Near-Infrared Fluorescent Turn-On Probe for Selective Detection of Hypochlorite in Aqueous Medium and Live Cell Imaging

Hypochlorite, as an important reactive oxygen species (ROS), plays a vital role in many physiological and pathological processes, but an excess concentration of hypochlorite (ClO-) may become toxic to humans and cause disease. Hence, the selective and rapid detection of hypochlorite (ClO-) is necessary for human safety. Here, we report a novel near-infrared (NIR) fluorescence "turn-on" and highly selective benzophenoxazinium chloride-based fluorescent probe, BPH (benzophenoxazinium dihydroxy benzaldehyde), for hypochlorite detection. Due to hypochlorite-induced vicinal diol oxidation to the corresponding ortho benzoquinone derivative, the photoinduced electron transfer (PET) process, which was operating from vicinal diol to the benzophenoxazinium chloride receptor moiety, was suddenly inhibited, as a result of which strong NIR fluorescence "turn-on" emission was observed. The detection limit of BPH was found to be 2.39 × 10-10 M, or 0.23 nM. BPH was successfully applied for exogenous and endogenous hypochlorite detection in live MDA-MB 231 cells.

Turn-on detection of Al3+ ions using quinoline-based tripodal probe: mechanistic investigation and live cell imaging applications

In this study, an easily synthesizable Schiff base probe TQSB having a quinoline fluorophore is demonstrated as a fluorescent and colorimetric turn-on sensor for Al3+ ions in a semi-aqueous medium (CH3CN/water; 4 : 1; v/v). Absorption, emission and colorimetric studies clearly indicated that TQSB exhibited a high selectivity toward Al3+, as observed from its excellent binding constant (Kb = 3.8 × 106 M-1) and detection limit (7.0 nM) values. TQSB alone was almost non-fluorescent in nature; however, addition of Al3+ induced intense fluorescence at 414 nm most probably due to combined CHEF (chelation-enhanced fluorescence) and restricted PET effects. The sensing mechanism was established via Job's plot, NMR spectroscopy, ESI-mass spectrometry, and density functional theory (DFT) analyses. Furthermore, to evaluate the applied potential of probe TQSB, its sensing ability was studied in real samples such as soil samples and Al3+-containing Digene gastric tablets as well as on low-cost filter paper strips. Fluorescence microscopy imaging experiments further revealed that TQSB can be used as an effective probe to detect intracellular Al3+ in live cells with no cytotoxicity.

A review on oxime functionality: an ordinary functional group with significant impacts in supramolecular chemistry

The oxime functional group is pivotal in chemistry, finding extensive applications in medical science, catalysis, organic functional group transformations, and the recognition of essential and toxic analytes. While the coordination chemistry of oxime derivatives has been thoroughly explored and several reviews have been published on this topic in reputable journals, a comprehensive review encompassing various aspects such as crystal engineering, cation and anion recognition, as well as coordination chemistry activities, is still in demand. This feature article highlights the diverse applications of oxime derivatives across multiple domains of chemistry, including medicine, agriculture, crystal engineering, coordination chemistry, and molecular recognition studies. Each of the oxime derivatives in this feature article are meticulously described in terms of their medicinal applications, crop protection, crystal engineering attributes, analyte recognition capabilities, and coordination chemistry aspects. By providing a comprehensive overview of their versatile applications, this article aims to inspire researchers to explore and develop novel oxime-based derivatives for future applications.

