BODIPY-based fluorescent probe for peroxynitrite detection and imaging in living cells

Affinity Studies of Hemicyanine Derived Water Soluble Colorimetric Probes with Reactive Oxygen/Nitrogen/Sulfur Species

Peroxynitrite (ONOO^- ) is an essential endogenous reactive oxygen species (ROS) generated in mitochondria under various pathological and physiological conditions. An increase in its level in mitochondria is related to numerous diseases. Herein, we report a series of hemicyanine-derived water-soluble colorimetric probes (1-4) and the reactivity of which was studied with various reactive oxygen, nitrogen, and sulfur species. Probes 1-4 are formed by conjugating 1,2,3,3-tetramethyl-3H-indolium iodide and 4-hydroxybenzaldehyde or its derivatives through an alkene linkage formed by the Knoevenagel reaction. Oxidative cleavage of the electron-rich double bond of the conjugated hemicyanine dye revealed a discerning affinity of probe 3 towards peroxynitrite among all reactive oxygen species. The rapid change in color of 3 provides a sensitive and selective method for detecting peroxynitrite with a low detection limit of 180 nM. Notably, the water solubility of the probe displays excellent performance for the selective detection of peroxynitrite among ROS and reactive nitrogen (RNS)/sulfur species (RSS). UV-vis, ¹ H NMR, and ¹³ C NMR spectroscopic data and results from theoretical calculations provide further information on the interaction of peroxynitrite with probe 3.

GNP-CeO2- polyaniline hybrid hydrogel for electrochemical detection of peroxynitrite anion and its integration in a microfluidic platform

Peroxynitrite anion (ONOO^-) is an important in vivo oxidative stress biomarker whose aberrant levels have pathophysiological implications. In this study, an electrochemical sensor for ONOO^- detection was developed based on graphene nanoplatelets-cerium oxide nanocomposite (GNP-CeO₂) incorporated polyaniline (PANI) conducting hydrogels. The nanocomposite-hydrogel platform exhibited distinct synergistic advantages in terms of large electroactive surface coverage and providing a conductive pathway for electron transfer. Besides, the 3D porous structure of hydrogel integrated the GNP-CeO₂ nanocomposite to provide hybrid materials for the evolution of catalytic activity towards electrochemical oxidation of ONOO^-. Various microscopic and spectroscopic characterization techniques endorsed the successful formation of GNP-CeO₂-PANI hydrogel. Cyclic voltammetry (CV) measurements of GNP-CeO₂-PANI hydrogel modified screen-printed electrodes (SPE) were carried out to record the current changes influenced by ONOO^-. The prepared sensor demonstrated a significant dose-dependent increase in CV peak current within a linear range of 5-100 µM (at a potential of 1.12 V), and a detection limit of 0.14 with a sensitivity of 29.35 ± 1.4 μA μM^-1. Further, a customized microfluidic flow system was integrated with the GNP-CeO₂-PANI hydrogel modified SPE to enable continuous electrochemical detection of ONOO^- at low sample volumes. The developed microfluidic electrochemical device demonstrated an excellent sensitivity towards ONOO^- under optimal experimental conditions. Overall, the fabricated microfluidic device with hybrid hydrogels as electrochemical interfaces provides a reliable assessment of ONOO^- levels. This work offers considerable potential for understanding the oxidative stress-related disease mechanisms through determination of ONOO^- in biological samples.

Methods to evaluate the scavenging activity of antioxidants toward reactive oxygen and nitrogen species (IUPAC Technical Report)

