Tissue lipid peroxidation and reduced glutathione depletion in hypochlorite-induced lung injury

A colorimetric fluorescent probe for reversible detection of HSO3-/H2O2 and effective discrimination of HSO3-/ClO- and its application in food and bioimaging

In view of the significant role of reactive sulfur species (RSS) and reactive oxygen species (ROS) in maintaining the redox homeostasis of organisms, we proposed a colorimetric fluorescent probe (HTN) for reversible detection of HSO3-/H2O2 and effective discrimination of HSO3-/ClO-. C = C is the active site for the Michael addition of HSO3- and the oxidation of ClO-. When HTN interacts with HSO3- and ClO-, it exhibits fluorescence quenching. The addition of oxidizing H2O2 to the system can restore the conjugate structure of the addition product of HSO3- (HTN-HSO3-) and the fluorescence recovery, but it cannot restore the structure of the oxidation product of ClO- (HTN-ClO-). By studying the change of the reversibility/non-reversibility of the probe structure with the addition of H2O2, the purpose of reversible detection of HSO3-/H2O2 and distinguishing HSO3-/ClO- is achieved. In addition, HTN can not only be used as a fluorescent ink to detect HSO3- on the test paper, but also has excellent detection effect on HSO3- and ClO- in real food samples and water samples. Meantime, HTN has good biocompatibility and can target mitochondria to achieve reversible detection of HSO3-/H2O2 and effective discrimination of HSO3-/ClO- in living cells. Therefore, HTN has great potential as a molecular tool for studying redox homeostasis in the interaction network of complex living systems.

A novel ratiometric colorimetric sensor for detecting hypochlorite and ascorbic acid based on cascade reaction

Hypochlorite and ascorbic acid (AA), play an indispensable role in numerous physiological activities. Herein, a ratiometric colorimetric sensing strategy for the determination of hypochlorite and AA was developed via the catalytic oxidation and reduction of 3,3',5,5'-tetramethylbenzidine (TMB). Interestingly, in the presence of Fe3O4-MOF-5(Fe) and hypochlorite, TMB complexes in acidic environments were oxidized to blue oxidized TMB and further diazotized to produce yellow-green diazotized TMB, resulting in the hypochlorite concentration-dependent ratiometric variation for the absorbance at 652 and 450 nm (A450/A652). Moreover, the diazotized TMB was restored to colorless TMB due to the reducibility of AA, and the detection limit of hypochlorite and AA were 0.027 and 0.677 μM, respectively. The ratiometric colorimetric sensing platform offered higher sensitivity and better selectivity because of the specific hypochlorite-induced reaction and the excellent peroxidase-like activity of Fe3O4-MOF-5(Fe). The proposed novel strategy provided the guidance to develop sensors for successive detection of hypochlorite and AA in complicated samples.

A Multimode Optical Sensor for Highly Selective and Sensitive Detection of Hypochlorous Acid in Water and Body Fluid

Hypochlorous acid (HClO), as an important reactive oxygen species (ROS), plays a crucial role in our daily life and in biological systems, and its convenient and accurate detection is significant and imperative. In this work, a self-calibrated multimode optical sensor for convenient and accurate HClO detection was elaborately fabricated based on a multifunctional metal-organic framework platform with catalytic active metal nodes, fluorescent responsive bridging ligands, and intrinsic pores for functional molecule accommodation. The sensor shows not only turn-on and ratiometric fluorescence response but also color change in response to HClO. The detection limits are as low as 16.9, 17.3, 66.5, and 63.2 nM for ratiometric fluorometry, absorbance-based colorimetry, and smartphone-based fluorescenceand color analysis, respectively. The accuracy and practicability of this sensor were also demonstrated by the detection of hypochlorous acid in actual water and body fluid samples, and the recovery rates ranged from 97.8 to 103.8%.

A selenium-based fluorescent sensor for the reversible detection of ClO- and H2S in foods

HClO/ClO- and H2S are two kinds of momentous biological small molecules in the organism, and the redox balance between them is considerable for the physiological and pathological properties of organisms. Hence, it is very crucial to monitor the redox course between HClO and H2S. Herein, a reversible fluorescent sensor (IPSe) for ClO- and H2S was firstly constructed with the selenium atom as the response site and the dicyanoisophorone as the fluorophore. The sensor IPSe could detect ClO- with good selectivity and sensitivity due to the oxidation reaction of the selenium atom triggered by ClO-. The recognition of IPSe to hypochlorite induced a hypsochromic shift of the absorption maximum from 420 nm to 380 nm. IPSe exhibited the prominent low detection limit of 55.3 nM for detecting ClO-, accompanied by distinct fluorescent attenuation. Moreover, H2S could efficiently return the fluorescence of the IPSe solution to the original level by H2S reducing selenoxide. The experimental results show that the suggested method has high precision and accuracy for the detection of ClO- and H2S. The applications in real water samples, beverages and cell imaging verified that the IPSe was capable of monitoring the changes in the concentration of ClO-/H2S, which indicates that it is of great meaning to survey the biological functions of ClO- and H2S via IPSe.

