A novel tryptanthrin-based "on-off-on" probe for sequential sensing Cu2+/S2- in water samples

Copper ions (Cu2+) and sulfide (S2-) play essential roles in many physiologies and pathologic processes. Herein, a new "on-off-on" tryptanthrin-based probe TR-1 (TR-1) has been designed and synthesized in a facile and economical way. TR-1 exhibited highly selective and sensitive response to Cu2+ without any interference over 14 competitive metal ions and the detection limit downs to 24 nM, which is far below the Chinese standard of fishery water quality (157 nM). The 'in situ' prepared complex TR-1 + Cu2+ could also be applied to detect S2- with the detection limit of 62 nM. Further, TR-1 was potentially applied for the analysis of copper ions in water samples.

Multimodal nanoimmunotherapy engages neutrophils to eliminate Staphylococcus aureus infections

The increasing prevalence of antimicrobial resistance in Staphylococcus aureus necessitates alternative therapeutic approaches. Neutrophils play a crucial role in the fight against S. aureus but suffer from deficiencies in function leading to increased infection. Here we report a nanoparticle-mediated immunotherapy aimed at potentiating neutrophils to eliminate S. aureus. The nanoparticles consist of naftifine, haemoglobin (Hb) and a red blood cell membrane coating. Naftifine disrupts staphyloxanthin biosynthesis, Hb reduces bacterial hydrogen sulfide levels and the red blood cell membrane modifies bacterial lipid composition. Collectively, the nanoparticles can sensitize S. aureus to host oxidant killing. Furthermore, in the infectious microenvironment, Hb triggers lipid peroxidation in S. aureus, promoting neutrophil chemotaxis. Oxygen supplied by Hb can also significantly enhance the bactericidal capability of the recruited neutrophils by restoring neutrophil respiratory burst via hypoxia relief. This multimodal nanoimmunotherapy demonstrates excellent therapeutic efficacy in treating antimicrobial-resistant S. aureus persisters, biofilms and S. aureus-induced infection in mice.

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.

HSA over BSA: Selective detection of Human Serum Albumin via a naphtho [2,1-b] furan-based system

Human serum albumin (HSA) is an important biomarker that can be used for the early diagnosis of many diseases. In this work, a TICT probe bearing fused naphtho-furan scaffold (NPNF) was developed and employed in the selective turn-on sensing of HSA. The probe's selectivity towards HSA was observed using steady-state fluorescence experiments, with limit of quantitation in micromolar levels. NPNF's capability to exclusively detect HSA over BSA was further studied/rationalized using anisotropy and time-resolved studies. Molecular docking was used to shed light on the location of NPNF in the subdomain IB of HSA. The practical application of the probe was also demonstrated by the detection of HSA in urine and the HSA-assisted detection of cerium.

A new highly sensitive fluorescent probe for visualization of phosgene in liquid and gas phases

Phosgene is an important and widely used highly toxic chemical that poses a serious potential threat to public health and property if leaked or abused. Therefore, developing an efficient and convenient detection method for phosgene is of great significance. In this work, we synthesized a novel fluorescent probe, BCyP, based on benzohemicyanine for highly selective and sensitive detection of phosgene in both liquid and gas phases. The probe uses amino alcohol as a specific recognition group for phosgene and does not fluoresce due to the strong intramolecular charge transfer effect (ICT). However, in the presence of phosgene, the amino alcohol part in the probe can form oxazolidinone in situ with phosgene, reducing the ICT effect in the probe molecule and lighting fluorescence, thus realizing the selective phosgene detection. The probe exhibits good specificity towards phosgene, with significant fluorescence enhancement (approximately 400-fold), a remarkable Stokes shift (139 nm), a fast response speed (less than 17 s), and a low detection limit (0.12 ppm). Additionally, we prepared a phosgene detection paper strip loaded with the probe on filter paper and combined it with color recognition software on a smartphone to achieve visual detection of phosgene in the gas phase.