This project was aimed to identify the quenching chemistry of biologically important reactive oxygen and nitrogen species (ROS/RNS, including radicals), to show antioxidant action against reactive species through H‐atom and electron transfer reactions, and to evaluate the ROS/RNS scavenging activity of antioxidants with existing analytical methods while emphasizing the underlying chemical principles and advantages/disadvantages of these methods. In this report, we focused on the applications and impact of existing assays on potentiating future research and innovations to evolve better methods enabling a more comprehensive study of different aspects of antioxidants and to provide a vocabulary of terms related to antioxidants and scavengers for ROS/RNS. The main methods comprise the scavenging activity measurement of the hydroxyl radical (•OH), dioxide(•1–) (O2 •–: commonly known as the superoxide radical), dihydrogen dioxide (H2O2: commonly known as hydrogen peroxide), hydroxidochlorine (HOCl: commonly known as hypochlorous acid), dioxidooxidonitrate(1–) (ONOO−: commonly known as the peroxynitrite anion), and the peroxyl radical (ROO•). In spite of the diversity of methods, there is currently a great need to evaluate the scavenging activity of antioxidant compounds in vivo and in vitro. In addition, there are unsatisfactory methods frequently used, such as non-selective UV measurement of H2O2 scavenging, producing negative errors due to incomplete reaction of peroxide with flavonoids in the absence of transition metal ion catalysts. We also discussed the basic mechanisms of spectroscopic and electrochemical nanosensors for measuring ROS/RNS scavenging activity of antioxidants, together with leading trends and challenges and a wide range of applications. This project aids in the identification of reactive species and quantification of scavenging extents of antioxidants through various assays, makes the results comparable and more understandable, and brings a more rational basis to the evaluation of these assays and provides a critical evaluation of existing ROS/RNS scavenging assays to analytical, food chemical, and biomedical/clinical communities by emphasizing the need for developing more refined, rapid, simple, and low‐cost assays and thus opening the market for a wide range of analytical instruments, including reagent kits and sensors.

BODIPY derivatives as fluorescent reporters of molecular activities in living cells

Fluorescent compounds have become indispensable tools for imaging molecular activities in the living cell. 4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) is currently one of the most popular fluorescent reporters due to its unique photophysical properties. This review provides a general survey and presents a summary of recent advances in the development of new BODIPY-based cellular biomarkers and biosensors. The review starts with the consideration of the properties of BODIPY derivatives required for their application as cellular reporters. Then review provides examples of the design of sensors for different biologically important molecules, ions, membrane potential, temperature and viscosity defining the live cell status. Special attention is payed to BODPY-based phototransformable reporters.

The bibliography includes 339 references.

A high-performance genetically encoded fluorescent biosensor for imaging physiological peroxynitrite

Peroxynitrite is a reactive nitrogen species (RNS) that plays critical roles in signal transduction, stress response, and numerous human diseases. Advanced molecular tools that permit the selective, sensitive, and noninvasive detection of peroxynitrite are essential for understanding its pathophysiological functions. Here, we present pnGFP-Ultra, a high-performance, reaction-based, genetically encodable biosensor for imaging peroxynitrite in live cells. pnGFP-Ultra features a p-boronophenylalanine-modified chromophore as the sensing moiety and exhibits a remarkable ~110-fold fluorescence turn-on response toward peroxynitrite while displaying virtually no cross-reaction with other reactive oxygen/nitrogen species. To facilitate the expression of pnGFP-Ultra in mammalian cells, we engineered an efficient noncanonical amino acid (ncAA) expression system that is broadly applicable to the mammalian expression of ncAA-containing proteins. pnGFP-Ultra robustly detected peroxynitrite production in activated macrophages and primary glial cells. pnGFP-Ultra fills an important technical gap and represents a valuable addition to the molecular toolbox for probing RNS biology.

Possible Role of Peroxynitrite in the Responses Induced by Fusicoccin in Plant Cultured Cells

Fusicoccin (FC) is a well-known phytotoxin able to induce in Acer pseudoplatanus L. (sycamore) cultured cells, a set of responses similar to those induced by stress conditions. In this work, the possible involvement of peroxynitrite (ONOO⁻) in FC-induced stress responses was studied measuring both in the presence and in the absence of 2,6,8-trihydroxypurine (urate), a specific ONOO⁻ scavenger: (1) cell death; (2) specific DNA fragmentation; (3) lipid peroxidation; (4) production of RNS and ROS; (5) activity of caspase-3-like proteases; and (6) release of cytochrome c from mitochondria, variations in the levels of molecular chaperones Hsp90 in the mitochondria and Hsp70 BiP in the endoplasmic reticulum (ER), and of regulatory 14-3-3 proteins in the cytosol. The obtained results indicate a role for ONOO⁻ in the FC-induced responses. In particular, ONOO⁻ seems involved in a PCD form showing apoptotic features such as specific DNA fragmentation, caspase-3-like protease activity, and cytochrome c release from mitochondria.

