Fluorescent probes based on nucleophilic aromatic substitution reactions for reactive sulfur and selenium species: Recent progress, applications, and design strategies

Unravelling the recent advancement in fluorescent probes for detection against reactive sulfur species (RSS) in foodstuffs and cell imaging

Sulfur-containing representative HSO3-/SO32-, H2S, and biothiols (Cys, Hcy, and GSH) present in food items and biological organisms have raised substantial global concerns about food safety due to their reactivity and potential health implications. Adhering to international health standards is essential for these compounds; in particular, plenty of challenges exist in ensuring product quality in the beverage industry. Many fluorescent probes are being employed in various spectroscopic techniques and have developed rapidly to selectively detect sulfur-related species in food products and bio-sensing for cell imaging. This comprehensive review provides a detailed overview of a wide range of fluorescent probes designed using different fluorophores for detecting reactive sulfur species (RSS) using spectroscopic techniques. Additionally, the review explores the detection of RSS components (HSO3-/SO32-, H2S, and biothiols) in food products and cell imaging using different cell lines, highlighting the crucial role of fluorescent probes in swiftly detecting these analytes in both natural and biological contexts. Furthermore, the review discusses future trends and perspectives, emphasizing the on-going progress in detecting these analytes in food products and cell imaging using various fluorescent probes.

Sulfur-based fluorescent probes for biological analysis: A review

The widespread adoption of small-molecule fluorescence detection methodologies in scientific research and industrial contexts can be ascribed to their inherent merits, including elevated sensitivity, exceptional selectivity, real-time detection capabilities, and non-destructive characteristics. In recent years, there has been a growing focus on small-molecule fluorescent probes engineered with sulfur elements, aiming to detect a diverse array of biologically active species. This review presents a comprehensive survey of sulfur-based fluorescent probes published from 2017 to 2023. The diverse repertoire of recognition sites, including but not limited to N, N-dimethylthiocarbamyl, disulfides, thioether, sulfonyls and sulfoxides, thiourea, thioester, thioacetal and thioketal, sulfhydryl, phenothiazine, thioamide, and others, inherent in these sulfur-based probes markedly amplifies their capacity for detecting a broad spectrum of analytes, such as metal ions, reactive oxygen species, reactive sulfur species, reactive nitrogen species, proteins, and beyond. Owing to the individual disparities in the molecular structures of the probes, analogous recognition units may be employed to discern diverse substrates. Subsequent to this classification, the review provides a concise summary and introduction to the design and biological applications of these probe molecules. Lastly, drawing upon a synthesis of published works, the review engages in a discussion regarding the merits and drawbacks of these fluorescent probes, offering guidance for future endeavors.

A novel LD-targeting cysteine-activated fluorescent probe for diagnosis of APAP-induced liver injury and its application in food analysis

Cysteine (Cys) not only plays an indispensable role in maintaining the redox balance in organisms, but is also an important nutrient in the food industry. Fluorescence-based detection systems have emerged as an effective method to track the locations and concentrations of different species. To achieve efficient monitoring of Cys in both food samples and biological systems, a novel lipid droplet (LD) targeted fluorescent probe (namely NIT-Cys) was constructed for the turn-on detection of Cys, characterized by a large Stokes shift (142 nm), a short response time (<8 min), and a low Cys detection limit (39 nM). Furthermore, the NIT-Cys probe has been successfully used not only to quantify the amounts of Cys in selected food samples, but also to enable the visualization of endogenous Cys in acetaminophen (APAP)-induced drug-induced liver injury cells, zebrafish larvae and mice models. Consequently, the work presented here provides an efficient tool for monitoring Cys.

A high-fidelity dual-channel fluorescence probe for benzoyl peroxide detection and toxicity early warning in food, zebrafish, and mice

Benzoyl peroxide (BPO), as a widely used organic peroxide, has attracted widespread attention from all sectors of society for its environmental hazards and potential risks to human health. Herein, we employed a Förster resonance energy transfer (FRET) strategy to construct a novel ratiometric fluorescent probe CY-DCI for BPO detection in food, zebrafish, and mice. Specifically, a hemicyanine fluorophore and a dicyanoisophorone fluorophore were connected with a piperazine group as donor and acceptor, respectively, and an olefinic unsaturated bond as the reaction site. CY-DCI has favorable selectivity and an excellent detection limit as low as 58.1 nM, and the recovery rates for real-sample detection ranged from 95.8 % to 104 %, with relative standard deviations (RSD) less than 2.58 %. To further improve its practicality, silica gel plates and test strips containing CY-DCI (0-50 μM) were developed for naked-eye detection of BPO with satisfactory results. Additionally, this novel probe was then applied for ratiometric imaging of living zebrafish and mice and showed high ratiometric imaging resolution in the green and red channels, thus demonstrating its practical application for BPO detection and toxicity early warning in food and biosystems.

