A mitochondria-targeted fluorescent probe for ratiometric detection of hypochlorite in living cells

Detection and application of hypochlorous acid in both aqueous environments and living organisms

The scarcity of water resources has raised concerns regarding drinking water safety. Excessive addition of hypochlorous acid (OCl-) as a disinfectant in drinking water can result in severe consequences. Moreover, abnormal levels of OCl- within the human body can lead to various diseases. Employing fluorescence analysis, the design and synthesis of specific fluorescent probes for simultaneous detection of OCl- in water environments and living organisms holds strategic significance in ensuring the safety of drinking water and mitigating potential risks caused by its abnormal concentrations. This article utilizes naphthalimide as a precursor to develop a novel probe enabling highly sensitive detection of OCl- in water environments and at the organelle level within living organisms. This endeavor serves to provide assurance for drinking water safety and offers health alerts.

A novel diarylethene-based fluorescence sensor for Zn2+ detection and its application

A series of fluorometric sensors of Zn2+ have been synthesized due to the significant function of Zn2+ in the human body and environment. However, most of probes reported for detecting Zn2+ have high detection limit or low sensitivity. In this paper, an original Zn2+ sensor, namely 1o, was synthesized by diarylethene and 2-aminobenzamide. When Zn2+ was added, the fluorescence intensity of 1o increased by 11 times within 10 s, along with a fluorescence color change from dark to bright blue, and the detection limit (LOD) was calculated to be 0.329 μM. According to Job's plot curves, the binding mode of 1o and Zn2+ was measured as 1:1, which was further proved by 1H NMR spectra, HRMS and FT-IR spectra. The logic circuit was designed to take advantage of the fact that the fluorescence intensity of 1o can be controlled by Zn2+, EDTA, UV and Vis. In addition, Zn2+ in actual water samples were tested, in which the recovery rate of Zn2+ was between 96.5 % and 109 %. Furthermore, 1o was successfully made into a fluorescent test strip, which could be used to detect Zn2+ in the environment economically and conveniently.

A long-wavelength mitochondria-targeted fluorescent probe for imaging of peroxynitrite during dexamethasone treatment

Peroxynitrite (ONOO^-), as a strong oxidizing reactive nitrogen substance (RNS), is generated endogenously by cells. Its visualization research is crucial to understand relevant disease processes. Herein, we reported a long-wavelength mitochondria-targeted fluorescence "turn on" probe TL. The probe TL could react with ONOO^- by using 4-(Bromomethyl)benzeneboronic as a reactive site, which exhibited outstanding characteristics for detection of ONOO^-, thus improving response time (about 50 s), sensitivity (DL, 10.1 nM), and emission wavelength (667 nm). Besides, TL displayed well mitochondria targeting and biological visualizing of exogenous and endogenous ONOO^- in biological systems. Finally, TL was used to monitor high concentration of dexamethasone-induced an up-regulation of ONOO^-. This indicated that TL has excellent potential to study the fluctuation of ONOO^- in the physiological and pathological system.

A turn-on fluorescent probe based on ESIPT and AIEE mechanisms for the detection of butyrylcholinesterase activity in living cells and in non-alcoholic fatty liver of zebrafish

Butyrylcholinesterase (BChE) and acetylcholinesterase (AChE) are two important cholinesterase enzymes in human metabolism which are closely related to various diseases of the liver. BChE and AChE are difficult to be distinguished due to their similarity in biochemical properties. Therefore, developing BChE-specific probes with high sensitivity and low background reading is desirable for the relevant biological applications. Herein, we reported the design and synthesis of a fluorescent probe HBT-BChE for biological detection and imaging of BChE. The probe is triggered by BChE-mediated hydrolysis, releasing a fluorophore that holds AIEE and ESIPT properties with large Stokes shift (>100 nm), rendering the probe features of low background interference and high sensitivity. The probe can also distinguish BChE from AChE with a low detection limit of 7.540 × 10^-4 U/mL. Further in vitro studies have shown the ability of HBT-BChE to detect intracellular BChE activity, as well as to evaluate the efficiency of the BChE inhibitor. More importantly, the in vivo studies of imaging the BChE activity level in liver tissues using zebrafish as the model animal demonstrated the potential of HBT-BChE as a powerful tool for non-alcoholic fatty liver disease.