Accurate detection depression cell model with a dual-locked fluorescence probe in response to noradrenaline and HClO

Due to the serious harm of depression to human health and quality of life, an accurate diagnosis of depression is warranted. For the complex etiology of depression, a single biomarker diagnostic method often leads to misdiagnosis. As noradrenaline and HClO are closely related to depression, a "dual-locked" fluorescence probe R-NE-HClO for diagnosing of depression through the simultaneous detection of noradrenaline and HClO was designed and synthesized. Fluorescence of R-NE-HClO can only be restored in the presence of both noradrenaline and HClO. The probe demonstrates excellent selectivity for noradrenaline and HClO and low cytotoxicity in cell imaging experiments. It is to be observed that we successfully applied the probe to accurately detect depressed cells which provides a possible tool for diagnosing depression.

De Novo Design of a Highly Stable Ratiometric Probe for Long-Term Continuous Imaging of Endogenous HClO Burst

Long-term continuous imaging of endogenous HClO burst is of great importance for the elucidation of various physiological or pathological processes. However, most of the currently reported HClO probes have failed to achieve this goal due to their insufficient photobleaching resistance under a laser source. Herein, a highly stable ratiometric probe, HFTC-HClO 1, which is capable of continuously monitoring endogenous HClO burst over a long period of time, has been judiciously developed. Briefly, the de novo development of HFTC-HClO 1 mainly involved three main steps: (1) novel coumarins (HFTC 1-5) were designed and synthesized; (2) the most stable scaffold, HFTC 3, was selected through dye screening and cell imaging validation; and (3) based on HFTC 3, three candidate HClO probes were constructed, and HFTC-HClO 1 was finally selected due to its superior sensing properties toward HClO. Furthermore, HFTC-HClO 1 can quantitatively measure HClO levels in various real samples with excellent recovery (>90.4%), and the use of HFTC-HClO 1-coated test strips for qualitative analysis of HClO in real samples was also achieved. In addition, the application of HFTC-HClO 1 for long-term continuous monitoring of intracellular HClO burst was successfully demonstrated. Significantly, HFTC-HClO 1 was able to visualize HClO generated in the rheumatoid arthritis mouse model.

Novel ultra-sensitive and highly selective cyanine sensors based on solvent-free microwave synthesis for the detection of trace hypochlorite ions in drinking water

The adoption of chlorine in drinking water disinfection with the determination of residual chlorine in the form of hypochlorite ion (ClO-) is in widespread demand. Several sensors including colorimetric, fluorometric, and electrochemical methods are currently in use, but detection limits and ease of application remain a challenge. In this work, two new cyanine derivatives-based ClO- sensors, that were prepared by solvent-free microwave synthesis, are reported. The two sensors are highly sensitive and selective to ClO-, exhibiting a noticeable color change visible to the naked eye. Additionally, the sensors can detect ClO- without interference from other potential water pollutants, with low detection limits of 7.43 ppb and 0.917 ppb based on absorption performance. When using fluorometric methods, the sensors' detection limits are pushed down to 0.025 ppb and 0.598 ppb for sensors I and II, respectively. The sensors can be loaded with paper strips for field and domestic detection of ClO- in tap water treatment installations. Using the quartz crystal microbalance (QCM) technique, these sensors showed strong detection sensitivity to ClO-, with detection limits of 0.256 ppm and 0.09 ppm for sensors I and II, respectively. Quantum chemical studies using density functional theory (DFT) calculations, natural bond orbital (NBO) analysis, molecular electrostatic potential (MESP), and time-dependent density functional theory (TD-DFT) supported the findings. The sensing mechanism is rationalized in terms of radical cation formation upon ClO- oxidation of cyanine sensors I and II.

