A Single Fluorescent Probe to Visualize Hydrogen Sulfide and Hydrogen Polysulfides with Different Fluorescence Signals

Illuminating Polysulfide Distribution in Lithium Sulfur Batteries; Tracking Polysulfide Shuttle Using Operando Optical Fluorescence Microscopy

High-energy-density lithium sulfur (Li-S) batteries suffer heavily from the polysulfide shuttle effect, a result of the dissolution and transport of intermediate polysulfides from the cathode, into the electrolyte, and onto the anode, leading to rapid cell degradation. If this primary mechanism of cell failure is to be overcome, the distribution, dynamics, and degree of polysulfide transport must first be understood in depth. In this work, operando optical fluorescence microscope imaging of optically accessible Li-S cells is shown to enable real-time qualitative visualization of the spatial distribution of lithium polysulfides, both within the electrolyte and porous cathode. Quantitative determinations of spatial concentration are also possible at a low enough concentration. The distribution throughout cycling is monitored, including direct observation of polysulfide shuttling to the anode and consequent dendrite formation. This was enabled through the optimization of a selective fluorescent dye, verified to fluoresce proportionally with concentration of polysulfides within Li-S cells. This ability to directly and conveniently track the spatial distribution of soluble polysulfide intermediates in Li-S battery electrolytes, while the cell operates, has the potential to have a widespread impact across the field, for example, by enabling the influence of a variety of polysulfide mitigation strategies to be assessed and optimized, including in this work the LiNO3 additive.

Development of fluorescent probes with specific recognition moiety for hydrogen polysulfide

Hydrogen polysulfide (H2Sn, n > 1) is an important component of reactive sulfur species (RSS), which is an important substance for maintaining the redox balance in cells. However, limited recognition moieties are available for hydrogen polysulfide probe design. In this study, we have constructed a small library containing several organic molecules to explore a new specific recognition moiety for H2Sn fluorescent probe design. To validate the discovery, two fluorescent probes, 7 and BCC, were further developed based on coumarin and its derivative. The probes exhibited desirable specificity for H2Sn monitoring, which can be used for detecting H2Sn in solution and cells. The new specific recognition moiety for H2Sn fluorescent probe design discovered in this work has certain guiding significance for development of H2Sn probes exploring biological roles in the future.

Designs and Applications of Multi-stimuli Responsive FRET Processes in AIEgen-Functionalized and Bi-fluorophoric Supramolecular Materials

Materials capable of displaying strong ratiometric fluorescence with Förster resonance energy transfer (FRET) processes have attracted much research interest because of various chemosensor and biomedical applications. This review highlights several popular strategies in designing FRET-OFF/ON mechanisms of ratiometric fluorescence systems. In particular, the developments of organic and polymeric FRET materials featuring aggregation-induced emission-based luminogens (AIEgens), supramolecular assemblies, photochromic molecular switches and surfactant-induced AIE/FRET mechanisms are presented. AIEgens have been frequently employed as FRET donor and/or acceptor fluorophores to obtain enhanced ratiometric fluorescences in solution and solid states. Since AIE effects and FRET processes rely on controllable distances between fluorophores, many interesting fluorescent properties can be designed by regulating aggregation states in polymers and supramolecular systems. Photo-switchable fluorophores, such as spiropyran and diarylethene, provide drastic changes in fluorescence spectra upon photo-induced isomerizations, leading to photo-switching mechanisms to activate/deactivate FRET processes. Supramolecular assemblies offer versatile platforms to regulate responsive FRET processes effectively. In rotaxane structures, the donor-acceptor distance and FRET efficiency can be tuned by acid/base-controlled shuttling of the macrocycle component. The tunable supramolecular interactions are strongly influenced by external factors (such as pH values, temperatures, analytes, surfactants, UV-visible lights, etc.), which induce the assembly and disassembly of host-guest systems and thus their FRET-ON/FRET-OFF behavior. In addition, the changes in donor or acceptor fluorescence profiles upon detections of analytes can also sufficiently alter the FRET behavior and result in different ratiometric fluorescence outputs. The strategies and examples provided in this review offer the insights and toolkits for future FRET-based material developments.