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.

An 'AND'-based ratiometric fluorescence probe for the sequential detection of biothiols and hypochlorous acid

An 'AND'-based ratiometric fluorescence probe for the sequential detection of biothiols and hypochlorous acid was developed. FRET was observed only when RSHClO reacted with biothiols before reacting with hypochlorous acid, a phenomenon that has been confirmed in aqueous solutions and cells. This feature enables the probe to mimic biological processes and is particularly suitable for imaging oxidizing and reducing substances that cannot coexist.

Rational construction of deep-red fluorescent probe for rapid detection of HClO and its application in bioimaging and paper-based sensing

Hypochlorous acid (HClO), the core bactericidal substance of the human immune system, plays a vital role in many physiological and pathological processes in the human body. In this work, we designed and synthesized a novel deep-red fluorescent probe TCF-ClO for the determination of hypochlorous acid through theoretical analysis. The results showed that probe TCF-ClO exhibited excellent characteristics of long-wavelength emission (635 nm), fast response (< 1 min), and low detection limit (24 nM). In addition, it had been successfully used for imaging of HClO in living HeLa cells. More importantly, the TCF-ClO composited paper-based sensing material was successfully constructed. The RGB/gray value was obtained from a mobile phone and computer, which could achieve the quantitative detection of HClO, with a linear detection range of 0-50 μM and a detection limit of 1.09 μM (RGB mode)/3.38 μM (gray mode). The function of the paper-based sensor extended from qualitative to quantitative detection of HClO, and it is expected to become a portable device widely used in the environmental area.

Synthetic Approaches to Biologically Active C-2-Substituted Benzothiazoles

Numerous benzothiazole derivatives are used in organic synthesis, in various industrial and consumer products, and in drugs, with a wide spectrum of biological activity. As the properties of the benzothiazole moiety are strongly affected by the nature and position of substitutions, in this review, covering the literature from 2016, we focus on C-2-substituted benzothiazoles, including the methods of their synthesis, structural modification, reaction mechanisms, and possible pharmacological activity. The synthetic approaches to these heterocycles include both traditional multistep reactions and one-pot atom economy processes using green chemistry principles and easily available reagents. Special attention is paid to the methods of the thiazole ring closure and chemical modification by the introduction of pharmacophore groups.

Benzothiazole derivatives based colorimetric and fluorescent probes for detection of amine/ammonia and monitoring the decomposition of urea by urease

Amines play critical roles in chemical, agrochemical and pharmaceutical industries. However, volatile amine vapours cause widespread pollution and threaten human health. An efficient, highly sensitive and recyclable sensor for monitoring amine vapours is highly demanded. Typically, 2-(2-hydroxy-5-methyl) benzothiazole (HBT) derivates exhibit excellent aggregation-induced emission (AIE) phenomena in keto form originated from a unique excited-state intramolecular proton transfer (ESIPT) process. In this work, we have designed and synthesized two HBT-based fluorescent probes for ratiometric detection toward amine vapours and ammonia. In addition, the detection limits for ammonia were calculated as 226 ppm and 13 ppm respectively. Additionally, the test strips and electrospinning film dopped with fluorescent probes were utilized to recognize amine vapours and ammonia colorimetric with high sensitivity in solid states. According to the above characteristics, probes could monitor the biological activity of urease conveniently and rapidly.

A deep-red lysosome-targetable fluorescent probe for detection of hypochlorous acid in pure water and its imaging application in living cells and zebrafish

Hypochlorite plays a significant role in physiological processes, particularly regulation of lysosomal functions, and is involved in various diseases. Thus, it is crucial to develop highly sensitive and selective molecule tools to detect HClO in lysosomes. Herein, a novel 2H-benzo[h]chromene-pyridine derivative (1) was synthesized through condensation reaction, which exhibited a notable deep-red emission at 640 nm in pure water. This deep-red emission was specifically quenched by adding ClO^-. The response of probe 1 toward ClO^- was rapid (within 10 s), sensitive (detection limit of 0.012 μM), and effective over a wide range of pH (1.0-12.0). Due to the existence of morpholine as the lysosome-targeting unit, the probe was successfully utilized to monitor lysosomal ClO^-. Moreover, the probe 1 was also applied to detecting ClO^- in zebrafish.