Bifunctional near-infrared fluorescent probe for the selective detection of bisulfite and hypochlorous acid in food, water samples and in vivo

We report the development of a bifunctional near-infrared fluorescent probe (QZB) for selective sensing of bisulfite (HSO3-) and hypochlorous acid (HOCl). The synergistic detection of HSO3- and HOCl was achieved via a C=C bond recognition site. In comparison with the red-fluorescence QZB, two different products with non-fluorescence and paleturquoise fluorescence were produced by the recognition of QZB towards HSO3- and HOCl respectively, which can realize effectively the dual-functional detection of HSO3- and HOCl. QZB features prominent preponderances of dual-function response, near-infrared emission, reliability at physiological pH, low cytotoxicity and high sensitivity to HSO3- and HOCl. The detection of HSO3- in actual food samples has been successfully achieved using QZB. Utilization of QZB-based test strip to semi-quantitatively detect HSO3- and HOCl in real-world water samples by the "naked-eye" colorimetry are then demonstrated. Simultaneously, the determination of HSO3- and HOCl in real-world water sample has been achieved by smartphone-based standard curves. Additionally, the applications of QZB for imaging HSO3- and HOCl in vivo are successfully demonstrated. Consequently, the successful development of QZB could be promising as an efficient tool for researching the role of HSO3-/HOCl in the regulation of redox homeostasis regulation in vivo and complex signal transduction and for future food safety evaluation.

Au@Ag Nanopencil with Au Tip and Au@Ag Rod: Multimodality Plasmonic Nanoprobe based on Asymmetric Etching for the Detection of SCN- and ClO. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2023;19:e2302302. [PMID: 37211700 DOI: 10.1002/smll.202302302]

In this paper, Au@Ag nanopencil is designed as a multimodality plasmonic nanoprobe based on asymmetric etching for the detection of SCN- and ClO- . Au@Ag nanopencil with Au tip and Au@Ag rod is prepared by asymmetric tailoring of uniformly grown silver-covered gold nanopyramids under the combined effect of partial galvanic replacement and redox reaction. By asymmetric etching in different systems, Au@Ag nanopencil exhibits diversified changes in the plasmonic absorption band: O2 •- facilitated by SCN- etches Au@Ag rod from the end to the tip, causing a blue shift of the localized surface plasmon resonance (LSPR) peak as the aspect ratio decreases; while the ClO- can retain Au@Ag shell and etch Ag within rod from the tip to the end, causing a redshift of the LSPR peak as the coupling resonance weakens. Based on peak shifts in different directions, a multimodality detection of SCN- and ClO- has been established. The results demonstrate the detection limits of SCN- and ClO- are 160 and 6.7 nm, and the linear ranges are 1-600 µm and 0.05-13 µm, respectively. The finely designed Au@Ag nanopencil not only broadens the horizon of designing heterogeneous structures, but also enriches the strategy of constructing multimodality sensing platform.

A dual-responsive fluorescent turn-on sensor for sensitively detecting and bioimaging of hydrazine and hypochlorite in biofluids, live-cells, and plants

Hydrazine (N₂H₄) and hypochlorite (ClO^-) are extremely harmful to the public health, so it is vitally necessary to detect them in living system. Herein, we developed a new phenthiazine-thiobarbituric acid based dual-analyte responsive fluorescent sensor PT for visually distinguishing and detecting N₂H₄ and ClO^-. PT underwent N₂H₄/ClO^--induced CC breakage, achieving olive-drab/brilliant green fluorescence lighting-up response towards N₂H₄/ClO^- with superb specifity, ultra-sensitivity (detection limit: 15.4 nM for N₂H₄, 13.7 nM for ClO^-), and ultra-fast response (N₂H₄: <15 s, ClO^-: <20 s). The mechanisms for sensing N₂H₄ and ClO^- were investigated with support of spectral measurements and DFT investigation. Sensor based paper-strip/silica-gel device was developed for in-field supervision and on-site monitoring of gaseous and aqueous N₂H₄ and ClO^- solution. In addition, the PT was also applied for quantitatively detecting N₂H₄ and ClO^- in soil, food, plants and bio-fluids. Moreover, PT was utilized to visualize exogenous N₂H₄ and ClO^- in living plants and live-cells, demonstrating this sensor utilized as a powerful tool to detect N₂H₄ and ClO^- in biological fields.

A bifunctional fluorescent probe based on PET & ICT for simultaneously recognizing Cys and H2S in living cells

Most reported probes that respond to Cysteine (Cys) and Hydrogen sulfide (H₂S) can only identify one analyte, or they were interfered with homocysteine (Hcy) and glutathione (GSH) when recognizing Cys and H₂S. In addition, nitrobenzoxadiazole (NBD) ether, as one of thiols recognition sites, inevitably encounters the situation that Cys, GSH and H₂S cannot be distinguished on the same channel at the cellular level. In this work, by introducing NBD ether and NBD amine, we constructed a bifunctional fluorescent probe NJB for dual-site response to Cys and H₂S via PET & ICT processes. NJB has wonderful selectivity for identifying Cys and HS^-, with limits of detection as low as 58.4 nM and 81.1 nM, respectively. Interestingly, NJB has been successfully applied to detect Cys and HS^- in MCF-7 cells. Therefore, the probe that serves as a great tool for inquiring the physiological and pathological functions of Cys and H₂S in living cells is promising.

