A highly selective turn-on fluorescent probe for hypochlorous acid based on hypochlorous acid-induced oxidative intramolecular cyclization of boron dipyrromethene-hydrazone

A BODIPY-based fluorescent probe, HBP, was developed for the detection of hypochlorous acid based on the specific hypochlorous acid-promoted oxidative intramolecular cyclization of heterocyclic hydrazone in response to the amount of HOCl. The reaction is accompanied by a 41-fold increase in the fluorescent quantum yield (from 0.004 to 0.164). The fluorescence intensity of the reaction between HOCl and HBP is linear in the HOCl concentration range of 1–8 μM with a detection limit of 2.4 nM (S/N = 3). Confocal fluorescence microscopy imaging using RAW264.7 cells showed that the new probe HBP could be used as an effective fluorescent probe for detecting HOCl in living cells.     

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

A new fl uorescent probe 1 was designed for mitochondrial localization and ratiometric detection of hypochlorite in living cells. It is noteworthy that a high Pearson’s co-localization coeffi cient (Rr) we have obtained was calculated to be 0.97.     

3-羟基邻苯二甲酰亚胺全水溶性次氯酸荧光探针及其应用

利用二甲基硫代氨基甲酸酯对次氯酸(HOCl)的特异性和吡啶盐的水溶性,以4-羟基异苯并呋喃-1,3-二酮作为原料,设计合成了一种检测HOCl的全水溶性激发态分子内质子转移(ESIPT)荧光探针.由于二甲氨基硫代甲酸酯对羟基的保护,探针分子内的ESIPT作用被阻碍,自身无荧光;当加入HOCl时,HOCl氧化二甲氨基硫代甲...     

A Novel Phenoxazine-based Fluorescent Probe for the Detection of HOCl in Living Cells

Hypochlorous acid (HOCl), one of the reactive oxygen species (ROS), is a key microbicidal agent which is used for natural defense. However, it is also linked to varieties of human diseases owing to the overproduction of HOCl. Much effort has been made to exploit selective fluorescent sensors for the detection of HOCl, but most of them have some disadvantages such as short excitation wavelength, low selectivity, and slow response and so on. These restrict the biological application of the probes. In this work, BR-O was designed and synthesized on the base of phenoxazine for the detection of HOCl. BR-O exhibited a violent fluorescence enhancement in the presence of HOCl, showing excellent selectivity and high sensitivity. More importantly, the probe BR-O was capable of detecting exogenous and endogenous HOCl in living cells.     

A Long-wavelength Emissive Phenothiazine Derived Fluorescent Probe for Detecting HOCl Upregulation in 5-FU Stimulated Living Cells

The endogenous hypochlorous acid(HOCl) has been evidenced in a variety of cellular courses. However, the role of HOCl in most pathophysiological processes still keeps unclear because of the limited detecting tools. In this work, we presented the pre- paration of a phenothiazine-derived fluorescent probe ClO-1 for HOCl detection with a cyanopyridinium moiety to improve its water solubility and lengthen its emission wavelength. The HOCl-promoted oxidation of sulfur atom in the probe resulted in a 460-fold emission intensity enhancement at 635 nm with high selectivity and sensitivity(detection limit: 1.12 nmol/L). The rapid response(5 s) also endowed the probe with real-time detection ability. Successfully, ClO-1 was devoted to the bioimaging of endogenous HOCl in inflamed RAW 264.7 cells and 5-fluorouracil-treated MCF-7 cells.     