Stimuli-Responsive Zinc (II) Coordination Polymers: A Novel Platform for Supramolecular Chromic Smart Tools

The unique role of the zinc (II) cation prompted us to cut a cross-section of the large and complex topic of the stimuli-responsive coordination polymers (CPs). Due to its flexible coordination environment and geometries, easiness of coordination-decoordination equilibria, "optically innocent" ability to "clip" the ligands in emissive architectures, non-toxicity and sustainability, the zinc (II) cation is a good candidate for building supramolecular smart tools. The review summarizes the recent achievements of zinc-based CPs as stimuli-responsive materials able to provide a chromic response. An overview of the past five years has been organised, encompassing 1, 2 and 3D responsive zinc-based CPs; specifically zinc-based metallorganic frameworks and zinc-based nanosized polymeric probes. The most relevant examples were collected following a consequential and progressive approach, referring to the structure-responsiveness relationship, the sensing mechanisms, the analytes and/or parameters detected. Finally, applications of highly bioengineered Zn-CPs for advanced imaging technique have been discussed.

Progress in Tuning Emission of the Excited-State Intramolecular Proton Transfer (ESIPT)-Based Fluorescent Probes

In this review, we will summarize our recent progress in the design and application of novel organic sensors with emission in the near-infrared region (600-900 nm). By coupling different functional groups with excited-state intramolecular proton transfer (ESIPT) segments, new probes are developed to achieve a large Stokes shift, high sensitivity, and selectivity and to tune the emission toward the near-infrared region. The developed probes exhibit attractive optical properties for bioimaging and environmental science applications. In addition, we further discuss the photophysical properties of ESIPT dyes and how their fluorescence could be affected by structural/environmental factors, which should be considered during the development of robust ESIPT-based fluorescence probes. Their potential applications as imaging reagents are illustrated for intracellular membranes, mitochondria, lysosomes, and some biomolecules.

A highly sensitive, fast responsive and reversible naphthalimide-based fluorescent probe for hypochlorous acid and ascorbic acid in aqueous solution and living cells

It is very important to exploit real-time, ultrasensitive and specific visualization detection methods for hypochlorous acid/hypochlorite (HOCl/ClO^-) in biological systems as they are the guardians of the human immune system against pathogens invasion. In our work, we designed a novel reversible naphthalimide-based fluorescent probe NAP-OH to recognize HClO/ClO^- with a unique selective colorimetric and fluorescent response, a short response time (<8 s) and a high sensitivity (10.3 nM). In addition, NAP-OH exhibits a novel on-off-on fluorescence response to ClO^-/ascorbic acid (AA) with good cycle stability. The fluorescence signal is quenched because HClO/ClO^- oxidizes the subunit of NAP-OH to the segment 2,2,6,6-tetramethyl-1-oxo-piperidinium in NAP-O, which can be reduced by AA with the recovery of fluorescence. Finally, the confocal fluorescence imaging has been performed, which proves that NAP-OH can satisfactorily monitor intracellular endogenous and exogenous HClO/AA redox cycles.

Carbazole-conjugated-coumarin by enone realizing ratiometric and colorimetric detection of hypochlorite ions and its application in plants and animals

Detection of hypochlorite ions (ClO^-) in the organisms is of great significance for finding effective treatments for inflammations and diseases. Recently, fluorescent probes have aroused wide public concern as one of the effective tools for detecting molecules and ions. Nevertheless, due to low sensitivity and poor biocompatibility, the effect of fluorescent probes for biological imaging is still not ideal. For this, we developed a novel ratiometric fluorescent probe, 7-(diethylamino)-3-((E)-3-(9-ethyl-9H-carbazol-3-yl)acryloyl)-2H-chromen-2-one (DCC), which could be used for colorimetric detection of ClO^-. Study showed that, the detection mechanism of DCC is that probe can be rapidly oxidized to an enoic acid by ClO^-, resulting in a series of changes in spectral properties. This mechanism was confirmed experimentally and verified by theoretical calculations. It is worth mentioning that DCC has not only been successfully applied to the detection of exogenous and endogenous OCl^- in living cells, but also used for the detection of ClO^- in zebrafish, and Arabidopsis.