A BODIPY-Based Far-Red-Absorbing Fluorescent Probe for Hypochlorous Acid Imaging

Hypochlorous acid (HClO) is produced by white blood cells to defend against injury and bacteria. However, as one of the reactive oxygen species, high intracellular HClO concentration could lead to chronic diseases that affect the cardiovascular and nervous systems. To monitor HClO concentrations in bio-samples, the fluorescent probe is preferred to have: a) absorbability in the far-red window with reduced light-toxicity and improved tissue penetration depth, b) ratiometric feature for accurate analysis. In this study, we reported a far-red ratiometric HClO fluorescence probe based on BODIPY chromophore and aldoxime sensing group. Not only the color change of the probe solution can be detected by naked eyes, but also the emission ratios (I₆₄₅/I₆₇₀) showed a significant increase upon the introduction of HClO. More importantly, the feasibility of HClO monitoring in bio-samples was demonstrated in vitro using a confocal microscope.

Sequential detection of hypochlorous acid and sulfur dioxide derivatives by a red-emitting fluorescent probe and bioimaging applications in vitro and in vivo

A red-emitting fluorescence probe (DP) has been successfully developed for the sequential detection of hypochlorous acid (HOCl) and sulfur dioxide derivatives (SO32−/HSO3−) in vitro and in vivo.

Fluorescent probe for the detection of hypochlorous acid in water samples and cell models

Hypochlorous acid (HClO) is a special kind of reactive oxygen species, which plays an important role in resisting pathogen invasion and maintaining cell redox balance and other physiological processes. In addition, HClO is commonly used in daily life as a bleaching and disinfectant agent. Its excessive use can also lead to death of water animals and serious respiratory and skin diseases in humans. Therefore, it is of great significance to develop a quick and convenient tool for detecting HClO in the environment and organisms. In this paper, we utilize the specific reaction of HClO with dimethylthiocarbamate to develop a novel naphthalene derivative fluorescent probe (BNA-HClO), it was designed and synthesized by using 6-(2-benzothiazolyl)-2-naphthol as the fluorophore and N,N-dimethylthiocarbamate as the recognition group. BNA-HClO shows large fluorescence enhancement (374-fold), high sensitivity (a detection limit of 37.56 nM), rapid response (<30 s), strong anti-interference ability and good specificity in vitro. Based on the outstanding in vitro sensing capability of BNA-HClO, it has been successfully used to detect spiked HClO in tap water, medical wastewater and fetal bovine serum with good recovery. BNA-HClO has also been successfully used as a portable test strip for the in situ semi-quantitative detection of HClO in tap water solutions. In addition, BNA-HClO can successfully enable the detection and imaging of exogenous and endogenous HClO in living cells. This work provides a simple and effective tool for the detection and imaging of HClO in environmental and biological systems, and provides some theoretical guidance for future exploration of biological and pathological studies related to HClO.

Quinoline-based fluorescent probe for the detection and monitoring of hypochlorous acid in a rheumatoid arthritis model

The development of effective bioanalytical methods for the visualization of hypochlorous acid (HOCl) in situ in rheumatoid arthritis (RA) directly contributes to better understanding the roles of HOCl in this disease. In this work, a new quinoline-based fluorescence probe (HQ) has been developed for the detection and visualization of a HOCl-mediated inflammatory response in a RA model. HQ possesses a donor–π–acceptor (D–π–A) structure that was designed by conjugating p-hydroxybenzaldehyde (electron donor) and 1-ethyl-4-methylquinolinium iodide (electron acceptor) through a C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C double bond. In the presence of HOCl, oxidation of phenol to benzoquinone led to the red-shift (93 nm) of the adsorption and intense quenching of the fluorescence emission. The proposed response reaction mechanism was verified by high performance liquid chromatography (HPLC) and high-resolution mass spectroscopy (HRMS) titration analysis. The remarkable color changes of the HQ solution from pale yellow to pink enabled the application of HQ-stained chromatography plates for the “naked-eye” detection of HOCl in real-world water samples. HQ featured high selectivity and sensitivity (6.5 nM), fast response time (<25 s) to HOCl, reliability at different pH (3.0 to 11.5) and low cytotoxicity. HQ's application in biological systems was then demonstrated by the monitoring of HOCl-mediated treatment response to RA. This work thus provided a new tool for the detection and imaging of HOCl in inflammatory disorders.