N-Aryl-DABCO Salts as an Unprecedented Sensing Platform for the Detection of Thiols and Selenols

Quaternary N-aryl-DABCO salts were introduced for the first time as a highly selective sensing platform for thiols and selenols. By employing this platform, a highly sensitive coumarin based "off-on" fluorescent probe was designed and synthesized. The probe possesses a good solubility in water, low background fluorescence, and, most importantly, demonstrates high selectivity to aryl thiols and selenols over their aliphatic counterparts and other common nucleophiles. A dramatic increase in fluorescence intensity is achieved through the selective cleavage of the quaternized DABCO-ring, yielding a piperazine derivatives with a high fluorescence quantum yield (~72 %). Moreover, stability of the probe to the most used reducing agents DTT and TCEP was demonstrated. The limits of detection for p-thiocresol and phenyl selenide were evaluated to be 22 nM and 6 nM, respectively.

Exploring the fluorescence properties of tellurium-containing molecules and their advanced applications

This review article explores the fascinating realm of fluorescence using organochalcogen molecules, with a particular emphasis on tellurium (Te). The discussion encompasses the underlying mechanisms, structural motifs influencing fluorescence, and the applications of these intriguing phenomena. This review not only elucidates the current state of knowledge but also identifies avenues for future research, thereby serving as a valuable resource for researchers and enthusiasts in the field of fluorescence chemistry with a focus on Te-based molecules. By highlighting challenges and prospects, this review sparks a conversation on the transformative potential of Te-containing compounds across different fields, ranging from environmental solutions to healthcare and materials science applications. This review aims to provide a comprehensive understanding of the distinct fluorescence behaviors exhibited by Te-containing compounds, contributing valuable insights to the evolving landscape of chalcogen-based fluorescence research.

Equivalent Response Strategy for Sensing Total Biothiols in Human Serums and Living Cells Using a Hemicyanine-Based Self-Immolative Probe

Biothiols including cysteine (Cys), homocysteine (Hcy), and glutathione (GSH) are crucial in maintaining the redox balance in the body, and the metabolism and transportation of biothiols rely on the coreaction of diverse proteins and enzymes. The abnormal concentrations and metabolism of biothiols are closely associated with many diseases. However, due to the same active reaction site of the sulfydryl group in biothiols, it is inevitable to bear a confused signal of mutual influence on both nonselective detection and discriminate detection, which presents a serious challenge of accurately sensing or imaging the three biothiols. By assigning an α,β-unsaturated ketone moiety as a Michael acceptor to trigger thiols to complete the irreversible equivalent domino response processes of nucleophilic addition, olefinic bond migration, and self-immolation, a targeted strategy was rationally pointed out, and herein, a hemicyanine-based probe CyOCy was prepared as a proof of strategy demonstration. The new probe could be equivalently lit up by Cys, Hcy, GSH, and even biothiol combinations (Cys/Hcy, Cys/GSH, Hcy/GSH, or Cys/Hcy/GSH) with unified linear ranges, detection limits, and response times. The probe CyOCy has been successfully used for the accurate quantification of total biothiols in the serum samples of healthy persons and coronary heart disease patients. In addition, the probe has been applied for cell screening, exogenous biothiol imaging, and monitoring drug-induced biothiol fluctuations. The purposive thinking of this work may provide an effective avenue for the accurate sensing of multicomponent samples.

A NIR ratiometric fluorescent probe for the rapid detection of hydrogen sulfide in living cells and zebrafish

Hydrogen sulfide (H2S) acts as a gas transporter and cell protector and plays a role in a number of disorders and signaling processes. Given that the half-life of H2S in biological systems is between seconds and minutes, the development of rapid and accurate technologies for reliable monitoring H2S levels and dynamics in organisms is critical. However, it is still difficult to design innovative near-infrared fluorescent probes that can quickly and accurately detect H2S. Here, we constructed a novel NIR ratiometric fluorescent probe based on the "aldehyde group auxiliary strategy", Cy-H2S, for the quantitative detection and precise imaging of H2S in living cells and zebrafish. Cy-H2S responded quickly (150 s) and was highly sensitive (0.179 μM) to H2S donor. Cy-H2S was further successfully employed to track endogenous H2S fluctuation in HCT116 cells and zebrafish and evaluated the release efficiency of the H2S prodrug in a NIR ratiometric imaging way. Cy-H2S has the potential to be used as a reliable indication of H2S levels in living cells and zebrafish, as well as an innovative and practical instrument for furthering the physiological research of H2S, which will encourage the creation of advanced NIR ratiometric probes for a variety of biological applications.

