A near-infrared “turn-on” fluorescent probe with a self-immolative linker for the in vivo quantitative detection and imaging of hydrogen sulfide

An Endocellulase-Triggered NO Targeted-Release Enzyme-Prodrug Therapy System and Its Application in Ischemia Injury

Nitric oxide (NO) is a crucial gaseous signaling molecules in regulating cardiovascular, immune, and nervous systems. Controlled and targeted NO delivery is imperative for treating cancer, inflammation, and cardiovascular diseases. Despite various enzyme-prodrug therapy (EPT) systems facilitating controlled NO release, their clinical utility is hindered by nonspecific NO release and undesired metabolic consequence. In this study, a novel EPT system is presented utilizing a cellobioside-diazeniumdiolate (Cel2-NO) prodrug, activated by an endocellulase (Cel5A-h38) derived from the rumen uncultured bacterium of Hu sheep. This system demonstrates nearly complete orthogonality, wherein Cel2-NO prodrug maintains excellent stability under endogenous enzymes. Importantly, Cel5A-h38 efficiently processes the prodrug without recognizing endogenous glycosides. The targeted drug release capability of the system is vividly illustrated through an in vivo near-infrared imaging assay. The precise NO release by this EPT system exhibits significant therapeutic potential in a mouse hindlimb ischemia model, showcasing reductions in ischemic damage, ambulatory impairment, and modulation of inflammatory responses. Concurrently, the system enhances tissue repair and promotes function recovery efficacy. The novel EPT system holds broad applicability for the controlled and targeted delivery of essential drug molecules, providing a potent tool for treating cardiovascular diseases, tumors, and inflammation-related disorders.

Activity-Based Fluorescent Probes for Hydrogen Sulfide and Related Reactive Sulfur Species

Hydrogen sulfide (H2S) is not only a well-established toxic gas but also an important small molecule bioregulator in all kingdoms of life. In contemporary biology, H2S is often classified as a "gasotransmitter," meaning that it is an endogenously produced membrane permeable gas that carries out essential cellular processes. Fluorescent probes for H2S and related reactive sulfur species (RSS) detection provide an important cornerstone for investigating the multifaceted roles of these important small molecules in complex biological systems. A now common approach to develop such tools is to develop "activity-based probes" that couple a specific H2S-mediated chemical reaction to a fluorescent output. This Review covers the different types of such probes and also highlights the chemical mechanisms by which each probe type is activated by specific RSS. Common examples include reduction of oxidized nitrogen motifs, disulfide exchange, electrophilic reactions, metal precipitation, and metal coordination. In addition, we also outline complementary activity-based probes for imaging reductant-labile and sulfane sulfur species, including persulfides and polysulfides. For probes highlighted in this Review, we focus on small molecule systems with demonstrated compatibility in cellular systems or related applications. Building from breadth of reported activity-based strategies and application, we also highlight key unmet challenges and future opportunities for advancing activity-based probes for H2S and related RSS.

Novel design of near-infrared fluorescent sensors for the detection of Hg2+ in living cells and real water samples

Mercury sensing and imaging in the bio-system is essential for comprehending its toxicity and therapies. Based on the merocyanine scaffold, we designed and synthesized two novel near-infrared (NIR) fluorescent probes for detecting Hg2+. The release of chloro-substituted merocyanine structure on the probe CyHg-Cl enables fluorescence enhancement rapidly by introducing Hg2+. In addition, the probe CyHg-Cl exhibits NIR emission and a low detection limit of 0.59 µM. Finally, the probe CyHg-Cl was used to detect Hg2+ in live cells and real water samples.

Modulation of Near-Infrared Mitochondria-Targetable fluorescent probe for H2S bioimaging through the modification of heavy atom iodine

H₂S is correlated with mitochondrial dysfunction, which results in the death of cells. Two near-infrared fluorescent probes, Mito-HS-1 and Mito-HS-2, were designed for mitochondrial H₂S imaging. Initially, the synthesis protocol of expensive IR-780-based hemicyanine (HXPI) was optimized with an appreciate yield of 80 % as compared with 14-56 % previously reported. Iodine atom was introduced to HXPI to obtain iodine-HXPI whose Stokes shift was increased to be 90 nm. On account of the rapid and fast nucleophilic attack of H₂S, HXPI-based Mito-HS-1 could be applied for the real time imaging of mitochondrial H₂S. Besides some similar optical properties with Mito-HS-1, iodine-HXPI-based Mito-HS-2 exhibited wider linear range (3-150 μM), more stable fluorescent imaging and more favorable specificity in vitro. Both Mito-HS-1 and Mito-HS-2 could be used to image exogenous H₂S in cells, with Mito-HS-2 showing fairly better signal-to-noise. Additionally, the Pearson correlation coefficient of two probes demonstrated that they could successfully monitor mitochondrial H₂S in A549 cells and Hela cells.

