A new lysosome-targetable fluorescent probe for detection of endogenous hydrogen polysulfides in living cells and inflamed mouse model

A lysosome-located and rhodamine-based fluorescence probe for recognizing hydrogen polysulfide

Hydrogen polysulfide (H2Sn, n≥2), as a kind of active sulfur species (RSS), has become a hot topic in RSS. It can regulate the biological activity of many proteins through S-sulfhydrylation of cysteine residues (protein Cys-SSH), and has a protective effect on cells. Although there have been some studies on hydrogen polysulfide, its production, degradation pathway and regulation mechanism still need further be researched. In presented study, an original lysosome-localized fluorescent probe for determining H2Sn was developed utilizing rhodamine as the fluorogen. The probe used morpholine as the locating unit of lysosomes and chose 2-fluoro-5-nitrobenzoate as the recognizing group. Before adding H2Sn, the proposed probe displayed a spironolactone structure and emitted very weak fluorescence. After adding H2Sn, a conjugated xanthene was formed and the probe demonstrated green fluorescence. When the H2Sn concentration was varied from 6.0×10-7 mol·L-1 to 10.0×10-5 mol·L-1, the fluorescence intensity of the probe was linearly dependent on the H2Sn concentration. And the detection limit was 1.5×10-7 mol·L-1. The presented probe owned a fast response speed, good selectivity, excellent sensitivity and broad pH work scope. In addition, the probe had been well utilized to sense endogenic and exogenic H2Sn in lysosomes.

NIR-II Fluorescence/Photoacoustic Dual Ratiometric Probes with Unique Recognition Site for Quantitatively Visualizing H2S2 in Vivo

Hydrogen persulfide (H2S2) plays a significant role in redox biology and signal transduction; therefore, quantitative visualization of H2S2 in the deep tissue of living organisms is essential for obtaining reliable information about relevant pathophysiological processes directly. However, currently reported H2S2 probes are unsuitable for this purpose because of their poor selectivity for many polysulfide species or their short wavelength, which hinders precise imaging in deep tissues. Herein, for the first time, we report a unique H2S2-mediated dithiole formation reaction. Based on this reaction, we construct the first NIR-II fluorescence (FL) and photoacoustic (PA) dual-ratiometric probe (NIR-II-H2S2) for quantitatively visualizing H2S2 in vivo. This probe shows dual-ratiometric NIR-II fluorescence (I840/I1000, 107-fold) and photoacoustic (PA800/PA900, 6.5-fold) responses towards Na2S2 species with high specificity, excellent sensitivity (1.8 nM), improved water solubility, and deep-tissue penetration. More importantly, using NIR-II dual-ratiometric FL/PA imaging, we successfully demonstrated that the probe could be used to accurately quantify the fluctuating H2S2 levels in the liver-injury mouse models induced by lipopolysaccharides or metformin drugs. Overall, this study not only presents a promising tool for H2S2-related pathological research, but also provides a unique recognition site that may be generalized for designing more useful H2S2 imaging agents in the future.

Sulfur-based fluorescent probes for biological analysis: A review

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

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.

Organelle-Targeted Fluorescent Probes for Sulfane Sulfur Species

Sulfane sulfurs, which include hydropersulfides (RSSH), hydrogen polysulfides (H2Sn, n > 1), and polysulfides (RSnR, n > 2), play important roles in cellular redox biology and are closely linked to hydrogen sulfide (H2S) signaling. While most studies on sulfane sulfur detection have focused on sulfane sulfurs in the whole cell, increasing the recognition of the effects of reactive sulfur species on the functions of various subcellular organelles has emerged. This has driven a need for organelle-targeted detection methods. However, the detection of sulfane sulfurs, particularly of RSSH and H2Sn, in biological systems is still a challenge due to their low endogenous concentrations and instabilities. In this review, we summarize the development and design of organelle-targeted fluorescent sulfane sulfur probes, examine their organelle-targeting strategies and choices of fluorophores (e.g., ratiometric, near-infrared, etc.), and discuss their mechanisms and ability to detect endogenous and exogenous sulfane sulfur species. We also present the advantages and limitations of the probes and propose directions for future work on this topic.