An inherently kidney-targeting near-infrared fluorophore based probe for early detection of acute kidney injury

Acute kidney injury (AKI) is common in hospital patients. Delayed diagnosis and treatment of AKI due to the lack of efficient early diagnosis is an important cause of its high mortality. While fluorescence imaging seems promising to non-intrusively interrogate AKI-related biomarkers, the low kidney contrast of many fluorophores conferred by their relatively low abundance of distribution in the kidney limits their application for AKI detection. Herein, we discovered a near-infrared fluorophore with inherent kidney-targeting ability. Based on this fluorophore, a fluorogenic probe (KNP-1) was developed by targeting peroxynitrite (ONOO^-), which is upregulated at the early onset of AKI. KNP-1 exhibits desirable kidney distribution after intravenous administration and is fluorescent only after activation by ONOO^-. These properties lead to excellent kidney contrast imaging results. KNP-1 is capable of detecting both nephrotoxin-induced and ischemia-reperfusion injury-induced AKI in live mice. Temporally resolved imaging of AKI-disease model mice with KNP-1 suggests a gradual increase in renal ONOO^- levels with disease progression. Notably, the upregulation of ONOO^- can be observed at least 24 h earlier than the clinically popular sCr and BUN methods. Blocking ONOO^- generation also proves beneficial. These results highlight the applicability of this inherently tissue targeting-based strategy for designing probes with desirable imaging contrast; potentiate ONOO^- as a biomarker and target for AKI early diagnosis and medical intervention; and imply the clinical relevance of KNP-1 for AKI early detection.

A 2-formylphenylboronic acid (2FPBA)-maleimide crosslinker: a versatile platform for Cys-peptide-hydrazine conjugation and interplay

In this work, we describe the preparation of a heterobifunctional 2-formylphenylboronic acid (2-FPBA)-maleimide crosslinker and explore its versatility in the preparation of various bioconjugates. We demonstrate the straightforward attachment of hydrazine payloads to cysteine residues in peptides, as well as the crosslinking of different thiol-bearing peptides or payloads with N-terminal cysteine peptides. Importantly, the dynamic nature of the 2-FPBA handle enables an interplay between the thiazolidine and diazaborine forms, which allows obtaining various products controlled by (and in some cases independent of) the order of addition of the components.

Resorufin-based responsive probes for fluorescence and colorimetric analysis

The fluorescence imaging technique has attracted increasing attention in the detection of various biological molecules in situ and in real-time owing to its inherent advantages including high selectivity and sensitivity, outstanding spatiotemporal resolution and fast feedback. In the past few decades, a number of fluorescent probes have been developed for bioassays and imaging by exploiting different fluorophores. Among various fluorophores, resorufin exhibits a high fluorescence quantum yield, long excitation/emission wavelength and pronounced ability in both fluorescence and colorimetric analysis. This fluorophore has been widely utilized in the design of responsive probes specific for various bioactive species. In this review, we summarize the advances in the development of resorufin-based fluorescent probes for detecting various analytes, such as cations, anions, reactive (redox-active) sulfur species, small molecules and biological macromolecules. The chemical structures of probes, response mechanisms, detection limits and practical applications are investigated, which is followed by the discussion of recent challenges and future research perspectives. This review article is expected to promote the further development of resorufin-based responsive fluorescent probes and their biological applications.

Activity-Based Sensing: A Synthetic Methods Approach for Selective Molecular Imaging and Beyond

Emerging from the origins of supramolecular chemistry and the development of selective chemical receptors that rely on lock-and-key binding, activity-based sensing (ABS)-which utilizes molecular reactivity rather than molecular recognition for analyte detection-has rapidly grown into a distinct field to investigate the production and regulation of chemical species that mediate biological signaling and stress pathways, particularly metal ions and small molecules. Chemical reactions exploit the diverse chemical reactivity of biological species to enable the development of selective and sensitive synthetic methods to decipher their contributions within complex living environments. The broad utility of this reaction-driven approach facilitates application to imaging platforms ranging from fluorescence, luminescence, photoacoustic, magnetic resonance, and positron emission tomography modalities. ABS methods are also being expanded to other fields, such as drug and materials discovery.

