probe based on coumarin-pyridine derivatives for hypochlorite imaging in living cells and zebrafish

Hypochlorite plays a critical role in various physiological processes and is involved in many diseases. Thus, real-time, rapid, and accurate monitoring of hypochlorite has important medical and physiological significance. Herein, a novel coumarin-pyridine derivative (CPD) probe was designed and synthesized, which exhibited fantastic advantages, such as a rapid response (within 10 s), naked eye recognition, large Stokes shift (185 nm), dual-channel detection, and high selectivity and sensitivity toward OCl^- (detection limit 0.012 μM, S/N = 3). Furthermore, the current CPD probe was successfully used to image OCl^- in the mitochondria of both A549 cells and zebrafish, which further demonstrated its suitability for practical applications in biological systems.