Cyanine-based NIR fluorescent probe for monitoring H2S and imaging in living cells and in vivo

Dye-sensitized lanthanide-doped upconversion nanoprobe for enhanced sensitive detection of Fe3+ in human serum and tap water

Iron ion (Fe3+) detection is crucial for human health since it plays a crucial role in many physiological activities. In this work, a novel Schiff-base functionalized cyanine derivative (CyPy) was synthesized, which was successfully assembled on the surface of upconversion nanoparticles (UCNPs) through an amphiphilic polymer encapsulation method. In the as-designed nanoprobe, CyPy, a recognizer of Fe3+, is served as energy donor and β-NaYF4:Yb,Er upconversion nanoparticles are adopted as energy acceptor. As a result, a 93-fold enhancement of upconversion luminescence is achieved. The efficient energy transfer from CyPy to β-NaYF4:Yb,Er endows the nanoprobe a high sensitivity for Fe3+ in water with a low detection limit of 0.21 μM. Moreover, the nanoprobe has been successfully applied for Fe3+ determination in human serum and tap water samples with recovery ranges of 95 %-105 % and 97 %-106 %, respectively. Moreover, their relative standard deviations are all below 3.72 %. This work provides a sensitive and efficient methodology for Fe3+ detection in clinical and environmental testing.

A Novel NIR Fluorescent Probe for Rapid Response to Hydrogen Sulfide

Hydrogen sulfide (H2S), as an important small molecule bioregulator, plays a key role in many physiological activities and signaling, and abnormal fluctuations in H2S concentration can lead to a variety of diseases. Therefore, it is of great significance to develop a near-infrared fluorescence probe to visualize fluctuations in H2S levels. This work is based on Sulfur-substituted dicyanomethylene-4 H-chromene (DCM), A novel NIR fluorescent probe (E) -3 - (2 - (4 - (dicyanomethylene) -6-methyl-4 H-Thiochromen-2-yl)vinyl-1-methylquinolin-1-ium (DMT) was synthesized successfully. Research has found that in weakly alkaline environments, the probe DMT reacts rapidly with H2S (only 10 s), the fluorescence intensity at 684 nm is enhanced by about 60 fold, the detection limit is as low as 0.1623 µM, the Stokes shift is large (94 nm), and strong selectivity as well as anti-interference ability towards H2S. This will provide a new method for the rapid detection and further application of H2S.

An Aggregation-Induced Fluorescence Probe for Detection H2S and Its Application in Cell Imaging

Monitoring hydrogen sulfide (H2S) in living organisms is very important because H2S acts as a regulator in many physiological and pathological processes. Upregulation of endogenous H2S concentration has been shown to be closely related to the occurrence and development of tumors, atherosclerosis, neurodegenerative diseases and diabetes. Herin, a novel fluorescent probe HND with aggregation-induced emission was designed. Impressively, HND exhibited a high selectivity, fast response (1 min) and low detection limit (0.61 μM) for H2S in PBS buffer (10 mM, pH = 7.42). Moreover, the reaction mechanism between HND and H2S was conducted by Job's plot, HR-MS, and DFT. In particular, HND was successfully employed to detect H2S in HeLa cells.

NBD-based colorimetric and ratiometric fluorescent probe in NIR for bisulfite

This work presented a FRET-ICT based fluorescent probe (named NTC) composed of coumarin-benzothiazole as the acceptor and 4-nitrobenzo[c][1,2,5] oxadiazole (NBD) as the donor for the detection of SO2 derivatives in NIR. Probe NTC possessed superior performance including selectivity, quickly response toward SO32-/HSO3- and high energy transfer efficiency (94 %). The test strips provided a simple and effective tool in detecting the presence of bisulfite. Besides, NTC was applied to test the sulfur dioxide derivatives in food samples and cells.

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.

Development of a H2S-responsive NIR Fluorescent Probe for H2S Detection and H2S Releasing Monitoring From Prodrug

H2S was deemed as a toxic gradient in the realm of food and environment but plays pivotal pathophysiological roles in organisms. H2S instabilities and disturbances are always responsible for multiple disorders. We fabricated a H2S-responsive NIR fluorescent probe (HT) for H2S detection and evaluation both in vitro and in vivo. HT exhibited rapid H2S response within 5 min, accompanied with visible color change and NIR fluorescence generation, and the fluorescent intensities were linearly correlated with corresponding H2S concentrations. When HT was incubated with A549 cells, the intracellular H2S and H2S fluctuations could be monitored ore rotundo via the responsive fluorescence. Meanwhile, when HT was co-administrated with H2S prodrug ADT-OH, the H2S release from ADT-OH could be visualized and monitored to evaluate its release efficacy.