A 3,5-dinitropyridin-2yl Substituted Flavonol-based Fluorescent Probe for Rapid Detection of H2S in Water, Foodstuff Samples and Living Cells

A novel flavonol-based fluorescent probe, Fla-DNT, has been synthesized for the rapid and specific detection of H2S. Fla-DNT exhibits excellent selectivity and anti-interference properties, a short response time (4 min), large Stokes shift (138 nm), and low detection limit (1.357 µM). Upon exposure to H2S, Fla-DNT displays a remarkable increase in fluorescence intensity at 542 nm. Meanwhile, the recognizing site of H2S was predicted through Electrostatic potential and ADCH charges calculations, while the sensing mechanism of H2S was determined via HRMS analysis and DFT calculation. More importantly, the probe owes multiple applications, such as a recovery rate ranging from 92.00 to 102.10% for detecting H2S in water samples, and it can be fabricated into fluorescent strips to track H2S production during food spoilage by tracking color changes, thereby enabling real-time monitoring of food freshness. The bioimaging experiments demonstrate the capability of Fla-DNT to detect both endogenous and exogenous H2S in living cells. These results provide a reliable method and idea for H2S detection in complex environments.

Recent Advancements on Self-Immolative System Based on Dynamic Covalent Bonds for Delivering Heterogeneous Payloads

The precisely spatial-temporal delivery of heterogeneous payloads from a single system with the same pulse is in great demand in realizing versatile and synergistic functions. Very few molecular architectures can satisfy the strict requirements of dual-release translated from single triggers, while the self-immolative systems based on dynamic covalent bonds represent the "state-of-art" of ultimate solution strategy. Embedding heterogeneous payloads symmetrically onto the self-immolative backbone with dynamic covalent bonds as the trigger, can respond to the quasi-bio-orthogonal hallmarks which are higher at the disease's microenvironment to simultaneously yield the heterogeneous payloads (drug A/drug B or drug/reporter). In this review, the modular design principles are concentrated to illustrate the rules in tailoring useful structures, then the rational applications are enumerated on the aspects of drug codelivery and visualized drug-delivery. This review, hopefully, can give the general readers a comprehensive understanding of the self-immolative systems based on dynamic covalent bonds for delivering heterogeneous payloads.

A highly selective and easily acquisitive near-infrared fluorescent probe for detection and imaging of hydrogen sulfide in cells

Hydrogen sulfide (H₂S) plays a substantial role as a messenger in the physiological and pathological processes of many diseases. Recently, the fluorescence probe of H₂S based on organic dye has attracted great attention. However, the emission of many probes is in the UV-vis region (400-600 nm), so it has the disadvantages of shallow tissue penetration and more vulnerable to spontaneous fluorescence interference. Although several H₂S probes have been developed that emit more than 650 nm, there is a complex structure difficult to synthesize or unstable in storage. Aimed at simply structural and easily synthesized H₂S fluorescent probes with emission wavelength more than 650 nm, a novel near-infrared (NIR) probe (NIR-H₂S) here was rationally designed with 4-(2-carboxyphenyl)-7-(diethylamino)-2-(4-hydroxystyryl)chromenylium (NIR-OH) as a fluorescent dye and 2,4-dinitrophenyl moiety as a recognition group. Addition of H₂S, the "turn-on" NIR fluorescence response at 736 nm of NIR-H₂S was displayed, accompanied by a visual colour change from purple to green when excited at 686 nm. As an easily acquisitive H₂S probe, NIR-H₂S has been successfully applied to cell imaging for H₂S detection with the advantages such as long fluorescence emission, low toxicity, high sensitivity and strong selectivity.

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.