A novel near-infrared fluorescent probe with large Stokes shift for imagining hydrogen sulfide

Hydrogen sulfide (H₂S) plays an important role in regulating varieties of important physiological and pathological processes. Thus the development of fluorescent probe for the detection of H₂S is of great significance and has attracted much attention recently. Herein, we reported a novel near-infrared (NIR) emitting fluorescent probe WFP-PC, which contained a positive charged hemicyanine-based WFP-OH as fluorophore and thiobenzoate unit as a specific reaction site. After treated with H₂S, the probe exhibited significant fluorescence enhancement and response time within 4 min and detection limit as low as 0.47 μM, accompanied by color changes from purple to blue. The probe was successfully applied to imaging the exogenous/endogenous H₂S in cells and mice, suggesting it could be a promising molecular tool for H₂S detection in living systems.

A novel benzo hemicyanine-based fluorescent probe for susceptible visualizing detection of phosgene

Leakage and misuse of phosgene, a common and highly hazardous industrial chemical, have always constituted a safety risk. Therefore, it is crucial to develop sensitive detection methods for gaseous phosgene. This work describes the design and development of a new fluorescent dye based on benzohemicyanine, as well as the synthesis of fluorescent probes for the sensitive detection of gaseous phosgene. Due to the excellent intramolecular charge transfer (ICT) effect from the strong electron-donating impact of the o-aminophenol group on benzo hemicyanine, the probe does not emit fluorescence. When the probe reacts with phosgene, the ICT effect is inhibited, and the result exhibits observable green fluorescence, thereby visualizing the response to phosgene. The probe offers exceptional sensitivity, a rapid response, and a low phosgene detection limit. In addition, we developed probe-loaded, portable test strips for the quick and sensitive detection of phosgene in the gas phase. Finally, the constructed probe-loaded test strips were utilized effectively to monitor the simulated phosgene leakage.

Recent progress in the development of fluorescent probes for imaging pathological oxidative stress

Oxidative stress is closely related to the physiopathology of numerous diseases. Reactive oxygen species (ROS), reactive nitrogen species (RNS), and reactive sulfur species (RSS) are direct participants and important biomarkers of oxidative stress. A comprehensive understanding of their changes can help us evaluate disease pathogenesis and progression and facilitate early diagnosis and drug development. In recent years, fluorescent probes have been developed for real-time monitoring of ROS, RNS and RSS levels in vitro and in vivo. In this review, conventional design strategies of fluorescent probes for ROS, RNS, and RSS detection are discussed from three aspects: fluorophores, linkers, and recognition groups. We introduce representative fluorescent probes for ROS, RNS, and RSS detection in cells, physiological/pathological processes (e.g., Inflammation, Drug Induced Organ Injury and Ischemia/Reperfusion Injury etc.), and specific diseases (e.g., neurodegenerative diseases, epilepsy, depression, diabetes and cancer, etc.). We then highlight the achievements, current challenges, and prospects for fluorescent probes in the pathophysiology of oxidative stress-related diseases.

A turn-on fluorescent nanosensor for H2S detection and imaging in inflammatory cells and mice

Hydrogen sulfide (H₂S) is an endogenously generated gaseous signaling molecule and is known to be involved in the occurrence and development of inflammation. To better understand its physiological and pathological process of inflammation, reliable tools for H₂S detection in living inflammatory models are desired. Although a number of fluorescent sensors have been reported for H₂S detection and imaging, water-soluble and biocompatibility nanosensors are more useful for imaging in vivo. Herein, we developed a novel biological imaging nanosensor, XNP1, for inflammation-targeted imaging of H₂S. XNP1 was obtained by self-assembly of amphiphilic XNP1, which was constructed by the condensation reaction of the hydrophobic, H₂S response and deep red-emitting fluorophore with hydrophilic biopolymer glycol chitosan (GC). Without H₂S, XNP1 showed very low background fluorescence, while a significant enhancement in the fluorescence intensity of XNP1 was observed in the presence of H₂S, resulting in a high sensitivity toward H₂S in aqueous solution with a practical detection limit as low as 32.3 nM, which could be meet the detection of H₂S in vivo. XNP1 also has a good linear response concentration range (0-1 μM) toward H₂S with high selectivity over other competing species. These characteristics facilitate direct H₂S detection of the complex living inflammatory cells and drug-induced inflammatory mice, demonstrating its practical application in biosystems.