High-Selectivity Fluorescent Reporter toward Peroxynitrite in a Coexisting Nonalcoholic Fatty Liver and Drug-Induced Liver Diseases Model

Peroxynitrite (ONOO^-), a highly reactive species, is profoundly involved in many physiological and pathological processes. Change of the ONOO^- level usually indicates an abnormal body function. Thus, it is desired to develop a highly reliable ONOO^- assay to elucidate its roles in a related disease environment. In this work, we have constructed a ratiometric molecule fluorescent probe RTFP toward ONOO^- with high specificity by the combination strategy of probe screening and a rational design method. RTFP displayed excellent detection sensitivity (detection limit: 4.1 nM) and produced a highly ratiometric emission signal (130-fold). Leveraging this probe, we showed the change of ONOO^- content in the free-fatty-acid-induced nonalcoholic fatty liver disease (NAFLD) and acetaminophen-induced drug-induced liver injury (DILI) cellular model and for the first time disclosed the involved mechanism of cytochrome P450 2E1 (CYP2E1) enzyme in NAFLD with a DILI pathological environment. Furthermore, RTFP also was utilized to visualize ONOO^- fluctuation of living liver tissues in a high-fat-diet-caused NAFLD model. We expected that this probe may help the study of liver injury in the exploration of mechanism and signal path.

Ultrafast Detection of Peroxynitrite in Parkinson's Disease Models Using a Near-Infrared Fluorescent Probe

Parkinson's disease (PD) is a neurodegenerative disease that devastatingly affects people's lives. Numerous research studies have shown that peroxynitrite (ONOO^-) plays a pivotal role in the pathogenesis of PD. However, a suitable tool that could quickly and sensitively detect ONOO^- in various PD models is still lacking. To this end, we designed and synthesized a series of near-infrared probes that could detect ONOO^- within seconds by near-infrared fluorescent imaging in an ultrafast and highly selective manner. It is noteworthy that one of those developed probes, NIR-PN1, showed excellent sensing performance and blood-brain barrier penetrating ability. NIR-PN1 was successfully applied for imaging of ONOO^- fluxes in multiple PD models including PC12 cell, Drosophila, C. elegans, and mouse brain, indicating its great potential application not only for understanding the biological roles that ONOO^- played in PD but also for early PD diagnosis and treatment.

Low endogenous NO levels in roots and antioxidant systems are determinants for the resistance of Arabidopsis seedlings grown in Cd

Cadmium (Cd), which is a toxic non-essential heavy metal capable of entering plants and thus the food chain, constitutes a major environmental and health concern worldwide. An understanding of the tools used by plants to overcome Cd stress could lead to the production of food crops with lower Cd uptake capacity and of plants with greater Cd uptake potential for phytoremediation purposes in order to restore soil efficiency in self-sustaining ecosystems. The signalling molecule nitric oxide (NO), whose function remains unclear, has recently been involved in responses to Cd stress. Using different mutants, such as nia1nia2, nox1, argh1-1 and Atnoa1, which were altered in NO metabolism, we analysed various parameters related to reactive oxygen and nitrogen species (ROS/RNS) metabolism and seedling fitness following germination and growth under Cd treatment conditions for seven days. Seedling roots were the most affected, with an increase in ROS and RNS observed in wild type (WT) seedling roots, leading to increased oxidative damage and fitness loss. Mutants that showed lower NO levels in seedling roots under Cd stress were more resistant than WT seedlings due to the maintenance of antioxidant systems which protect against oxidative damage.

The first hydride-Meisenheimer adduct of electron-deficient 3-nitronaphthalimide: application to colorimetric borohydride determination

The first hydride-Meisenheimer adduct of 3-nitronaphthalimide was used for the colorimetric borohydride assay. To explain the regioselectivity of the adduct, the reaction enthalpies of the two most plausible Meisenheimer adducts were obtained via computational calculation. Using the adduct formation, the assay of borohydride reagents was successfully conducted.