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.

Novel 2-Benzo[d]thiazolyl-4-quinolinylphenol Skeleton-Based Turn-on Fluorescent Probe for H2S Detection and its Multiple Applications in Water Environment, Foodstuffs, and Living Organisms

Hydrogen sulfide (H₂S) has comprehensive contributions to maintaining the normal operation and stability of organisms, and it also occurs in the wastewater environment and is related to the deterioration of foodstuffs. Therefore, developing high-sensitive detection techniques for tracing H₂S is promising and meaningful. Inspired by this, a novel nopinone-based fluorescent probe NPS for the recognition of H₂S was designed and synthesized with excellent sensitivity, low limit of detection (79 nM), good selectivity, and wide pH range (5-9). NPS could emit strong yellow fluorescence and its emission intensity showed a remarkable augmentation at 520 nm upon the supplement of H₂S. Furthermore, the recognition mechanism of NPS for H₂S was verified by the HRMS analysis, ¹H NMR spectra titration, and DFT computation. What is more, NPS also had broad applications in the monitoring of real water samples, red wine, beer, and eggs samples, which showed its development prospect and value in environmental pollution, foodstuffs quality analysis fields. NPS also was applied to monitor trace exogenous H₂S and bioimaging in living cells and zebrafish.

A biotin-guided near-infrared fluorescent probe for imaging hydrogen sulfide and differentiating cancer cells

Imaging cancer specific biomarkers with near-infrared (NIR) fluorescent probes can help inaccurate diagnosis. Hydrogen sulfide (H₂S) has been reported to be involved in many physiological and pathological processes and is considered as one of the key gasotransmitters during the development of cancer. To achieve specific H₂S detection in cancer cells, we reported a biotin-guided NIR fluorescent sensor P1 targeting a cancer cell surface biomarker, based on the H₂S-specific thiolysis of the NBD-amine-hemicyanine conjugate. The probe showed a fast turn-on signal at 754 nm upon H₂S activation and good selectivity towards H₂S over millimolar levels of other biothiols. We successfully employed P1 to image endogenous H₂S and demonstrated its tumor-targeting ability in live cells. P1 could differentiate multiple cancer cells with various levels of H₂S from normal cells, indicating its potential for cancer imaging.

Recent Advancements in the Design and Development of Near Infrared (NIR) Emitting Fluorescent Probes for Sensing and their Bio-Imaging Applications

Fluorescent bio-imaging will be the future in the medical diagnostic for visualising inner cellular and tissues. Near-infrared (NIR) emitting fluorescent probes serve dynamically for targeted fluorescent imaging of live cells and tissues. NIR imaging is advantageous because of its merits like deep tissue penetration, minimum damage to the tissue, reduced auto fluorescence from the background, and improved resolution in imaging. The Development of the NIR emitting probe was well explored recently and growing drastically. In this review, we summarise recent achievements in NIR probes in between 2018-2021. The merits and future applications have also been discussed in this review.

'Lights, squaraines, action!' - the role of squaraine dyes in photodynamic therapy

Since they were first synthesized in 1965 by Treibs and Jacob, squaraine dyes have revolutionized the polymethine dyes' 'universe' and their potential applications due to their indisputable physical, chemical and biological properties. After 30 years and up to the present, various research teams have dedicated themselves to studying the squaraines' photodynamic therapy application using in vitro and in vivo models. The various structural modifications made to these compounds, as well as the influence they have shown to have in their phototherapeutic activity, are the main focus of the present review. Finally, the most evident limitations of this class of dyes, as well as future perspectives in the sense of hypothetically successfully overcoming them, are suggested by the authors.

Small-Molecule Fluorescent Probes for Detecting Several Abnormally Expressed Substances in Tumors

Malignant tumors have always been the biggest problem facing human survival, and a huge number of people die from cancer every year. Therefore, the identification and detection of malignant tumors have far-reaching significance for human survival and development. Some substances are abnormally expressed in tumors, such as cyclooxygenase-2 (COX-2), nitroreductase (NTR), pH, biothiols (GSH, Cys, Hcy), hydrogen sulfide (H2S), hydrogen sulfide (H2O2), hypochlorous acid (HOCl) and NADH. Consequently, it is of great value to diagnose and treat malignant tumors due to the identification and detection of these substances. Compared with traditional tumor detection methods, fluorescence imaging technology has the advantages of an inexpensive cost, fast detection and high sensitivity. Herein, we mainly introduce the research progress of fluorescent probes for identifying and detecting abnormally expressed substances in several tumors.