Excited state potential energy surfaces of N-phenylpyrrole upon twisting: reference values and comparison between BSE/GW and TD-DFT

The puzzling case of the mixing between the charge transfer (CT) and local excited (LE) characters upon twisting of the geometry of N-phenylpyrrole (N-PP) is investigated considering the six low-lying singlet excited states (ES). The theoretical calculations of the potential energy surfaces (PES) have been performed for these states using a Coupled Cluster method accounting for the impact of the contributions from the triples, many-body Green's function GW and Bethe-Salpeter equation (BSE) formalisms, as well as Time-Dependent Density Functional Theory (TD-DFT) using various exchange-correlation functionals. Our findings confirm that the BSE formalism is more reliable than TD-DFT for close-lying ES with mixed CT/LE nature. More specifically, BSE/GW yields a more accurate evolution of the excited state PES than TD-DFT when compared to the reference coupled cluster values. BSE/GW PES curves also show negligible exchange-correlation functional starting point dependency in sharp contrast with their TD-DFT counterparts.

H2S Sensors: Synthesis, Optical Properties, and Selected Biomedical Applications under Visible and NIR Light

Hydrogen sulfide (H₂S) is an essential signaling gas within the cell, and its endogenous levels are correlated with various health diseases such as Alzheimer's disease, diabetes, Down's syndrome, and cardiovascular disease. Because it plays such diverse biological functions, being able to detect H₂S quickly and accurately in vivo is an area of heightened scientific interest. Using probes that fluoresce in the near-infrared (NIR) region is an effective and convenient method of detecting H₂S. This approach allows for compounds of high sensitivity and selectivity to be developed while minimizing cytotoxicity. Herein, we report a review on the synthesis, mechanisms, optical properties, and selected biomedical applications of H₂S sensors.

Photophysical properties of furan-bridged dimeric boron-dipyrromethene derivatives (BODIPYs)

In order to investigate the changes in the spectroscopic properties of dimeric boron-dipyrromethenes (BODIPYs), four BODIPY derivatives are synthesized, including a monomer BODIPY in which a furyl group is substituted at the meso position and a dimer BODIPY with a furan group as a bridge. The four synthesized BODIPY derivatives are characterized through nuclear magnetic resonance and mass spectrometry. Photophysical properties such as ultraviolet–visible absorbance and the fluorescence emission of monomers (mT1 and mT2) and dimers (biT1 and biT2) are studied in eight different solvents. In addition, the relationship of their structural properties and optical properties are also considered through density functional theory calculations. The covalent link between the two BODIPY units using a furan group has a profound effect on the optical properties of the dimeric BODIPYs. We believe that an understanding of the synthesis and physical properties of dimeric BODIPYs will have a promising perspective in designing new BODIPY derivatives and predicting their spectroscopic characteristics in the future.

An NBD tertiary amine is a fluorescent quencher and/or a weak green-light fluorophore in H2S-specific probes

The thiolysis of NBD piperazinyl amine (NBD-PZ) is highly selective for H₂S over GSH and has been widely used for the development of many H₂S fluorescent probes. Whether the NBD amine in H₂S-specific probes could be a fluorescent quencher should be further clarified, because NBD amines have been used as environment-sensitive fluorophores for many years. Here, we compared the properties of NBD-based secondary and tertiary amines under the same conditions. For example, the emission of NBD-N(Et)2 is much smaller in water and less responsive to changes in polarity than that of NBD-NHEt. The emission of NBD-PZ-TPP is also smaller than that of NBD-NH-TPP both in aqueous buffer and in live cells. In addition, confocal bioimaging signals of NBD-PZ-TPP with excitation at 405 nm and 454 nm are much weaker than that at 488 nm. Based on these results as well as the previous work on NBD-based probes, we discuss and summarize the design strategies and sensing mechanisms for different NBD-based H₂S probes. Moreover, NBD-PZ-TPP may be a useful tool for reaction with and imaging of mitochondrial H₂S in live cells. This work should be useful for clarification of the roles of NBD in H₂S-specific fluorescent probes as well as for facilitating the development of future NBD-based probes.

