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.     

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 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.     

Development of a BODIPY-based ratiometric fluorescent probe for hypochlorous acid and its application in living cells

A BODIPY-based ratiometric fluorescent probe for HOCl has been designed based on the transduction of thioether to sulfoxide function. This probe features a marked absorption and emission blue-shift upon the HOCl-promoted rapid transduction, enabling the highly selective and ratiometric detection. In addition, the probe works excellently within a wide pH range of 4–10, addressing the existing pH dependency issue. Living cells studies demonstrate that the probe is cell membrane permeable and can be employed successfully to image endogenous HOCl generation in macrophage cells.     

Development of a new fluorescence ratiometric switch for endogenous hypochlorite detection in monocytes of diabetic subjects by dye release method

Increased oxidative stress in metabolic complications like type 2 diabetes, dyslipidemia and cardiovascular disorders exerts potential health hazards in many facets. Enhanced production of reactive oxygen species (ROS) due to increased oxidative stress promotes the damage of many biologically important macromolecules. Hypochlorous acid (HOCl), a microbicidal agent is also known to be an important ROS sub-species. An enhanced generation of endogenous HOCl due to diseased condition therefore can be detrimental to health. In present work, a new quinoline-diaminomaleonitrile based probe (HQMN) has been designed for the selective detection of hypochlorite. The probe in hand shows a selective ratiometric emission change towards OCl^?. The probe behaves as a highly selective and sensitive tool for the detection of OCl^? over other analytes with a fast response time (within 100 s). Bioimaging study revealed that HQMN can detect endogenous OCl^? in human monocytes and an increase in endogenous HOCl concentration has been witnessed in diabetic condition compared to healthy control. Thus HQMN can be used as an excellent fluorescent probe for dynamic tracking of hypochorite in living biological cells especially to identify diabetic conditions.     

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.     

Assembly of Water-soluble AIE-active Fluorescent Organic Nanoparticles for Ratiometric Detection of Hypochlorite in Living Cells

Hypochlorous acid (HOCl) plays a crucial role in many physiological processes and is widely used as bleach, deodorant and fungicide. In this work, we designed an amphiphilic hydrazone fluorescent molecule THG-1 containing hydrophilic sugar units and hydrophobic tetraphenylethylene unit for ratiometric detection of HOCl with high sensitivity and excellent selectivity based on HOCl-triggered hydrolyzation reaction and aggregation-induced emission (AIE) effect. The detection mechanism was verified by liquid chromatograph mass spectrometry experiments and scanning electron microscope (SEM) tests. Contrast experiments revealed that the numbers of lactose unit and hydrazone linker were essential for assembly of THG-1 and detection of HOCl. In addition, THG-1 was successfully used for imaging of exogenous and endogenous HOCl in living 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.     

Sensitive and selective off-on rhodamine hydrazide fluorescent chemosensor for hypochlorous acid detection and bioimaging

A rhodamine 6G hydrazide fluorescent chemosensor was prepared for the rapid HOCl detection in aqueous media. The system makes good use of the irreversible HOCl-mediated selective oxidation reaction to generate fluorescent response proportional to the amount of HOCl in neutral buffer. This probe exhibits great photostability, high sensitivity, and good selectivity for HOCl over other reactive species and most of the common metal ions. Furthermore, the probe is cell membrane permeable, and its applicability has been successfully demonstrated for fluorescence imaging of both exogenous and endogenous HOCl within living cells. Cytotoxicity assays prove that this probe is almost nontoxic to the cultured cell lines under the experimental conditions.     

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 near-infrared fluorescent probe for monitoring fluvastatin-stimulated endogenous H2S production

Most reported fluorescent probes have limitations in practical applications in living systems due to the strong autofluorescence background,construction of probes with near-infrared(NIR) fluorescence emission is an accessible approach for addressing this challenge.We here designed a NIR fluorescent probe for monitoring the endogenous production of H_2S in living cells.The designed probe showed significant NIR fluorescence turn-on response to H_2S with high selectivity,enabling the sensitive detection H_2S.Importantly,the probe could be applied in monitoring the endogenous production of H_2S in raw 264.7 macrophages.This study showed that fluvastatin can promote the activity of cystathionineγ-lyase(CSE) for generation H_2S.     

