Research progress of hydrogen sulfide fluorescent probes targeting organelles

Hydrogen sulfide (H2S) is implicated in numerous physiological and pathological processes in living organisms. Abnormal levels of H2S can result in various physiological disorders, highlighting the crucial need for effective identification and detection of H2S at the organellar level. Although numerous H2S fluorescent probes targeting organelles have been reported, a comprehensive review of these probes is required. This review focuses on the strategic selection of organelle-targeting groups and recognition sites for H2S fluorescent probes. This review examines H2S fluorescent probes that can specifically target lysosomes, mitochondria, endoplasmic reticulum, Golgi apparatus, and lipid droplets. These fluorescent probes have been meticulously classified and summarized based on their distinct targets, emphasizing their chemical structure, reaction mechanisms, and biological applications. We carefully designed fluorescent probes to efficiently enhance their ability to recognize target substances and exhibit significant fluorescence variations. Furthermore, we discuss the challenges inherent in the development of fluorescent probes and outline potential future directions for this exciting field.

Multiple Applications of a Novel Fluorescence Probe with Large Stokes Shift and Sensitivity for Rapid H2S Detection

Herein, a novel fluorescence probe Fla-DNP based on flavonol has been designed and synthesized for rapid, specific detection of H2S. With the addition of H2S, Fla-DNP triggered thiolysis and released Fla displaying the "turn-on" fluorescence response at 566 nm, which is consistent with the reaction site predicted by calculating Electrostatic potential and ADCH charges. As an easily available H2S probe, Fla-DNP has the advantages of high selectivity, anti-interference, low detection limit (0.834 μM), short response time (6 min), and large Stokes shift (124 nm). The sensing mechanism of H2S was determined by HRMS analysis and DFT calculation. Moreover, Fla-DNP processes a wide range of multiple applications, including the detection of H2S in environmental water samples with good recovery rates ranging from 89.6% to 102.0%, as well as tracking the production of H2S during food spoilage. Meanwhile, the probe exhibits superior biocompatibility and can not only be available used for H2S detection in living cells but be further designed as an H2S-activated CO photoreleaser, based on which it can be developed as a targeted anti-cancer drug.

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.

A naphthalimide functionalized chitosan-based fluorescent probe for specific detection and efficient adsorption of Cu2

As one of the most abundant metal ions, Cu²⁺ has turned into a great threat to human health and the natural environment due to its widely utilized in various industries. In this paper, a chitosan-based fluorescent probe CTS-NA-HY for detection and adsorption of Cu²⁺ was rationally prepared. CTS-NA-HY exhibited a specific "turn off" fluorescence response to Cu²⁺ and the fluorescence color changed from bright yellow to colorless. It possessed satisfactory detection performance to Cu²⁺ including good selectivity and anti-interference, low detection limit (29 nM) and wide pH range (4-9). The detection mechanism was confirmed by Job's plot, X-ray photoelectron spectroscopy, FT-IR and ¹H NMR analysis. Additionally, the probe CTS-NA-HY was capacity of determining Cu²⁺ in environmental water and soil samples. Besides, CTS-NA-HY-based hydrogel could also remove Cu²⁺ in aqueous solution effectively, which the ability of adsorption was greatly improved compared with original chitosan hydrogel.

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.

Naphthalimide derivatives as fluorescent probes for imaging endogenous gasotransmitters

Gasotransmitters have gained significant recognition attributed to their evident biological impacts, and is accepted as a promising and less-explored area with immense research scope. The three-member family comprising of nitric oxide, carbon monoxide and hydrogen sulphide as endogenous gaseous signaling molecules have been found to elicit a plethora of crucial biological functions, spawning a new research area. The sensing of these small molecules is vital to gain deeper insights into their functions, as they can act both as a friend or a foe in mammalian systems. The initial sections of the review present the physiological and pathophysiological roles of these endogenous gas transmitters and their synergistic interactions. Further, various detection approaches, especially the usage of fascinating features of 1,8-naphthalimide as fluorescent probe in the detection and monitoring of these small signaling molecules are highlighted. The current limitations and the future scope of improving the sensing of the three gasotransmitters are also discussed.

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.

Chemically fueled materials with a self-immolative mechanism: transient materials with a fast on/off response

There is an increasing demand for transient materials with a predefined lifetime like self-erasing temporary electronic circuits or transient biomedical implants. Chemically fueled materials are an example of such materials; they emerge in response to chemical fuel, and autonomously decay as they deplete it. However, these materials suffer from a slow, typically first order decay profile. That means that over the course of the material's lifetime, its properties continuously change until it is fully decayed. Materials that have a sharp on-off response are self-immolative ones. These degrade rapidly after an external trigger through a self-amplifying decay mechanism. However, self-immolative materials are not autonomous; they require a trigger. We introduce here materials with the best of both, i.e., materials based on chemically fueled emulsions that are also self-immolative. The material has a lifetime that can be predefined, after which it autonomously and rapidly degrades. We showcase the new material class with self-expiring labels and drug-delivery platforms with a controllable burst-release.