New Rofecoxib-Based Mechanochromic Luminescent Materials and Investigations on Their Aggregation-Induced Emission, Acidochromism, and LD-Specific Bioimaging

Development of new mechanochromic luminescent (MCL) materials from aggregation-induced emission luminogens (AIEgens) has attracted wide attention due to their potential application in multiple areas. However, rational design and crafting of new MCL materials from the simple AIEgens skeleton is still a big challenge because of the undesirable concentration quenching effect. In this study, we have constructed a new class of MCL materials by adding one phenyl as a new rotator and incorporating one pair of electron donor (D) and acceptor (A) into the system of rofecoxib skeleton. This strategy endowed the compounds (Y1-Y8) with tunable emission behavior and some of them with the AIE effect and reversible MCL behavior. These properties may be caused by the highly twisted conformation and loosely molecular packing modes, which were elucidated clearly by analyzing the data of single-crystal X-ray diffraction, powder X-ray diffraction, and differential scanning calorimetry. Further investigation revealed that Y7 displayed acidochromic property due to the protonation of the nitrogen atom. Moreover, Y7, as a typical compound, showed its potential applications in the area of anticounterfeiting, pH sensor, and LD-specific bioimaging.

Synthesis and Investigation of Derivatives of 1,8-Naphthalimide with a Red Emission via an Aromatic Nucleophilic Substitution Reaction

1,8-Napthalimides (NIs) have been widely used as fluorescent molecules in biological, chemical, and medical fields because NIs shows high stability and various fluorescence properties under different conditions. However, NIs typically display a fluorescence emission wavelength in the range of 350 - 550 nm which can be notably interfered with by autofluorescence in living cells, significantly limiting their bio-applications. Moreover, low solubility in aqueous media is another major limitation for NIs. In this project, four derivatives of NIs (1-4) have been synthesized via an aromatic nucleophilic substitution reaction and their photophysical properties have been investigated in various media (water, MeOH, MeCN, DMSO, EtOAc, and THF). All of these derivatives (1-4) show a long emission wavelength around 600 nm and high solubility in polar solvents. Particularly molecules (1-4) show the longest emission (624-629 nm) in water and the fluorescence intensity is not significantly varied in the range of pH 4-11. These unique features, long emission wavelength, high solubility, and high stability in difference pH media, will allow these derivative (1-4) to be used as excellent labeling reagents in the biological system.

An ESIPT-based fluorescent probe with fast-response for detection of hydrogen sulfide in mitochondria

Excited-state intramolecular proton transfer (ESIPT) has recently received considerable attention due to its dual fluorescent changes and large Stokes shift. Hydrogen sulfide (H₂S) is a gas signal molecule that plays important roles in modulating the functions of different systems. Herein, by modifying 2-(2́-hydroxyphenyl) benzothiazole (HBT) scaffold, a novel near-infrared mitochondria-targeted fluorescent probe HBTP-H₂S has been rationally designed based on excited-state intramolecular proton transfer (ESIPT) effect. The nucleophilic addition reaction of the H₂S with probe HBTP-H₂S caused the break of the conjugated skeleton, resulting the shifting of maximum emission peak from 658 nm to 470 nm. HBTP-H₂S showed fast-response response time, good selectivity and a large Stokes shift (188 nm) toward H₂S. Most importantly, inspired by the inherent advantages of the probe, HBTP-H₂S was successfully employed to monitor mitochondrial H₂S in HepG2 cells.

A phenothiazine-based turn-on fluorescent probe for the selective detection of hydrogen sulfide in food, live cells and animals

In this work, a phenothiazine-based fluorescent probe (PR) has been developed for the selective detection of hydrogen sulfide (H₂S) in biosystems and monitoring H₂S produced in the food spoilage process. The nucleophilic attack of H₂S on the CC double bond of PRvia a Michael addition interdicted the ICT process to trigger 34-fold enhancement of the fluorescence emission. PR featured high selectivity and sensitivity (1.8 μM), low cytotoxicity and reliability at physiological pH. "Naked-eye" monitoring of H₂S produced in the food spoilage process using PR was successfully accomplished. The preliminary fluorescence imaging studies showed that PR is suitable for the visualization of exogenous and endogenous H₂S in living cells and live animals. Moreover, PR has been successfully applied to the visualization of H₂S generation in an inflammation model. The results indicated that PR is an effective tool to monitor H₂S production in the fields of biomedicine and food safety.