Detection and quantification of nitric oxide-derived oxidants in biological systems

The free radical nitric oxide (NO^•) exerts biological effects through the direct and reversible interaction with specific targets (e.g. soluble guanylate cyclase) or through the generation of secondary species, many of which can oxidize, nitrosate or nitrate biomolecules. The NO^•-derived reactive species are typically short-lived, and their preferential fates depend on kinetic and compartmentalization aspects. Their detection and quantification are technically challenging. In general, the strategies employed are based either on the detection of relatively stable end products or on the use of synthetic probes, and they are not always selective for a particular species. In this study, we describe the biologically relevant characteristics of the reactive species formed downstream from NO^•, and we discuss the approaches currently available for the analysis of NO^•, nitrogen dioxide (NO₂ ^•), dinitrogen trioxide (N₂O₃), nitroxyl (HNO), and peroxynitrite (ONOO^-/ONOOH), as well as peroxynitrite-derived hydroxyl (HO^•) and carbonate anion (CO₃ ^•-) radicals. We also discuss the biological origins of and analytical tools for detecting nitrite (NO₂ ^-), nitrate (NO₃ ^-), nitrosyl-metal complexes, S-nitrosothiols, and 3-nitrotyrosine. Moreover, we highlight state-of-the-art methods, alert readers to caveats of widely used techniques, and encourage retirement of approaches that have been supplanted by more reliable and selective tools for detecting and measuring NO^•-derived oxidants. We emphasize that the use of appropriate analytical methods needs to be strongly grounded in a chemical and biochemical understanding of the species and mechanistic pathways involved.

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.

State-of-the-art: functional fluorescent probes for bioimaging and pharmacological research

Cardiovascular diseases, neuropsychiatric disorders, and cancers seriously endanger human health. Mechanistic and pharmacological mechanisms of candidate drugs are central to the translational paradigm. Since many signal transduction and molecular events are implicated in these diseases, a novel method to interrogate the key pharmacological mechanisms is required to accelerate innovative drug discovery. Much attention now focuses on the real-time visualization of molecular disease events to yield new insights to the pathogenesis of the diseases. This review focuses on recent advances in the development of chemical probes for imaging pathological events to facilitate the study of the underlying pharmacodynamics and toxicity involved. As reviewed here, optical imaging is now frequently viewed as an indispensable technique in the field of biological research. Promoting interdisciplinary collaboration among chemistry, biology and medicine, is necessary to further refine functional fluorescent probes for diagnostic and therapeutic applications.

A naphthalimide-based lysosome-targeting fluorescent probe for the selective detection and imaging of endogenous peroxynitrite in living cells

The morpholine (ML) group can be used as a targeting unit for lysosomes. Here, a novel turn-off fluorescence probe for the highly selective imaging of peroxynitrite (ONOO^-) produced by the endogenous stimulation of lysosomes in living cells is presented. The probe, denoted ML-NAP-DPPEA, comprises ML and 2-(diphenylphosphino)ethylamine (DPPE) groups attached to the fluorophore naphthalimide (NAP). ML-NAP-DPPEA shows excellent properties, including high selectivity for ONOO^-, low cytotoxicity, and no interference, leading to low detection limits (17.6 nM). In the presence of ONOO^-, the secondary amine group (NH) is oxidized to an electron-withdrawing group (HN → O), which quenches the fluorescence of ML-NAP-DPPEA. This intracellular lysosomal imaging technique was tested, and the results pointed to its potential use as a probe for studying the biological function and pathological effects of ONOO^- in subcellular structure. Graphical abstract.

Observation of the generation of peroxynitrite in mouse liver after acetaminophen overdose with a boronate-based ratiometric fluorescence probe

A ratiometric fluorescent probe, BTPB, for the selective monitoring of hepatic peroxynitrite in situ after acetaminophen overdose has been developed.

Rational design of a boron-dipyrromethene-based fluorescent probe for detecting Pd2+ sensitively and selectively in aqueous media

A novel fluorescent probe for Pd²⁺ based on the BODIPY fluorophore exploiting the PET (Photoinduced Electron Transfer) mechanism was designed and successfully synthesized.