Theoretical investigation on a simple turn on fluorescent probe for detection of biothiols based on coumarin unit

The discovery of a simple and efficient detection method for biothiols would be scientifically significant due to the crucial role of them in various physiological processes. Recently, a simple fluorescent probe, DEMCA-NBSC, based on coumarin fragments, was developed by Ding et al., and provided an efficient way for real-time sensing of biothiols both in vivo and vitro. Theoretical insights to the fluorescence sensing mechanism of the probe were provided in this work. Details of the electron transfer process in the probe under optical excitation and the fluorescent character of the probe were analyzed using a quantum mechanical method. All these theoretical results could inspire the development of a highly convenient and efficient fluorescent probe to sense biothiols both in vivo and vitro.

Emergency Treatment and Photoacoustic Assessment of Spinal Cord Injury Using Reversible Dual-Signal Transform-Based Selenium Antioxidant

Spinal cord injury (SCI), following explosive oxidative stress, causes an abrupt and irreversible pathological deterioration of the central nervous system. Thus, preventing secondary injuries caused by reactive oxygen species (ROS), as well as monitoring and assessing the recovery from SCI are critical for the emergency treatment of SCI. Herein, an emergency treatment strategy is developed for SCI based on the selenium (Se) matrix antioxidant system to effectively inhibit oxidative stress-induced damage and simultaneously real-time evaluate the severity of SCI using a reversible dual-photoacoustic signal (680 and 750 nm). Within the emergency treatment and photoacoustic severity assessment (ETPSA) strategy, the designed Se loaded boron dipyrromethene dye with a double hydroxyl group (Se@BDP-DOH) is simultaneously used as a sensitive reporter group and an excellent antioxidant for effectively eliminating explosive oxidative stress. Se@BDP-DOH is found to promote the recovery of both spinal cord tissue and locomotor function in mice with SCI. Furthermore, ETPSA strategy synergistically enhanced ROS consumption via the caveolin 1 (Cav 1)-related pathways, as confirmed upon treatment with Cav 1 siRNA. Therefore, the ETPSA strategy is a potential tool for improving emergency treatment and photoacoustic assessment of SCI.

Recent progress in the development of small-molecule fluorescent probes for detection and imaging of selenocysteine and application in thyroid disease diagnosis

Selenocysteine (SeCys) is the 21st genetically encoded amino acid present in proteins and is involved in various biological functions. Inappropriate levels of SeCys can be considered as a sign of various diseases. Therefore, small molecular fluorescent probes for the detection and imaging of SeCys in vivo in biological systems are considered to be of significant interest for understanding the physiological role of SeCys. Thus, this article mainly provides a critical evaluation of recent advances made in SeCys detection along with the biomedical applications based on small molecular fluorescent probes published in the literature during the past half a dozen years. Therefore, the article primarily deals with the rational design of fluorescent probes, wherein these were selective towards SeCys over other biologically abundant molecules, in particular the thiol-based ones. The detection has been monitored by different spectral techniques, such as fluorescence and absorption spectroscopy and in some cases even visual color changes. Further, the detection mechanism and the utility of fluorescent probes for in vitro and in vivo cell imaging applications are addressed. For clarity, the main features have been conveniently divided into four categories based on the chemical reactions of the probe, viz., in terms of the cleavage of the responsive group by the SeCys nucleophile: (i) 2,4-dinitrobene sulphonamide group, (ii) 2,4-dinitrobenesulfonate ester group, (iii) 2,4-dinitrobenzeneoxy group and (iv) miscellaneous types. Overall this article deals with the analysis of more than two dozen fluorescent probes demonstrated for selective detection of SeCys along with their applications towards disease diagnosis.