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.

Heptamethine Cyanine–Based Application for Cancer Theranostics

Cancer is the most common life-threatening malignant disease. The future of personalized cancer treatments relies on the development of functional agents that have tumor-targeted anticancer activities and can be detected in tumors through imaging. Cyanines, especially heptamethine cyanine (Cy7), have prospective application because of their excellent tumor-targeting capacity, high quantum yield, low tissue autofluorescence, long absorption wavelength, and low background interference. In this review, the application of Cy7 and its derivatives in tumors is comprehensively explored. Cy7 is enormously acknowledged in the field of non-invasive therapy that can “detect” and “kill” tumor cells via near-infrared fluorescence (NIRF) imaging, photothermal therapy (PTT), and photodynamic therapy (PDT). Furthermore, Cy7 is more available and has excellent properties in cancer theranostics by the presence of multifunctional nanoparticles via fulfilling multimodal imaging and combination therapy simultaneously. This review provides a comprehensive scope of Cy7’s application for cancer NIRF imaging, phototherapy, nanoprobe-based combination therapy in recent years. A deeper understanding of the application of imaging and treatment underlying Cy7 in cancer may provide new strategies for drug development based on cyanine. Thus, the review will lead the way to new types with optical properties and practical transformation to clinical practice.

Near-infrared (NIR) fluorescence-emitting small organic molecules for cancer imaging and therapy

We discuss recent advances made in the development of NIR fluorescence-emitting small organic molecules for tumor imaging and therapy.

A novel fluorescent probe for detecting hydrogen sulfide in osteoblasts during lipopolysaccharide-mediated inflammation under periodontitis

Periodontitis, one of the most common chronic inflammatory diseases, affects the quality of life. Osteogenesis plays an important role in the disease. There is a connection between hydrogen sulfide (H₂S) and periodontitis, but according to the study has been published, the precise role of H₂S in inflammation remains in doubt. The main reason for the lack of research is that H₂S is an endogenous gasotransmitter, difficult to discern through testing. So, we synthesized a novel fluorescence probe which can detect H₂S in vitro. By using the novel H₂S fluorescence probe, we found that H₂S changes in osteoblasts mainly by cystathionine-γ-lyase, and H₂S increases under LPS stimulation. H₂S could be a potential marker for diagnosis of inflammatory diseases of bone, and might help deepen studies of the changes of H₂S level and promote the progression on the researches about pathogenesis of periodontitis.

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 highly sensitive upconversion nanoparticles@zeolitic imidazolate frameworks fluorescent nanoprobe for gallic acid analysis

In this work, a core-shell structured upconversion nanoparticles@zeolitic imidazolate frameworks (ZIF-8) fluorescent nanoprobe (NaErF₄:Tm@SiO₂@ZIF-8) has been designed for the detection of gallic acid (GA). The mechanism is according to the 3, 3', 5, 5'-tetramethylbenzidine (TMB) can be oxidized to oxidized TMB (oxTMB) by Ag⁺. Under 980 nm laser excitation, NaErF₄:Tm@SiO₂@ZIF-8 can emit red light at 652 nm, which have a good overlap with the absorption spectra of oxTMB, resulting in the fluorescence quenching at 652 nm. Continually adding GA into the above solution, oxTMB will restore to TMB, and the fluorescence intensity at 652 nm gradually recovers, which can realize the detection towards GA. The linear detection range of GA is from 0 to 30 μM, and the limit of detection (LOD) of GA is 0.35 μM. The ZIF-8 can largely enhance the sensitivity of the nanoprobe, due to the physical absorption and the electrostatic attraction between ZIF-8 and the oxTMB. More importantly, this is the first time to realize the detection of GA with high sensitivity by using upconversion fluorescence. Besides, we have realized the analysis of GA in real samples, which certify the feasible of the nanoprobe in potential applications.