Fluorescence and chemiluminescence approaches for peroxynitrite detection

In the last two decades, there has been a significant advance in understanding the biochemistry of peroxynitrite, an endogenously-produced oxidant and nucleophile. Its relevance as a mediator in several pathologic states and the aging process together with its transient character and low steady-state concentration, motivated the development of a variety of techniques for its unambiguous detection and estimation. Among these, fluorescence and chemiluminescence approaches have represented important tools with enhanced sensitivity but usual limited specificity. In this review, we analyze selected examples of molecular probes that permit the detection of peroxynitrite by fluorescence and chemiluminescence, disclosing their mechanism of reaction with either peroxynitrite or peroxynitrite-derived radicals. Indeed, probes have been divided into 1) redox probes that yield products by a free radical mechanism, and 2) electrophilic probes that evolve to products secondary to the nucleophilic attack by peroxynitrite. Overall, boronate-based compounds are emerging as preferred probes for the sensitive and specific detection and quantitation. Moreover, novel strategies involving genetically-modified fluorescent proteins with the incorporation of unnatural amino acids have been recently described as peroxynitrite sensors. This review analyzes the most commonly used fluorescence and chemiluminescence approaches for peroxynitrite detection and provides some guidelines for appropriate experimental design and data interpretation, including how to estimate peroxynitrite formation rates in cells.

Small-molecule luminescent probes for the detection of cellular oxidizing and nitrating species

Reactive oxygen species (ROS) have been implicated in both pathogenic cellular damage events and physiological cellular redox signaling and regulation. To unravel the biological role of ROS, it is very important to be able to detect and identify the species involved. In this review, we introduce the reader to the methods of detection of ROS using luminescent (fluorescent, chemiluminescent, and bioluminescent) probes and discuss typical limitations of those probes. We review the most widely used probes, state-of-the-art assays, and the new, promising approaches for rigorous detection and identification of superoxide radical anion, hydrogen peroxide, and peroxynitrite. The combination of real-time monitoring of the dynamics of ROS in cells and the identification of the specific products formed from the probes will reveal the role of specific types of ROS in cellular function and dysfunction. Understanding the molecular mechanisms involving ROS may help with the development of new therapeutics for several diseases involving dysregulated cellular redox status.

An ESIPT Probe for the Ratiometric Imaging of Peroxynitrite Facilitated by Binding to Aβ-Aggregates

A series of 3-hydroxyflavone (3-HF) ESIPT (excited-state intramolecular proton transfer) boronate-based fluorescent probes have been developed for the detection of peroxynitrite (ONOO^-). The dyes are environmentally sensitive, and each probe exhibited a ratiometric response toward ONOO^- in a micellar environment. The probes were used to image different aggregation states of amyloid-β (Aβ) in the presence of ONOO^-. The 3-HF-OMe probe was found to produce a ratiometric response toward ONOO^- when bound to Aβ aggregates, resulting in a novel host-guest ensemble, which adds insight into the development of other ESIPT-based probes for the simultaneous sensing of fibrous proteins/peptides and environmental ROS/RNS.

Challenges and Opportunities for Small-Molecule Fluorescent Probes in Redox Biology Applications

SIGNIFICANCE

The concentrations of reactive oxygen/nitrogen species (ROS/RNS) are critical to various biochemical processes. Small-molecule fluorescent probes have been widely used to detect and/or quantify ROS/RNS in many redox biology studies and serve as an important complementary to protein-based sensors with unique applications. Recent Advances: New sensing reactions have emerged in probe development, allowing more selective and quantitative detection of ROS/RNS, especially in live cells. Improvements have been made in sensing reactions, fluorophores, and bioavailability of probe molecules.

CRITICAL ISSUES

In this review, we will not only summarize redox-related small-molecule fluorescent probes but also lay out the challenges of designing probes to help redox biologists independently evaluate the quality of reported small-molecule fluorescent probes, especially in the chemistry literature. We specifically highlight the advantages of reversibility in sensing reactions and its applications in ratiometric probe design for quantitative measurements in living cells. In addition, we compare the advantages and disadvantages of small-molecule probes and protein-based probes.

FUTURE DIRECTIONS

The low physiological relevant concentrations of most ROS/RNS call for new sensing reactions with better selectivity, kinetics, and reversibility; fluorophores with high quantum yield, wide wavelength coverage, and Stokes shifts; and structural design with good aqueous solubility, membrane permeability, low protein interference, and organelle specificity. Antioxid. Redox Signal. 29, 518-540.