A simple 'turn-on' fluorescence chemosensor for Al(iii) detection in aqueous solution and solid matrix

A simple fluorescence chemosensor of FHS-OH based on salicylaldehyde Schiff base was developed via a one-step reaction, which achieved a fast and highly selective response for Al(iii). Mechanism studies showed that when FHS-OH was exposed to Al(iii) with 1 : 2 binding stoichiometry in an aqueous solution at neutral pH, C[double bond, length as m-dash]N isomerization and PET processes were limited, resulting in a 'turn-on' fluorescence response with a low detection limit of 63 nmol L-1 and a satisfying linear range of 0.0-20.0 μmol L-1. Compared to traditional detection methods for Al(iii), fluorometry using FHS-OH has several advantages, including simplicity, quick response, and capability of real-time detection. More importantly, the detection of Al(iii) on a solid matrix (test paper) was successfully achieved. After the addition of Al(iii), a significant emission colour change from green to bright blue was observed by the naked eye owing to the intrinsic aggregation-induced emission (AIE) characteristic of FHS-OH.

Novel Near-Infrared Iridium(III) Complex for Chemiluminescence Imaging of Hypochlorous Acid

Chemiluminescence (CL) probes that possess near-infrared (NIR) emission are highly desirable for in vivo imaging due to their deeper tissue penetration ability and intrinsically high sensitivity. Herein, a novel iridium-based CL probe (NIRIr-CL-1) with direct NIR emission was reported as the result of hypochlorous acid (HClO)-initiated oxidative deoximation. To improve its biocompatibility and extend the CL time for in vivo imaging applications, this NIRIr-CL-1 was prepared as a CL nanoparticle probe (NIRIr-CL-1 dots) through encapsulation by an amphiphilic polymer Pluronic F127 (F127). All results demonstrate that the NIRIr-CL-1 dots have good selectivity and sensitivity for visualization of HClO even at the depth of 1.2 cm. Owing to these advantages, the CL imaging of exogenous and endogenous HClO in mice was achieved. This study could provide new insights into the construction of new NIR emission CL probes and expand their applications in biomedical imaging.

A new ratiometric switch "two-way" detects hydrazine and hypochlorite via a "dye-release" mechanism with a PBMC bioimaging study

A new ratiometric fluorescent probe (E)-2-(benzo[d]thiazol-2-yl)-3-(8-methoxyquinolin-2-yl)acrylonitrile (HQCN) was synthesised by the perfect blending of quinoline and a 2-benzothiazoleacetonitrile unit. In a mixed aqueous solution, HQCN reacts with hydrazine (N₂H₄) to give a new product 2-(hydrazonomethyl)-8-methoxyquinoline along with the liberation of the 2-benzothiazoleacetonitrile moiety. In contrast, the reaction of hypochlorite ions (OCl^-) with the probe gives 8-methoxyquinoline-2-carbaldehyde. In both cases, the chemodosimetric approaches of hydrazine and hypochlorite selectively occur at the olefinic carbon but give two different products with two different outputs, as observed from the fluorescence study exhibiting signals at 455 nm and 500 nm for hydrazine and hypochlorite, respectively. A UV-vis spectroscopy study also depicts a distinct change in the spectrum of HQCN in the presence of hydrazine and hypochlorite. The hydrazinolysis of HQCN exhibits a prominent chromogenic as well as ratiometric fluorescence change with a 165 nm left-shift in the fluorescence spectrum. Similarly, the probe in hand (HQCN) can selectively detect hypochlorite in a ratiometric manner with a shift of 120 nm, as observed from the fluorescence emission spectra. HQCN can detect hydrazine and OCl^- as low as 2.25 × 10^-8 M and 3.46 × 10^-8 M, respectively, as evaluated from the fluorescence experiments again. The excited state behaviour of the probe HQCN and the chemodosimetric products with hydrazine and hypochlorite are studied by the nanosecond time-resolved fluorescence technique. Computational studies (DFT and TDDFT) with the probe and the hydrazine and hypochlorite products were also performed. The observations made in the fluorescence imaging studies with human blood cells manifest that HQCN can be employed to monitor hydrazine and OCl^- in human peripheral blood mononuclear cells (PBMCs). It is indeed a rare case that the single probe HQCN is found to be successfully able to detect hydrazine and hypochlorite in PBMCs, with two different outputs.