Responsive Fluorescence Probe for Selective and Sensitive Detection of Hypochlorous Acid in Live Cells and Animals

The development of effective bioanalytical methods for rapid, sensitive and specific detection of HOCl in vitro and in vivo plays a key role for better understanding the roles of this molecule in normal and diseased conditions, but remains challenging due to the highly reactive nature of HOCl and the complicated biological conditions. In this work, a new fluorescence probe, PQI , was developed for monitoring of the HOCl level in biological samples. PQI was easily synthesized by a one‐step condensation reaction. Upon addition of HOCl, significant changes in the absorption spectra and the color of the solution were noticed, facilitating the “naked eye” detection of HOCl in PBS buffer. The fluorescence of PQI was found to be significantly increased within a few seconds, leading to “OFF‐ON” fluorescence response towards HOCl. The sensing mechanism, oxidation of thioether by HOCl, was confirmed by HRMS titration analysis. PQI features a large Stokes shift, high sensitivity and selectivity, and rapid fluorescence response towards HOCl. Quantitative detection of HOCl in single live cells was demonstrated through fluorescence imaging and flow cytometry analysis. PQI was then successfully used in visualisation of HOCl in live zebrafish and nude mice.     

Fluorescent Detection of Hypochlorous Acid from Turn‐On to FRET‐Based Ratiometry by a HOCl‐Mediated Cyclization Reaction

Hypochlorous acid (HOCl), a reactive oxygen species (ROS), plays a significant biological role in living systems. However, abnormal levels of HOCl are implicated in many inflammation‐associated diseases. Therefore, the detection of HOCl is of great importance. In this work, we describe the HOCl‐promoted cyclization of rhodamine‐thiosemicarbazides to rhodamine‐oxadiazoles, which is then exploited as a novel design strategy for the development of a new fluorescence turn‐on HOCl probe 2 . On the basis of the fluorescence resonance energy transfer (FRET) signaling mechanism, 2 was further converted into 1 a and 1 b , which represent the first paradigm of FRET‐based ratiometric fluorescent HOCl probes. The outstanding features of 1 a and 1 b include well‐resolved emission peaks, high sensitivity, high selectivity, good functionality at physiological pH, rapid response, low cytotoxicity, and good cell‐membrane permeability. Furthermore, these excellent attributes enable us to demonstrate, for the first time, the ratiometric imaging of endogenously produced HOCl in living cells by using these novel ratiometric probes. We expect that 1 a and 1 b will be useful molecular tools for studies of HOCl biology. In addition, the HOCl‐promoted cyclization reaction of rhodamine‐thiosemicarbazides to rhodamine‐oxadiazoles should be widely applicable for the development of different types of fluorescent HOCl probes.     

A pinacol boronate caged NIAD-4 derivative as a near-infrared fluorescent probe for fast and selective detection of hypochlorous acid

A pinacol boronate caged NIAD-4 derivative was demonstrated to be a near-infrared fluorescent probe for fast and selective detection of hypochlorite over other ROS species.     

Fluorescent detection of hypochlorous acid from turn-on to FRET-based ratiometry by a HOCl-mediated cyclization reaction

Hypochlorous acid (HOCl), a reactive oxygen species (ROS), plays a significant biological role in living systems. However, abnormal levels of HOCl are implicated in many inflammation-associated diseases. Therefore, the detection of HOCl is of great importance. In this work, we describe the HOCl-promoted cyclization of rhodamine-thiosemicarbazides to rhodamine-oxadiazoles, which is then exploited as a novel design strategy for the development of a new fluorescence turn-on HOCl probe 2. On the basis of the fluorescence resonance energy transfer (FRET) signaling mechanism, 2 was further converted into 1a and 1b, which represent the first paradigm of FRET-based ratiometric fluorescent HOCl probes. The outstanding features of 1a and 1b include well-resolved emission peaks, high sensitivity, high selectivity, good functionality at physiological pH, rapid response, low cytotoxicity, and good cell-membrane permeability. Furthermore, these excellent attributes enable us to demonstrate, for the first time, the ratiometric imaging of endogenously produced HOCl in living cells by using these novel ratiometric probes. We expect that 1a and 1b will be useful molecular tools for studies of HOCl biology. In addition, the HOCl-promoted cyclization reaction of rhodamine-thiosemicarbazides to rhodamine-oxadiazoles should be widely applicable for the development of different types of fluorescent HOCl probes.     