A multifunctional fluorescent probe for visualizing H2S in wastewater with portable smartphone via fluorescent paper strip and sensing GSH in vivo

In this paper, a bifunctional tri-site fluorescent probe was designed for the first time not only for visualization and quantitative analysis of sensing H₂S in wastewater by coupling paper strip and smartphone (Color recognizer, Xiyi Technology) but also for sensitively monitoring GSH in living cells, which relied on different emission channels and the pH of solutions. The recognition properties of GH towards H₂S/GSH were satisfactorily demonstrated through fluorescence, UV-vis, ¹H NMR and DFT calculations. More importantly, integrated with the paper strip, portable smartphone-sensing platform with a color recognizer app would accomplish cost-effective and rapid assays for colorimetric water quality testing, which displayed huge application potential in fields of environmental monitoring.

Dye-sensitized core-shell NaGdF4:Yb,Er@NaGdF4:Yb,Nd upconversion nanoprobe for determination of H2S

The core-shell NaGdF₄:Yb,Er@NaGdF₄:Yb,Nd upconversion nanoparticles (UCNPs) were successfully obtained with the method of co-precipitation, and the water-solubility of UCNPs was improved by the ligand exchange reaction between nitrosyl tetrafluoroborate (NOBF₄) and nanoparticles. The IR-783 dye with negative charge and NOBF₄-UCNPs with positive charge can bind together by electrostatic action to sensitize UCNPs through the energy transfer from IR-783 to UCNPs. However, with the presence of Na₂S (a commonly used H₂S donor), a highly selective reaction between H₂S and IR-783, which destoried the structure of IR-783 and blocked the energy transfer, thus led to the quenching of luminescent intensity. Based on this, a sensing system for determination of H₂S has been constructed successfully. The linear range of H₂S detection by this system is 0.5-15 μM, and the detection limit is 34.17 nM. Furthermore, the dye-sensitized core-shell NaGdF₄:Yb,Er@NaGdF₄:Yb,Nd upconversion nanoprobe was applied to real sample analysis with satisfactory results.

Non-covalent binding and selective fluorescent sensing of dipyrone with a carbocyanine dye and cetyltrimethylammonium bromide

The work is aimed at the search of selective fluorescent sensors without using specific artificial receptors, antibodies, enzymes etc. With this end in view, methods based on non-covalent binding of target analytes are sought. We observed dramatic changes in the emission spectrum of a carbocyanine dye in a micellar surfactant solution (cetyltrimethylammonium bromide, CTAB) in the presence of dipyrone (metamizol, analgin): the 480 nm band intensity increases with a simultaneous decrease in intensity in near-IR region (720 nm). MALDI and NMR-¹H data show the intact molecules of dipyrone and the dye. The detection can be performed in the presence of other organic species and inorganic salts. Dipyrone testing is feasible within 5 × 10^-7-5 × 10^-4M with RSDs of 3.5% by using a visualizer instead of a spectrofluorimeter.

A dicyanomethylene-4H-pyran-based fluorescence probe with high selectivity and sensitivity for detecting copper (II) and its bioimaging in living cells and tissue

Copper (Cu) plays a significant role in the process of oxygenic photosynthesis in living systems. The detection of copper ion (Cu²⁺) is valuable and meaningful for further investigating the functions of Cu²⁺ under physiological and pathological conditions. In this paper, a novel fluorescence probe DCM-Cu based on the near-infrared (NIR) fluorophore dicyanomethylene-4H-pyran (DCM) was designed for Cu²⁺ detection. The probe DCM-Cu possessed characteristic of "turn-on" fluorescent signal in the presence of Cu²⁺ through the enhanced ICT process. It exhibited satisfactory sensitivity and selectivity toward Cu²⁺. A good linear correlation was observed between the concentrations of Cu²⁺ and the fluorescence intensities at 700 nm. The detection limit (LOD) of DCM-Cu toward Cu²⁺ was calculated to be 2.54 × 10^-8 M. Importantly, DCM-Cu was successfully applied in the detection of Cu²⁺ in living MCF-7 cells and tumor tissue with low cytotoxicity. Therefore, this probe would have the potential to monitor cellular Cu²⁺ in the living system and be applied to the diagnosis of related diseases.

A novel fast-responsive fluorescent probe based on 1,3,5-triazine for endogenous H2S detection with large Stokes shift and its application in cell imaging

A novel fast-responsive fluorescent probe TzAr-H2S based on 1,3,5-triazine was constructed to monitor endogenous H₂S. The probe TzAr-H2S can quickly (only 20 s) detect H₂S with good selectivity, large Stokes shift (100 nm) and low cytotoxicity.

