Polydimethylsiloxane permeability-based method for the continuous and specific detection of hydrogen sulfide

Facile preparation of dihydrolipoic acid-stabilized red-emitting silver nanoclusters as a sensitive fluorometric probe for sulfide ions detection

In this work, we report a smartphone-integrated paper-based sensor for the determination of sulfide ions (S2-) using water-soluble dihydrolipoic acid stabilized silver nanoclusters (DHLA-AgNCs) as a nanoprobe. The optical properties of red emitting fluorescent DHLA-AgNCs was confirmed by UV-visible, steady state flourometric spectroscopic studies. The HR-TEM analysis revealed that the morphology of DHLA-AgNCs was quasi spherical with a grain size of ∼ 5.2 nm. The DHLA-AgNCs exhibited bright red luminescence with strong emission band centered at 650 nm upon the excitation at 420 nm. The excellent fluorescence property of DHLA-AgNCs was further utilized for fluorometric determination of S2- ions. The DHLA-AgNCs can be effectively quenched by increasing concentration of S2- ions owing to the formation of Ag2S complex. The DHLA-AgNCs probe could detect S2- ions preferentially even in the presence of other possible interfering anions with a limit of detection of 32.71 nM. In addition, the proposed technique was effectively used to detect S2- ions in environmental water samples such as tap and drinking water. The detect S2- ions detection was assay and showed good agree compared with the conventional methylene blue approach and showed comparable results. Moreover, a smartphone-paper-based detection assay was developed using the DHLA-AgNCs probe for highly selective and sensitive determination of S2- ions.

A Metal-Phenolic Nanosensitizer Performs Hydrogen Sulfide-Reprogrammed Oxygen Metabolism for Cancer Radiotherapy Intensification and Immunogenicity

Radiotherapy (RT) is hampered by the limited oxygen in tumors, which could be potentiated via reprogramming the oxygen metabolism and increasing the oxygen utilization efficiency. Herein, a metal-phenolic nanosensitizer (Hf-PSP-DTC@PLX) was integrated via an acid-sensitive hydrogen sulfide (H₂ S) donor (polyethylene glycol-co-polydithiocarbamates, PEG-DTC) and a hafnium-chelated polyphenolic semiconducting polymer (Hf-PSP) in an amphiphilic polymer (poloxamer F127, PLX). Hf-PSP-DTC@PLX elicited a high imaging performance for precise RT and generated H₂ S to reduce the cellular oxygen consumption rate via mitochondrial respiration inhibition, which reprogrammed the oxygen metabolism for improvement of the tumor oxygenation. Then, Hf-sensitization could fully utilize the well-preserved oxygen to intensify RT efficacy and activate immunogenicity. Such a synergistic strategy for improvement of oxygenation and oxygen utilization would have great potential in optimizing oxygen-dependent therapeutics.

Fluorescein isothiocyanate, a platform for the selective and sensitive detection of S-Nitrosothiols and hydrogen sulfide

Here we show that the fluorescence of fluorescein isothiocyanate (FITC) is not altered by its reaction with primary amines. However, the fluorescence is rapidly quenched upon reaction with small molecular weight thiols including cysteine, glutathione, homocysteine, dithiothreitol, and sulfide. We have taken advantage of the thiol-dependent quenching of FITC to devise a sulfide specific assay by utilizing polydimethylsiloxane (PDMS) membranes that are permeable to hydrogen sulfide but not to larger charged thiols. In addition, we have discovered that the fluorescein dithiocarbamate (FDTC) formed by the reaction with sulfide can specifically react with S-nitrosothiols (RSNO) to regenerate FITC, thus serving as a specific, fluorogenic reagent to detect picomol levels of RSNO. FDTC was tested as an intracellular RSNO-sensor in germinating tomato seedlings (Solanum lycopersicum) via epifluorescence microscopy. Control plant roots exposed to FDTC showed low intracellular fluorescence which increased ∼3-fold upon exposure to extracellular S-nitrosoglutathione and ∼4-fold in the presence of N6022, a S-nitrosoglutathione reductase (GSNOR) inhibitor, demonstrating that FDTC can be used to visualize intracellular RSNO levels.

