A Selective Imidazoline-2-thione-Bearing Two-Photon Fluorescent Probe for Hypochlorous Acid in Mitochondria

Development of a Concise Rhodamine-Formylhydrazine Type Fluorescent Probe for Highly Specific and Ultrasensitive Tracing of Basal HOCl in Live Cells and Zebrafish

Hypochlorous acid (HOCl) has received special attention by virtue of its pivotal antimicrobial nature, and the appropriate amount of HOCl is beneficial to innate immunity of host to cope with microbial invasion. However, the uncontrollable accumulation of HOCl is implicated in many human diseases and even cancers. Thus, to determine its deeper biological functions, it is significantly important to specifically monitor intracellular HOCl in biosystems. Herein, we rationally designed a simple fluorescent probe FH-HA on the basis of the formylhydrazine recognition receptor and rhodamine B fluorophore. It is worth noting that the formylhydrazine moiety for the first time is adopted as the recognition receptor for specifically recognizing HOCl. Additionally, probe FH-HA also exhibited excellent performance in many areas including satisfactory water-solubility, high specificity, and excellent sensitivity. Notably, probe FH-HA could quickly respond to HOCl (within 3 s), which facilitates the tracing of transient HOCl. More importantly, probe FH-HA was capable of specifically tracing the fluctuations of endogenous HOCl in living cells and zebrafish, and it could monitor basal HOCl in cancer cells to distinguish cancer cells from normal ones.

Design Principles, Sensing Mechanisms, and Applications of Highly Specific Fluorescent Probes for HOCl/OCl

Hypochlorous acid/hypochlorite (HOCl/OCl^-), one of the most important reactive oxygen species (ROS), plays vital roles in various physiological and pathological processes. At normal concentrations, OCl^- acts as part of an immune defense system by destroying invasive bacteria and pathogens. However, nonproperly located or excessive amounts of OCl^- are related to many diseases, including cancers. Thus, detection of OCl^- has great importance. Owing to their high sensitivities, selectivities, fast response times, technical simplicities, and high temporal and spatial resolution, fluorescent probes are powerful tools for in vitro and in vivo sensing of target substances. This Account focuses on the development of new chemosensors for detection of OCl^-, which operate by undergoing a chemical reaction with this ROS in conjunction with a change in emission properties. As part of the presentation, we first introduce several important factors that need to be considered in the design of fluorescent chemosensors for OCl^-, including fluorophores, reaction groups, cosolvents, and buffers. Discussion here revolves around the need to select fluorophores that resist oxidation by OCl^-. As well, attention is given to the sensitivities and selectivities of groups in the sensors that react with OCl^- to trigger a fluorescence response. Moreover, well-known reaction groups, which react with highly reactive ROS (hROS), have been redesigned to be specific for OCl^-. In addition, it is pointed out that several cosolvents and buffers such as DMSO and HEPES are not suitable for use in systems for the detection of OCl^- because they are readily oxidized by this ROS. We further discuss recent investigations carried out by us and others aimed at the development of fluorescent probes for in vitro and in vivo detection of OCl^-. These efforts led to the new "dual lock" strategy for designing OCl^- chemosensors as well as several new specific reaction groups such as imidazoline-2-thiones and imidazoline-2-boranes. Probes created using this strategy and the new reacting groups have been successfully applied to imaging exogenous and endogenous OCl^- in live cells and/or tissues. The design concepts and strategies emanating from our studies of fluorescent OCl^- probes have provided insight into the general field of fluorescent probes. Despite the progress made thus far, challenges still remain in developing and applying fluorescent OCl^- probes. For example, more highly specific and sensitive fluorescent OCl^- probes are still in great demand for studies of the biological roles played by OCl^-. Thus, interdisciplinary collaborations of chemists, biologists, and medical practitioners are needed to drive future developments of OCl^- probes for disease diagnosis and drug screening.