Metal Peptide Conjugates in Cell and Tissue Imaging and Biosensing

Metal complex luminophores have seen dramatic expansion in application as imaging probes over the past decade. This has been enabled by growing understanding of methods to promote their cell permeation and intracellular targeting. Amongst the successful approaches that have been applied in this regard is peptide-facilitated delivery. Cell-permeating or signal peptides can be readily conjugated to metal complex luminophores and have shown excellent response in carrying such cargo through the cell membrane. In this article, we describe the rationale behind applying metal complexes as probes and sensors in cell imaging and outline the advantages to be gained by applying peptides as the carrier for complex luminophores. We describe some of the progress that has been made in applying peptides in metal complex peptide-driven conjugates as a strategy for cell permeation and targeting of transition metal luminophores. Finally, we provide key examples of their application and outline areas for future progress.

An optical strategy for detecting hypochlorite in vitro and cells with high selectivity and stability based on a lanthanide-doped upconversion probe

The excessive use of sodium hypochlorite disinfectant for preventing COVID-19 can be harmful to the water environment and humans. More importantly, owing to hypochlorite being a biomarker of immune responses in living organisms, its abnormal production can damage nucleic acids and protein molecules, eventually causing many diseases (even cancer). Exploring a reliable, rapid, and non-invasive method to monitor the hypochlorite level in vitro and in cells can be significant. Herein, we report a novel ratiometric fluorescence sensing strategy based on Astrazon Brilliant Red 4G dye-sensitized NaGdF₄:Yb³⁺, Er³⁺@NaYF₄ core–shell upconversion nanoparticles (UCNPs@ABR 4G). Based on the combination mechanism of the fluorescent resonant energy transfer effect (FRET) and redox, a linear model of fluorescence intensity ratio and hypochlorite concentration was constructed for a fast response and high selectivity monitoring of hypochlorite in vitro and in vivo. The detection limit was calculated to be 0.39 μM. In addition, this sensing strategy possessed good stability and circularity, making it valuable both for the quantitative detection of hypochlorite in water and for the visualization of intracellular hypochlorite. The proposed optical probe is promising for the efficient and stable non-invasive detection of hypochlorite.

The excessive use of sodium hypochlorite disinfectant for preventing COVID-19 can be harmful to the water environment and humans.

Development of a new water-soluble fluorescence probe for hypochlorous acid detection in drinking water

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A responsive small-molecule fluorescence probe is developed for hypochlorous acid (HOCl) detection.

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The new probe has good solubility and stability in water, can rapidly and selectively respond to HOCl in pure aqueous solution.

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HOCl-triggered specific reaction leads to a blue shift of UV–vis absorption and enhancement in fluorescence that are recorded for HOCl detection.

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The application of this probe for HOCl detection in drinking water samples is demonstrated.

Responsive small-molecule fluorescence probe specific for target analyte detection is an emerging technology for food safety and quality analysis. In this work, we report a new water soluble small-molecule fluorescence probe (PG) for the detection of hypochlorous acid (HOCl) in drinking water samples. Probe PG was developed by coupling of a glucosamine into 10-methyl-10H-phenothiazine fluorophore with a HOCl-responsive C=N bond. The thioether is another recognition site that can be oxidized to be sulfoxide in water. Due to the specific reactions triggered by HOCl, probe PG’s absorption band is blue shifted from 388 to 340 nm, and fluorescence at 488 nm is more than 55-fold enhanced. Probe PG features high fluorescence stability in PBS buffer with varied pH, fast response and high selectivity to HOCl. The application of the probe PG for HOCl detection in real-world samples is demonstrated by HOCl detection in drinking water, including tap water, purified water, and spring water samples. The recoveries of this method for HOCl detection in drinking water are in the range of 99.17–102.3%. This work thus provides a new method for HOCl detection in drinking water with high precision and accuracy.