Rational Design of Ratiometric Fe3+ Fluorescent Probes Based on FRET Mechanism

As the most abundant transition metal element in mammals, iron(Fe) plays a vital role in life activities. It is of great significance to study the variation of Fe³⁺ level in living organisms. In virtue of the advantages of high sensitivity, good selectivity and low damage to living systems, the fluorescence detection of Fe³⁺ has attracted much attention. Compared with the intensity-based fluorescent probe, the ratiometric fluorescent probe has less interference of environmental and can realize quantitative detection. In this study, four ratiometric Fe³⁺ fluorescent probes, R1, R2, R3 and R4_, were designed and synthesized using fluorescence resonance energy transfer(FRET) mechanism to achieve quantitative detection of Fe³⁺. In the FRET systems, 1,8-naphthalimide fluorophore derivatives were adopted as donors while rhodamine B derivatives were selected as receptors. The connection sites of the donor and acceptor in R3 and R4 are different from those in R1 and R2. All the four probes showed good response and selectivity to Fe³⁺. The energy transfer efficiencies of R3 and R4 were obviously higher than those of R1 and R2. This work provided a promising strategy for the development of fluorescent ratiometic Fe³⁺sensors.     

A Ratiometric Fluorescent Probe Based on a Through‐Bond Energy Transfer (TBET) System for Imaging HOCl in Living Cells

A simple ratiometric probe (Naph‐Rh) has been designed and synthesized based on a through‐bond energy transfer (TBET) system for sensing HOCl. In this probe, rhodamine thiohydrazide and naphthalene formyl were connected by simple synthesis methods to construct a structure of monothio‐bishydrazide. Free probe Naph‐Rh showed only the emission of naphthalene. When probe Naph‐Rh reacted with HOCl, monothio‐bishydrazide could be converted into 1,2,4‐oxadiazole, which not only ensured that the donor and the acceptor were connected with electronically conjugated bonds, but also resulted in the spiro‐ring opening and the emission of rhodamine. Therefore, a typical TBET process took place. The probe possessed high‐energy transfer efficiency and large pseudo‐Stokes shifts. As the first TBET probe for HOCl, Naph‐Rh showed excellent selectivity and sensitivity toward HOCl over other reactive oxygen species (ROS)/reactive nitrogen species (RNS), and could respond fast to a low concentration of HOCl in the real sample. In addition, the probe was suitable for imaging HOCl in living cells due to its real‐time response, excellent resolution, and reduced cytotoxicity.     

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.     

Molecular engineering of ultra-sensitive fluorescent probe with large Stokes shift for imaging of basal HOCl in tumor cells and tissues

Fluorescent probes have been widely employed in biological imaging and sensing. However, it is always a challenge to design probes with high sensitivity. In this work, based on rhodamine skeleton, we developed a general strategy to construct sensitivity-enhanced fluorescent probe with the help of theoretical calculation for the first time. As a proof of concept, we synthesized a series of HOCl probes. Experiment results showed that with the C-9 of pyronin moiety of rhodamine stabilized by an electron donor group, probe DQF-S exhibited an importantly enhanced sensitivity (LOD: 0.2 nmol/L) towards HOCl together with fast response time (<10 s). Moreover, due to the breaking symmetrical electron distribution by another electron donor group, the novel rhodamine probe DQF-S displayed a far red to near-infrared emission (>650 nm) and large Stokes shift. Bioimaging studies indicated that DQF-S can not only effectively detect basal HOCl in various types of cells, but also be successfully applied to image tumor tissue in vivo. These results demonstrate the potential of our design as a useful strategy to develop excellent fluorescent probes for bioimaging.     

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 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.     

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.     

Development of an Si-rhodamine-based far-red to near-infrared fluorescence probe selective for hypochlorous acid and its applications for biological imaging

A far-red to near-infrared (NIR) fluorescence probe, MMSiR, based on Si-rhodamine, was designed and synthesized for sensitive and selective detection of HOCl in real time. MMSiR and its oxidized product SMSiR have excellent properties, including pH-independence of fluorescence, high resistance to autoxidation and photobleaching, and good tissue penetration of far-red to NIR fluorescence emission. The value of MMSiR was confirmed by real-time imaging of phagocytosis using a fluorescence microscope. wsMMSiR, a more hydrophilic derivative of MMSiR, permitted effective in vivo imaging of HOCl generation in a mouse peritonitis model. This probe is expected to be a useful tool for investigating the wide range of biological functions of HOCl.     

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.