A novel ratiometric and colorimetric fluorescent probe for hypochlorite based on cyanobiphenyl and its applications

Reported here is a novel ratiometric and colorimetric fluorescent probe 1 for hypochlorite based on cyanobiphenyl and diaminomaleonitrile. This probe 1 was designed based on the mechanism that ClO^- selectively cleaved the hydrazone bond (-C=N-) in this probe and released the fluorophore, 3`-formyl-4`-hydroxy-4-biphenylcarbonitrile. The addition of ClO^- to the solution of probe 1 resulted in a very large blue-shift in both fluorescence (107 nm) spectra and an obvious fluorescence color change from red to green. Furthermore, this probe displays a rapid response (30 s) and a low detection limit (3.34 × 10^-7 M, based on LOD = 3σ/slope) in detecting ClO^-. Importantly, practical utility of this probe for the selective detection of ClO^- in living cells has been successfully demonstrated, illustrating the great potential for biological analysis. Additionally, the probe 1 was also successfully applied to the detection of ClO^- in real water sample.

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.

Small-Molecule-Based Fluorescent Sensors for Selective Detection of Reactive Oxygen Species in Biological Systems

Reactive oxygen species (ROS) encompass a collection of intricately linked chemical entities characterized by individually distinct physicochemical properties and biological reactivities. Although excessive ROS generation is well known to underpin disease development, it has become increasingly evident that ROS also play central roles in redox regulation and normal physiology. A major challenge in uncovering the relevant biological mechanisms and deconvoluting the apparently paradoxical roles of distinct ROS in human health and disease lies in the selective and sensitive detection of these transient species in the complex biological milieu. Small-molecule-based fluorescent sensors enable molecular imaging of ROS with great spatial and temporal resolution and have thus been appreciated as excellent tools for aiding discoveries in modern redox biology. We review a selection of state-of-the-art sensors with demonstrated utility in biological systems. By providing a systematic overview based on underlying chemical sensing mechanisms, we wish to highlight the strengths and weaknesses in prior sensor works and propose some guiding principles for the development of future probes.

Fluorescent probes for organelle-targeted bioactive species imaging

The dynamic fluctuations of bioactive species in living cells are associated with numerous physiological and pathological phenomena. The emergence of organelle-targeted fluorescent probes has significantly facilitated our understanding on the biological functions of these species. This review describes the design, applications, challenges and potential directions of organelle-targeted bioactive species probes.

Bioactive species, including reactive oxygen species (ROS, including O₂˙^–, H₂O₂, HOCl, ¹O₂, ˙OH, HOBr, etc.), reactive nitrogen species (RNS, including ONOO^–, NO, NO₂, HNO, etc.), reactive sulfur species (RSS, including GSH, Hcy, Cys, H₂S, H₂S_n, SO₂ derivatives, etc.), ATP, HCHO, CO and so on, are a highly important category of molecules in living cells. The dynamic fluctuations of these molecules in subcellular microenvironments determine cellular homeostasis, signal conduction, immunity and metabolism. However, their abnormal expressions can cause disorders which are associated with diverse major diseases. Monitoring bioactive molecules in subcellular structures is therefore critical for bioanalysis and related drug discovery. With the emergence of organelle-targeted fluorescent probes, significant progress has been made in subcellular imaging. Among the developed subcellular localization fluorescent tools, ROS, RNS and RSS (RONSS) probes are highly attractive, owing to their potential for revealing the physiological and pathological functions of these highly reactive, interactive and interconvertible molecules during diverse biological events, which are rather significant for advancing our understanding of different life phenomena and exploring new technologies for life regulation. This review mainly illustrates the design principles, detection mechanisms, current challenges, and potential future directions of organelle-targeted fluorescent probes toward RONSS.