Near-infrared fluorescence probes to detect reactive oxygen species for keloid diagnosis

Development of molecular probes for the detection of reactive oxygen and nitrogen species (RONS) is important for the pathology and diagnosis of diseases. Although an abnormally high RONS level has been identified in keloids - a benign dermal tumour developed after lesion, the ability of employing RONS probes for keloid detection has not yet been exploited. Herein, we report two near-infrared (NIR) fluorescent probes (CyTF and CyBA) that can specifically distinguish keloid fibroblasts from normal dermal fibroblasts. Both CyTF and CyBA show a 15-fold NIR fluorescence enhancement at 717 nm upon reaction with RONS. However, because CyTF has higher specificity towards ONOO- than CyBA, CyTF can detect stimulated fibroblasts in a more sensitive way, showing 3.76 and 2.26-fold fluorescence increments in TGF-β1 stimulated dermal fibroblasts and keloid fibroblasts, respectively. Furthermore, CyTF permits specific detection of implanted keloid fibroblasts in a xenograft live mouse model. Our work thus developed a new optical imaging approach that has the potential for early diagnosis and drug screening of keloids.

A chemiluminescent probe for cellular peroxynitrite using a self-immolative oxidative decarbonylation reaction

Peroxynitrite is a damaging agent of oxidative stress that has been difficult to monitor in living cells. Here, an isatin-based chemiluminescent probe for peroxynitrite is reported.

Peroxynitrite (ONOO^–) is a highly reactive oxygen species which has been recognized as an endogenous mediator of physiological activities like the immune response as well as a damaging agent of oxidative stress under pathological conditions. While its biological importance is becoming clearer, many of the details of its production and mechanism of action remain elusive due to the lack of available selective and sensitive detection methods. Herein, we report the development, characterization, and biological applications of a reaction-based chemiluminescent probe for ONOO^– detection, termed as PNCL. PNCL reacts with ONOO^–via an isatin moiety through an oxidative decarbonylation reaction to initiate light emission that can be observed instantly with high selectivity against other reactive sulphur, oxygen, and nitrogen species. Detailed studies were performed to study the reaction between isatin and ONOO^–, which confirm selectivity for ONOO^– over NO₂˙. PNCL has been applied for ONOO^– detection in aqueous solution and live cells. Moreover, PNCL can be employed to detect cellular ONOO^– generated in macrophages stimulated to mount an immune response with lipopolysaccharide (LPS). The sensitivity granted by chemiluminescent detection together with the specificity of the oxidative decarbonylation reaction provides a useful tool to explore ONOO^– chemistry and biology.

Detection of Reactive Oxygen and Nitrogen Species (ROS/RNS) During Hypersensitive Cell Death

Reactive oxygen and nitrogen species (ROS/RNS) are signaling molecules involved in a plethora of physiological processes in plants. Especially, ROS and nitric oxide (NO) are key players that are required for programmed cell death (PCD). The PCD associated with the hypersensitive response (HR) has been well characterized and the role of H₂O₂ and NO as key signaling molecules inducing HR has been established. Localization of ROS and NO production in plant tissues in response to pathogens can be imaged by confocal laser microscopy by using specific fluorescent probes. Deciphering the time and spatial regulation of ROS and NO is very important to establish the cellular response of plants to adverse conditions. This chapter is mainly focused on the imaging of ROS and RNS accumulation in vivo in plant tissues undergoing PCD.

Introduction

Primordial life forms on earth comprised oxygen-sensitive organisms: the anaerobic fermenters and cyanobacteria, which released oxygen as a metabolic by-product, causing the oxygen levels in the atmosphere to rise Benzie (Eur J Nutr 39:53–61, 2000 [1]), Halliwell (Free Radic Res 31:261–272, 1999 [2]).

Peroxynitrite-biosignal-responsive polymer micelles as intracellular hypersensitive nanoprobes

Copolymerization of a trifluoromethyl ketone-bearing monomer and a rhodamine monomer has led to the formation of peroxynitrite (ONOO⁻) signaling molecule-responsive polymer fluorescent micelles.

