A ratiometric two-photon fluorescent probe for imaging hydrogen sulfide in lysosomes

Analysis of optical properties and response mechanism of H2S fluorescent probe based on rhodamine derivatives

H2S plays a crucial role in numerous physiological and pathological processes. In this project, a new fluorescent probe, SG-H2S, for the detection of H2S, was developed by introducing the recognition group 2,4-dinitrophenyl ether. The combination of rhodamine derivatives can produce both colorimetric reactions and fluorescence reactions. Compared with the current H2S probes, the main advantages of SG-H2S are its wide pH range (5-9), fast response (30 min), and high selectivity in competitive species (including biological mercaptan). The probe SG-H2S has low cytotoxicity and has been successfully applied to imaging in MCF-7 cells, HeLa cells, and BALB/c nude mice. We hope that SG-H2S will provide a vital method for the field of biology.

A novel iridium(III) complex-based ratiometric luminescence probe for monitoring hydrogen sulfide in living cells and zebrafish

Hydrogen sulfide exhibits crucial functions in many biological and physiological processes. The abnormal levels of H2S have been revealed to be associated with numerous human diseases. The majority of existing fluorescent probes toward H2S may still need to be improved in terms of single output signal, water solubility, biotoxicity and photostability. The construction of a ratiometric fluorescent probe based on metal complex is one effective strategy for avoiding the mentioned problems for precisely detecting H2S. Herein, we report an iridium(III) complex-based ratiometric luminescence probe (Ir-PNBD), which is designed by coupling the 7-nitro-2,1,3-benzoxadiazoles (NBD) to one of the bipyridine ligands of Ir (III) complex luminophore through a piperazition moiety. Ir-PNBD owns high selectivity and sensitivity toward H2S, and an excellent ability to target mitochondria. Moreover, Ir-PNBD was further successfully utilized to visualize exogenous and endogenous H2S in HeLa cells and zebrafish. Our work offers new opportunities to gain deeper insights into the construction of transition metal complex-based ratiometric luminescent probes and expands their applications in biomedical imaging and disease diagnosis.

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.

Lysosome-targeted fluorescent probes: Design mechanism and biological applications

As an integral organelle in the eukaryote, the lysosome is the degradation center and metabolic signal center in living cells, and partakes in significant physiological processes such as autophagy, cell death and cellular senescence. Fluorescent probe has become a favorite tool for studying organelles and their chemical microenvironments because of its high specificity and non-destructive merits. Over recent years, it has been reported that increasingly new lysosome-targeted probes play a major role in the diagnosis and monitor of diseases, in particular cancer and neurodegenerative diseases. In order to deepen the relevant research on lysosome, it is challenging and inevitability to design novel lysosomal targeting probes. This review first introduces the concepts of lysosome and its closely related biological activities, and then introduces the fluorescent probes for lysosome in detail according to different detection targets, including targeting mechanism, biological imaging, and application in diseases. Finally, we summarize the specific challenges and discuss the future development direction facing the current lysosome-targeted fluorescent probes. We hope that this review can help biologists grasp the application of fluorescent probes and broaden the research ideas of researchers targeting fluorescent probes so as to design more accurate and functional probes for application in diseases.

Sensitive Detection of Various Forms of Hydrogen Sulfide via Highly Selective Naphthalimide-Based Fluorescent Probe

Hydrogen sulfide (H2S) is an important gasotransmitter, but only a few methods are available for real-time detection. Fluorescent probes are attractive tools for biological applications because of their high sensitivity, convenience, rapid implementation, noninvasive monitoring capability, and simplicity in fluorescent imaging of living cells and tissues. Herein, we report on a pro-fluorescent probe, NAP-Py-N3 based on naphthalimide derivative, which was found to show high selectivity toward H2S over various other analytes, including biothiols, making it feasible to detect H2S. After reaction with H2S, this probe showed rapid and significant turn-on green fluorescent enhancement at 553 nm (about 54-fold, k2 = 9.62 M-1s-1), high sensitivity (LOD: 15.5 nM), significant Stokes shift (118 nm), and it was found that the fluorescence quantum yield of fluorescence product can reach 0.36. Moreover, the probe has also been successfully applied to detect the gaseous H2S and to confirm the presence of H2S released from modern organic donors, which in recent years have been commonly used to investigate the role of H2S in biological systems. All the results indicate that this probe is excellent and highly valuable.

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 single dual-targeting fluorescent probe enables exploration of the correlation between the plasma membrane and lysosomes

The interactions between organelles can maintain normal cell activity. Lysosomes, as waste disposal systems of cells, have many important interactions with the plasma membrane, especially in the repair of cracked plasma membrane. Unfortunately, a way to study the relationship between them synchronously is still lacking. Therefore, in this work, we constructed a dual-targeting probe (Mem-Lyso) to simultaneously visualize the plasma membrane and lysosomes for the first time. Taking advantage of dual-targeting, the probe Mem-Lyso could successfully track and analyze the dynamic changes of the plasma membrane and lysosomes in different bioprocesses. The experimental results demonstrated that, compared to the normal status, there was obvious fusion between the plasma membrane and lysosomes in the apoptosis process. Furthermore, because of the sensitivity to polarity, Mem-Lyso could label the plasma membrane and lysosomes with red and yellow colors in cells, respectively. Moreover, the skeleton and gastrointestinal wall of zebrafish were visualized by dual-color imaging, respectively. More importantly, the dual-targeting property endowed Mem-Lyso with the ability to spatially distinguish the cholesterol (CL) content in the plasma membrane, which provided a potential detection tool for biological research and diagnosis of related diseases.