Biosynthesis, Quantification and Genetic Diseases of the Smallest Signaling Thiol Metabolite: Hydrogen Sulfide

Hydrogen sulfide (H2S) is a gasotransmitter and the smallest signaling thiol metabolite with important roles in human health. The turnover of H2S in humans is mainly governed by enzymes of sulfur amino acid metabolism and also by the microbiome. As is the case with other small signaling molecules, disease-promoting effects of H2S largely depend on its concentration and compartmentalization. Genetic defects that impair the biogenesis and catabolism of H2S have been described; however, a gap in knowledge remains concerning physiological steady-state concentrations of H2S and their direct clinical implications. The small size and considerable reactivity of H2S renders its quantification in biological samples an experimental challenge. A compilation of methods currently employed to quantify H2S in biological specimens is provided in this review. Substantial discrepancy exists in the concentrations of H2S determined by different techniques. Available methodologies permit end-point measurement of H2S concentration, yet no definitive protocol exists for the continuous, real-time measurement of H2S produced by its enzymatic sources. We present a summary of available animal models, monogenic diseases that impair H2S metabolism in humans including structure-function relationships of pathogenic mutations, and discuss possible approaches to overcome current limitations of study.

A copper-based metal-organic framework for ratiometric detection of hydrogen sulfide with high sensitivity and fast response

Metal-organic framework (MOF) is a class of crystalline porous solid materials which could be designed as sensors for bioactive molecules. In this study, charge transition between the ligand and the metal ions related emission and the ligand-based emission were formed simultaneously within a novel luminescent MOF with the copper reactive site as nodes. It can serve as a rare example of MOFs implicated ratiometric sensor for selective luminescent detection of H₂S. The luminescent detection limitations for H₂S is 0.21 μM, and it possesses a fast response of 30 s. The sensing mechanism is also discussed.

(Gold triangular nanoplate core)@(silver shell) nanostructures as highly sensitive and selective plasmonic nanoprobes for hydrogen sulfide detection

Hydrogen sulfide plays a significant role in living beings, while its abnormal concentration is related to many diseases. Besides, H2S gas is harmful to human beings and the environment. The detection of H2S has therefore attracted much attention in the past several decades. Herein, highly sensitive and selective H2S plasmonic nanoprobes (gold triangular nanoplate core)@(silver shell) (AuTNP@Ag) are reported. By virtue of the high refractive index sensitivity of Au TNPs to the surrounding medium and facile sulfurization of silver by sulfur ions, AuTNP@Ag exhibits great sensitivity to both sulfur ions and H2S gas. The shifts of the plasmon peak are as large as 16 nm for the ventilation of 1 ppm hydrogen sulfide. AuTNP@Ag nanoprobes also exhibit very good sensing linearity at low concentrations of sulfur ions. Moreover, excellent sensing selectivity for sulfur ions is obtained. A type of test gel, which can produce a naked-eye observable color change when exposed to 1-100 ppm hydrogen sulfide gas, is developed using AuTNP@Ag nanoprobes. Owing to the high sensitivity, linearity, and selectivity of the Au TNP@Ag nanoprobes for hydrogen sulfide sensing, this work paves the way for the plasmonic detection of hydrogen sulfide in both biological and environmental applications.

Highly Selective and Sensitive Detection of Hydrogen Sulfide by the Diffraction Peak of Periodic Au Nanoparticle Array with Silver Coating

The two-dimensional (2D) periodic Au nanosphere array with silver coating was prepared by using a colloidal monolayer template to obtain a Au nanosphere array and subsequently depositing silver thin coating on it, which could be used as an optical sensor to effectively detect H₂S. Such periodic Au nanosphere array with silver coating displayed a surface plasmonic resonance (SPR) peak and an optical diffraction peak. Compared with the SPR peak, the diffraction peak, originated from the periodic arrangements of the obtained array, demonstrated a more sensitive optical change to detect H₂S with a significant redshift as the H₂S concentration increased. It was attributed to the increase of the refractive index of the environment around the Au nanosphere arrays with silver coating due to the partial formation of Ag₂S after detecting H₂S. Furthermore, the H₂S sensor based on the change of the optical diffraction peak, showed an excellent selectivity and it was very sensitive to detect H₂S from 2 to 30 μM. This method was investigated by the analysis in H₂S-spiked blood samples, which indicates that the method has the potential to detect H₂S in blood samples. The presented work provides a new strategy of utilizing the optical diffraction peak of the periodic array to develop promising sensors.