Near-Infrared Aggregation-Induced Emission-Active Probe Enables in situ and Long-Term Tracking of Endogenous β-Galactosidase Activity

High-fidelity tracking of specific enzyme activities is critical for the early diagnosis of diseases such as cancers. However, most of the available fluorescent probes are difficult to obtain in situ information because of tending to facile diffusion or inevitably suffering from aggregation-caused quenching (ACQ) effect. In this work, we developed an elaborated near-infrared (NIR) aggregation-induced emission (AIE)-active fluorescent probe, which is composed of a hydrophobic 2-(2-hydroxyphenyl) benzothiazole (HBT) moiety for extending into the NIR wavelength, and a hydrophilic β-galactosidase (β-gal) triggered unit for improving miscibility and guaranteeing its non-emission in aqueous media. This probe is virtually activated by β-gal, and then specific enzymatic turnover would liberate hydrophobic AIE luminogen (AIEgen) QM-HBT-OH. Simultaneously, brightness NIR fluorescent nanoaggregates are in situ generated as a result of the AIE-active process, making on-site the detection of endogenous β-gal activity in living cells. By virtue of the NIR AIE-active performance of enzyme-catalyzed nanoaggregates, QM-HBT-βgal is capable of affording a localizable fluorescence signal and long-term tracking of endogenous β-gal activity. All results demonstrate that the probe QM-HBT-βgal has potential to be a powerful molecular tool to evaluate the biological activity of β-gal, attaining high-fidelity information in preclinical applications.

Evaluation of HOCl-generating anticancer agents by an ultrasensitive dual-mode fluorescent probe

Hypochlorous acid (HOCl), a reactive oxygen species (ROS), plays a crucial role in the process of pathogenic oxidative stress. Some powerful anticancer agents, such as elesclomol, specifically induce cancer cell apoptosis by increasing HOCl levels. However, sensitive tools to monitor subtle changes of biological HOCl in vivo are limited. To achieve this, we herein present rationally designed probes C1-C7 through introducing a bioorthogonal dimethylthiocarbamate receptor. All the probes were shown to sensitively and rapidly detect HOCl in the nanomolar/biologically relevant concentration range with fluorescence turn-on observed in their respective optical regions, resulting in a blue-to-red "fluorescence rainbow" and providing a broad selection of colors for imaging HOCl in vivo. Remarkably, probe C7 exhibited both a turn-on signal at biologically relevant concentrations (LOD1 = 18 nM) and a ratiometric response at the high risk pathogenic concentrations (LOD2 = 0.47 μM), which gives a higher reliability compared to a single signal and avoids cross-talk caused by the combined use of several probes. C7 was used to monitor the oxidative stress process induced by elesclomol in live cancer cells, and using this probe it was further discovered that an evodiamine derivative was capable of generating cancer-cell HOCl.

Two coumarin-based turn-on fluorescent probes based on for hypochlorous acid detection and imaging in living cells

This work, two turn-on fluorescent probes (3-acetyl-2H-chromen-2-one (ACO) & (1E)-1-(1-(2-oxo-2H-chromen-3-yl)ethylidene)thiosemicarbazide (CETC)) based on coumarin have been designed and synthesized, which could selectively and sensitively recognize ClO^- with fast response time. ACO &CETC were almost non fluorescent possibly due to both the lacton form of coumarin and unbridged CN bonds which can undergo a nonradiative decay process in the excited state. Upon the addition of ClO^-, ACO &CETC were oxidized to ring - opened by cleavage the CO and CN and the fluorescence intensity were increased considerably. Fluorescence titration experiments showed that the detection limit ACO &CETC is as low as 22 nm and 51 nm respectively. In particular, some relevant reactive species, including OH, ¹O₂, H₂O₂, KO₂, some anions and cations cannot be interference with the test. In live cell experiments, ACO &CETC were successfully applied to image exogenous ClO^- in HepG2 cells. Therefore, ACO &CETC not only could image ClO^- in living cells but also proved that CO and CN can be cleavage by ClO^-.