Light-Emitting Probes for Labeling Peptides

Peptides are versatile biopolymers composed of 2-100 amino acid residues that present a wide range of biological functions and constitute potential therapies for numerous diseases, partly due to their ability to penetrate cell membranes. However, their mechanisms of action have not been fully elucidated due to the lack of appropriate tools. Existing light-emitting probes are limited by their cytotoxicity and large size, which can alter peptide structure and function. Here, we describe the available fluorescent, bioluminescent, and chemiluminescent probes for labeling peptides, with a focus on minimalistic options.

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 review: Red/near-infrared (NIR) fluorescent probes based on nucleophilic reactions of H2 S since 2015

The topics of human health and disease are always the focus of much attention. Hydrogen sulfide (H₂ S), as a double-edged sword, plays an important role in biological systems. Studies have revealed that endogenous H₂ S is important to maintain normal physiological functions. Conversely, abnormal levels of H₂ S may contribute to various diseases. Due to the importance of H₂ S in physiology and pathology, research into the effects of H₂ S has been active in recent years. Fluorescent probes with red/near-infrared (NIR) emissions (620-900 nm) are more suitable for imaging applications in vivo, because of their negligible photodamage, deep tissue penetration, and maximum lack of interference from background autofluorescence. H₂ S, an 'evil and positive' molecule, is not only toxic, but also produces significant effects; a 'greedy' molecule, is not only a strong nucleophile under physiological conditions, but also undergoes a continuous double nucleophilic reaction. Therefore, in this tutorial review, we will highlight recent advances made since 2015 in the development and application of red/NIR fluorescent probes based on nucleophilic reactions of H₂ S.

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.

A turn-on fluorescence probe for hydrogen sulfide in absolute aqueous solution

A turn-on hydrogen sulfide (H₂S) fluorescence probe, 4-{2-[4-(2,4-dinitrophenoxy)-phenyl]-vinyl}-1-methyl-pyridinium iodide (DPPVP), based on the thiolysis reaction of dinitrophenyl ethers (DNP) has been proposed. Pyridinium structure enhanced the water solubility of DPPVP, which could quickly respond to H₂S in absolute PBS solution and the fluorescence spectra of DPPVP at 520 nm were turned on by H₂S. The spectra results exhibited that DPPVP could sensitively detect H₂S with satisfied linear range (0-40 μM) and detection limit (13.4 nM). The high selectivity for H₂S against biothiols was attributed to the significant difference in the pKa and the molecular size. Moreover, DPPVP has been successfully used for detecting H₂S in vegetable.

A novel highly selective fluorescent probe with new chalcone fluorophore for monitoring and imaging endogenous peroxynitrite in living cells and drug-damaged liver tissue

As a member of the reactive nitrogen species (RNS) family, peroxynitrite (ONOO^-) as an oxidant and nitrating mediator plays a significant role in some physiopathologic processes. The excessive production of peroxynitrite anion in a drug-damaged liver is a culprit of hepatotoxicity. The detection of peroxynitrite is of vital importance for the treatment of some diseases including cancer and liver injury. In this study, a novel turn-on fluorescent probe IC-ONOO with new chalcone fluorophore was designed and synthesized for the detection of in vitro and in vivo. The probe responded rapidly towards ONOO^- (only within 15 min did the fluorescent intensity maximize), and was endowed with high sensitivity and excellent selectivity. Given the fact that the linear correlation between the fluorescent intensity at 560 nm and the concentrations of the probe ranged from 0 to 9 μM, the limit of detection (LOD) was calculated to be 3.1 × 10^-8 M. With all the merits, probe IC-ONOO was qualified as a robust tool to monitor peroxynitrite anion under physiopathologic condition. Moreover, it was successfully applied in the imaging of endogenous peroxynitrite in living MCF-7 cells (Human breast carcinoma cells) and mouse drug-damaged liver tissue with low cytotoxicity. Given all the extraordinary merits, great potential has been seen in its application to other peroxynitrite related diseases.

Modulation of fluorescence sensing properties of coumarin-based fluorescent probe for H2S and its application in cell imaging

A coumarin-based turn on probe, named 3-((E)-3-(1H-indol-3-yl)acryloyl)-2H-chromen-2-one(IAC) was designed and synthesized for the detection of H₂S in aqueous medium. IAC showed no obvious red fluorescence in Tris-HCl(pH = 7.2, 60% DMF), a 28.2-fold fluorescence enhancement was found when 40 equiv. H₂S was added. Other analytes such as anions, metal ions and GSH, Cys, Gly did no significant fluorescence enhancement at 580 nm to IAC. The red fluorescence enhancement mechanism between IAC and H₂S was considered by DFT and ESI-MS. Overall, IAC was successfully applied in cell imaging.