Determination of Hypochlorite via Fluorescence Change from Blue to Green Based on 4-(1 H-imidazo [4,5-f] [1,10]-phenanthrolin-2-yl) Benzaldehyde Oxime

The new design strategy will provide the possibility for preparing a dynamic sensor by employing the inhibition of C = N isomerization. In this work, the functional probe 4-(1 H-imidazo [4,5-f] [1,10]-phenanthrolin-2-yl) benzaldehyde oxime (compound 4) has been synthesized and such molecule gives rise to blue emission. Due to the incorporation of hypochlorite, the oxime group can be oxidized to the structure of aldehyde. As a result, the molecular motif exhibits sharp emission change from blue to green due to the addition of hypochlorite with enough sensitivity and selectivity (detection limit = 53 nM, linear range 0.5-8.0 µM). It has also been used for monitoring ClO^- by employing solution color change and the absorption signal difference could effectively rule out the effects of interference species. To our knowledge, it will be the first case of a highly selective hypochlorite sensor derived from oxime isomerization reaction based on phenanthroline backbone.

A Two-Photon Excited Near-Infrared Iridium(III) Complex for Multi-signal Detection and Multimodal Imaging of Hypochlorite

Hypochlorite (ClO^-), as a type of reactive oxygen species (ROS), plays a crucial role in the process of oxidative stress and is closely related to many diseases. Thus, developing a method for detecting and imaging of ClO^- with high sensitivity and selectivity is of great significance. However, the applications of most luminescent probes are limited to the fact that the excitation and emission wavelengths of them are in the visible light region rather than in the near-infrared (NIR) region. Hence, an NIR iridium(III) complex (Mul-NIRIr) with two-photon excitation is designed for the detecting and imaging of ClO^-. In the presence of ClO^-, the luminescent intensity and lifetime of Mul-NIRIr are remarkably enhanced. Interestingly, Mul-NIRIr also exhibits excellent electrochemiluminescence (ECL) properties, and the ECL signal is significantly enhanced with the addition of ClO^-. What is more, Mul-NIRIr is also suitable for the detection and analysis ClO^- by flow cytometry. Therefore, Mul-NIRIr is developed to detect multiple signals and is successfully applied to detect exogenous and endogenous ClO^- in living cells with one-photon, two-photon, and phosphorescence lifetime image microscopy (PLIM). In addition, Mul-NIRIr was successfully used for imaging of ClO^- in tissues and inflammatory mouse models. All of the above results indicate that Mul-NIRIr is highly effective in detecting ClO^- in living systems.

Multimodal Imaging Iridium(III) Complex for Hypochlorous Acid in Living Systems

Biomolecule tracing with different imaging methods is of great significance for more accurately unravelling the fundamental processes in living systems. However, considering the different principles of each imaging method for probe design, it is still a great challenge to apply one molecular probe to achieve two or even more imaging analyses for biomarkers. In general, traditional oxime was reported as a recognition group for fluorescence imaging of HOCl. Herein, for the first time, we designed the oxime decorated iridium(III) complex, which can be directly used for chemiluminescence as well as two-photon luminescence and photoluminescence lifetime imaging of HOCl in living systems. Moreover, the novel chemiluminescence mechanism of Ir-CLFLPLIM for HOCl was also proposed and explored by continuously monitoring chemiluminescence peak shapes and mass spectra, inferring the reaction intermediate and calculating the chemical reaction energy range of the reaction process. This strategy could lead us to expand the chemiluminescence application of transition metal complexes and develop more multimodal imaging probes.

Recent Advances in Fluorescent Probes for Detection of HOCl and HNO

It is known that reactive oxygen (ROS) and nitrogen (RNS) species play a diverse role in various biological processes, such as inflammation, signal transduction, and neurodegenerative injury, apart from causing various diseases caused by oxidative and nitrosative stresses, respectively, by ROS and RNS. Thus, it is very important to quantify the concentration level of ROS and RNS in live cells, tissues, and organisms. Various small-molecule-based fluorescent/chemodosimetric probes are reported to quantify and map the effective distribution of ROS/RNS under in vitro/in vivo conditions with a great spatial and temporal resolution. Such reagents are now appreciated as an excellent tool for aiding breakthroughs in modern redox biology. This mini-review is a brief, but all-inclusive, account of such molecular probes that have been developed recently.