Copper ion modified graphitic C3N4 nanosheets enhanced luminol-H2O2 chemiluminescence system: Toward highly selective and sensitive bioassay of H2S in human plasma

A high-efficient chemiluminescence (CL) platform for highly selective and sensitive H₂S detection was constructed on the basis of the quenching effect of S^2- on the copper ion modified graphitic carbon nitride nanosheets (Cu²⁺-g-C₃N₄ NSs) enhanced luminol-H₂O₂ system. Cu²⁺-g-C₃N₄ NSs with horseradish peroxidase-like catalytic activity were prepared and provide a great improvement for luminol-H₂O₂ system. The presence of S^2- induced the formation of CuS precipitate on g-C₃N₄ NSs surface. The precipitate can block the catalytic Cu²⁺ sites on the g-C₃N₄ NSs surface, resulting in a great CL decrease of CL system. Based on such a mechanism, a simple, highly selective and sensitive CL biosensor for H₂S detection was designed. Under the optimized conditions, luminol-H₂O₂-Cu²⁺-g-C₃N₄ NSs system gave a decrease of CL intensity with the Na₂S concentration increasing. The CL biosensor is in a linear range of 10.0 pM-50.0 nM and the detection limit for detecting Na₂S is as low as 2.0 pM. Moreover, the method here has enjoyed a successful application for determining H₂S in human plasma samples and the recovery is between 95.7% and 110.0%.

A Review of Hydrogen Sulfide Synthesis, Metabolism, and Measurement: Is Modulation of Hydrogen Sulfide a Novel Therapeutic for Cancer?

Significance: Hydrogen sulfide (H2S) has been recognized as the third gaseous transmitter alongside nitric oxide and carbon monoxide. In the past decade, numerous studies have demonstrated an active role of H2S in the context of cancer biology. Recent Advances: The three H2S-producing enzymes, namely cystathionine γ-lyase (CSE), cystathionine β-synthase (CBS), and 3-mercaptopyruvate sulfurtransferase (3MST), have been found to be highly expressed in numerous types of cancer. Moreover, inhibition of CBS has shown anti-tumor activity, particularly in colon cancer, ovarian cancer, and breast cancer, whereas the consequence of CSE or 3MST inhibition remains largely unexplored in cancer cells. Intriguingly, H2S donation at high amounts or a long time duration has also been observed to induce cancer cell apoptosis in vitro and in vivo while sparing noncancerous fibroblast cells. Therefore, a bell-shaped model has been proposed to explain the role of H2S in cancer development. Specifically, endogenous H2S or a relatively low level of exogenous H2S may exhibit a pro-cancer effect, whereas exposure to H2S at a higher amount or for a long period may lead to cancer cell death. This indicates that inhibition of H2S biosynthesis and H2S supplementation serve as two distinct ways for cancer treatment. This paradoxical role of H2S has stimulated the enthusiasm for the development of novel CBS inhibitors, H2S donors, and H2S-releasing hybrids. Critical Issues: A clear relationship between H2S level and cancer progression remains lacking. The possibility that the altered levels of these byproducts have influenced the cell viability of cancer cells has not been excluded in previous studies when modulating H2S producing enzymes. Future Directions: The consequence of CSE or 3MST inhibition in cancer cells need to be examined in the future. Better portrayal of the crosstalk among these gaseous transmitters may not only lead to an in-depth understanding of cancer progression but also shed light on novel strategies for cancer therapy.

Generation of controllable gaseous H2S concentrations using microfluidics

Hydrogen sulfide (H₂S) plays an important role as an intercellular and intracellular signaling molecule, yet its targets are not well understood. As a molecule it easily evaporates and it is hard to acquire stable concentration for in vitro studies, constituting a major problem for the field to identify its downstream targets and function. Here we develop a microfluidic system that can provide consistent and controllable H₂S levels in contrast to the current method of delivering large bolus doses to cells. The system relies on the permeability of H₂S gas through a polydimethylsiloxane thin membrane. A hydrogen sulfide donor, sodium hydrosulfide, is perfused in the microchannels below the gas permeable membrane and gaseous H₂S diffuses across the membrane, providing a stable concentration for up to 5 hours. Using electrochemical sensors within 3 ppm range, we found that H₂S concentration was dependent on two parameters, the concentration of H₂S donor, sodium hydrosulfide and the flow rate of the solution in the microchannels. Additionally, different H₂S concentration profiles can be obtained by alternating the flow rate, providing an easy means to control the H₂S concentration. Our approach constitutes a unique method for H₂S delivery for in vitro and ex vivo studies and is ideally suited to identify novel biological processes and cellular mechanisms regulated by H₂S.

Living cell imaging and sensing of hydrogen sulfide using high-efficiency fluorescent Cu-doped carbon quantum dots

A simple Cu-doped carbon quantum dot-based fluorescent sensor for H₂S sensing and intracellular bioimaging was constructed.