Smart nanomedicine agents for cancer, triggered by pH, glutathione, H2O2, or H2S

Effective tumor diagnosis and therapy have always been a significant but challenging issue. Although nanomedicine has shown great potential for improving the outcomes of tumor diagnosis and therapy, the nonspecial targeted distribution of nanomedicine agents in the whole body causes a low diagnosis signal-to-noise ratio and a potential risk of systemic toxicity. Recently, the development of smart nanomedicine agents with diagnosis and therapy functions that can only be activated by the tumor microenvironment (TME) is regarded as an effective strategy to improve the theranostic sensitivity and selectivity, as well as reduce the potential side effects during treatment. This article will introduce and summarize the latest achievements in the design and fabrication of TME-responsive smart nanomedicine agents, and highlight their prospects for enhancing tumor diagnosis and therapy.

A dual-function colorimetric probe based on Carbazole-Cyanine dyad for highly sensitive recognition of cyanide and hypochlorous acid in aqueous media

A dual-function colorimetric probe (Cz-Cy7) with an electron-donating carbazole tethered at the central position of heptamethine cyanine was designed and synthesized, and the performance on CN^- and HClO detection were systematically investigated. With the addition of CN^-, Cz-Cy7 exhibited remarkable changes in both UV-vis and fluorescence spectra with a good linear relationship to CN^- concentration, and a discernible color change under daylight was observed. The limit of detection for CN^- was found to be 9.1 nM in DMF and 0.09 μM in DMF/H₂O. Meanwhile, Cz-Cy7 exhibited a highly sensitive response to HClO in the presence of other ROS (reactive oxygen species) based on the sensing mechanism of oxidative cleavage of olefinic C =  = C bond. The limit of detection for HClO was evaluated to be 14 nM in PBS buffer solution (containing 50% CH₃CN). More importantly, the probe Cz-Cy7 showed good recovery and analytical precision in real water samples for both CN^- and HClO detection, indicating it was feasible and reliable for practical application. Moreover, the test strips loaded with Cz-Cy7 were fabricated and validated to be a portable tool for the efficient detection of CN^- and HClO by the naked eye.

Fast response near-infrared fluorescent probe for hydrogen sulfide in natural waters

Rapid and sensitive detection of hydrogen sulfide (H₂S) is of great importance for the environmental monitoring. Near-infrared fluorescent probes are recently developed for the sensitive H₂S detection thanks to their low background interference, while often hampered by relatively long response time (around 30 min). In this work, we reported a fast response (within 5 min), highly sensitive near-infrared (NIR) fluorescent probe (DCM-OCN) for H₂S. The rapid nucleophilic reaction between cyanate moiety and H₂S endowed fast response of the NIR probe. The influence of experimental parameters (including CTAB concentration, reaction time, pH value etc.), interference study, and possible mechanism were investigated in detail. The fluorescence increment was linear with H₂S concentration in 1-10 μM with a detection limit of 0.28 μM (3σ). The probe was successfully applied to environmental water samples including river water, tap water, lake water, mineral water and artificial wastewater.

The design of hydrogen sulfide fluorescence probe based on dual nucleophilic reaction and its application for bioimaging

Hydrogen sulfide (H₂S) can undergo dual nucleophilic reaction, which is a wise and effective way to distinguish biothiols and H₂S. A novel H₂S fluorescence probe, 4-{2-[4-(2-disulfide pyridyl-benzoyloxy)-phenyl]-vinyl}-1-methyl-pyridinium[e]iodide (DSPBP), with two nucleophilic reaction sites has been developed. The spectra results showed that DSPBP could detect H₂S in ratiometric and colorimetric signals and has excellent selectivity and sensitivity. The fluorescence ratiometric signals (F₅₂₀/F₄₅₀) displayed a prominent increase from 0.74 to 7.08, the fluorescence color turned to yellow form blue simultaneously. The linear range was 2-14 μM and its detection limit was 25.7 nM. Moreover, the biocompatibility of DSPBP was fine and its toxicity was very low. It has been successfully used for imaging H₂S in cells.

Living cell imaging and sensing of hydrogen sulfide using high-efficiency fluorescent Cu-doped carbon quantum dots

A simple Cu-doped carbon quantum dot-based fluorescent sensor for H₂S sensing and intracellular bioimaging was constructed.