The reduction performance of double bonds regulated by the competition of push-pull electron groups to realize the colorimetric and fluorescence recognition of hypochlorous acid

Based on its reducibility, the double bond can act as a reaction site for hypochlorous acid (HOCl), which had been demonstrated by a great deal of work. Nevertheless, the reactivity is influenced by the adjacent chemical environment. Therefore, in this work, we constructed a probe (QI) by methoxy-substituted quinoline conjugating dicyanoisoflurone, in which dicyano and pyridine N act as electron-withdrawing groups and the methoxy acts as an electron-donating group, to regulate their adjacent C[double bond, length as m-dash]C reactivity. The "push-pull" electron effect between the methoxy group and the pyridine N led to the C[double bond, length as m-dash]C bond being passivated. On the other hand, another C[double bond, length as m-dash]C bond was activated by the strong electron-pulling effect of the dicyano group. Thus, the previously weak intramolecular charge transfer became stronger after the dicyano adjacent to the C[double bond, length as m-dash]C was oxidized by HOCl, and showed a strong emission shifted from 570 to 520 nm along with a color change. The reaction mechanism was verified by mass spectrometry, NMR and theoretical calculation, and further bioimaging demonstrated the practical application of the probe.

A lysosome-targeted ratiometric fluorescent probe with a large blue shift for monitoring hypochlorous acid in living cells and zebrafish

A new phenothiazine derivative as lysosome-targeted fluorescent probe with a large blue-shift (128 nm) for ClO^- detection in a fine ratiometric manner has been designed and synthesized. Probe Lyso-PTB has remarkable fluorescence ratiometric variations (98-fold), low cytotoxicity, rapid response time (50 s) and a low detection limit (23 nM). In particular, the application of Lyso-PTB for ClO^- detection was successfully demonstrated in lysosome and in zebrafish.

Mitochondria-targeting turn-on fluorescent probe for HClO detection and imaging in living cells

Hypochlorous/hypochlorite (HClO/ClO^-), one of the most important signal molecule, plays a crucial role in many cellular signaling pathways. It is reported that the HClO/ClO^- level in mitochondria is important to maintain the normal mitochondrial function. Herein, we present two simple fluorescent probes BAC and mitochondria-targeting fluorescent probe TACB for the detection of ClO^-. Probes BAC &TACB could be sensitively and selectivity detecting ClO^- at the nanomolar levels with the detection limit of 1.64 × 10^-9 M and 9.86 × 10^-8 M, respectively. Additionally, probes BAC &TACB with the response unit of CO moiety could selectively detect ClO^- over other various analytes such as anions, metal ions and OH, ¹O₂, H₂O₂. The response time of probe TACB for ClO^- (<20 s), implying that it could offer a real-time analytical assay of ClO^-. Finally, probe BAC was used for monitoring the ClO^- in HEK293T cells and probe TACB could be utilized to track the fluctuations of exogenous ClO^- levels in the mitochondria of Hela cells.

A naphthalimide-based turn-on fluorescence probe for peroxynitrite detection and imaging in living cells

Peroxynitrite (ONOO⁻) is a potent biological oxidant that plays a significant role in diverse physiological and pathological processes. A novel fluorescent probe HCA-OH was developed for specific and sensitive detection of peroxynitrite, and displayed a significant fluorescence turn-on signal. With low cytotoxicity and good photostability, the probe HCA-OH could be applied in imaging ONOO⁻ distribution in HepG2 cells and live C. elegans in real time. Therefore, the probe can be a promising tool for imaging in vivo.

A novel fluorescent probe HCA-OH was designed for selective detection of peroxynitrite and imaging in HepG2 cells and C. elegans.