Rational Development of Dual-Ratiometric Fluorescent Probes for Distinguishing between H2S and SO2 in Living Organisms

For better investigating the complicated relationships between H₂S and SO₂, simultaneously detecting and visualizing them with good selectivity is crucial. However, most sensing mechanisms for H₂S and SO₂ probes are based on the addition reactions with the double bonds, which have no selectivity. In this work, by introducing an active triple bond into 4-dicyanovinyl-7-diethylamino-coumarin, we construct two unique sensors for not only distinguishing between H₂S and SO₂ but also sensing H₂S and SO₂ in a dual-ratiometric manner. Moreover, the modified sensor was successfully applied in living cells and zebrafish for discriminating H₂S and SO₂.

Inhibitors of bacterial H2S biogenesis targeting antibiotic resistance and tolerance

Emergent resistance to all clinical antibiotics calls for the next generation of therapeutics. Here we report an effective antimicrobial strategy targeting the bacterial hydrogen sulfide (H2S)-mediated defense system. We identified cystathionine γ-lyase (CSE) as the primary generator of H2S in two major human pathogens, Staphylococcus aureus and Pseudomonas aeruginosa, and discovered small molecules that inhibit bacterial CSE. These inhibitors potentiate bactericidal antibiotics against both pathogens in vitro and in mouse models of infection. CSE inhibitors also suppress bacterial tolerance, disrupting biofilm formation and substantially reducing the number of persister bacteria that survive antibiotic treatment. Our results establish bacterial H2S as a multifunctional defense factor and CSE as a drug target for versatile antibiotic enhancers.

Hypoxia-activated probe for NIR fluorescence and photoacoustic dual-mode tumor imaging

Construction of tumor microenvironment responsive probe with more than one imaging modality, in particular toward hypoxia of solid tumors, is an appealing yet significantly challenging task. In this work, we designed a hypoxia-activated probe TBTO (Triphenylamine-Benzothiadiazole-Triphenylamine derivative featuring four diethylamino N-Oxide groups) for in vivo imaging. TBTO could undergo bioreduction in a hypoxic microenvironment to yield compound TBT sharing both near-infrared (NIR) aggregation-induced emission and strong twisted intramolecular charge transfer features, which endows the probe with excellent performance in NIR fluorescence and photoacoustic dual-mode tumor imaging. This study offers useful insights into designing a new generation agent for clinical cancer diagnosis.

Construction of a dual-response fluorescent probe for copper (II) ions and hydrogen sulfide (H2S) detection in cells and its application in exploring the increased copper-dependent cytotoxicity in present of H2S

Multiple types of metal ions and active small molecules (reactive nitrogen species, reactive oxygen species, reactive sulfur species, etc.) exist in living organisms. They have connections to each other and can interact and/or interfere with each other. To investigate the relationship of metal ions and active small molecules in living cells, it is necessary and critical to develop molecular tools that can track two kinds of associated certain metal ions and reactive molecules with multiple fluorescence signals. However, this is a challenging task that requires an ingenious molecular design to achieve this goal. Here, we present a fluorescent probe (D-CN) that can offer fluorescence imaging of H₂S and copper (II) ions with different response signals. Recognition of H₂S and Cu (II) by the new probe can result in green and red emissions, respectively, providing different signal responses to the two substances in living cells and zebrafish. In addition, we used this probe to visually prove that the cytotoxicity of copper ions in living cells increases in the presence of hydrogen sulfide and could lead to cell apoptosis.

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.

Ultrasensitive and specific two-photon fluorescence detection of hypochlorous acid by a lysosome-targeting fluorescent probe for cell imaging

Hypochlorous acid (HOCl) is involved in numerous cellular processes, such as pathogen response, immune regulation, and anti-inflammation. Consequently, the development of HOCl detection at the cellular level has been an important issue in investigating the dynamic distributions of HOCl. Herein, a fluorescent probe, Lyso-NA, containing a HOCl-reactive aminophenol group and a lysosomal-targeting morpholine group, has been effectively designed for detecting lysosomal HOCl. The reaction of Lyso-NA with HOCl induces the oxidation of aminophenol and accompanied by a 136-fold fluorescence enhancement. The detection limit is found at 13 nM. The fluorescence enhancement is accomplished through the suppression of twisted intramolecular charge transfer (TICT). With morpholine, the probe Lyso-NA shows the great lysosomal targetable ability for imaging endogenous lysosomal HOCl in living cells and tissues by two-photon microscopy, providing an opportunity to monitor HOCl in the lysosomes for understanding its biological functions.