New Protocol-Guided Exploitation of a Lysosomal Sulfatase Inhibitor to Suppress Cell Growth in Glioblastoma Multiforme

Glioblastoma multiforme (GBM) is a highly invasive and aggressive malignant glioma. Current treatment modalities are unable to significantly prolong survival in patients diagnosed with glioblastoma, so more effective strategies of antitumor treatments are in urgent demand. Here, we found that lysosomal sulfatase expression was significantly correlated with poor prognosis of GBM. Hence, a new probe, MNG, was developed with a new protocol utilizing glucose groups to detect lysosomal sulfatase. It also exhibits potential for monitoring GBM cells, depending on the hyperactive lysosomal sulfatase expression of tumor cells. Meantime, we identified that sulbactam as the first reported lysosomal sulfatase inhibitor inhibits the tumor growth of GBM. Collectively, our work highlights that lysosomal sulfatase was detected using a new protocol and its potential as a therapeutic target in GBM and reveals a distinct mechanism that sulbactam inhibits cell proliferation related to lysosomal sulfatase, indicating that sulbactam could be a promising therapeutic agent against GBM.

Construct a lysosome-targeting and highly selective fluorescent probe for imaging of hydrogen sulfide in living cells and inflamed tissues

Since the fluctuation of cellular hydrogen sulfide (H₂S) is a very important third endogenously generated gaseous signaling molecule and plays a key role in the development of numerous human disorders, the real-time fluorescence detection of H₂S in living systems has attracted plenty of interest during past decade. Although a lot of H₂S fluorescent probes have been reported, the relationship between the physiology and pathology of H₂S in organelles remains unclear, especially for inflammatory tissue. In this work, by adopting a weakly basic morpholine group as the lysosome-targeting site, a naphthalimide derivative as the signal reporter group and a 4-dinitrobenzene-ether (DNB) as fluorescence signal quencher and H₂S-selective recognition moiety, we reported a new lysosome-targeting TP fluorescent probe LyNP-H₂S for H₂S detection and imaging in living cells and inflamed tissues. The probe LyNP-H₂S exhibits very low fluorescence signal in the absence of H₂S, and displays a significant 262-fold fluorescence intensity enhancement in the presence of H₂S at 540 nm. Moreover, LyNP-H₂S has the capability of quantitative detection of H₂S at concentrations ranging from 0 to 12.0 μM (limit of detection = 9.8 nM), rapid response, as well as high sensitivity and selectivity toward H₂S. Impressively, the results of living cell and inflamed tissues imaging test demonstrate that LyNP-H₂S has the potentiality of being an ideal probe for real-time H₂S detection in biosystems.

Biocompatible fluorescent probe for detecting mitochondrial alkaline phosphatase activity in live cells

Alkaline phosphatase (ALP) is an enzyme that actively plays a significant role in the various metabolic processes by transferring a phosphate group to the protein, nucleic acid, etc. The elevated level of ALP in blood plasma is the hallmark of inflammation/cancer. The hyperactive mitochondria in cancer cells produce an excess of ATP to fulfill the high energy demand. Thus, we have developed a fluorescent probe Mito-Phos for ALP, which can detect phosphatase expression in mitochondria in live cells. The probe Mito-Phos has shown ~15-fold fluorescence intensity increments at 450 nm in the presence of 500 ng/mL of ALP. It takes about 60 min to consume the whole amount of ALP (500 ng/mL) in physiological buffer saline. It can selectively react with ALP even in the presence of other probable cellular reactive components. It is highly biocompatible and nontoxic to the live cells. It has shown ALP expression in a dose-dependent manner by providing concomitant fluorescence images in the blue-channel region. It has localized exclusively in the mitochondria in live cells. The probe Mito-Phos is highly biocompatible with the ability to assess ALP expression in mitochondria in live cells.

An effective biocompatible fluorescent probe for bisulfite detection in aqueous solution, living cells, and mice

Sulfur dioxide, an air pollutant, is easily hydrated to sulfites and bisulfites and extremely harmful to human health. On the other hand, endogenous sulfur dioxide is the fourth gasotransmitter. In view of the above, it is worth developing an effective method for the detection of these compounds. In this paper, a novel colorimetric fluorescent probe (Hcy-Mo), based on hemi-cyanine, for bisulfites is reported. Hcy-Mo shows excellent selectivity for bisulfites over various other species including cysteine, glutathione, CN⁻, and HS⁻, and undergoes 1,4-addition reactions at the C-4 atom of the ethylene group. The reaction can be completed in 30 s in a PBS buffer solution and displays high sensitivity (limit of detection is 80 nM) for bisulfites. Test paper experiments show that the probe can be used for bisulfite detection in aqueous solutions. In addition, Hcy-Mo exhibits excellent cell permeability and low cytotoxicity for the successful detection of bisulfites in living MDA-MB-231 cells and in living mice, implying that this probe would be of great benefit to biological researchers for investigating the detailed biological and pharmacological functions of bisulfites in biological systems.

Sulfur dioxide, an air pollutant, is easily hydrated to sulfites and bisulfites and extremely harmful to human health.

A Lysosome-Targetable Fluorescent Probe for Simultaneously Sensing Cys/Hcy, GSH, and H2S from Different Signal Patterns

Biothiols, a vital branch of reactive sulfur species (RSS) family, are indispensable in human physiology. However, the exact functional roles of each biothiol involved in complicated physiological activities are still not fully clarified. A critical barrier is a lack of robust molecular tools which can simultaneously visualize different biothiols with distinct emission signals. Herein, the first lysosome-targetable fluorescent probe, Lyso-RC, which could respond to Cys/Hcy, GSH, and H₂S with different sets of signal patterns was developed. Lyso-RC responds to Cys/Hcy, GSH, and H₂S with the fluorescence signal patterns of blue-red, green-red, and red, respectively. Significantly, Lyso-RC is capable of discriminating lysosomal Cys/Hcy, GSH, and H₂S in HeLa cells.