An HBT-based fluorescent probe for nitroreductase determination and its application in Escherichia coli cell imaging

HBTPN exhibited excellent performance such as rapid response time, large Stokes shift, good selectivity and sensitivity, and long-wavelength emission.

A lysosome-targetable and ratiometric fluorescent probe for hypochlorous acid in living cells based on a 1,8-naphthalimide derivative

Hypochlorous acid (HClO) is an important reactive oxygen species (ROS) and plays a significant role in living organisms. Highly selective and lysosome-targetable probes for sensing hypochlorous acid are rare. In this article, we designed and prepared a new lysosome-targeting and ratiometric fluorescent probe for monitoring the levels of hypochlorous acid. 4-Aminonaphthalimide was chosen as the fluorescent group and (2-aminoethyl) thiourea group was used as a specific recognition group for HClO. A morpholine unit was employed as a lysosome-targeting group. In the absence of HClO the probe underwent intramolecular charge transfer (ICT) and showed a green emission. When excess HClO is present, the ICT process was interrupted which caused a 57 nm blue-shift of fluorescence emission from 533 nm to 476 nm. The ratiometric fluorescent probe showed outstanding selectivity toward HClO over other various bioactive species. Furthermore, the ratiometric fluorescent probe exhibited rapid response time and ability of working in a wide pH range. The linear response of I_476nm/I_533nm toward HClO was obtained in a concentration range of HClO from 1.0 × 10^-6 to 1.0 × 10^-4 mol·L^-1. The detection limit was estimated to be 8.0 × 10^-7 mol·L^-1 for HClO. Moreover, the probe showed a perfect lysosome-targeting ability, and has been successfully used to the confocal imaging of HClO in lysosomes of HepG2 cells with little cell toxicity. All of such good properties illustrated that it could be applied to determine HClO at lysosomes in living cells.

A HBT-based bifunctional fluorescent probe for the ratiometric detection of fluoride and sulphite in real samples

Based on a core of 2-(benzo[d]thiazol-2-yl)phenol (HBT), a bifunctional ratiometric fluorescent probe, HBT-FS, was constructed for the discriminative detection of fluoride (F^-) and sulphite (SO₃^2-) with high sensitivity and selectivity. HBT-FS itself displayed a green fluorescence with λ_Em^max = 498 nm. The treatment of HBT-FS with F^- resulted in a red fluorescence (λ_Em^max = 634 nm) with a large Stokes shift and a 291-fold enhancement in the ratio of the fluorescence intensity (I_{634 nm}/I_{498 nm}). Upon the addition of SO₃^2-, HBT-FS exhibited a blue fluorescence (λ_Em^max = 371 nm) and the ratiometric fluorescence enhancement was remarkable (9445 folds for I_{371 nm}/I_{498 nm}). HBT-FS was successfully used to qualitatively and quantitatively determine F^- and SO₃^2- in a ratiometric manner in real samples.

A mitochondria-targetable two-photon fluorescent probe with a far-red to near-infrared emission for sensing hypochlorite in biosystems

Hypochlorite (ClO^-), one of reactive oxygen species (ROS), is closely related with many physiological and pathological processes. Especially as one of cellular reactive oxygen species in mitochondria, ClO^- can induce mitochondrial permeability, which leads to apoptosis. Thus, developing an effective method which is able to sense ClO^- in mitochondria is important. Although fluorescent probe has become a powerful tool for imaging ClO^- in mitochondria, most of them suffered from phototoxicity to biosamples, autofluorescence, and photobleaching phenomenon due to their short-wavelength excitations and emissions. Based on advantages of two-photon fluorescent probe and far-red to NIR fluorescent probe, a mitochondria-targetable two-photon fluorescent probe with a turn-on signal in far-red to NIR region, Mito-TP-ClO, was developed for ClO^- in this paper. Mito-TP-ClO is consisted of a triphenylphosphonium cations as a mitochondria-targetable unit and a structure of dibenzoylhydrazine as a response unit to ClO^-. Mito-TP-ClO exhibited a high sensitivity and a high selectivity to ClO^-, with a linear range from 6.0 × 10^-8 to 1.0 × 10^-5 M and a detection limit of 2.5 × 10^-8 M. Due to its large two-photon cross section (267 GM) and far-red to NIR emission, Mito-TP-ClO exhibits excellent performances including low autofluorescence, photostable fluorescence signal, and deep tissue penetration (230 μM). Moreover, Mito-TP-ClO was successfully used to detect endogenous ClO^- in bacteria-infected cells and inflammatory mouse model, which confirmed that Mito-TP-ClO is a powerful tool to monitor ClO^- in mitochondria and study on effects of hypochlorite on mitochondria.