Bioluminescent probe for detecting endogenous hypochlorite in living mice

As a kind of biologically important reactive oxygen species (ROS), hypochlorite (ClO^-) plays a crucial role in many physiological processes. As such, endogenous ClO^- is a powerful antibacterial agent during pathogen invasion. Nonetheless, excessive endogenous ClO^- could pose a health threat to mammalian animals including humans. However, the detection of endogenous ClO^- by bioluminescence probes in vivo remains a considerable challenge. Herein, based on a caged strategy, we developed a turn-on bioluminescent probe 1 for the highly selective detection of ClO^-in vitro and imaging endogenous ClO^- in a mouse inflammation model. We anticipate that such a probe could help us understand the role of endogenous ClO^- in a variety of physiological and pathological processes.

A novel porphyrin-based near-infrared fluorescent probe for hypochlorite detection and its application in vitro and in vivo

Reactive oxygen species (ROS), especially HOCl/ClO-, have been demonstrated to play essential roles in both physiological and pathological processes, and an abnormal level of HOCl/ClO- is related to some diseases. In this work, a very fast responsive (within 30 seconds) porphyrin-based fluorescent probe, TPP-TCF, for ClO- with a NIR emissive wavelength was prepared. This probe exhibited excellent selectivity towards ClO- and would not be interfered with by other ROS and typical nucleophiles. The limit of detection (LOD) for ClO- was evaluated to be 0.29 μM, indicating high sensitivity towards ClO-. In further bioimaging experiments, TPP-TCF displayed low-cytotoxicity and good cell penetrability for recognizing exogenous ClO- in HeLa cells. Moreover, this probe was successfully applied in imaging endogenous ClO- in living animals.

Detection of hypochlorous acid fluctuation via a selective near-infrared fluorescent probe in living cells and in vivo under hypoxic stress

The near-infrared fluorescent probe Cy-HOCl for monitoring HOCl in living cells, zebrafish and mice under hypoxic stress.

A novel highly specific and ultrasensitive fluorescent probe for monitoring hypochlorous acid and its application in live cells

Based on the important role of hypochlorous acid (HOCl) in the immune system and numerous physiological processes, the detection of intracellular basal HOCl is of significant interest. In this work, we present a simple thiocarbamate-protected fluorescein fluorescent probe, TCFL, for imaging basal HOCl in live cells. Surprisingly, probe TCFL could determine HOCl quantitatively in a large concentration range with a detection limit of 0.65 nM. In addition, probe TCFL showed excellent specificity for HOCl in the presence of other higher concentration analytes (1 mM). Moreover, probe TCFL exhibited a rapid response (within 3 s) to HOCl and thus could provide a tool for real-time monitoring of HOCl. Importantly, probe TCFL with outstanding response features could be applied for monitoring basal HOCl in live cells.

A highly specific, ultrasensitive, thiocarbamate-caged fluorescein probe was developed for real-time detection of HOCl in live cells.

Light-driven visualization of endogenous cysteine, homocysteine, and glutathione using a near-infrared fluorescent probe

Light-driven visualization of endogenous cysteine, homocysteine, and glutathione using a near-infrared fluorescent probe.

Enhanced fluorescence sensing of hypochlorous acid using serum albumin as a signal amplifier

A mitochondria-targeting fluorescent probe for ClO⁻ was developed and a signal amplifier BSA was utilized to promote the fluorescent signal.

Fluorescent Chemosensors for Various Analytes Including Reactive Oxygen Species, Biothiol, Metal Ions, and Toxic Gases

The development of fluorescent chemosensors for various analytes has been actively pursued by chemists. Since their inception, these efforts have led to many new sensors that have found wide applications in the fields of chemistry, biology, environmental science, and physiology. The search for fluorescent chemosensors was initiated by a few pioneering groups in the late 1970s and 1980s and blossomed during the last two decades to include more than hundreds of research groups around the world. The targets for these sensors vary from metal ions, anions, reactive oxygen/nitrogen species, biothiols, and toxic gases. Our group has made contributions to this area in last 18 years. In this perspective, we briefly introduce the history of chemosensors and review studies that we have carried out.