Molecular Design of Bioorthogonal Probes and Imaging Reagents Derived from Photofunctional Transition Metal Complexes

For more than 15 years, bioorthogonal chemistry has received increasing attention due to its successful applications in the detection and imaging of biomolecules in their native biological environments. The method typically proceeds with the incorporation of a biological substrate appended with a bioorthogonal functional group (chemical reporter), followed by the introduction of the substrate to biological systems. Biomolecules containing the substrate are then recognized by an exogenously delivered bioorthogonal probe. Despite the fact that many useful chemical reporters and bioorthogonal reactions have been developed, most of the bioorthogonal probes reported thus far are fluorescent dyes. A limitation is that stringent washing is required due to the interference caused by the background fluorescence of unreacted probes. Thus, fluorogenic probes with turn-on emission properties upon bioorthogonal labeling have been designed as an alternative strategy. These probes are highly appealing because excellent images can be obtained without the need for washing steps. Nearly all fluorogenic bioorthogonal probes designed are essentially organic dyes, their emission is limited to fluorescence, and the utilization of the probes is confined to bioimaging applications. Recently, there has been a growing interest in the bioimaging and therapeutic applications of luminescent inorganic and organometallic transition metal complexes due to their intriguing photophysical and photochemical properties, high membrane permeability, controllable cellular uptake, intracellular localization, and cytotoxicity. We anticipate that photofunctional transition metal complexes can be exploited as valuable bioorthogonal probes due to these appealing advantages. In this Account, we introduce the molecular design, photophysical and photochemical properties, and biological applications of various bioorthogonal probes and imaging reagents based on photofunctional transition metal complexes. The presence of a cationic metal center significantly enhances the bioorthogonal reactivity of the probes, yet their stability in aqueous solutions can be maintained. Interestingly, some of these metal complexes are strategically modified to display phosphorogenic properties, that is, phosphorescence turn-on upon bioorthogonal labeling reactions. Importantly, these probes not only exhibit favorable photophysical properties after bioorthogonal labeling, but also efficient photoinduced singlet oxygen (¹O₂) generation. This interesting bioorthogonal reaction-triggered photosensitization capability allows the modulation of ¹O₂ generation efficiency and contributes to the development of controllable photocytotoxic agents. The exploration of transition metal complex-based probes not only significantly widens the scope of bioorthogonal labeling but also further highlights the unique advantages of these complexes in the design of theranostic reagents. The development of these innovative reagents is expected to contribute to the basic understanding of biological processes in living systems and provide exciting opportunities for new diagnostic and therapeutic applications.

Imaging of Hypochlorous Acid by Fluorescence and Applications in Biological Systems