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.

Tuning of hyperpolarizability, and one- and two-photon absorption of donor-acceptor and donor-acceptor-acceptor-type intramolecular charge transfer-based sensors

The present work aims to study the effect of solvent as well as arrangement of donor-acceptor groups on linear and non-linear optical (NLO) response properties of two experimentally studied intramolecular charge-transfer (ICT)-based fluorescent sensors. One of them (molecule 1) is a donor-acceptor (D-A) system with hemicyanine and dimethylanilino as electron withdrawing and donating groups, respectively, while the other one (molecule 3) is molecule 1 fused with a boron-dipyrromethene (BODIPY) moiety. BODIPY acts as the electron acceptor group of molecule 2 that as well consists of dimethylanilino as the electron donor. Density functional theory (DFT) as well as time-dependent DFT has been employed to optimize the geometry of the molecules, followed by computation of dipole moment (μ), static first hyperpolarizability (β_total), and one- and two-photon absorption (TPA) strengths. The results reveal that dipole moment as well as total static first hyperpolarizability (β_total) of the studied molecules is dominated by the respective components in the direction of charge transfer. The ratio of vector component of first hyperpolarizability (β_vec) to β_total also supports the unidirectional charge transfer in the studied systems. In molecule 3, which is a donor-acceptor-acceptor (D-A-A)-type system, the BODIPY moiety is found to play a major role in controlling the NLO response over the other acceptor group. Solvents are also found to play an important role in controlling the linear as well as NLO response of the studied systems. A significant increase in the first hyperpolarizability as well as TPA cross-section of the studied molecules is predicted due to an increase in the dielectric constant of the medium. The results presented are expected to provide a clue in tuning the NLO response of many ICT-based chromophores, especially those with D-A-A arrangements.

A novel lysosome-targeted fluorogenic probe based on 5-triazole-quinoline for the rapid detection of hydrogen sulfide in living cells

A fluorogenic probe based on the novel fluorophore 5-triazole-quinoline was developed for the detection of hydrogen sulfide, an endogenous signaling molecule associated with the development of various diseases. The lysosome-targeted probe Lyso-HS was synthesized via C-H direct azidation from 8-aminoquinoline; it was able to detect H₂S in 1 min and exhibited excellent turn-on ability with 95-fold fluorescence enhancement based on a new fluorochrome. The high quenching efficiency was further verified using time-dependent density functional theory (TDDFT). The probe also exhibited high selectivity and a low detection limit (as low as 214.5 nM), which has practical applications for disease detection and monitoring.

A dinitro-functionalized metal-organic framework featuring visual and fluorogenic sensing of H2S in living cells, human blood plasma and environmental samples

Here, we describe a new dinitro-functionalized Zr(iv) MOF (MOF = metal-organic framework) having a UiO-66 (UiO = University of Oslo) framework topology called UiO-66-(NO₂)₂ (1). It shows fluorescence turn-on behavior towards H₂S in simulated biological medium (HEPES buffer, pH = 7.4). By employing solvothermal conditions, 1 was successfully synthesized by reacting ZrCl₄, H₂BDC-(NO₂)₂ [H₂BDC-(NO₂)₂ = 2,5-dinitro-1,4-benzenedicarboxylic acid] ligand and benzoic acid with a molar ratio of 1 : 1 : 10 in DMF (DMF = N,N-dimethylformamide) at 130 °C for 24 h. The material was characterized by infrared spectroscopy, X-ray powder diffraction (XRPD) and thermogravimetric (TG) analyses. The compound not only displays highly sensitive fluorometric sensing of H₂S but also exhibits a visually detectable colorimetric change towards H₂S in daylight. Moreover, the high selectivity of 1' towards H₂S is retained even when several other biologically intrusive species co-exist in the sensing medium. The limit of detection (LOD) of the compound is 14.14 μM which lies in the range of the H₂S concentration found in biological systems. Fluorescence microscopy studies on J774A.1 cells revealed the efficacy of the probe for imaging H₂S in living cells. Moreover, this material can detect H₂S in human blood plasma (HBP) and monitor the sulfide concentration in real water samples. All these features clearly demonstrate that the material has huge potential for highly selective sensing of both extracellular and intracellular H₂S.