A near-infrared fluorescent probe based on photostable Si-rhodamine for imaging hypochlorous acid during lysosome-involved inflammatory response

Hypochloric acid (HClO) is mainly distributed in acidic lysosomes of phagocytes and closely associated with numerous physiological and pathological processes, especially inflammatory response. Fluorescent probe has become an important tool for imaging HClO in lysosomes, but suffered from interference from autofluorescence in vivo, phototoxicity to biosamples and photobleaching phenomenon due to their short-wavelength excitation and emission. Unfortunately, up to now, no near-infrared (NIR) lysosome-targetable fluorescent probe has been reported for imaging HClO. In this paper, a near-infrared fluorescent probe Lyso-NIR-HClO for imaging lysosomal HClO was reported for the first time. Lyso-NIR-HClO based on Si-rhodamine is consisted of a morpholine unit as a lysosome-targetable group and a HClO-mediated cyclization reaction site as a response group, which was applied for highly selective and sensitive detection and imaging for endogenous and exogenous HClO in lysosomes, with a linear range from 5.0 × 10^-8 to 1.0 × 10^-5 M and a detection limit of 2.0 × 10^-8 M in vitro. Attributed to NIR emission and excellent photostability of Si-rhodamine, Lyso-NIR-HClO exhibits excellent performances in vivo, such as low interference from intracellular autofluorescence, stable and persistent fluorescence signal and good tissue penetration, which are in favor of accurate, time-lapse and long-term imaging for HClO. Finally, we applied the probe Lyso-NIR-HClO to visualize endogenous HClO during lysosome-involved inflammatory response including bacteria-infected cells and inflamed mouse model with satisfactory results. The above results proved that Lyso-NIR-HClO would be a potentially useful tool for the study of biological functions and pathological roles of HClO in lysosomes, especially role of lysosome in the inflammatory response.

Rapid Response Fluorescence Probe Enabled In Vivo Diagnosis and Assessing Treatment Response of Hypochlorous Acid-Mediated Rheumatoid Arthritis

Diagnosis and early assessment of the treatment response of rheumatoid arthritis (RA) necessitates a reliable bioanalytical method for rapid, sensitive, and specific detection of the hypochlorous acid (HOCl) biomarker in inflammatory diseases. Herein, two fluorescence probes, Probe-1 and Probe-2 are developed for quantitative monitoring and visualization of inflammatory response-related HOCl levels in vitro and in vivo. In the presence of HOCl, fluorescence "OFF-ON" response is obtained for both the probes as a result of specific HOCl-triggered C=N bond cleavage reaction. Probe-1 and Probe-2 feature rapid response (<4 s), a high degree of sensitivity and selectivity toward HOCl, which allow them to be used for quantification of HOCl in a simulated physiological condition. Using Probe-2 as the probe, fluorescence imaging and flow cytometry analysis of HOCl levels in lysosome of inflammatory mimic cells, visualization of HOCl generation in endotoxin-induced inflammation of adult zebrafish and RA of mice are possible. Probe-2 exhibits high effectiveness for early assessment of the treatment response of HOCl-mediated RA in mice with an antiarthritic drug, methotrexate (MTX). The results demonstrate that Probe-2 is a powerful tool for future studies on diagnosis and monitoring treatment efficiency in a broad range of inflammatory diseases, including RA.

Design of a ratiometric two-photon probe for imaging of hypochlorous acid (HClO) in wounded tissues

HClO plays crucial roles in a wide range of biological and pathological processes. Recent studies have revealed that the generation of HClO has close links with the wound healing process. It's thus meaningful to develop a reliable method for monitoring HClO in wounded tissues. Toward this purpose, we herein report a rationally designed quinolone-based ratiometric two-photon fluorescent probe, QClO, for HClO. The probe QClO rapidly displays a drop in blue emission and an increase of green emission in response to HClO due to the oxidation of oxathiolane. The fluorescence intensity ratio (green/blue) can serve as the ratiometric detection signal for HClO with high sensitivity. After confirming its excellent sensing performance in vitro, the probe was validated by detecting exogenous and endogenous HClO in living cells. The probe was capable of monitoring HClO in situ in the wounded tissues of mice by two-photon microscopy, which demonstrated the production profile of HClO during the wound-healing process. This work affords a simple and reliable tool for the detection and imaging of HClO, which promises to find more applications in HClO-related biological and pathological studies.