A quinoline-based fluorescent probe (HQ) has been designed and synthesized for the monitoring of HOCl-mediated treatment response of a rheumatoid arthritis (RA) model and “naked-eye” detection of HOCl in real water samples.

Novel Mitochondria-Targeting and Naphthalimide-based Fluorescent Probe for Detecting HClO in Living Cells

As a key reactive oxygen species (ROS), hypochlorous acid (HClO) plays an important role in many physiological and pathological processes. The mitochondria-targeting probes for the highly sensitive detection of HClO are desirable. In present work, we designed and synthesized an original mitochondria-localizing and turn-on fluorescent probe for detecting HClO. 4-Aminonaphthalimide was employed as the fluorescent section, the (2-aminoethyl)-thiourea unit was utilized as a typical sensing unit, and the quaternized pyridinium moiety was used as a mitochondria-targeted localization group. When HClO was absent, the probe showed weak fluorescence. In the existence of HClO, the probe revealed a blue fluorescence. Moreover, the turn-on fluorescent probe was able to function in a broad pH scope. There was an excellent linearity between the fluorescence emission intensity at 488 nm and the concentrations of HClO in the range of 5.0 × 10^-7 to 2.5 × 10^-6 mol·L^-1. Additionally, the probe had almost no cell toxicity and possessed an excellent mitochondria-localizing capability. Furthermore, the probe was able to image HClO in mitochondria of living PC-12 cells. The above remarkable properties illustrated that the probe was able to determine HClO in mitochondria of living cells.

The Multifaceted Regulation of Mitochondria in Ferroptosis

Ferroptosis is characterized as a novel form of regulated cell death, which is initiated by the lethal accumulation of lipid peroxidation catalyzed by cellular labile free iron. This iron driven cell death sharply differs from other well characterized forms of regulated cell death at morphological, genetic and biochemical levels. Increasing research has elaborated a high relevance between dysregulated ferroptosis and the pathogenesis of degenerative diseases and organs injury in human patients. Additionally, targeted induction of ferroptosis is considered as a potentially therapeutic design for the clinical intervention of other therapy-resistant cancers. It is well understood that mitochondria, the cellular powerhouse, determine several types of regulated cell death. Recently, compromised mitochondrial morphology and functionalities have been primarily formulated in ferroptosis. Several mitochondria associated proteins and metabolic processes have been elaborated to fine-tune ferroptotic program. Herein, we critically review the recent advances in this booming field, with focus on summarizing the multifaceted mitochondrial regulation of ferroptosis and providing a perspective on the potential biochemical basis. Finally, we are attempting to shed light on an integrative view on the possibility of mitochondria- and ferroptosis-targeting therapeutics as novel treatment designs for the intervention of ferroptosis related diseases.

Synthesis, molecular docking calculation, fluorescence and bioimaging of mitochondria-targeted ratiometric fluorescent probes for sensing hypochlorite in vivo

A novel mitochondria-targeted ratio fluorescent probe Mi-OCl-RP was constructed. High binding energy may explain the mitochondria selectivity of the probe. The probe has excellent spectral properties and as a robust tool for monitoring OCl⁻in vivo.

A novel dual-site ICT/AIE fluorescent probe for detecting hypochlorite and polarity in living cells

A novel dual-site fluorescent probe (CTPA) was rationally designed and synthesized for the detection of hypochlorite (ClO−) and polarity.

Imino-thiolate-templated synthesis of a chloride-selective neutral macrocyclic host with a specific “turn-off–on” fluorescence response for hypochlorite (ClO−)

A precise replacement of one oxygen atom with sulfur allowed a novel thioimidate anion-templated macrocyclization to form a crowded host 2 with the ability to act as a highly selective and sensitive fluorescence probe for hypochlorite (ClO−).

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

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

Nanomedicines for Subcellular Targeting: The Mitochondrial Perspective

BACKGROUND

Over the past decade, there has been a surge in the number of mitochondrialactive therapeutics for conditions ranging from cancer to aging. Subcellular targeting interventions can modulate adverse intracellular processes unique to the compartments within the cell. However, there is a dearth of reviews focusing on mitochondrial nano-delivery, and this review seeks to fill this gap with regards to nanotherapeutics of the mitochondria.