Enlightening the Path to Protein Engineering: Chemoselective Turn-On Probes for High-Throughput Screening of Enzymatic Activity

Many successful stories in enzyme engineering are based on the creation of randomized diversity in large mutant libraries, containing millions to billions of enzyme variants. Methods that enabled their evaluation with high throughput are dominated by spectroscopic techniques due to their high speed and sensitivity. A large proportion of studies relies on fluorogenic substrates that mimic the chemical properties of the target or coupled enzymatic assays with an optical read-out that assesses the desired catalytic efficiency indirectly. The most reliable hits, however, are achieved by screening for conversions of the starting material to the desired product. For this purpose, functional group assays offer a general approach to achieve a fast, optical read-out. They use the chemoselectivity, differences in electronic and steric properties of various functional groups, to reduce the number of false-positive results and the analytical noise stemming from enzymatic background activities. This review summarizes the developments and use of functional group probes for chemoselective derivatizations, with a clear focus on screening for enzymatic activity in protein engineering.

Excited-state intramolecular proton transfer (ESIPT)-based fluorescent probes for biomarker detection: design, mechanism, and application

Biomarkers are essential in biology, physiology, and pharmacology; thus, their detection is of extensive importance. Fluorescent probes provide effective tools for detecting biomarkers exactly. Excited state intramolecular proton transfer (ESIPT), one of the significant photophysical processes that possesses specific photoisomerization between Keto and Enol forms, can effectively avoid annoying interference from the background with a large Stokes shift. Hence, ESIPT is an excellent choice for biomarker monitoring. Based on the ESIPT process, abundant probes were designed and synthesized using three major design methods. In this review, we conclude probes for 14 kinds of biomarkers based on ESIPT explored in the past five years, summarize these general design methods, and highlight their application for biomarker detection in vitro or in vivo.

Non-genetic factors affecting the meat quality and flavor of Inner Mongolian lambs: A review

The Inner Mongolia Autonomous Region ranks first among the five major pastoral areas in terms of lamb breeding of China. The Inner Mongolia Autonomous Region has a vast territory, with many famous grasslands and thousands of forage plants and multiple local high-quality lamb breeds. After hundreds of years of artificial breeding and improvement, Mongolian sheep have developed many varieties. Different diets, feeding and treatment methods have effects on the production performance, lipid deposition and flavor composition of mutton sheep. Therefore, understanding the relationship among Inner Mongolian lamb, meat quality, and flavor will improve the production of high-quality mutton. The regulation of meat quality and flavor will have a profound impact on the deep processing and income-generating capabilities of mutton. Non-genetic factors affect the quality and flavor of mutton, which are more intuitive than genetic factors. In this review, we cover the contributions made by scientists to explore and improve the quality and flavor of Inner Mongolia lambs through non-genetic means, compare the differences between grazing and drylot-feeding in detail, and summarize some feed additives. We hope that based on our review, we can provide some inspiration to improve the meat quality of Mongolian sheep.

Activity-Based Fluorescent Probes Based on Hemicyanine for Biomedical Sensing

In recent years, fluorescent probes, as an analytical tool that can target and rapidly detect analytes, have been increasingly used for applications related to medical treatment, detection, and bioimaging. Researchers are interested in hemicyanine-based fluorescent probes because of their high quantum yield, tunable spectrum characteristics, absorption and emission in the near-infrared (NIR) region, and good photo-stability. The development of these dyes and their derivatives as NIR fluorescent probes for biological applications has advanced significantly in the last ten years. This review introduces processes for making hemicyanine dyes and the methodology for creating functional activity-based fluorescent probes. A variety of hemicyanine-based probes have been systematically developed for the detection of small biomolecules in various illnesses. Finally, the potential drawbacks of hemicyanine-based functional probes, and the prospects for future research and translation into clinical medicine, are also discussed. This study is intended to provide strategies for the development and design of novel fluorescence probes.

Recent development of small-molecule fluorescent probes based on phenothiazine and its derivates

Fluorescence probes, as analytical tools with the ability to perform rapid and sensitive detection of target analytes, have made outstanding contributions to environmental analysis and bioassays. Considering the expanding developments in these areas, fluorophores play a key role in the de-sign of fluorescence probes. Compared to classical fluorophores, phenothiazines with elec-tron-rich characteristics have been widely applied to construct electron donor-acceptor dyes, which exhibit outstanding performance in both fluorimetric and colorimetric analysis. In addition, these probes also exhibit the pronounced ability in both solution and solid-state, achieving portable detection for environmental analysis. In this review, we summarize recent advances in the performance of phenothiazine-based fluorescent probes for detecting various analytes, especially in cations, anions, ROS/RSS, enzyme and other small molecules. The general design rules, response mechanisms and practical applications of the probes are analyzed, followed by a discussion of exiting challenges and future research perspectives. It is hoped that this review will provide a few strategies for the development of phenothiazine-based fluorescent probes.