Fluorescence probe for selectively monitoring biothiols within cells and mouse depression diagnosis

As a global mental disorder, depression is associated with oxidative stress in the brain. Cysteine, a reductive biothiols, regulates the oxidative situation in many biological events including the stress that occurs in the tissues. Exploring the pathology and physiology of depression is still a challenge and always in an urgent need. Thus, developing a new method that could track Cys level without the interferes from other competing substances is of great importance. Herein, we developed a fluorescence probe that could selectively sensing Cys over other biothiols. Besides, we have demonstrated its desirable performance in cellular applications and mouse brain. This work provides a new method for Cys imaging and understanding pathogenesis of depression. We hope the work described here could be used as a potential chemical approach for the diagnosis of Cys associated diseases in clinical applications.

A Cell Trappable Methyl Rhodol-Based Fluorescent Probe for Hydrogen Sulfide Detection

Hydrogen sulfide is a biologically important molecule and developing chemical tools that enable further investigations into the functions of H2 S is essential. Fluorescent turn-on H2 S probes have been developed for use in cellulo and in vivo, but the membrane permeability of these probes can lead to probe leakage and signal attenuation over time. Here we report a cell trappable fluorescent probe for H2 S, CT-MeRhoAz, which is based on a methylrhodolazide scaffold derivatized with an acetoxymethyl ester group. Prior to ester cleavage, the CT-MeRhoAz probe generates a 2500-fold turn-on response to H2 S, which is enhanced to a 3000-fold response for the carboxylic acid form of the probe. Additionally, the probe is highly selective for H2 S over other biologically relevant sulfur, oxygen, and nitrogen-based analytes. Live cell imaging experiments confirmed the biocompatibility of CT-MeRhoAz and also that it is cell trappable, unlike the parent MeRhoAz scaffold.

Lipid Droplet-Specific Dual-Response Fluorescent Probe for the Detection of Polarity and H2O2 and Its Application in Living Cells

H₂O₂ and polarity are quite important in many physiological and pathological processes, and their relationship is complicated and obscure for researchers. Thus, it is vital and challenging to achieve simultaneous detection of H₂O₂ and polarity in vivo. Herein, the first naphthalimide-triphenylamine-based dual-site fluorescent probe NATPA is developed for simultaneously imaging intracellular H₂O₂ and polarity fluctuations. It exhibits excellent sensitivity (LOD = 44 nM), selectivity, and fast response (15 min) to H₂O₂ and a superior capacity for detecting polarity upon the intramolecular charge transfer (ICT) effect. Besides, the probe displays low cytotoxicity and lipid droplet targeting and is further applied in imaging H₂O₂ and polarity fluctuations in HepG2 and L-02 cells, so that NATPA is qualified to distinguish cancer cells from normal cells. This research contributes a new design principle for the construction of dual-site fluorescent probes for simultaneously detecting active molecules and polarity.

Monitoring thiophenols in both environmental water samples and bio-samples: A method based on a fluorescent probe with broad pH adaptation

Thiophenol, which is a highly toxic sulfhydryl compound widely used in chemical industry, is an environmental pollutant that threatens human health significantly. It is of great importance to detect highly toxic thiophenols in both environmental and biological system. Thus, the need to develop rapid response, selective and sensitive probes is urgent. In this study, a novel probe was presented for the detection of thiophenols based on an intramolecular charge transfer (ICT) mechanism. This probe exhibits rapid response, broad pH adaptation (2-10), highly selectivity, a large Stokes shift (131 nm) and 40-fold enhancement in fluorescence. Besides, this probe showed low toxicity towards human cell HEK293 and could be applied to detect thiophenol both in living cells, zebrafish and environmental water samples with good recovery (over 94%). All the results indicated that this probe could be a promising sensor for applications for thiophenol derivatives detection in both environmental and biological sciences.