METHODS

Besides its potential for a higher therapeutic index than targeting at the tissue and cell levels, subcellular targeting takes into account the limitations of systemic drug administration and significantly improves pharmacokinetics. Hence, an extensive literature review was undertaken and salient information was compiled in this review.

RESULTS

From literature, it was evident that nanoparticles with their tunable physicochemical properties have shown potential for efficient therapeutic delivery, with several nanomedicines already approved by the FDA and others in clinical trials. However, strategies for the development of nanomedicines for subcellular targeting are still emerging, with an increased understanding of dysfunctional molecular processes advancing the development of treatment modules. For optimal delivery, the design of an ideal carrier for subcellular delivery must consider the features of the diseased microenvironment. The functional and structural features of the mitochondria in the diseased state are highlighted and potential nano-delivery interventions for treatment and diagnosis are discussed.

CONCLUSION

This review provides an insight into recent advances in subcellular targeting, with a focus on en route barriers to subcellular targeting. The impact of mitochondrial dysfunction in the aetiology of certain diseases is highlighted, and potential therapeutic sites are identified.

A novel nopinone-based fluorescent probe for colorimetric and ratiometric detection of hypochlorite and its applications in water samples and living cells

A novel fluorescent probe (OFN) based on nopinone for the detection of hypochlorite has been developed. The probe OFN exhibited a colorimetric and ratiometric response to hypochlorite with good selectivity, high sensitivity (the low detection limit is 0.136 μM) and fast response time (30 s). In response to ClO-, an obvious change was observed in both the fluorescence and absorption spectra, followed by the visible color change from colorless to yellow and the fluorescence color change from yellow to green. The sensing mechanism confirmed that the oxime group of OFN was oxidized to the aldehyde group, which was proved by HRMS and 1H NMR. What is more, the probe was used not only to detect the concentration of ClO- in water samples but also for monitoring ClO- in living cells.

Smart Bimodal Imaging of Hypochlorous Acid In Vivo Using a Heterobimetallic Ruthenium(II)-Gadolinium(III) Complex Probe

A unique heterobimetallic Ru(II)-Gd(III) complex, Ru-AN-Gd, is reported to serve as an effective probe for bimodal phosphorescence-magnetic resonance (MR) imaging of hypochlorous acid (HClO) in vitro and in vivo. The probe was designed by incorporating a MR contrast agent, Gd-DOTA, into a HClO-responsive bipyridine-Ru(II) complex derivative. The specific reaction between Ru-AN-Gd and HClO triggers the cleavage of an ether bond in the probe molecule, resulting in phosphorescence turn-on and MR turn-off responses to HClO. The integration of MR and phosphorescence detection modes allows the probe to be employed for detecting HClO in a quite wide concentration range (0.6-2000 μM) and for imaging HClO at various resolutions ranging from the subcellular level to the whole body without a depth limit. Its applicability was demonstrated by phosphorescence imaging of lysosomal HClO in live cells, visualization of HClO generation in a mouse arthritis model, and bimodal phosphorescence-MR imaging of HClO in drug-induced acute liver and kidney injury of a mouse. The research achievements suggested the potential of Ru-AN-Gd for diagnosis and treatment monitoring of HClO-related disease.

A novel fluorescent probe with extremely low background fluorescence for sensing hypochlorite in zebrafish

Development of an efficient fluorescent probe for sensing hypochlorite in water samples and biological samples is highly demanded. However, the currently reported fluorescent probes for hypochlorite frequently suffered from the problem of high background fluorescence. Herein, based on the combined effect of two different fluorescence quenching groups, we rationally developed a novel fluorescent probe for hypochlorite with extremely low background fluorescence. Notably, due to the doubly quenching groups, the probe could even keep low background fluorescence in a solution with high viscosity. Furthermore, the probe displayed highly sensitive and selective response to hypochlorite, with the detection limits calculated to be 10.5 nM. Practical application demonstrated that the probe was able to quantitatively detect hypochlorite in various water samples with good recovery. Significantly, the probe showed extremely low background fluorescence in living cells and was capable of detecting minor variation of endogenous hypochlorite in RAW 264.7 cells. Moreover, the fluorescence imaging different concentration of hypochlorite in zebrafish has been successfully conducted. The probe developed herein will be widely used as a reliable tool to accurately monitor the variation of hypochlorite in living organism.

An endoplasmic reticulum-targeting and ratiometric fluorescent probe for hypochlorous acid in living cells based on a 1,8-naphthalimide derivative

A novel reticulum-targeting and ratiometric fluorescent probe for determining hypochlorous acid has been developed.