A New Ratiometric Fluorescent Probe Based on BODIPY for Highly Selective Detection of Hydrogen Sulfide

Hydrogen sulfide (H₂S) as small molecular signal messenger plays key functions in numerous biological processes. The imaging detection of intracellular hydrogen sulfide is of great significance. In this work, a ratiometric fluorescent probe BH based on an asymmetric BODIPY dye for detection of H₂S was designed and synthesized. After the interaction with hydrogen sulfide, probe display colorimetric and ratiometric fluorescence response, with its maximum emission fluorescence wavelength red-shifted from 542 nm to 594 nm, which is attributed to the sequential nucleophilic reaction of H₂S leading to enhanced molecular conjugation after ring formation of the BODIPY skeleton. A special response mechanism has been fully investigated by NMR titration and MS, so that the probe has excellent detection selectivity. Furthermore, probe BH has low cytotoxicity and fluorescence imaging experiments indicate that it can be used to monitor hydrogen sulfide in living cells.

The design strategies and biological applications of probes for the gaseous signaling molecule hydrogen sulfide

H₂S, the smallest and simplest biological thiol in living systems, is the third member of the family of signaling mediators. H₂S participates in the regulation of a series of complex physiological and pathological functions in the body, making it a critical fulcrum that balances health and disease in human physiology. Small-molecule fluorescent probes have been proven to possess the unique advantages of high temporal and spatial resolution, good biocompatibility and high sensitivity, and thus their use is a powerful approach for monitoring the level and dynamics of H₂S in living cells and organisms and better understanding its basic cellular functions. The field of small-molecule fluorescent probes for monitoring the complex biological activities of H₂S in vivo has been thriving in recent years. Herein, we systematically summarize the latest developments in the field of fluorescent probes for the detection of H₂S, illustrate their biological applications according to the classification of target-responsive sites, and emphasize the development direction and challenges of H₂S-responsive fluorescent probes, hoping to give implications of researchers on fluorescent probes for future research.

A nitrobenzoxadiazole-based near-infrared fluorescent probe for the specific imaging of H2S in inflammatory and tumor mice

As a common gaseous signaling molecule, hydrogen sulfide (H₂S) plays a vital role in physiology and pathology. The development of fluorescent probes for detecting H₂S has attracted widespread attention. However, most of the reported fluorescent probes with nitrobenzoxadiazole (NBD) as the recognition group have been widely used to simultaneously detect biothiols and H₂S, instead of specifically detecting H₂S. Herein, a novel NBD-based near-infrared (NIR) fluorescent probe named CX-N for the detection of H₂S is synthesized. The selectivity of CX-N for H₂S is significantly higher than that for biothiols and other potential interferences. After reacting with H₂S, CX-N shows a significant increase in NIR fluorescence (75-fold), large Stokes shift (155 nm) and fast response (4 min). And the possible response mechanism of CX-N to H₂S is given and confirmed by HPLC and HRMS. Based on the low cytotoxicity of CX-N, it has been used for H₂S imaging in live cells and zebrafish. More importantly, CX-N has also been successfully applied for the real-time imaging of H₂S in inflammatory and tumor mice based on its NIR emission, which provides a reliable platform for the specific recognition of H₂S in complex biological systems.

Fluorescent-based nanosensors for selective detection of a wide range of biological macromolecules: A comprehensive review

Thanks to their unique attributes, such as good sensitivity, selectivity, high surface-to-volume ratio, and versatile optical and electronic properties, fluorescent-based bioprobes have been used to create highly sensitive nanobiosensors to detect various biological and chemical agents. These sensors are superior to other analytical instrumentation techniques like gas chromatography, high-performance liquid chromatography, and capillary electrophoresis for being biodegradable, eco-friendly, and more economical, operational, and cost-effective. Moreover, several reports have also highlighted their application in the early detection of biomarkers associated with drug-induced organ damage such as liver, kidney, or lungs. In the present work, we comprehensively overviewed the electrochemical sensors that employ nanomaterials (nanoparticles/colloids or quantum dots, carbon dots, or nanoscaled metal-organic frameworks, etc.) to detect a variety of biological macromolecules based on fluorescent emission spectra. In addition, the most important mechanisms and methods to sense amino acids, protein, peptides, enzymes, carbohydrates, neurotransmitters, nucleic acids, vitamins, ions, metals, and electrolytes, blood gases, drugs (i.e., anti-inflammatory agents and antibiotics), toxins, alkaloids, antioxidants, cancer biomarkers, urinary metabolites (i.e., urea, uric acid, and creatinine), and pathogenic microorganisms were outlined and compared in terms of their selectivity and sensitivity. Altogether, the small dimensions and capability of these nanosensors for sensitive, label-free, real-time sensing of chemical, biological, and pharmaceutical agents could be used in array-based screening and in-vitro or in-vivo diagnostics. Although fluorescent nanoprobes are widely applied in determining biological macromolecules, unfortunately, they present many challenges and limitations. Efforts must be made to minimize such limitations in utilizing such nanobiosensors with an emphasis on their commercial developments. We believe that the current review can foster the wider incorporation of nanomedicine and will be of particular interest to researchers working on fluorescence technology, material chemistry, coordination polymers, and related research areas.