In recent decades, HOCl research has attracted a lot of scientists from around the world. This chemical species is well known as an important player in the biological systems of eukaryotic organisms including humans. In the human body, HOCl is produced by the myeloperoxidase enzyme from superoxide in very low concentrations (20 to 400 μm); this species is secreted by neutrophils and monocytes to help fight pathogens. However, in the condition called "oxidative stress", HOCl has the capability to attack many important biomolecules such as amino acids, proteins, nucleotides, nucleic acids, carbohydrates, and lipids; these reactions could ultimately contribute to a number of diseases such as neurodegenerative diseases (AD, PD, and ALS), cardiovascular diseases, and diabetes. In this review, we discuss recent efforts by scientists to synthesize various fluorophores which are attached to receptors to detect HOCl such as: chalcogen-based oxidation, oxidation of 4-methoxyphenol, oxime/imine, lactone ring opening, and hydrazine. These synthetic molecules, involving rational synthetic pathways, allow us to chemoselectively target HOCl and to study the level of HOCl selectivity through emission responses. Virtually all the reports here deal with well-defined and small synthetic molecular systems. A large number of published compounds have been reported over the past years; this growing field has given scientists new insights regarding the design of the chemosensors. Reversibility, for example is considered important from the stand point of chemosensor reuse within the biological system; facile regenerability using secondary analytes to obtain the initial probe is a very promising avenue. Another aspect which is also important is the energy of the emission wavelength of the sensor; near-infrared (NIR) emission is favorable to prevent autofluorescence and harmful irradiation of tissue; thus, extended applicability of such sensors can be made to the mouse model or animal model to help image internal organs. In this review, we describe several well-known types of receptors that are covalently attached to the fluorophore to detect HOCl. We also discuss the common fluorophores which are used by chemist to detect HOCl, Apart from the chemical aspects, we also discuss the capabilities of the compounds to detect HOCl in living cells as measured through confocal imaging. The growing insight from HOCl probing suggests that there is still much room for improvement regarding the available molecular designs, knowledge of interplay between analytes, biological applicability, biological targeting, and chemical switching, which can also serve to further sensor and theurapeutic agent development alike.

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

Development of high performance fluorescent chemosensors for the detection of ClO- in vitro and in vivo is very desirable, because many human diseases are caused by ClO-. In this paper, a highly selectivity and sensitive fluorescent probe, EDPC, based on 3-acetylcoumarin, was synthesized, which could respond to ClO- and exhibit an "off-on" mode in Tris-HCl buffer (pH = 7.2, 10 mM, 50% C2H5OH) solutions. The detection limit of the EDPC probe for ClO- was as low as 1.2 × 10-8 M. Moreover, the high selectivity and high sensitivity of EDPC towards ClO- are attributed to the oxidation reaction between the C-O of the coumarin lactone and the C[double bond, length as m-dash]C formed by aldol condensation and the mechanism was further verified using ESI-MS and DFT. Additionally, the concentrations of ClO- in real water were also calculated using the EDPC probe and showed good recovery. Finally, the distribution of intracellular endogenous ClO- was gained by confocal fluorescence microscopy in living HEK293T cells.

A highly specific fluorescent probe for rapid detection of hypochlorous acidin vivoand in water samples

We report the development of a new chromogenic and fluorogenic probe for the detection of HOCl in zebrafish, mice with arthritis and environmental water samples.

Overriding Phthalate Decomposition When Exploring Mycophenolic Acid Intermediates as Selenium-Based ROS Biological Probes

Hypochlorous (OCl^-) acid is the most well-known bacterial oxidant to be produced by neutrophils. Excess amounts of OCl^- can cause various disorders in living systems. Herein, we have designed, synthesized, and characterized two novel organoselenium-based target molecules (Probe-1 and Probe-OCl) based on a synthetic intermediate of mycophenolic acid for the aqueous detection of OCl^-. Probe 1 has been recently reported (Org. Lett. 2018, 20, 3557-3561); both probes show immediate "turn-on" fluorescence (<1 s) upon the addition of OCl^-, display an increase in the fluorescence quantum yield (3.7-fold in Probe-1 and 11.6-fold in Probe-OCl), and are completely soluble in aqueous media without the help of any cosolvent. However, a decrease in the "turn-on" intensity with the oxidized version of Probe-1 in cell assays due to the anhydride/phthalate functionality suggests that probe degradation occurs based on hydrolytic action (a probe degradation half-life of ∼1500 s at 15 μM Probe-1 and 150 μM OCl). Thus, the change of "anhydride" to "methylamide" begets Probe-OCl, which possesses more stability without sacrificing its water solubility properties and responses at short times. Further studies suggest that Probe-OCl is highly stable within physiological pH (pH = 7.4). Surprisingly, in live cell experiments involving U-2 OS cells and HeLa cells, Probe-OCl accumulated and aggregated in lipid droplets and gives a "turn-on" fluorescence response. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays confirmed that Probe-OCl is not toxic. Cuvette aggregation studies were also performed (tetrahydrofuran/H₂O) to demonstrate aggregation-induced fluorescence at longer times. Our current hypothesis is that the "turn-on" fluorescence effect is caused by the aggregation-induced emission mechanism available for Probe-OCl. In this case, in tandem, we reanalyzed the Mes-BOD-SePh derivative to compare and contrast cell localization as imaged by confocal microscopy; fluorescence emission occurs in the absence of, or prior to, Se oxidation.