Superb-selective chemodosimetric signaling of sulfide in the absence and in the presence of CT-DNA and imaging in living cells by a plant alkaloid berberine analogue

New berberine analogue (BER-S), as a colorimetric probe in the absence of DNA and turn-on fluorometric probe in the presence of DNA towards S²⁻ detection is reported.

A ratiometric fluorescent chemosensor for the convenient monitoring of hydrogen sulfide concentration by the dual fluorescence fluctuation mode of two distinct emission bands in living cells and zebrafish

An interplaying ICT-FRET-based chemosensor with two response sites having differentiated sensitivities to H₂S was engineered to conveniently determine the concentration of H₂S by the dual fluorescence fluctuation mode of two distinct emission bands.

A novel near-infrared fluorescent hydrogen sulfide probe for live cell and tissue imaging

A novel sensitive near-infrared fluorescence enhanced NIR-NP probe with a large Stokes shift for H₂S analysis was developed.

A targetable fluorescent probe for real-time monitoring of fluoride ions in mitochondria

Fluorion are pivotal anions in biology because they play an important role in dental care, treating osteoporosis, preventing tooth decay and promoting the healthy growth of bone. Studies have shown that high levels of fluoride will lead to the inactivation of the mitochondria. Therefore, it is urgent to develop a method to detect the fluoride anions in the mitochondria. Herein, we have developed a novel mitochondrial-target fluorescent probe for detecting F^- in living cells. The probe exhibited excellent sensitivity and high selectivity for F^- over the other relative species. With changing fluoride ions, the fluorescence spectrum of the probe changed significantly with a large turn-on fluorescence signal. Cell imaging indicated that the probe can penetrate viable cell membranes and rapidly detects and images fluorion over other anions in the mitochondria.

Naked-eye and ratiometric fluorescence probe for fast and sensitive detection of hydrogen sulfide and its application in bioimaging

A sensitive and ultrafast ratiometric fluorescence probe for the detection of hydrogen sulfide (H₂S) in HeLa cells and zebrafish.

A novel long-wavelength fluorescent probe for selective detection of hydrogen sulfide in living cells

Sensitive detection of endogenous H₂S by a low cytotoxicity probe.

Luminescent gold nanocluster-based sensing platform for accurate H2S detection in vitro and in vivo with improved anti-interference

Gold nanoclusters (Au NCs) are promising luminescent nanomaterials due to their outstanding optical properties. However, their relatively low quantum yields and environment-dependent photoluminescence properties have limited their biological applications. To address these problems, we developed a novel strategy to prepare chitosan oligosaccharide lactate (Chi)-functionalized Au NCs (Au NCs@Chi), which exhibited emission with enhanced quantum yield and elongated emission lifetime as compared to the Au NCs, as well as exhibited environment-independent photoluminescence properties. In addition, utilizing the free amino groups of Chi onto Au NCs@Chi, we designed a FRET-based sensing platform for the detection of hydrogen sulfide (H₂S). The Au NCs and the specific H₂S-sensitive merocyanine compound were respectively employed as an energy donor and acceptor in the platform. The addition of H₂S induced changes in the emission profile and luminescence lifetime of the platform with high sensitivity and selectivity. Utilization of the platform was demonstrated to detect exogenous and endogenous H₂S in vitro and in vivo through wavelength-ratiometric and time-resolved luminescence imaging (TLI). Compared to previously reported luminescent molecules, the platform was less affected by experimental conditions and showed minimized autofluorescence interference and improved accuracy of detection.

2,5-bis(4-alkoxycarbonylphenyl)-1,4-diaryl-1,4-dihydropyrrolo[3,2-b]pyrrole () AIEgens: tunable RIR and TICT characteristics and their multifunctional applications

Novel propeller-like AIEgens with tunable emission were readily prepared and used as a fluorescent thermometer and selective chemosensor for Cd(ii) detection.