Nanoparticulate Photoluminescent Probes for Bioimaging: Small Molecules and Polymers

Recent interest in research on photoluminescent molecules due to their unique properties has played an important role in advancing the bioimaging field. In particular, small molecules and organic dots as probes have great potential for the achievement of bioimaging because of their desirable properties. In this review, we provide an introduction of probes consisting of fluorescent small molecules and polymers that emit light across the ultraviolet and near-infrared wavelength ranges, along with a brief summary of the most recent techniques for bioimaging. Since photoluminescence probes emitting light in different ranges have different goals and targets, their respective strategies also differ. Diverse and novel strategies using photoluminescence probes against targets have gradually been introduced in the related literature. Among recent papers (published within the last 5 years) on the topic, we here concentrate on the photophysical properties and strategies for the design of molecular probes, with key examples of in vivo photoluminescence research for practical applications. More in-depth studies on these probes will provide key insights into how to control the molecular structure and size/shape of organic probes for expanded bioimaging research and applications.

Activity-based NIR fluorescent probes based on the versatile hemicyanine scaffold: design strategy, biomedical applications, and outlook

The discovery of a near-infrared (NIR, 650-900 nm) fluorescent chromophore hemicyanine dye with high structural tailorability is of great significance in the field of detection, bioimaging, and medical therapeutic applications. It exhibits many outstanding advantages including absorption and emission in the NIR region, tunable spectral properties, high photostability as well as a large Stokes shift. These properties are superior to those of conventional fluorogens, such as coumarin, fluorescein, naphthalimides, rhodamine, and cyanine. Researchers have made remarkable progress in developing activity-based multifunctional fluorescent probes based on hemicyanine skeletons for monitoring vital biomolecules in living systems through the output of fluorescence/photoacoustic signals, and integration of diagnosis and treatment of diseases using chemotherapy or photothermal/photodynamic therapy or combination therapy. These achievements prompted researchers to develop more smart fluorescent probes using a hemicyanine fluorogen as a template. In this review, we begin by describing the brief history of the discovery of hemicyanine dyes, synthetic approaches, and design strategies for activity-based functional fluorescent probes. Then, many selected hemicyanine-based probes that can detect ions, small biomolecules, overexpressed enzymes and diagnostic reagents for diseases are systematically highlighted. Finally, potential drawbacks and the outlook for future investigation and clinical medicine transformation of hemicyanine-based activatable functional probes are also discussed.

Near-Infrared Fluorescent Heptamethine Cyanine Dyes for COX-2 Targeted Photodynamic Cancer Therapy

We designed and synthesized two heptamethine cyanine based theranostic probes that aimed to target COX-2 in cancer cells. One is I-IR799-CXB which I-IR799 was conjugated to COX-2 specific inhibitor, celecoxib, and another is I-IR799-IMC , where the non-selective COX inhibitor, indomethacin, was used. I-IR799 is a heptamethine cyanine derivative that can be activated by near infrared light for photodynamic therapy (PDT) purposes. I-IR799-CXB and I-IR799-IMC were tested for their cancer targeting and photodynamic efficiency towards liver hepatocellular carcinoma cells (HepG2) compared to normal liver cell, alpha mouse liver 12 cells (AML12). Interestingly, after conjugation, I-IR799-IMC exhibited superior tumour targetability and PDT efficiency than I-IR799-CXB .

Hydrogen sulfide detection and zebrafish imaging by a designed sensitive and selective fluorescent probe based on resorufin

A new long-wavelength fluorescent probe 1 that could specifically identify H₂S has been successfully synthesized and applied for imaging H₂S in zebrafish. Probe 1 was readily prepared by featuring nitrobenzene as the recognition unit coupled to resorufin. The fluorescence off-on response is based on the fact that H₂S can reduce the nitro group to an amino group, followed by the 1,6-rearrangement-elimination and the release of resorufin. By evaluating the application abilities of probe 1 in vivo and vitro, it is shown that probe 1 has high sensitivity and selectivity to H₂S, low background fluorescence interference, with a low detection limit of 17.30 μM. Notably, the occurrence of the reaction can be observed by the naked eye, and the color of the solution changes from yellow to pink. More importantly, it is the first time that using paper chips as carrier to detect H₂S, which lays a foundation for the practical application of detecting H₂S. The excellent analysis and application capabilities of probe 1 make it an effective tool for further application in practice.