Extending Hypochlorite Sensing from Cells to Elesclomol-Treated Tumors in Vivo by Using a Near-Infrared Dual-Phosphorescent Nanoprobe

Reactive oxygen species (ROS), when beyond the threshold, can exhaust the capacity of cellular antioxidants and ultimately trigger cell apoptosis in tumor biology. However, the roles of hypochlorite (ClO^-) in this process are much less clear compared with those of ROS, and its detection is easily obstructed by tissue penetration and endogenous fluorophores. Herein, we first synthesized a near-infrared (NIR) ratiometric ClO^- probe (Ir NP) composed of two kinds of phosphorescent iridium(III) complexes (Ir1 and Ir2) encapsulated with amphiphilic DSPE-mPEG5000. Ir NPs are dual-emissive and show obvious changes in phosphorescence intensity ratios and lifetimes of two emission bands upon exposure to ClO^-. During the ClO^- detection, ratiometric photoluminescence imaging is much more reliable over the intensity-based one for its self-calibration, while time-resolved photoluminescence imaging (TRPI) could distinguish the phosphorescence with long lifetime of Ir NPs from short-lived autofluorescence of tissues, resulting in the high accuracy of ClO^- determination. With NIR emission, a long phosphorescence lifetime, fast response, and excellent biocompatibility, Ir NPs were applied to the detection of ClO^- in vitro and in vivo by means of ratiometric phosphorescence imaging and TRPI with high signal-to noise-ratios (SNR). Importantly, we demonstrated the elevated ClO^- in elesclomol-stimulated tumors in living mice for the first time, which holds great potential for the visualization of the boost of ClO^- in anti-carcinogen-treated tumors and the further investigation of ROS-related oncotherapeutics.

A benzothiazole-based fluorescent probe for hypochlorous acid detection and imaging in living cells

A benzothiazole-based turn-on fluorescent probe with a large Stokes shift (190nm) has been developed for hypochlorous acid detection. The probe displays prompt fluorescence response for HClO with excellent selectivity over other reactive oxygen species as well as a low detection limit of 0.08μM. The sensing mechanism involves the HClO-induced specific oxidation of oxime moiety of the probe to nitrile oxide, which was confirmed by HPLC-MS technique. Furthermore, imaging studies demonstrated that the probe is cell permeable and can be applied to detect HClO in living cells.

A methylene blue-based near-infrared fluorescent probe for rapid detection of hypochlorite in tap water and living cells

A methylene blue-based near-infrared fluorescent probe was designed for the selective determination of hypochlorite (ClO-), over other reactive oxygen species or interfering agents. Acetylated methylene blue was synthesized by introducing the acetyl group into the methylene blue framework, which can specifically recognize exogenous and endogenous ClO-. The acetylated methylene blue fluorescent probe was characterized by 1H NMR, 13C NMR and HRMS. The response process and possible mechanism were studied using products of the probe. The emission response of the probe to ClO- presented good linear relationship in the 0-60 μM concentration range, with the detection limit of 0.1 μM (measured at 660 nm and 690 nm). The absorption and emission wavelengths of acetylated methylene blue are both in the near-infrared region; in addition, the probe itself and the degradation products were well-dissolved in water and have almost no toxicity. The probe was used for intracellular ClO- imaging and showed a large fluorescence enhancement (about 200-fold increase).