An imidazo[1,5-α]pyridines-based ratiometric fluorescent probe for sensing sulfur dioxide derivatives in real samples based on a FRET mechanism

A novel fluorescence resonance energy transfer (FRET)-based ratiometric emission fluorescent probe AT was designed and developed in which the imidazo[1,5-α]pyridine was served as a FRET donor and tricyanofuran (TCF) as the FRET acceptor to detect SO₃^2-/HSO₃^- based on the Michael addition reaction. Probe AT had a high energy transfer efficiency (95%) and a large pseudo-Stokes shift (259 nm) in EtOH/PBS buffer (5/5, v/v). It also possessed good selectivity and quick response to SO₃^2-/HSO₃^-. There was good linearity between the ratio of fluorescence intensity (F₄₉₉/F₆₄₅) and the concentrations of SO₃^2-/HSO₃^- in the ranges of 1.5-7.5 μM and 9-20 μM, with calculated detection limits (LOD) of 55 nM. In addition, the probe could also detect the concentrations of SO₃^2-/HSO₃^- in real samples such as environmental water and sugar, allowing the probe to be used in a variety of applications.

A ratiometric fluorescent probe for hydrogen sulfide in neat aqueous solution and its application in lysosome-targetable cell imaging

Hydrogen sulfide (H₂S) has been recently regarded as one of the most important gasotransmitters in the metabolic system, while abnormal H₂S concentration is associated with various diseases. Although numerous fluorescent probes have been developed for the detection of cellular H₂S, only a few of them can monitor lysosomal H₂S with ratiometric fluorescent output. Here, we developed a water-soluble probe 1 toward H₂S by introducing 2,4-dinitrophenyl ether into a novel merocyanine-based dye. As expected, H₂S induced an obvious red-shift of the probe from 520 nm to 580 nm in neat aqueous solution, and this fluorescent ratiometric response is highly selective and sensitive (with the detection limit of 0.81 nM), rapid (within 10 s), and effective in a wide pH range (2.0-10.0). In particular, the probe was successfully applied for tracing H₂S in the lysosomes of living cells and in zebrafish.

A novel lysosome-located fluorescent probe for highly selective determination of hydrogen polysulfides based on a naphthalimide derivative

Hydrogen polysulfides (H₂S_n, n > 1) belongs to sulfane sulfur in the reactive sulfur species (RSS) family and plays a significant regulatory role in organisms. Highly selective and lysosome-located probes for detecting hydrogen polysulfides are rare. Thus, it is important to develop a technique to detect the changes of H₂S_n level in lysosomes. In this work, a lysosome-targeting fluorescent probe for H₂S_n was designed and developed based on a naphthalimide derivative. 4-Hydroxynaphthalimide was selected as the fluorescent group and 2-chloro-5-nitrobenzoate group was used as a specific recognition unit for H₂S_n. A morpholine unit was chosen as a lysosome-located group. In the absence of H₂S_n, the fluorescent probe exhibited almost no fluorescence. In the presence of H₂S_n, the fluorescent probe showed strong fluorescence owing to H₂S_n-mediated aromatic substitution-cyclization reactions. The fluorescence emission intensity at 548 nm of the probe showed a good linear relationship toward H₂S_n in the range of 2.0 × 10^-7 - 9.0 × 10^-5 mol·L^-1, and the detection limit was found to be 1.5 × 10^-7 mol·L^-1. The probe possessed a wide work range of pH, including the pH of physiological environment, and high selectivity for H₂S_n. There are almost no cytotoxicity and the ability of detecting endogenous and exogenous H₂S_n in lysosomes. These results indicate that the fluorescent probe can provide a good tool for intracellular and extracellular detection of H₂S_n.

A mitochondrial and lysosomal targeted ratiometric probe for detecting intracellular H2S

Based on coumarin and benzopyran derivatives, a dual-wavelength excitation ratiometric fluorescent probe, HABA, was prepared to detect H₂S. The HABA probe showed good selectivity and anti-interference abilities during H₂S detection. Fluorescence co-localization experiments showed that HABA had excellent localization abilities toward mitochondria and lysosomes. More importantly, HABA can not only detect exogenous H₂S, but it can also detect endogenous H₂S, indicating that HABA has high application potential and value in the biological field.