A novel 2,5-bis(benzo[d]thiazol-2-yl)phenol scaffold-based ratiometric fluorescent probe for sensing cysteine in aqueous solution and serum

An efficient and novel 2,5-bis(benzo[d]thiazol-2-yl)phenol scaffold-based ratiometric fluorescent probe BTP-Cys for the sensing of cysteine has been developed. The probe BTP-Cys with acrylates moiety, as recognition site, has been successfully constructed on account of the excited state intramolecular proton transfer (ESIPT) mechanism. Upon the treatment with Cys (0-250 μM), this probe BTP-Cys exhibits a dramatic fluorescent intensity ratios enhancement (from 0.03 to 18.3) and a large emission shift (113 nm). The detection limit of this probe is as low as 3.8 × 10^-7 M. Importantly, the concentration and time dependent of Cys in bovine serum albumin (BSA) has also been measured, indicating that BTP-Cys could be a biocompatible and rapid probe for Cys in vitro.

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

It is necessary to develop simple and highly sensitive methods for the detection of hypochlorous acid (HOCl)/hypochlorite (ClO^-) to ravel its relationship with disease. In this paper, a novel bio-compatible fluorescent (Z)-8-(hydrazonomethyl)-7-hydroxy-4-methyl-2H-chromen-2-one (probe 1b) based on coumarin was synthesized and used for detecting ClO^- in PBS buffer (pH = 7.2, 10 mM, 60% C₂H₅OH). Probe 1b showed a remarkable fluorescence change from yellow to blue with the limit of detection as low as 2.4 × 10^-9 M^-1 when ClO^- was added. The coexisted anions, metal ions and reactive oxygen species (•OH, ¹O₂, H₂O₂, KO₂) showed any competitiveness towards ClO^-. In response to ClO^-, the fluorescence emission intensity of probe 1b was obviously enhanced within 20 s. The mechanism was confirmed by the ESI - MS and density functional theory calculations (DFT) to reveal that the coumarin lactone bonds C - O was cleavaged by oxidation of ClO^-. What's more, probe 1b could be used in practical water samples and showed well recovery. Additionally, the cell imaging experiment was demonstrated that probe 1b could be effectively exploited to imaging exogenous ClO^- in vitro.

A "reactive" turn-on fluorescence probe for hypochlorous acid and its bioimaging application

An aza-BODIPY-CNOH probe attached aldoxime group demonstrated the specific detection for hypochlorous acid by the turn-on red emission signal. NMR and HRMS experiments confirmed that the fluorescence originated from the oxidation degradation of the non-fluorescence, aldoxime-based aza-BODIPY-CNOH probe into the red-fluorescence, nitrile oxide-based aza-BODIPY compound aza-BODIPY-CNO. The aza-BODIPY-CNOH probe showed good biocompatibility and was low toxic to living cells as shown from MTT experiments. Living RAW264.7 cells imaging indicated the aza-BODIPY-CNOH probe had good permeability and either exogenous or endogenous HClO caused the intracellular bright-red fluorescence, showing its potential hypochlorous acid-specific sensing ability in biological systems.

A fast-response and highly specific Si-Rhodamine probe for endogenous peroxynitrite detection in living cells

Peroxynitrite (ONOO⁻) is involved in a variety of physiological and pathological processes.

A highly specific and sensitive turn-on fluorescence probe for hypochlorite detection and its bioimaging applications

A new probe, EDPC, was designed and synthesized for highly specific and sensitive detection of ClO⁻ with a fast response time in living cells.