Mitochondria-targeted near-infrared fluorescent probe for the detection of carbon monoxide in vivo

Carbon monoxide is a critical gasotransmitter in the body and related with mitochondrial respiration. To date, various fluorescent probes for CO have been well proposed, but two main problems remain. One is that most of the probes are not mitochondria-targeting, even if the probes claim to be able to detect CO in living cells. The other is that the probes for CO display excitation and emission within the ultraviolet or visible range, which hinders their applications in vivo. Herein, a hemicyanine-based near-infrared (NIR) fluorescent probe named CyAPC is first synthesized and used to detect mitochondrial CO. The characteristics of probe CyAPC are as follows: (1) The fluorescence emission of the sensing system is at 736 nm belonging to NIR region, which is suitable for bioimaging in vivo. (2) CyAPC, a positively charged molecule, would have a high tendency to localize in mitochondria of cells. (3) The fluorescence change of the probe is attributed to the fact that CO with Pd²⁺ induced cleavage of the allyl formate group from the probe and CyAPC (fluorescence off) is transformed into CyOH (fluorescence on), which is proved by HPLC, MS and DFT calculation. (4) The NIR fluorescent probe is applied for the detection of exogenous and endogenous CO in various biological samples such as cell, tissue and in vivo with satisfactory results.

Mitochondria and lysosome-targetable fluorescent probes for HOCl: recent advances and perspectives

Hypochlorous acid (HOCl), as one of the reactive oxygen species (ROS), plays an important role in the destruction of pathogens in the immune system. However, abnormal concentration of biogenic HOCl can also damage host tissues, and it has been shown to be associated with many diseases. Accordingly, detection of HOCl at the subcellular level is important for understanding inflammation and cellular apoptosis. Toward this end, in the past few years, a wide variety of fluorescent HOCl probes have been engineered and applied for imaging of HOCl in subcellular organelles. In this review, we highlight the representative cases of the fluorescent HOCl probes with mitochondria and lysosome-targetable ability. The discussion includes their design strategies, sensing mechanisms, and applications in bio-imaging of HOCl in mitochondria and lysosomes.

A highly specific and ultrasensitive near-infrared fluorescent probe for imaging basal hypochlorite in the mitochondria of living cells

The development of highly specific and ultrasensitive fluorescent probes for tracking basal mitochondrial hypochlorite is very important to unravel its diverse cellular functions in the mitochondria of living cells. In this paper, we have developed a water-soluble, mitochondria-targeted near-infrared fluorescent probe NB-OCl for selectively measuring OCl^- in the presence of higher concentration (500 μM) other biologically important substances. Surprisingly, the obtained results demonstrated that probe NB-OCl could sensitively determine OCl^- in the range of 0-200 pM with the detection limit of 10.8 pM. To the best of our knowledge, NB-OCl is the first fluorescent probe for the specific determination of OCl^- at the picomolar level. Moreover, probe NB-OCl exhibits a fast response for OCl^- (< 5 s), which would be in favor of tracking the highly reactive and short-lived OCl^- in the living systems. The preeminent recognition properties of probe NB-OCl enable its applications in the monitoring of basal OCl^- and the fluctuations of endogenous/exogenous OCl^- levels in the mitochondria of living cells.

A fluorescent probe for the detection of HOCl in lysosomes

A novel lysosome-targeting fluorescent probe (LR1) for HOCl was developed based on the rhodamine framework. Probe LR1 was able to target lysosomes and detect endogenous HOCl with low cytotoxicity.