Label-free chemical imaging of cytochrome P450 activity by Raman microscopy

Although investigating drug modulation of cytochrome P450 (CYP) activity under physiological conditions is crucial in drug development to avoid severe adverse drug reactions, the current evaluation approaches that rely on the destructive and end-point analysis can be misleading due to invasive treatments and cellular heterogeneity. Here, we propose a non-destructive and high-content method for visualizing and quantifying intracellular CYP activity under drug administration by Raman microscopy. The redox-state and spin-state sensitive Raman measurement indicated that the induced CYPs in living hepatocytes were in oxidized and low-spin state, which is related to monooxygenase function of CYP. Moreover, glycogen depletion associated with CYP induction was simultaneously observed, indicating a relevant effect on glucose metabolism. By deciphering the overall changes in the biochemical fingerprints of hepatocytes, Raman microscopy offers a non-destructive and quantitative chemical imaging method to evaluate CYP activity at the single-cell level with the potential to facilitate future drug development schemes.

Real-time, sensitive and simultaneous detection of GSH and Cys/Hcy by 8-substituted phenylselenium BODIPYs: a structure-activity relationship

Real-time and sensitive detection of biothiols is the key to biomedical research and clinical diagnosis. It is necessary to develop a highly sensitive and selective fluorescent probe for the detection of biothiols. In this paper, we have developed a series of meso-arylselenium BODIPY probes for the rapid and sensitive detection of biothiols and the dual-channel discrimination of GSH and Cys/Hcy. A structure-activity relationship was established from five p-substituted phenylselenium (R = NO₂, F, H, OCH₃ or N(CH₂CH₂)₂O) BODIPYs. Compared with most reported fluorescent probes, such as meso-BODIPY sulfur ethers, these probes display much lower LODs (∼nM levels) and more rapid responses, which are ascribed to the higher fluorescence efficiencies of the sensing products (Φ_f = 0.48 for GSH, 0.18 for Cys and 0.14 for Hcy) and the introduction of arylselenium, which is more active than arylthiol. Among them, the best sensing performance is that of probe 2a (R = NO₂); therefore, a structure-activity relationship of these fluorescent probes was also obtained. The excellent sensing performance was further revealed in the detection of GSH and Cys/Hcy in live cells.

Rational construction of a new water soluble turn-on colorimetric and NIR fluorescent sensor for high selective Sec detection in Se-enriched foods and biosystems

As a naturally occurring amino acid, selenocysteine (Sec) plays a key role in a variety of cellular functions and Se-enriched foods. In this work, a robust water soluble fluorescence turn-on near-infrared (NIR) sensor NIR-Sec was constructed for Sec detection over biothiols in Se-enriched foods. Specifically, NIR-Sec contains a readily prepared water soluble NIR dicyanoisophorone fluorophore and a well-known response-site 2,4-dinitrobenzenesulfonyl moiety with strong intramolecular charge transfer (ICT) effect to quench the fluorescence intensity of NIR fluorophore. Upon addition of Sec, the NIR dicyanoisophorone fluorophore was released and a bright red emission at 663 nm was observed. Moreover, NIR-Sec toward Sec exhibited rapid response time (∼1 min), a large stoke shift (183 nm), and high selectivity and sensitivity (LOD: 52 nM). Impressively, NIR-Sec was successfully employed to detect and image Sec in Se-enriched foods and shrimp, indicating NIR-Sec could provide a robust tool for investigating the role of Sec in complex real-food samples.

Fluorescent probes for the detection of disease-associated biomarkers

Fluorescent probes have emerged as indispensable chemical tools to the field of chemical biology and medicine. The ability to detect intracellular species and monitor physiological processes has not only advanced our knowledge in biology but has provided new approaches towards disease diagnosis. In this review, we detail the design criteria and strategies for some recently reported fluorescent probes that can detect a wide range of biologically important species in cells and in vivo. In doing so, we highlight the importance of each biological species and their role in biological systems and for disease progression. We then discuss the current problems and challenges of existing technologies and provide our perspective on the future directions of the research area. Overall, we hope this review will provide inspiration for researchers and prove as useful guide for the development of the next generation of fluorescent probes.