A ratiometric fluorescent probe for peroxynitrite prepared by de novo synthesis and its application in assessing the mitochondrial oxidative stress status in cells and in vivo

A ratiometric fluorescent probe is prepared by de novo synthesis for assessing the mitochondrial oxidative stress status in cells and in vivo.

Investigation of Drug-Induced Hepatotoxicity and Its Remediation Pathway with Reaction-Based Fluorescent Probes

Drug-induced liver injury (DILI) is considered a serious problem related to public health, due to its unpredictability and acute response. The level of peroxynitrite (ONOO^-) generated in liver has long been regarded as a biomarker for the prediction and measurement of DILI. Herein we present two reaction-based fluorescent probes (Naph-ONOO^- and Rhod-ONOO^-) for ONOO^- through a novel and universally applicable mechanism: ONOO^--mediated deprotection of α-keto caged fluorophores. Among them, Rhod-ONOO^- can selectively accumulate and react in mitochondria, one of the main sources of ONOO^-, with a substantial lower nanomolar sensitivity of 43 nM. The superior selectivity and sensitivity of two probes enable real-time imaging of peroxynitrite generation in lipopolysaccharide-stimulated live cells, with a remarkable difference from cells doped with other interfering reactive oxygen species, in either one- or two-photon imaging modes. More importantly, we elucidated the drug-induced hepatotoxicity pathway with Rhod-ONOO^- and revealed that CYP450/CYP2E1-mediated enzymatic metabolism of acetaminophen leads to ONOO^- generation in liver cells. This is the first time to showcase the drug-induced hepatotoxicity pathways by use of a small-molecule fluorescent probe. We hence conclude that fluorescent probes can engender a deeper understanding of reactive species and their pathological revelations. The reaction-based fluorescent probes will be a potentially useful chemical tool to assay drug-induced hepatotoxicity.

Nanoscale metal-organic frameworks coated with poly(vinyl alcohol) for ratiometric peroxynitrite sensing through FRET

This work describes a facile yet powerful approach to energy-transfer NMOF (nanoscale metal–organic framework) fabrication for ratiometric peroxynitrite (ONOO^–) sensing.

This work describes a facile yet powerful approach to energy-transfer NMOF (nanoscale metal–organic framework) fabrication for ratiometric peroxynitrite (ONOO^–) sensing. Poly(vinyl alcohol) (PVA) is chosen to organize the energy donor (NMOF) and acceptor (molecular probes). PVA can conveniently graft onto the NMOF surface and bind to the molecular probes bearing the arylboronic acid group through multiple weak coordination interactions. Due to efficient Förster resonance energy transfer (FRET), the bright blue fluorescence of the NMOF is quenched while the green or red emission from the acceptor is enhanced. Upon reacting with ONOO^–, the ONOO^– sensors depart from the NMOF and the FRET is interrupted and the fluorescence of the NMOF recovered. Based on this strategy, we developed two ratiometric ONOO^– nanosensors for the detection of ONOO^– in solutions and living cells. This work is the first report of NMOF ONOO^– sensors through FRET and could inspire the design of other NMOF based chemical sensors and biosensors.

A 1,8-naphthalimide-based fluorescent probe for selective and sensitive detection of peroxynitrite and its applications in living cell imaging

An “off–on” fluorescent probe for sensitive and selective detection of peroxynitrite was synthesized and showed good photostability and low cytotoxicity.

A fluorogenic and red-shifted diphenyl phosphinate-based probe for selective peroxynitrite detection as demonstrated in fixed cells

A new dicyanomethylene-4H-pyran-based fluorescent probe has been designed, synthesized and characterized. It shows selective “TURN-ON” fluorescence response upon reaction with ONOO⁻.

A visible-light-excited Eu3+complex-based luminescent probe for highly sensitive time-gated luminescence imaging detection of intracellular peroxynitrite

A visible-light-excited europium complex was developed for highly sensitive imaging of intracellular peroxynitrite with time-gated luminescence mode.

Long-wavelength fluorescent boronate probes for the detection and intracellular imaging of peroxynitrite

Two boronate fluorescent probes have been developed for the detection of peroxynitrite (TCFB1andTCFB2).