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

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

Ratiometric fluorogenic determination of endogenous hypochlorous acid in living cells

Hypochlorous acid (HClO) is one of the most important ROS (reactive oxygen species) and common pollutant in tap-water. However, the determination of HClO with fast response and high sensitivity/selectivity is still an urgent demanding. Here we fabricated a ratiometric fluorescent probe RC based on TBET (through-bond energy transfer) on the platform of coumarin and rhodamine with the thiosemicarbazide group as the linker. This probe could display the characteristic fluorescence emission of coumarin. Upon addition of HClO, the linker was reacted into an oxadiazole, resulting in the opening of spiro-ring of rhodamine. The resultant then gives ratiometric fluorogenic changes. The probe exhibits fast response and high selectivity and sensitivity towards HClO with a low limit of detection (~140 nM). Eventually, RC is successfully applicated for determining spiked HClO in water samples and imaging endogenous HClO in living cells.

A water-soluble BODIPY-based fluorescent probe for rapid and selective detection of hypochlorous acid in living cells

We designed and synthesized 4,4-di-(4'-methylmercaptophenoxy)-8-(N-methylpyridinium-2-yl)-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene (probe 1) as a water-soluble BODIPY derivative for rapid and selective detection of hypochlorous acid. The pyridinium-2-yl linked at the meso position of BODIPY core was used to maintain highly fluorescent nature and to increase water solubility. Methylmercaptophenoxy was selected as responsive site installed on the boron atom (to replace the fluorine atom) and induced the photoinduced electron-transfer (PeT) effect to quench the fluorescence of BODIPY. The probe exhibited 83.9 μg mL^-1 solubility in PBS (10 mM, pH 7.4), and possessed very low fluorescence (Φ_f = 0.0013). Upon addition of HClO, the probe could display a distinct response in 1 min and generate marked fluorescence enhancement by 100-fold due to the oxidation of thioether into sulfoxide to terminate PeT process. A limit of detection of 53 nM was calculated for HClO in the linear response range from 0 μM to 10 μM, and the probe was successfully applied to image HClO in living cells.

A twist six-membered rhodamine-based fluorescent probe for hypochlorite detection in water and lysosomes of living cells

A novel six-membered rhodamine-based fluorescent probe (6G-ClO) was developed from 2-formyl rhodamine (6G-CHO) and used for hypochlorite detection in water and HUVEC cells. Different from planar penta cycle of rhodamine spirolactam, there was a twist six-membered spirocyclic hydrazone in 6G-ClO optimized by Gaussian software at DFT/B3LYP/6-31G(d) level. The high selectivity, high sensitivity and fast response of 6G-ClO towards ClO^- would be attributed to the twist six-membered spirocycle. Test-strip prepared with 6G-ClO was successfully used to semi-quantitatively indicate the concentration of ClO^- in water. 6G-ClO can also quantitatively detect the concentration of ClO^- in tap water and swimming pool water. The detection limit of 6G-ClO was as low as 12 nM. The co-localization staining of HUVEC cells further verified that 6G-ClO could specifically accumulate in lysosomes and capture exogenous/endogenous ClO^- in living lysosomes. 6G-ClO would be a practical probe for real-time monitoring of ClO^- in the biological and real water samples.

In Vivo Biosensing Using Resonance Energy Transfer

Solution-phase and intracellular biosensing has substantially enhanced our understanding of molecular processes foundational to biology and pathology. Optical methods are favored because of the low cost of probes and instrumentation. While chromatographic methods are helpful, fluorescent biosensing further increases sensitivity and can be more effective in complex media. Resonance energy transfer (RET)-based sensors have been developed to use fluorescence, bioluminescence, or chemiluminescence (FRET, BRET, or CRET, respectively) as an energy donor, yielding changes in emission spectra, lifetime, or intensity in response to a molecular or environmental change. These methods hold great promise for expanding our understanding of molecular processes not just in solution and in vitro studies, but also in vivo, generating information about complex activities in a natural, organismal setting. In this review, we focus on dyes, fluorescent proteins, and nanoparticles used as energy transfer-based optical transducers in vivo in mice; there are examples of optical sensing using FRET, BRET, and in this mammalian model system. After a description of the energy transfer mechanisms and their contribution to in vivo imaging, we give a short perspective of RET-based in vivo sensors and the importance of imaging in the infrared for reduced tissue autofluorescence and improved sensitivity.