Release of Amino‐ or Carboxy‐Containing Compounds Triggered by HOCl: Application for Imaging and Drug Design

The overproduction of HOCl is highly correlated with diseases such as atherosclerosis, rheumatoid arthritis, and cancer. Whilst acting as a marker of these diseases, HOCl might also be used as an activator of prodrugs or drug delivery systems for the treatment of the corresponding disease. In this work, a new platform of HOCl probes has been developed that integrates detection, imaging, and therapeutic functions. The probes can detect HOCl, using both NIR emission and the naked eye in vitro, with high sensitivity and selectivity at ultralow concentrations (the detection limit is at the nanomolar level). Basal levels of HOCl can be imaged in HL‐60 cells without special stimulation. Moreover, the probes provided by this platform can rapidly release either amino‐ or carboxy‐containing compounds from prodrugs, during HOCl detection and imaging, to realize a therapeutic effect.     

Enhanced Fluorescence Turn‐on Imaging of Hypochlorous Acid in Living Immune and Cancer Cells

Two closely related phenyl selenyl based boron‐dipyrromethene (BODIPY) turn‐on fluorescent probes for the detection of hypochlorous acid (HOCl) were synthesized for studies in chemical biology; emission intensity is modulated by a photoinduced electron‐transfer (PET) process. Probe 2 intrinsically shows a negligible background signal; however, after reaction with HOCl, chemical oxidation of selenium forecloses the PET process, which evokes a significant increase in fluorescence intensity. The fluorescence intensity of probes 1 and 2 with HOCl involves an ～18 and ～50‐fold enhancement compared with the respective responses from other reactive oxygen/nitrogen species (ROS/RNS) and low detection limits (30.9 nm for 1 and 4.5 nm for 2 ). Both probes show a very fast response with HOCl; emission intensity reached a maximum within 1 s. These probes show high selectivity for HOCl, as confirmed by confocal microscopy imaging when testing with RAW264.7 and MCF‐7 cells.     

Selective Detection and Visualization of Exogenous/endogenous Hypochlorous Acid in Living Cells using a BODIPY‐based Red‐emitting Fluorescent Probe

Herein, a red‐emitting fluorescent probe DM‐BDP‐OCl containing a para‐DMTC benzyl pyridinium moiety at the meso position of BODIPY as self‐immolative portion for the detection of HOCl was designed and synthesized. DM‐BDP‐OCl exhibited excellent specificity and a fast response for HOCl beyond other ROS/RNS. It was used for the accurately measurable detection of HOCl with a linear range from 0 μM to 50 μM, and the detection limit for HOCl reached 60 nM. Moreover, the probe could directly monitor fluctuations of exogenous and endogenous HOCl in living HeLa and RAW 264.7 cells. This work provided a powerful and convenient imaging tool for probing pathological and physiological actions of HOCl.     

A general strategy for selective detection of hypochlorous acid based on triazolopyridine formation

Triazolopyridines are an important kind of fused-ring compounds. A HOCl-promoted triazolopyridine formation strategy is reported here for the first time in which hypochlorous acid (HOCl) mildly and efficiently promotes the formation of 1,2,4-triazolo[4,3-a]pyridines NT1-NT6 from various 2-pyridylhydrazones N1-N6. N6, a rhodol-pyridylhydrazone hybrid, was developed into a fluorescent probe for the selective detection of HOCl, and successfully applied to probe endogenous HOCl in living cells and zebrafish in situ and in real time. The present intramolecular cyclization reaction is selective and atom-economical, thereby not only providing an important approach for the convenient synthesis of triazolopyridines, but also offering a general strategy for sensitive, selective and biocompatible detection of endogenous HOCl in complex biosystems.     

A ratiometric fluorescent probe for cyanide based on FRET

On the basis of FRET from 4-(N,N-dimethylamino)benzamide to fluorescein, a new ratiometric fluorescence probe bearing a hydrazone binding unit was developed for highly selective and sensitive detection of CN(-) in aqueous solution.     