Photoinduced Chemo-, Site- and Stereoselective α-C(sp3 )-H Functionalization of Sulfides

The ubiquity of sulfur-containing molecules in biologically active natural products and pharmaceuticals has long attracted synthetic chemists to develop efficient strategies towards their synthesis. The strategy of direct α-C(sp³ )-H modification of sulfides provides a streamlining access to complex sulfur-containing molecules. Herein, we report a photoinduced chemo-, site- and stereoselective α-C(sp³ )-H functionalization of sulfides using isatins as the photoredox reagent and coupling partner catalyzed by a chiral gallium(III)-N,N'-dioxide complex. The reaction proceeds through a verified single-electron transfer (SET) mechanism with high efficiency, excellent functional group tolerance, as well as a broad substrate scope. Importantly, this cross-coupling protocol is highly selective for the direct late-stage functionalization of methionine-related peptides, regardless of the inherent structural similarity and complexity of diverse residues.

A naphthimide fluorescent probe for the detection of selenols in selenium-enriched Tan sheep

An "off-on" fluorescent probe, Nap-DNB, which is based on naphthimide, was designed and developed for the detection of biological selenols in vitro. We have adopted a combination of a low-pH detection environment and reaction sites that are more difficult to destroy to avoid the interference of a large number of biological thiols in biological samples. Nap-DNB can completely respond to selenocysteine within 15 mins, with a detection limit of 92 nM. Nap-DNB was successfully used for the detection of selenols in the serum, liver, and longissimus dorsi of selenium-enriched Tan sheep. Through comparison, we found that the detection of selenols by the Nap-DNB is similar to that by thioredoxin reductase and glutathione peroxidase in a commercial kit method. Nap-DNB can be used for the detection of selenols in selenium-enriched Tan sheep.

Chemical Design of Activatable Photoacoustic Probes for Precise Biomedical Applications

Photoacoustic (PA) imaging technology, a three-dimensional hybrid imaging modality that integrates the advantage of optical and acoustic imaging, has great application prospects in molecular imaging due to its high imaging depth and resolution. To endow PA imaging with the ability for real-time molecular visualization and precise biomedical diagnosis, numerous activatable molecular PA probes which can specifically alter their PA intensities upon reacting with the targets or biological events of interest have been developed. This review highlights the recent developments of activatable PA probes for precise biomedical applications including molecular detection of the biotargets and imaging of the biological events. First, the generation mechanism of PA signals will be given, followed by a brief introduction to contrast agents used for PA probe design. Then we will particularly summarize the general design principles for the alteration of PA signals and activatable strategies for developing precise PA probes. Furthermore, we will give a detailed discussion of activatable PA probes in molecular detection and biomedical imaging applications in living systems. At last, the current challenges and outlooks of future PA probes will be discussed. We hope that this review will stimulate new ideas to explore the potentials of activatable PA probes for precise biomedical applications in the future.

A fluorescent pH probe for evaluating the freshness of chicken breast meat

A fluorescent probe, Nap-MOR, based on the naphthalimide fluorophore, was designed and developed for pH measurement in aqueous solutions. Nap-MOR had a close linear relationship between fluorescence intensity and pH, in the range 4.5-8, which covers the full range of pH found in normal fresh, defective and spoiled meat. pH measurement with Nap-MOR was free from interference by a wide range of ions and biochemicals found in meat and the results were not significantly different in comparison with a pH meter. Therefore, Nap-MOR is a robust and convenient way to evaluate the freshness of chicken breast meat by measuring its pH.

Selenium-Based Fluorescence Probes for the Detection of Bioactive Molecules

Chemistry of organoselenium reagents have now become an important tool of synthetic organic and medicinal chemistry. These reagents activate the olefinic double bonds and used to archive the number of organic transformations under mild reaction conditions. A number of organoselenium compounds have been identified as potent oxidants. Recently, various organoselenium species have been employed as chemical sensors for detecting toxic metals. Moreover, a number of selenium-based fluorescent probes have been developed for detecting harmful peroxides and ROS. In this review article, the synthesis of selenium-based fluorescent probes will be covered including their application in the detection of toxic metals and harmful peroxides including ROS.

An α-naphtholphthalein-derived colorimetric fluorescent chemoprobe for the portable and visualized monitoring of Hg2+ by the hydrolysis mechanism

An ɑ-naphtholphthalein-derived colorimetric fluorescent chemoprobe was elaborately designed for the portable and visual monitoring of Hg2+ in environmental and biological samples.

Recent Research Progress of Red-Emitting/Near-Infrared Fluorescent Probes for Biothiols

Small-molecule biological thiols, including cysteine (Cys), homocysteine (Hcy) and glutathione (GSH), occupy a vital position in physiological and pathological activities. Abnormal fluctuations of their concentrations are often closely connected with...