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

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

A sensitive and selective fluorescence probe for detection of hypochlorite (OCl-) and its bioimaging in live cells

A novel indolium-based fluorescent probe (probe 1) for the recognition and detection of hypochlorite (OCl^-) has been explored via a double oxidation reaction mechanism. Probe 1 exhibited excellent selectivity and sensitivity for OCl^- over other analytes, and with a detection limit of 0.11 μM. Meanwhile, probe 1 showed fast response toward OCl^- in less than 3 min with obvious changes in color, which could be observed by naked eye. Moreover, fluorescence imaging experiments by using Eca109 cells were performed utilizing the new probe, demonstrating its practical applications in living cells.

A coumarin based fluorescent probe for rapidly distinguishing of hypochlorite and copper (II) ion in organisms

A dual-functional fluorescent probe based on coumarin fluorophore for monitoring ClO^- and Cu²⁺ was synthesized and characterized. The identification mechanisms for ClO^- and Cu²⁺ induced different colorimetric and ratiometric changes. ClO^- caused a colorimetric change from yellow to colorless and 120 nm blue-shifted emission spectra from red to blue. Besides, Cu²⁺ induced a remarkable fluorescence quenching behavior and 36 nm blue-shifted absorption spectra accompanied by the color change from yellow to luminous yellow. As expected, Probe 1 displayed excellent selectivity and sensitivity for detecting ClO^- and Cu²⁺ over other competing ions in their respective systems. The limits of detection for ClO^- and Cu²⁺ were 24.62 nM and 0.39 nM, respectively. The recognition mechanisms were proved by ¹H NMR, mass spectrum and theoretical calculations. More importantly, the reversibility of Cu²⁺ could be applicable to rapid quantification for ClO^-/Cu²⁺. Thus, the strategy for sensing ClO^-/Cu²⁺ was carried out, which revealed broad applications of Probe 1 in multiple actual water and biology.

Photoacoustic Imaging: Contrast Agents and Their Biomedical Applications

Photoacoustic (PA) imaging as a fast-developing imaging technique has great potential in biomedical and clinical applications. It is a noninvasive imaging modality that depends on the light-absorption coefficient of the imaged tissue and the injected PA-imaging contrast agents. Furthermore, PA imaging provides superb contrast, super spatial resolution, and high penetrability and sensitivity to tissue functional characteristics by detecting the acoustic wave to construct PA images. In recent years, a series of PA-imaging contrast agents are developed to improve the PA-imaging performance in biomedical applications. Here, recent progress of PA contrast agents and their biomedical applications are outlined. PA contrast agents are classified according to their components and function, and gold nanocrystals, gold-nanocrystal assembly, transition-metal chalcogenides/MXene-based nanomaterials, carbon-based nanomaterials, other inorganic imaging agents, small organic molecules, semiconducting polymer nanoparticles, and nonlinear PA-imaging contrast agents are discussed. The applications of PA contrast agents as biosensors (in the sensing of metal ions, pH, enzymes, temperature, hypoxia, reactive oxygen species, and reactive nitrogen species) and in bioimaging (lymph nodes, vasculature, tumors, and brain tissue) are discussed in detail. Finally, an outlook on the future research and investigation of PA-imaging contrast agents and their significance in biomedical research is presented.

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.

Recent progress in development of 2,3-diaminomaleonitrile (DAMN) based chemosensors for sensing of ionic and reactive oxygen species

2,3-Diaminomaleonitrile (DAMN) has proved to be a valuable organic π-conjugated molecule having many applications in the area of chemosensors for sensing of ionic and neutral species because of its ability to act as a building block for well-defined molecular architectures and scaffolds for preorganised arrays of functionality. In this article, we discussed the utilization of 2,3-diaminomaleonitrile (DAMN) for the design and development of chemosensor molecules and their application in the area of metal ion, anion and reactive oxygen species sensing. Along with these, we present different examples of DAMN based chemosensors for multiple ion sensing. We also discuss the ion sensing mechanism and potential uses in other related areas of research.

2,3-Diamniomaleonitrile (DAMN) is valuable π-conjugated organic scaffold molecule for designing of efficient chemosensors for sensing of ionic and Reactive Oxygen Species (ROS).

A novel rhodamine-based fluorescent probe for selective detection of ClO– and its application in living cell imaging

A novel fluorescent rhodamine-based probe L for selective responding to ClO– has been synthesized and characterized. The spectroscopy showed that probe L can detect ClO– in aqueous solution without interaction with other interfering ions, and the detection is also evident by the colour change from colourless to reddish purple under white light. The remarkable fluorescence enhancement showed the high selectivity and sensitivity of probe L for the detection of ClO–. Furthermore, probe L was applied to intracellular fluorescent imaging of HeLa cells treated with ClO– and MTT assay showed nontoxicity in living cells.