A phase-transfer catalyst-based nanoreactor for accelerated hydrogen sulfide bio-imaging

Hydrogen sulfide (H₂S) is an important signaling molecule in various biological processes; however, its real-time monitoring in living cells is hampered by long detection time for current fluorescent probes. To overcome this challenge, we designed a phase-transfer catalyst (PTC) approach to accelerate the reaction between the probe and the analyte by conjugating common fluorescent probes - mostly hydrophobic small molecules - with an amphiphilic PEG-PPG-PEG polymer, enabling the controllable assembly of H₂S nanoprobes in an aqueous solution. The PEG block helps to establish a PTC microenvironment that endows the assembled nanoprobes with a significantly reduced detection time (3-10 min; versus 20-60 min for small-molecule probes). Based on this approach, we synthesised two nanoprobes of different wavelengths, DS-Blue-nano and DN-Green-nano, which can sensitively detect H₂S in living macrophage cells with bright fluorescence starting at as early as 7 min and reaching stability at 15 min. These data suggest PTC-based nanoprobes as a new and generic approach for constructing sensitive fluorescent probes for the real-time imaging of H₂S, and perhaps other molecules in future, under biological conditions.

Sensing and Bioimaging of the Gaseous Signaling Molecule Hydrogen Sulfide by Near-Infrared Fluorescent Probes

A fluorescent probe for the monitoring of H₂S levels in living cells and organisms is highly desirable. In this regard, near-infrared (NIR) fluorescent probes have emerged as a promising tool. NIR-I and NIR-II probes have many significant advantages; for instance, NIR light penetrates deeper into tissue than light at visible wavelengths, and it causes less photodamage during biosample analysis and less autofluorescence, enabling higher signal-to-background ratios. Therefore, it is expected that fluorescent probes having emission in the NIR region are more suitable for in vivo imaging. Consequently, a considerable increase in reports of new H₂S-responsive NIR fluorescent probes appeared in the literature. This review highlights the advances made in developing new NIR fluorescent probes aimed at the sensitive and selective detection of H₂S in biological samples. Their applications in real-time monitoring of H₂S in cells and in vivo for bioimaging of living cells/animals are emphasized. The selection of suitable dyes for designing NIR fluorescent probes, along with the principles and mechanisms involved for the sensing of H₂S in the NIR region, are described. The discussions are focused on small-molecule and nanomaterials-based NIR probes.

A novel dual-function fluorescent probe for the rapid detection of bisulfite and hydrogen peroxide in aqueous solution and living cells

In this work, Hcy-OB, a novel hemicyanine-based biocompatible dual-function fluorescence probe for bisulfite and H₂O₂ detection is designed and synthesized. Based on a 1,4-addition reaction, Hcy-OB can be used for bisulfite detection with fast response, high sensitivity and low detection limit (120 nM). In addition, the probe is successfully applied to the detection of bisulfite in aqueous solution. Furthermore, Hcy-OB shows excellent performance for hydrogen peroxide detection with the oxidation of phenylboronic acid. Hcy-OB shows excellent selectivity to H₂O₂ over other interfering substances with detection limit of H₂O₂ is calculated to be 70 nM. Most importantly, due to its good cell membrane permeability and low cytotoxicity, Hcy-OB has been applied to monitor and image H₂O₂ in living cells and mice.

An azido coumarin-quinoline conjugated fluorogenic dye: Utilizing amide-iminol tautomerism for H2S detection in live MCF-7 cells

Detection of H₂S to analyze some diseases in living lives demands fast response, high selectivity and biocompatibility. Here we designed an azide containing coumarin attached with 8-aminoquinoline via amide backbone (ACAQ) fluorophore as the H₂S sensing probe. Excellent response time of 6 min, high sensitivity with the limit of detection (LOD) of 14.6 nM and high selectivity with other possible interferences are revealed for ACAQ after characterized by spectroscopy, ¹H NMR titration and LC-MS measurements. The sensing strategy is explained by amide-iminol tautomerism and azide reduction. In addition, the successful visualization measurement suggests the practicability of the probe ACAQ for H₂S detection in live samples.