One-step synthesis of PY-NBD to distinguish Cys/Hcy and GSH in aqueous solutions and living cells by dual channels

An easy-to-synthesize fluorescent probe PY-NBD was developed to distinguish Cys/Hcy and GSH by two channels in aqueous solutions and living cells.

A rhodamine–TPE scaffold-based fluorescent probe for visualizing phosgene with a portable smartphone via test TLC strips

A rhodamine–TPE scaffold-based ratiometric signal readout probe was developed for sensitive, rapid, and in situ phosgene determination.

A novel ratiometric fluorescent chemosensor for detecting malononitrile and application assisted with smartphone

Malononitrile can be transformed into hypertoxic hydrogen cyanide which induces severely jeopardizes to human beings and environment. However, an effective detection technology for malononitrile was still lacking, which means that it is necessary to develop new sensitive analysis technology for malononitrile. Here in, a high sensitive fluorescent probe NQBS for detecting malononitrile was designed and synthesized from the derivative of natural product nopinone. NQBS could selectively recognize malononitrile from 26 kinds of competitive compounds in N, N-dimethylformamide (DMF) solution. The detection limit of NQBS for malononitrile was calculated to be 1.96 μM at the concentration range of 0-25 μM. In addition, the sensing mechanism of NQBS towards malononitrile was proved with high resolution mass spectrometer (HRMS), nuclear magnetic resonance hydrogen spectroscopy (¹H NMR), and density functional theory (DFT) calculation analysis as Knoevenagel condensation process and intramolecular cyclization reaction. With the assistance of smartphone and color recognition software, NQBS was well applied in the on-site recognition of malononitrile in real time by analyzing the change trend of the red-greenblue (RGB) value of the NQBS solution.

Squaraine-Based Optical Sensors: Designer Toolbox for Exploring Ionic and Molecular Recognitions

Small molecule-based chromogenic and fluorogenic probes play an indispensable role in many sensing applications. Ideal optical chemosensors should provide selectivity and sensitivity towards a variety of analytes. Synthetic accessibility and attractive photophysical properties have made squaraine dyes an enticing platform for the development of chemosensors. This review highlights the versatility of modular assemblies of squaraine-based chemosensors and chemodosimeters that take advantage of the availability of various structurally and functionally diverse recognition motifs, as well as utilizing additional recognition capabilities due to the unique structural features of the squaraine ring.

An 8-arylselenium BODIPY fluorescent probe for rapid and sensitive discrimination of biothiols in living cells

By introducing 8-arylselenium as the active group, a BODIPY fluorescent probe ASeBD was constructed for rapid and sensitive detection and dual-channel discrimination of GSH and Cys/Hcy in solution and in living cells, and its mechanism was demonstrated.

Discovery of a Broad-Spectrum Fluorogenic Agonist for Strigolactone Receptors through a Computational Approach

Strigolactones (SLs) are plant hormones that play various roles in plant physiology, including provoking the germination of parasitic weeds Orobanche and Striga. A family of α/β-hydrolases have been proposed to be the SL receptor proteins. Effective assays for measuring the activity of SL receptors could promote the development of SL-related biology and chemistry. In this study, we developed a new approach called pharmacophore-linked probe virtual screening (PPVS). Its application yielded an effective "off-on" probe named Xilatone Red (XLR). This probe showed a broad spectrum and excellent sensitivity toward SL receptors, including ShD14 (Striga D14), for which the detection limit was determined to be in the micromolar range, outperforming that of the commercial fluorogenic agonist Yoshimulactone Green (YLG). Upon hydrolysis by SL receptors, XLR provided fluorogenic and colorimetric signaling responses. Furthermore, XLR could induce germination of Phelipanche aegyptiaca seeds and prevent Arabidopsis max4-1 branching defects at micromolar concentrations. Our molecular simulations revealed the essential factors in the molecular perception of XLR. We anticipate that this study can prompt the discovery of high-performance SL agonists/antagonists to combat parasitic weeds.

Thiolysis of CBD arylethers for development of highly GSH-selective fluorescent probes

Thiolysis of 7-cyanobenzoxadiazole (CBD) arylether was investigated for development of GSH-selective fluorescent probes for the first time. The results demonstrate that CBD-based probes have tunable reactivities and appropriate dissociation constants for GSH, and are highly GSH-selective and suitable for bioimaging.