Progress on the reaction-based methods for detection of endogenous hydrogen sulfide

Hydrogen sulfide (H₂S) is a biologically signaling molecule that mediates a wide range of physiological functions, which is frequently misregulated in numerous pathological processes. As such, measurement of H₂S holds great attention due to its unique physiological and pathophysiological roles. Currently, a variety of methods based on the H₂S-involved reactions have been reported for detection of endogenous H₂S, bearing the advantages of good specificity and high sensitivity. This review describes in detail the types of reactions, their mechanisms, and their applications in biological research, thus hopefully providing some guidelines to the researchers in this field for further investigation.

A highly selective and sensitive fluorescent probe based on the chromone fluorophore for imaging hydrogen sulfide in living cells

A fluorescent probe that was designed based on the 6-amino chromone fluorophore for detecting H₂S can distinguish H₂S from Cys/GSH under acidic conditions.

Tuning the π-bridge of quadrupolar triarylborane chromophores for one- and two-photon excited fluorescence imaging of lysosomes in live cells

A series of tetracationic quadrupolar chromophores containing three-coordinate boron π-acceptors linked by different π-bridges, namely 4,4'-biphenyl, 2,7-pyrene, 2,7-fluorene, 3,6-carbazole and 5,5'-di(thien-2-yl)-3,6-diketopyrrolopyrrole, were synthesized. While their neutral precursors 1-5 displayed highly solvatochromic fluorescence, the water-soluble tetracationic target molecules 1M-5M, did not, but their emission colour could be tuned from blue to pink by changing the π-bridge. Compound 5M, containing the diketopyrrolopyrrole bridge, exhibits the most red-shifted absorption and emission maxima and the largest two-photon absorption cross-section (4560 GM at 740 nm in MeCN). Confocal laser scanning fluorescence microscopy studies in live cells confirm localization of the dye at the lysosome. Moreover, the low cytotoxicity, and high photostability of 5M combined with two-photon excited fluorescence imaging studies demonstrate its excellent potential for lysosomal imaging in live cells.

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.

Lysosome-targeted two-photon fluorescent probes for rapid detection of H2S in live cells

Two novel two-photon fluorescent probes (BHNP-DA and M2) were designed and synthesized and show good selectivity and high sensitivity to H₂S.

Facile, rapid one-pot synthesis of multifunctional gold nanoclusters for cell imaging, hydrogen sulfide detection and pH sensing

In this study, we have developed a facile, rapid one-pot strategy for synthesis of orange fluorescent gold nanoclusters (MBISA-AuNCs) at room temperature by using 2-Mercapto-5-benzimidazolesulfonic acid (MBISA) as both reducing and protecting reagent. The prepared AuNCs exhibited prominent advantages including high fluorescent quantum yield, good water solubility, excellent biocompatibility and low toxicity. Based on these superior properties, the AuNCs have been multi-talented applied in cell imaging, hydrogen sulfide detection and pH sensing. Confocal fluorescence imaging showed that the MBISA-AuNCs could enter living cells and distribute in the cytoplasm. Additionally, the obtained AuNCs could visualize H₂S fluctuations in living cells without interference of autofluorescence based on their high sensitivity and selectivity detection for H₂S with a linear range of 2.7 × 10^-11-8.5 × 10^-4 M and a detection limit of 0.024 nM. Most strikingly, the AuNCs exhibited strong pH dependent behavior and responded linearly, rapidly and reversibly to minor pH fluctuations within the range of 2.01-12.00. Therefore, the AuNCs could also image pH fluctuations in live cells with negligible autofluorescence and provided a new method of analysis to visualize monitoring wide pH range change in live cells.

A naphthalene-based fluorescent probe for ratiometric imaging of lysosomal hydrogen sulfide in living cells

Hydrogen sulfide is an important gasotransmitter that exhibits various functions in physiological processes. We present a ratiometric fluorescence probe (SN-N₃) for H₂S by functionalizing naphthalene imide with 4-(azidomethyl)benzene as a H₂S recognition moiety and morpholine moiety as a lysosomal targeting unit. After reaction with H₂S, the azido moiety is reduced to amine group, and the probe releases the self-immolative linker and regenerates the fluorophore with internal charge transfer effect. SN-N₃ is responsive to H₂S in a ratiometric mode, exhibiting excellent sensitivity and high selectivity. The probe is demonstrated to be localized in lysosomes with high specificity. More importantly, SN-N₃ is successfully demonstrated to image lysosomal H₂S in a ratiometric manner. Our design provides a novel tool to image H₂S in living cells that would hold great potential in exploring various H₂S-related physiological and pathological cellular processes.

Theoretical design and investigation of 1,8-naphthalimide-based two-photon fluorescent probes for detecting cytochrome P450 1A with separated fluorescence signal

Two-photon fluorescent probe for detecting CYP1A enzyme with separated fluorescence signal.

Selective visualization of endogenous hydrogen sulfide in lysosomes using aggregation induced emission dots

The AIE dots (AIED) with superior sensor properties have been developed for selective imaging of lysosomal H₂S in living cells.