A Two-Photon Ratiometric Fluorescent Probe for Imaging of Hydrogen Peroxide Levels in Rat Organ Tissues

Hydrogen peroxide (H2O2) is important in the regulation of a variety of biological processes and is involved in various diseases. Quantitative measurement of H2O2 levels at the subcellular level is important for understanding its positive and negative effects on biological processes. Herein, a two-photon ratiometric fluorescent probe (SHP-Cyto) with a boronate-based carbamate leaving group as the H2O2 reactive trigger and 6-(benzo[d]thiazol-2'-yl)-2-(N,N-dimethylamino) naphthalene (BTDAN) as the fluorophore was synthesized and examined for its ability to detect cytosolic H2O2 in situ. This probe, based on the specific reaction between boronate and H2O2, displayed a fluorescent color change (455 to 528 nm) in response to H2O2 in the presence of diverse reactive oxygen species in a physiological medium. In addition, ratiometric two-photon microscopy (TPM) images with SHP-Cyto revealed that H2O2 levels gradually increased from brain to kidney, skin, heart, lung, and then liver tissues. SHP-Cyto was successfully applied to the imaging of endogenously produced cytosolic H2O2 levels in live cells and various rat organs by using TPM.

Ultra-sensitive fluorescent probes for hypochlorite acid detection and exogenous/endogenous imaging of living cells

Two fluorescent probes have been developed to detect HOCl with ultra-high sensitivity and employed to image exogenous/endogenous HOCl in living cells.

Lysosomal-Targeted Two-Photon Fluorescent Probe to Sense Hypochlorous Acid in Live Cells

A two-photon reversible fluorescent probe L1 was designed and synthesized. The fluorescence intensity of the probe solution was strong, while the fluorescence of the solution was obviously quenched and the color of the solution was changed after the addition of hypochlorous acid, indicating this is "naked-eye sensor" for the detection of HClO. The probe showed great selectivity for hypochlorous acid over other reactive oxygen species (ROS) and anions. Fluorescence titration experiments showed that the probe has a low detection limit of 0.674 μM. Because of a morpholine group introduced to the naphathalimide framework, probe L1 was successfully applied to detect intracellular HClO in lysosome.

Real-Time Monitoring ATP in Mitochondrion of Living Cells: A Specific Fluorescent Probe for ATP by Dual Recognition Sites

Adenosine triphosphate (ATP) is mainly produced in the mitochondrion and used as a universal energy source for various cellular events. Various fluorescent probes for ATP have been established successfully, but most of them are not appropriate for monitoring the fluctuation of the mitochondrial ATP level. Herein, a fluorescent probe named Mito-Rh is first synthesized and used to recognize ATP in mitochondrion. In the probe, rhodamine, diethylenetriamine, and triphenylphosphonium are selected as fluorophore, reaction site, and mitochondrion-targeting group, respectively. Probe Mito-Rh shows high sensitivity to ATP with 81-fold fluorescence enhancement, and the detection range (0.1-10 mM) can match the concentration level of ATP in the mitochondrion. Moreover, Mito-Rh provides excellent selectivity toward ATP over other biological anions (ADP, AMP, GTP, CTP, UTP) owing to a concurrent effect of dual recognition sites (hydrogen bond and π-π stacking). In particular, the probe can localize in mitochondrion specifically and demonstrates utility in the real-time detection of mitochondrial ATP concentration changes.

A fast-response fluorescent probe for hypochlorous acid detection and its application in exogenous and endogenous HOCl imaging of living cells

A facile fluorescent probe for exogenous and endogenous HOCl detection in living cells.

A two-photon ratiometric fluorescent probe for the synergistic detection of the mitochondrial SO2/HClO crosstalk in cells and in vivo

We report herein a mitochondria-targeted two-photon ratiometric fluorescent probe to respectively or successively detect HSO₃⁻/HClO in cells and zebrafish.