A FRET-based upconversion nanoprobe assembled with an electrochromic chromophore for sensitive detection of hydrogen sulfide in vitro and in vivo

Hydrogen sulfide (H2S) as an important gaseous signaling molecule is closely related to numerous biological processes in living systems. To further study the physiological and pathological roles of H2S, convenient and efficient detection techniques for endogenous H2S in vivo are still in urgent demand. In this study, an electrochromic chromophore, dicationic 1,1,4,4-tetra-aryl butadiene (EM1), was innovatively introduced into upconversion nanoparticles (UCNPs) and a nanoprobe, PAAO-UCNPs-EM1, was constructed for the detection of H2S. This nanosystem was made of core-shell upconversion nanoparticles (NaYF4:Yb,Tm@NaYF4:Yb,Er), EM1, and polyacrylic acid (PAA)-octylamine. The EM1 with strong absorption ranging from 500 to 850 nm could serve as an energy acceptor to quench the upconversion luminescence of UCNPs through the Förster resonance energy transfer (FRET) process. In the presence of H2S, the EM1 in the nanoprobe was reduced to a colorless diene (EM2), resulting in the linear enhancement of luminescence emissions at 660 nm and 800 nm under the excitation of 980 nm light because the FRET was switched off. The nanoprobe PAAO-UCNPs-EM1PAAO-UCNPs-EM1 exhibited fast response and high sensitivity to H2S with a LoD of 1.21 × 10-7 M. Moreover, it was successfully employed in detecting the endogenous and exogenous H2S in living cells with high selectivity and low cytotoxicity. Also, this nanoprobe could distinguish normal and tumor cells by an upconversion luminescence imaging of endogenous H2S. Furthermore, the nanoprobe could significantly monitor H2S in a tumor-bearing nude mouse model. Therefore, we anticipate that this novel nanoprobe assembled with an electrochromic chromophore for responding to H2S and for bioimaging this molecule would have a promising prospect in biological and clinical investigations.

Tetrahydro[5]helicene fused nitrobenzoxadiazole as a fluorescence probe for hydrogen sulfide, cysteine/homocysteine and glutathione

Biological thiols including homocysteine (Hcy), cysteine (Cys), hydrogen sulfide (H₂S) and glutathione (GSH) play crucial roles in various pathological and physiological processes. The development of optical probes for biothiols has been an active research area in recent years. Herein, a new turn-on fluorescence probe (HD-NBD) was designed and synthesized by fusing tetrahydro[5]helicene and 7-nitro-2,1,3-benzoxadiazole (NBD) for simultaneous discrimination of Hcy/Cys, H₂S and GSH in aqueous solution. This probe is able to show unique absorbance enhancement at 548 nm for H₂S and additional fluorescence enhancement at 536 nm only for Cys/Hcy, which can be used to discriminate H₂S, Cys/Hcy and GSH simultaneously. In addition, HD-NBD also shows low background without any self-fluorescence, as well as high selectivity toward common biothiols. The low detection limits of this probe are about 0.15 μM for Hcy with a wide linear range (1-80 μM), 0.36 μM for Cys (linear range: 1-45 μM), 0.79 μM for H₂S (linear range: 1-80 μM) and 4.44 μM for GSH (linear range: 1-60 μM). Moreover, HD-NBD can identify Hcy/Cys, H₂S from GSH and other amino acids with high sensitivity and selectivity, therefore it could be used for detecting endogenous and exogenous Hcy/Cys under biological condition.

Thiol-Chromene "Click" Reaction Triggered Self-Immolative for NIR Visualization of Thiol Flux in Physiology and Pathology of Living Cells and Mice

Understanding the pathological process of biological systems can greatly improve the prevention and treatment of diseases. The study of pathological processes has now reached the molecular level, and molecular fluorescent probes have become a powerful tool. Chromene, also known as benzo-pyran molecule, is a structural element of natural products with good biological compatibility and was developed as a fluorescent probe. The thiol-chromene "click" nucleophilic pyran ring-opening reaction allows the quick detection of thiol. In this work, the chromene alcohol can function as an efficient self-immolative spacer, which covalently links NIR fluorophore via a carbonyl ester. Due to its favorable characteristics and superior applicability, the self-immolative amplifier NIR-HMPC achieves the specific, rapid, sensitive, NIR fluorescent detection of thiols. Furthermore, the indoles iodized salt in the system can specifically target thiols in mitochondria. Thus, this probe was used to visualize the fluctuations of thiols during oxidative stress and cell apoptosis, cerebral ischemia reperfusion, demonstrating that it is valuable for elucidating pathophysiology process in living organism. This discovery provides an effective means for studying the pathological process of thiol related diseases.