A highly specific BODIPY-based fluorescent probe for the detection of hypochlorous acid

A fluorescent probe, HKOCl-1, has been successfully developed for the detection of hypochlorous acid on the basis of a specific reaction with p-methoxyphenol. The formation of HOCl has been successfully detected not only in an abiotic system but also in an enzymatic system (myeloperoxidase/H2O2/Cl(-) system) and in living macrophage cells upon stimulation. This new probe might be used as an efficient tool for probing the roles HOCl plays in biological systems.     

HOCl can appear in the mitochondria of macrophages during bacterial infection as revealed by a sensitive mitochondrial-targeting fluorescent probe

Macrophages, important cells of the innate immune system, can produce abundant HOCl in the cytoplasm to fight against bacteria. Recent studies suggest that mitochondria in macrophages play a role in antibacterial responses. During bacterial infection, however, it is uncertain whether HOCl is present in the mitochondria, mainly because of the lack of a suitable research method. Herein, by developing a new mitochondrial-targeting fluorescent HOCl probe, combined with confocal fluorescence imaging, we show for the first time that HOCl can appear in the mitochondria of macrophages (Raw264.7 cells) during bacterial infection, as confirmed with non-phagocytic cells and inhibitors as control experiments. Moreover, the developed probe exhibits an accurate mitochondrial-targeting ability, a fast response, and high selectivity and sensitivity (detection limit 9 nM), and is thus expected to be employed for further revealing the biological function of subcellular mitochondria.     

Revealing HOCl burst from endoplasmic reticulum in cisplatin-treated cells via a ratiometric fluorescent probe

The reactive oxygen species (ROS) are tightly associated with endoplasmic reticulum (ER) stress. Thus, the deep and visual insight of aberrant ROS fluctuations in the ER can help us better investigate the ER stress-associated pathology. In this work, a fluorescent probe ERC for HOCl detection in the ER based on phenothiazine-derived coumarin platform was developed. In the presence of HOCl, ERC exhibited an emission change from 609 nm to 503 nm within seconds. It also showed high sensitivity (0.44 μmol/L) and superb photostability. Significantly, ERC displayed low cytotoxicity, good cell membrane permeability, and appreciable ER-targetability. Ultimately, the probe was successfully utilized to image exogenous and endogenous HOCl in living cells and reveal the HOCl burst in cisplatin-treated cancer cells.     

A general strategy for selective detection of hypochlorous acid based on triazolopyridine formation

Triazolopyridines are an important kind of fused-ring compounds. A HOCl-promoted triazolopyridine formation strategy is reported here for the first time in which hypochlorous acid (HOCl) mildly and efficiently promotes the formation of 1,2,4-triazolo[4,3-a]pyridines NT1-NT6 from various 2-pyridylhydrazones N1-N6. N6, a rhodol-pyridylhydrazone hybrid, was developed into a fluorescent probe for the selective detection of HOCl, and successfully applied to probe endogenous HOCl in living cells and zebrafish in situ and in real time. The present intramolecular cyclization reaction is selective and atom-economical, thereby not only providing an important approach for the convenient synthesis of triazolopyridines, but also offering a general strategy for sensitive, selective and biocompatible detection of endogenous HOCl in complex biosystems.     

Hypochlorous acid turn-on boron dipyrromethene probe based on oxidation of methyl phenyl sulfide

A boron dipyrromethene (BODIPY)-based fluorometric probe, HCS, has been successfully developed for the highly sensitive and selective detection of hypochlorous acid (HOCl). The probe is based on the specific HOCl-promoted oxidation of methyl phenyl sulfide. The reaction is accompanied by a 160-fold increase in the fluorescent quantum yield (from 0.003 to 0.480). The fluorescent turn-on mechanism is accomplished by suppression of photoinduced electron transfer (PET) from the methyl phenyl sulfide group to BODIPY. The fluorescence intensity of the reaction between HOCl and HCS shows a good linearity in the HOCl concentration range 1–10 μM. The detection limit is 23.7 nM (S/N = 3). In addition, confocal fluorescence microscopy imaging using RAW264.7 macrophages demonstrates that the HCS probe could be an efficient fluorescent detector for HOCl in living 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.