Fluorescent Probes and Mass Spectrometry-Based Methods to Quantify Thiols in Biological Systems

Significance: Fluorescent probes and mass spectrometry are the two most popular and complementary methods to quantify thiols in biological systems. In this review, we focus on the widely used and commercially available methods to detect and quantify thiols in living cells and the general approaches applied in mass spectrometry-based thiol quantification. We hope that this review can serve as a general guide for redox biologists who are interested in thiol species. Sulfur, one of the most important elements in living systems, contributes to every aspect of physiology and pathology. Thiols, including cysteine, homocysteine, glutathione, hydrogen sulfide, and hydropersulfides, are the main players in the redox biology system. Therefore, quantifying these thiol species in biological systems is one of the important steps to understand their roles in biology. Recent Advances: Fluorescent probes and mass spectrometry-based methods have been developed to detect and/or quantify thiols in biological systems. Mass spectrometry-based methods have been the gold standard for metabolite quantification in cells. Fluorescent probes can directly detect or quantify thiol species in living cells with spatial and temporal resolutions. Additionally, organelle-specific fluorescent probes have been widely developed. These two methods are complementary to each other. Critical Issues: Reliable quantification of thiol species using fluorescent probes remains challenging. Future Directions: When developing fluorescent probes, we suggest using both the fluorescent probes and mass spectrometry-based thiol quantification methods to cross-check the results. In addition, we call on chemical biologists to move beyond qualitative probes and focus on probes that can provide quantitative results in live cells. These quantitative measurements based on fluorescent probes should be validated with mass spectrometry-based methods. More importantly, chemical biologists should make their probes accessible to the biology end users. Regarding mass spectrometry-based methods, quantification of the derivatized thiol specifies should fit into the general metabolomics workflow. Antioxid. Redox Signal. 36, 354-365.

Simultaneous Quantification of Biothiols and Deciphering Diverse GSH Stability in Different Live Cells by 19F-Tag

GSH, Cys, Hcy, and H₂S are important biothiols and play important roles in the living systems. Quantitative and simultaneous determination of these biothiols under physiological conditions is still a challenge. Herein, we developed an effective ¹⁹F-reactive tag that readily interacts with these four biothiols for the generation of stable thioether products that have distinguishable ¹⁹F-chemical shifts. These thioester compounds encode the characteristic fingerprint profiles of each biothiols, allowing one to simultaneously quantify and determine these biothiols by 1D ¹⁹F NMR spectroscopy. The intra-/extracellular GSH in live cells was assessed by the established strategy, and remarkable variations in the GSH stability were determined between the normal mammalian cells and cancer cells. It is notable that GSH hydrolyzes efficiently in the out-membrane of the cancer cells and the lysates. In contrast, GSH remains stable in the tested normal cells.

Facile synthesis of ultrahigh fluorescence N,S-self-doped carbon nanodots and their multiple applications for H2S sensing, bioimaging in live cells and zebrafish, and anti-counterfeiting

Green-emissive N,S-self-doped carbon nanodots (N,S-self-CNDs) with an ultrahigh fluorescence (FL) quantum yield (QY) of 60% were synthesized using methyl blue as the only source by a facile hydrothermal approach. The -NH- and -SOx- groups of methyl blue were simultaneously used as nitrogen and sulfur co-dopants to dope into CNDs. The prepared N,S-self-CNDs have an extremely large Stokes shift (∼130 nm) and excitation-independent fluorescence, and are demonstrated to have multiple applications for H2S sensing, bioimaging and anti-counterfeiting. Taking advantage of their excellent optical properties, N,S-self-CNDs could act as a label-free nanoprobe for the detection of H2S. The FL of N,S-self-CNDs could be significantly quenched by H2S because of dynamic quenching, along with excellent selectivity toward H2S from 0.5-15 μM with a detection limit of 46.8 nM. They were successfully employed for the analysis of H2S content in actual samples. Additionally, the nanoprobe was extended to bioimaging in both living PC12 cells and zebrafish, and monitoring H2S in live cells. Furthermore, N,S-self-CNDs have been used to prepare highly fluorescent polymer films by incorporating N,S-self-CNDs in polyvinyl alcohol (PVA). The as-prepared N,S-self-CNDs/PVA films show a prominent dual-mode FL property, implying that they are potential nanomaterials in the anti-counterfeiting field.

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.