The synthesis and bioimaging of a biocompatible hydrogen sulfide fluorescent probe with high sensitivity and selectivity

Hydrogen sulfide (H₂S), a well-known poisonous gas, has been recognized as a critical endogenous gas transmitter in the past decade.

FRET-based fluorescent ratiometric probes for the rapid detection of endogenous hydrogen sulphide in living cells

FRET strategy was adopted for designing ratiometric fluorescent H₂S sensors using Coumarin-derived merocyanine fluorophore.

Real-time in vivo detection techniques for neurotransmitters: a review

Functional synapses in the central nervous system depend on a chemical signal exchange process that involves neurotransmitter delivery between neurons and receptor cells in the neuro system.

A colorimetric and near-infrared fluorescent probe for detection of hydrogen sulfide and its real multiple applications

A novel colorimetric and near-infrared fluorescent probe (L) with D-π-A structure derived from 4-diethylaminosalicylaldehyde and 2-(3-cyano-4,5,5-trimethylfuran-2(5H)-ylidene)malononitrile has been developed. Probe L displays highly selective and sensitive recognition for H₂S over various anions with a large Stokes shift (96 nm) in DMF/H₂O (3/7, v/v, PBS-HCl 10 mM, pH = 7.4). A naked-eye observable color change of L solution from colorless to bluish-purple occurred on treatment with H₂S. The potential applications of probe L were evaluated and the results show that probe L can detect H₂S vapor and H₂S in real water, red wine and living cells.

Nitrobenzoxadiazole Ether-Based Near-Infrared Fluorescent Probe with Unexpected High Selectivity for H2S Imaging in Living Cells and Mice

H₂S is an important endogenous gasotransmitter, and its detection in living systems is of great significance. Especially, selective and sensitive near-infrared (NIR) fluorescent H₂S probes with rapid response and large Stokes shift are highly desirable because of their superiority for in vivo detection. Probes with nitrobenzoxadiazole (NBD) ether as reaction sites have been well-explored recently to detect biothiols or H₂S/biothiols simultaneously, rather than to detect H₂S selectively. In this work, a new NBD ether-based NIR fluorescent probe was developed, which was unexpectedly found to show high selectivity for H₂S over various other analytes including biothiols, making it practical for specific detection of H₂S both in vitro and in vivo. Upon response to H₂S, this probe showed rapid and significant turn-on NIR emission changes centered at 744 nm within 3 min, together with a remarkable large Stokes shift (166 nm) and high sensitivity (LOD: 26 nM). Moreover, imaging exogenous and endogenous H₂S in living cells and rapid imaging of H₂S in living mice with this probe was successfully applied with excellent performance.

Construction of a novel cell-trappable fluorescent probe for hydrogen sulfide (H2S) and its bio-imaging application

Fluorescence detection of H₂S in living organisms is greatly advantageous because it is nondestructive and can be used for in situ analysis. We have constructed a novel rhodamine analogue dye (Rho630) by extending the conjugated system of rhodamine to create a novel cell-trappable H₂S fluorescent probe Rho630-AM-H₂S with red light emission. Its application for H₂S fluorescence detection in living HeLa cells and zebrafish was investigated. As expected, Rho630-AM-H₂S showed a huge fluorescence turn-on response of about 20-fold at 630 nm and good selectivity toward H₂S in solution. An MTT assay demonstrated that the probe showed negligible cytotoxicity in the concentrations typically used in fluorescence imaging experiments. Cell imaging experiments revealed that compared with compound 4 without cell-trappable unit modification, Rho630-AM-H₂S exhibited remarkably enhanced cell penetration ability, as an enormous fluorescence signal increase was observed at the red channel within 5 min after Rho630-AM-H₂S was incubated with HeLa cells. Finally, the probe Rho630-AM-H₂S was used to detect H₂S in living HeLa cells and zebrafish with great fluorescence enhancement in the red channel. Graphical abstract.