A naphthalimide based fast and selective fluorescent probe for hypochlorous acid/hypochlorite and its application for bioimaging

A reversible and mitochondria targetable fluorescent probe (Nap-Se) bearing 1,8-naphthalimide and a selenomorpholine fragment was designed and synthesized.

A novel pyridyl triphenylamine-BODIPY aldoxime: Naked-eye visible and fluorometric chemodosimeter for hypochlorite

An aldoxime containing fluorescent probe based on vinylpydine-appended triphenylamine-BODIPY has been designed and used for hypochlorite detection. OX-PPA-BODIPY was developed by introducing an aldoxime group into the 2-position of BODIPY, which can be used for the detection of hypochlorite with a sharp color change from pink to green. The attachment of 4-vinylpyridine moiety to triphenylamine-BODIPY constructs a fluorogen with desirable conjugated system. The probe, which displays extremely weak fluorescence owing to the CN isomerization mechanism at 2-position of BODIPY, responds to HClO/ClO^- through a dramatic enhancement of its fluorescence intensity. This new probe, a naked-eye visible and fluorometric chemodosimeter, exhibits high selectivity and sensitivity toward hypochlorite over other reactive oxygen species (ROS) and anions. The detection is accompanied by a 20-fold increase in fluorescent intensity (Φ_F from 0.02 to 0.43). The detection limit of the probe for hypochlorite is 7.37×10^-7M. Moreover, OX-PPA-BODIPY can be used to detect hypochlorite in real water samples.

Recent progress in chromogenic and fluorogenic chemosensors for hypochlorous acid

Due to the biological and industrial importance of hypochlorous acid, the development of optical probes for HOCl has been an active research area. Hypochlorous acid and hypochlorite can oxidize electron-rich analytes with accompanying changes in molecular sensor spectroscopic profiles. Probes for such processes may monitor HOCl levels in the environment or in an organism and via bio-labeling or bioimaging techniques. This review summarizes recent developments in the area of chromogenic and fluorogenic chemosensors for HOCl.

A novel method for the synthesis of 1,2-benzisoxazoline-3-one and its application to hypochlorite recognition

The reaction of salicylhydroxamic acid with hypochlorite produces 1,2-benzisoxazoline-3-one, a heterocycle that contains a fluorophore.

Fluorescent probes for the selective detection of chemical species inside mitochondria

This feature article systematically summarizes the development of fluorescent probes for the selective detection of chemical species inside mitochondria.

An activatable fluorescent probe with an ultrafast response and large Stokes shift for live cell bioimaging of hypochlorous acid

A novel “turn-on” fluorescent probe for high selectivity, rapid detection and imaging of HOCl based on the protection of carbaldehyde with 2-mercaptoethanol.

Recent developments in curcumin and curcumin based polymeric materials for biomedical applications: A review

Turmeric (Curcuma longa) is a popular Indian spice that has been used for centuries in herbal medicines for the treatment of a variety of ailments such as rheumatism, diabetic ulcers, anorexia, cough and sinusitis. Curcumin (diferuloylmethane) is the main curcuminoid present in turmeric and responsible for its yellow color. Curcumin has been shown to possess significant anti-inflammatory, anti-oxidant, anti-carcinogenic, anti-mutagenic, anticoagulant and anti-infective effects. This review summarizes and discusses recently published papers on the key biomedical applications of curcumin based materials. The highlighted studies in the review provide evidence of the ability of curcumin to show the significant vitro antioxidant, diabetic complication, antimicrobial, neuroprotective, anti-cancer activities and detection of hypochlorous acid, wound healing, treatment of major depression, healing of paracentesis, and treatment of carcinoma and optical detection of pyrrole properties. Hydrophobic nature of this polyphenolic compound along with its rapid metabolism, physicochemical and biological instability contribute to its poor bioavailability. To redress these problems several approaches have been proposed like encapsulation of curcumin in liposomes and polymeric micelles, inclusion complex formation with cyclodextrin, formation of polymer-curcumin conjugates, etc.