Aggregation-induced emission luminogens (AIEgens) have attracted extensive interest for their outstanding luminescence properties in the aggregated state and even in the solid state. In this work, we developed a series of novel AIEgens based on 2,5-bis(4-alkoxycarbonylphenyl)-1,4-diaryl-1,4-dihydropyrrolo[3,2-b]pyrrole (AAPP). The AIEgens can be facilely synthesized through a single-step reaction under mild conditions with satisfactory yields. Interestingly, AAPP was found to have multiple luminous mechanisms that result in variable fluorescence properties. The propeller-like structure of AAPP enables a restricted intramolecular rotation (RIR) process which significantly enhances its fluorescence in the aggregated state (i.e. AIE fluorescence). In addition, there is a donor–acceptor interaction between the heterocycle center and the alkoxycarbonyl units in AAPP which allows a typical twisted intramolecular charge transfer (TICT) process in the dispersed state, resulting in strong fluorescence emissions in non-polar or low-polarity solvents but fluorescence quenching in high-polarity solvents. Due to the tunable RIR and TICT processes and the multiple fluorescence, AAPP compounds exhibit multifunctional applications: (1) as a reversible fluorescent thermometer, AAPP exhibited excellent fatigue resistance. There was a good linear relationship between its fluorescence intensity and temperature from 10 °C to 60 °C. (2) The desethyl AAPP derivative (CAPP) was successfully applied in the detection of Cd(ii) in aqueous solution at neutral pH, and showed a 500-fold fluorescence “turn-on” response to Cd(ii) with good selectivity.

A multi-signal fluorescent probe for simultaneously distinguishing and sequentially sensing cysteine/homocysteine, glutathione, and hydrogen sulfide in living cells

A multi-signal fluorescent probe was engineered for simultaneously distinguishing and sequentially sensing cysteine/homocysteine, glutathione, and hydrogen sulfide in living cells.

Biothiols, which have a close network of generation and metabolic pathways among them, are essential reactive sulfur species (RSS) in the cells and play vital roles in human physiology. However, biothiols possess highly similar chemical structures and properties, resulting in it being an enormous challenge to simultaneously discriminate them from each other. Herein, we develop a unique fluorescent probe (HMN) for not only simultaneously distinguishing Cys/Hcy, GSH, and H₂S from each other, but also sequentially sensing Cys/Hcy/GSH and H₂S using a multi-channel fluorescence mode for the first time. When responding to the respective biothiols, the robust probe exhibits multiple sets of fluorescence signals at three distinct emission bands (blue-green-red). The new probe can also sense H₂S at different concentration levels with changes of fluorescence at the blue and red emission bands. In addition, the novel probe HMN is able to discriminate and sequentially sense biothiols in biological environments via three-color fluorescence imaging. We expect that the development of the robust probe HMN will provide a powerful strategy to design fluorescent probes for the discrimination and sequential detection of biothiols, and offer a promising tool for exploring the interrelated roles of biothiols in various physiological and pathological conditions.

Mechanism of H2S-mediated protection against oxidative stress in Escherichia coli

Endogenous hydrogen sulfide (H₂S) renders bacteria highly resistant to oxidative stress, but its mechanism remains poorly understood. Here, we report that 3-mercaptopyruvate sulfurtransferase (3MST) is the major source of endogenous H₂S in Escherichia coli Cellular resistance to H₂O₂ strongly depends on the activity of mstA, a gene that encodes 3MST. Deletion of the ferric uptake regulator (Fur) renders ∆mstA cells hypersensitive to H₂O₂ Conversely, induction of chromosomal mstA from a strong pLtetO-1 promoter (P _tet -mstA) renders ∆fur cells fully resistant to H₂O₂ Furthermore, the endogenous level of H₂S is reduced in ∆fur or ∆sodA ∆sodB cells but restored after the addition of an iron chelator dipyridyl. Using a highly sensitive reporter of the global response to DNA damage (SOS) and the TUNEL assay, we show that 3MST-derived H₂S protects chromosomal DNA from oxidative damage. We also show that the induction of the CysB regulon in response to oxidative stress depends on 3MST, whereas the CysB-regulated l-cystine transporter, TcyP, plays the principle role in the 3MST-mediated generation of H₂S. These findings led us to propose a model to explain the interplay between l-cysteine metabolism, H₂S production, and oxidative stress, in which 3MST protects E. coli against oxidative stress via l-cysteine utilization and H₂S-mediated sequestration of free iron necessary for the genotoxic Fenton reaction.