Carbolong chemistry: nucleophilic aromatic substitution of a triflate functionalized iridapentalene

The reactivity of the triflate functionalized iridapentalene 1, [Ir{[double bond, length as m-dash]CHC(CH₂C(CO₂Me)₂CH₂)[double bond, length as m-dash]CC[double bond, length as m-dash]CHC(OTf)[double bond, length as m-dash]CH}(CO)(PPh₃)₂]OTf, with C-, N-, O- and S-centered neutral nucleophiles was studied, leading to the isolation of a wide array of irida-carbolong derivatives. As an extension, a polycyclic complex with a rare six-fused-ring structure was constructed. This strategy provides a new route for the construction of functionalized metallaaromatic complexes, and the resulting iridacycles exhibit broad spectral absorption ranges, making them potential photoelectric materials.

NBD-based synthetic probes for sensing small molecules and proteins: design, sensing mechanisms and biological applications

Compounds with a nitrobenzoxadiazole (NBD) skeleton exhibit prominent useful properties including environmental sensitivity, high reactivity toward amines and biothiols (including H2S) accompanied by distinct colorimetric and fluorescent changes, fluorescence-quenching ability, and small size, all of which facilitate biomolecular sensing and self-assembly. Amines are important biological nucleophiles, and the unique activity of NBD ethers with amines has allowed for site-specific protein labelling and for the detection of enzyme activities. Both H2S and biothiols are involved in a wide range of physiological processes in mammals, and misregulation of these small molecules is associated with numerous diseases including cancers. In this review, we focus on NBD-based synthetic probes as advanced chemical tools for biomolecular sensing. Specifically, we discuss the sensing mechanisms and selectivity of the probes, the design strategies for multi-reactable multi-quenching probes, and the associated biological applications of these important constructs. We also highlight self-assembled NBD-based probes and outline future directions for NBD-based chemosensors. We hope that this comprehensive review will facilitate the development of future probes for investigating and understanding different biological processes and aid the development of potential theranostic agents.

A Fluorescent Probe for the Specific Staining of Cysteine Containing Proteins and Thioredoxin Reductase in SDS-PAGE

A naphthalimide-based fluorescent probe, Nap-I, with iodoacetamide as the alkylating group, has been synthesized, and its specific fluorescent staining of proteins containing cysteine (Cys) and selenocysteine (Sec) residues in sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) has been evaluated. This molecule shows good fluorescence properties in the labeling of protein Cys/Sec residues, while reducing steric hindrance and minimizing changes in the water solubility of proteins. Reaction parameters, such as labeling time and pH, have been investigated, and the optimal labeling conditions for Cys-containing proteins have been determined. Thioredoxin reductase (TXNRD) is best stained at low pH. The probe Nap-I has been successfully used for the quantification of serum proteins and hemoglobin in Tan sheep serum, and TXNRD in Tan sheep liver and muscle has been labeled at low pH. Based on the probe Nap-I, we have also distinguished TXNRD1 and TXNRD2 by SDS-PAGE. The results showed that, compared with the normal microenvironment in which the protein resides, the lower the pH value, the greater the TXNRD activity.

A new ESIPT-based fluorescent probe for the highly sensitive detection of amine vapors

A new ESIPT-based fluorescent probe has been developed as a rapid, highly sensitive, and selective sensor for amine vapors.

A new fluorescent probe for ultrasensitive detection of phosgene in solution and the gas phase

A new fluorescent probe has been developed for sensitive and selective detection of phosgene in solution and vapor.

Investigation of thiolysis of 4-substituted SBD derivatives and rational design of a GSH-selective fluorescent probe

In order to evaluate 7-sulfonamide benzoxadiazole (SBD) derivatives for the development of fluorescent probes, herein we investigated the thiolysis reactivity and selectivity of a series of SBD compounds with different atoms (N/O/S/Se) at the 4-position. Both SBD-amine and SBD-ether are stable toward biothiols in buffer (pH 7.4), while SBD-selenoether can react efficiently with biothiols GSH/Hcy, Cys, and H2S to produce SBD-SG/S-Hcy, SBD-NH-Cys, and SBD-SH, respectively, with three different sets of spectral signals. Therefore, the SBD-selenoether compounds should be useful platforms for the differentiation of these biothiols. Though SBD-alkylthioether shows much lower reactivity than SBD-selenoether, SBD-arylthioether is a tunable motif and structural modifications at the aryl moiety enable the rate of thiol-mediated thiolysis to be modified. To this end, an ER-targeted GSH-selective fluorescent probe 7 was rationally designed via thiolysis of SBD-arylthioether. Compared with control probe SBD-Cl, probe 7 exhibits improved GSH selectivity and better biocompatibility. In total, this study highlights that the modification at the 4-position of SBD is an efficient strategy for the development of new fluorescent probes with tunable reactivity and selectivity.