A fluorescent probe based on tetrahydro[5]helicene derivative with large Stokes shift for rapid and highly selective recognition of hydrogen sulfide

In this work, we have designed and synthesized a dinitrobenzene-sulfonate tetrahydro[5]helicene (H-DNP) as an effective fluorescent probe for detection of hydrogen sulfide (H₂S). Upon the addition of H₂S, a significant fluorescence enhancement (75-fold) at 495 nm can be observed with a distinct color change from colorless to yellow. Additionally, H-DNP shows low background spectroscopic signal, large Stokes Shift up to ~140 nm, good sensitivity, rapid response time less than 2 min, low detection limit (48 nM) and high selectivity toward common bio-thiols (Cysteine, Homocysteine and Glutathione). Compared with the previous dinitrophenoxy tetrahydro[5]helicene, this probe has shorter response time and lower detection limit. Most importantly, this probe H-DNP has low toxicity to cells and excellent cell permeability, which can be applied to visualize H₂S in living cells.

A fluorescent probe based on aggregation-induced emission for hydrogen sulfide-specific assaying in food and biological systems

An AIE-based fluorescent probe was developed for monitoring food spoilage via its response toward hydrogen sulfide.

A fluorescent probe based on tetrahydro[5]helicene for highly selective recognition of hydrogen sulfide

Endogenous hydrogen sulfide plays an important role in various physiological and pathological processes and the convenient and selective recognition of hydrogen sulfide has become a research hotspot. We designed and synthesized a tetrahydro[5]helicene and 2,4-dinitrobenzene conjugate (HD-DNP) as an effective fluorescent probe for selective detection of H₂S. The selective deprotection of 2,4-dinitrophenyl ether group of HD-DNP by H₂S led to a dramatic fluorescent enhancement (101-fold) at 500 nm and colorimetric change in DMSO-PBS solution. HD-DNP displays many advantages including low background without any self-fluorescence, as well as high selectivity towards common bio-thiols such as Cysteine, Homocysteine and Glutathione. The detection limit of this probe for H₂S was found to be about 2.4 μM with a wide linear range (10-70 μM). The response mechanism of the probe with HS^- is confirmed to be thiolysis of the dinitrophenyl ether induced by HS^- through ¹H NMR comparison investigations.

The synthesis, crystal, hydrogen sulfide detection and cell assement of novel chemsensors based on coumarin derivatives

A series of chemsensors (1–4) containing fluorobenzene group based on coumarin derivatives have been developed for the selective and sensitive detection of H₂S. The advantages of the synthesized fluorescent probe (compound 1) were the low detection limit (4 × 10⁻⁶ mol·L⁻¹), good selectivity and high sensitivity which had been demonstrated through UV-vis, fluorescent titration experiments. Besides cytotoxicity test of compounds (1 and 2) was studied and the results indicated that compounds (1 and 2) showed almost no cytotoxicityat at a concentration of 150 μg·mL⁻¹. The interacted mechanism was the thiolysis reaction of dinitrophenyl ether which had been confirmed by fluorescence and HRMS titration experiment. In addition, probe 1 can also detect HS⁻ selectively by naked eye in pure DMSO solvent.

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

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

Organic Dye Based Nanoparticles for Cancer Phototheranostics

Phototheranostics, which simultaneously combines photodynamic and/or photothermal therapy with deep-tissue diagnostic imaging, is a promising strategy for the diagnosis and treatment of cancers. Organic dyes with the merits of strong near-infrared absorbance, high photo-to-radical and/or photothermal conversion efficiency, great biocompatibility, ready chemical structure fine-tuning capability, and easy metabolism, have been demonstrated as attractive candidates for clinical phototheranostics. These organic dyes can be further designed and fabricated into nanoparticles (NPs) using various strategies. Compared to free molecules, these NPs can be equipped with multiple synergistic functions and show longer lifetime in blood circulation and passive tumor-targeting property via the enhanced permeability and retention effect. In this article, the recent progress of organic dye-based NPs for cancer phototheranostic applications is summarized, which extends the anticancer arsenal and holds promise for clinical uses in the near future.

A highly sensitive near-infrared fluorescent probe for the detection of hydrogen sulfide and its application in living cells and mice

Hydrogen sulfide (H₂S), an endogenous gaseous signalling molecule, has attracted attention in biochemical research.

A new fluorescent probe for quick and highly selective detection of hydrogen sulfide and its application in living cells

Hydrogen sulfide (H₂S) is one of the endogenous regulators of many physiological processes.