Colorimetric detection of biological hydrogen sulfide using fluorosurfactant functionalized gold nanorods

As a well-known environmental pollutant but also an important gaseous transmitter, the specific detection of hydrogen sulfide (H2S) is significant in biological systems. In this study, fluorosurfactant functionalized gold nanorods (FSN-AuNRs) have been proposed to act as selective colorimetric nanoprobes for H2S. With the combination of strong gold-S interactions and small FSN bilayer interstices, FSN-AuNRs demonstrate favorable selectivity and sensitivity toward H2S over other anions and small biological molecules. The practical application of the present method in biological H2S detection was validated with human and mouse serum samples. Moreover, the proposed nanoprobe can also be used for evaluating the activity of H2S synthetase.

Chemiluminescent detection of enzymatically produced H2S

Hydrogen sulfide (H2S) has emerged as an important biological signaling molecule. To better understand the multifaceted biological roles of H2S, the development of selective and sensitive biocompatible assays for H2S is becoming increasingly important. Motivated by these challenges, our laboratory is developing new methods to further detect and monitor biological H2S. Here, we describe in detail our recent advances in the development and the use of chemiluminescence-based H2S sensors to assist other investigators with use of these chemical tools. We highlight the use of these tools use by displaying their selectivity and high sensitivity toward H2S and provide examples of assays we have developed to detect enzymatically produced H2S.

Highly sensitive and colorimetric detection of hydrogen sulphide by in situ formation of Ag2S@Ag nanoparticles in polyelectrolyte multilayer film

Ag ion reacted with H₂S gas in polyelectrolyte multilayer film to form Ag₂S nanoparticles that catalyze the formation of Ag NPs.

A highly selective fluorescent probe for sulfide ions based on aggregation of Cu nanocluster induced emission enhancement

S²⁻ ions can enhance the fluorescence of cysteine-capped Cu nanoclusters (Cu NCs) as a result of the S²⁻ ion-induced aggregation of the dispersed Cu NCs. In addition, a highly selective fluorescent probe was developed for the determination of H₂S from toys called “Fart Bomb”.

Chemiluminescent detection of enzymatically produced hydrogen sulfide: substrate hydrogen bonding influences selectivity for H2S over biological thiols

Hydrogen sulfide (H2S) is now recognized as an important biological regulator and signaling agent that is active in many physiological processes and diseases. Understanding the important roles of this emerging signaling molecule has remained challenging, in part due to the limited methods available for detecting endogenous H2S. Here we report two reaction-based ChemiLuminescent Sulfide Sensors, CLSS-1 and CLSS-2, with strong luminescence responses toward H2S (128- and 48-fold, respectively) and H2S detection limits (0.7 ± 0.3, 4.6 ± 2.0 μM, respectively) compatible with biological H2S levels. CLSS-2 is highly selective for H2S over other reactive sulfur, nitrogen, and oxygen species (RSONS) including GSH, Cys, Hcy, S2O3(2–), NO2(–), HNO, ONOO(–), and NO. Despite its similar chemical structure, CLSS-1 displays lower selectivity toward amino acid-derived thiols than CLSS-2. The origin of this differential selectivity was investigated using both computational DFT studies and NMR experiments. Our results suggest a model in which amino acid binding to the hydrazide moiety of the luminol-derived probes provides differential access to the reactive azide in CLSS-1 and CLSS-2, thus eroding the selectivity of CLSS-1 for H2S over Cys and GSH. On the basis of its high selectivity for H2S, we used CLSS-2 to detect enzymatically produced H2S from isolated cystathionine γ-lyase (CSE) enzymes (p < 0.001) and also from C6 cells expressing CSE (p < 0.001). CLSS-2 can readily differentiate between H2S production in active CSE and CSE inhibited with β-cyanoalanine (BCA) in both isolated CSE enzymes (p < 0.005) and in C6 cells (p < 0.005). In addition to providing a highly sensitive and selective reaction-based tool for chemiluminescent H2S detection and quantification, the insights into substrate–probe interactions controlling the selectivity for H2S over biologically relevant thiols may guide the design of other selective H2S detection scaffolds.

Hydrogen sulfide chemical biology: pathophysiological roles and detection

Hydrogen sulfide (H2S) is the most recent endogenous gasotransmitter that has been reported to serve many physiological and pathological functions in different tissues. Studies over the past decade have revealed that H2S can be synthesized through numerous pathways and its bioavailability regulated through its conversion into different biochemical forms. H2S exerts its biological effects in various manners including redox regulation of protein and small molecular weight thiols, polysulfides, thiosulfate/sulfite, iron-sulfur cluster proteins, and anti-oxidant properties that affect multiple cellular and molecular responses. However, precise measurement of H2S bioavailability and its associated biochemical and pathophysiological roles remains less well understood. In this review, we discuss recent understanding of H2S chemical biology, its relationship to tissue pathophysiological responses and possible therapeutic uses.