Microplate-Based Colorimetric Detection of Free Hydrogen Sulfide

A portable/miniaturized analytical kit for on-site analysis: Chemical vapor generation-visual colorimetric and smartphone RGB dual-mode for detection of sulfide ion in water and food additives

Chemical vapor generation (CVG) was used as a gaseous sample introduction technique for the visual/smartphone RGB readout colorimetric system, with the advantages of efficient matrix elimination and high vapor generation efficiency, this analytical system exhibits a good selectivity and sensitivity. Sulfide ion (S2-) in solution was transformed to its volatile form (H2S), the generated H2S reacted with a silver-containing metal organic framework (Ag-BTC) selectively, Ag2S was thus generated. Ag-BTC (fabricated on paper sheet) changed from white to dark brown, the color variance was identified by smartphone and naked-eye simultaneously. Under the optimized conditions, a limit of detection of 0.02 μg/mL was obtained by naked-eye. Several water samples and commercial food additives were analyzed for confirming its accuracy and potential application for on-site detection, recoveries ranging 94-110 % were obtained. To meet the demand of on-site analysis of S2-, this colorimetric system was integrated in a portable/miniaturized analytical kit. It is an easy-used, affordable and portable analytical kit for S2- detection in field.

A novel fluorescent probe with a phosphofluorene molecular structure for selective detection of hydrogen sulfide in living cells

Hydrogen sulfide (H2S) gas plays a significant role in biological regulation. With advancements in technology, H2S has been discovered across diverse fields, necessitating a comprehensive understanding of its physiological functions through monitoring changes in H2S within complex environments and physiological processes. In this study, we designed a phosphofluorene-based conjugate probe PPF-CDNB with an asymmetric π-conjugated phosphine structure and utilized dinitrophenyl ether as the recognition site for H2S. PPF-CDNB exhibited exceptional resistance to interference and demonstrated stability over a broad pH range (3.0-10.0), making it suitable for various environmental conditions. Intracellular experiments revealed that PPF-CDNB effectively monitored both endogenous and exogenous levels of H2S.

Responsive luminescent silver-based metal-organic frameworks for highly sensitive and selective detection of hydrogen sulfide in biological system via a self-assembled headspace separation device

As a highly toxic gas pollutant and also an endogenous gaseous signaling molecule existing in a variety of physiological processes, the rapid and accurate in-field detection of hydrogen sulfide is of great concern. Nevertheless, two drawbacks as for the optical probes for H2S detection, taking about a long time to reach the optical signal balance or the low selectivity, always exist. Herein, by using a highly photoluminescent and H2S-stimuli responsive silver-based metal-organic frameworks (MOFs): Ag-BDC (BDC = 1, 4-benzene dicarboxylate), we demonstrated that the luminescence intensity of Ag-BDC MOFs was inversely proportional to the concentration of H2S due to the Ag-S coordination and the obstruction of ligand-to-metal charge transfer (LMCT) transition process, and there was a quick response time of below 3.0 min. Combined with a simple customized device to separate H2S from the sample, the selectivity of the method for H2S detection could be greatly improved, and no interference would be caused even if the other sulfur-containing species coexisted. The luminescence probe presented a favorable sensitivity within a linear range of 0.1-1000 μM along with a detection limit of 23.7 nM. When employed to assay the endogenous sulfide level in the human serum and mouse brain tissue, the approach showed recoveries from 96.3% to 102% with relative standard derivation (RSD) less than 2.0%. By the integration of the responsive luminescent silver-based MOFs with a simple self-assembled headspace separation device, obviously the present strategy could be beneficial to the development and design of the in-field fast H2S measurement, possessing particular advantages in biological systems to eliminate the potential interferences.

BSA-assisted ultrasound synthesis of water stable CsPbBr3 nanocrystals for sensitive fluorescent detection of hydrogen sulfide in human serum

A bovine serum albumin (BSA)-assisted ultrasonication strategy was developed for the synthesis of CsPbBr₃ nanocrystals (NCs) with stable fluorescence properties in aqueous solution. Such a preparation method is simple, fast and does not require complex equipment. The results show that the synthesized CsPbBr₃ NCs are homogeneous in particle size and have good solubility and stability in water. The CsPbBr₃ NCs have been utilized as fluorescence probe for rapid detection of hydrogen sulfide (H₂S) in human serum. The reaction of H₂S with the lead sites on the surface of CsPbBr₃ NCs produces lead sulfide (PbS), resulting in the decrease of fluorometric intensity of CsPbBr₃ NCs. Our designed fluorescent assay has a linear S^2- detecting range of 10 ~ 800 nM with a detection limit of 7.05 nM. The assay was used to determine H₂S in human serum with spiked recoveries ranging from 94.98% to 102.69%. This work opens new avenues for the application of halide lead perovskite in different biosensing areas.

Pineapple-Leaf-Derived, Copper-PAN-Modified Regenerated Cellulose Sheet Used as a Hydrogen Sulfide Indicator

Regenerated cellulose (RC) produced from waste pineapple leaves was used to develop a colorimetric sensor as a Cu-PAN sheet (RCS). Microcrystalline cellulose derived from dried pineapple leaves was combined with Cu-PAN, dissolved in NaOH and urea, and made into an RC sheet using Na₂SO₄ as a coagulant. The RCS was used as an H₂S indicator at various H₂S concentrations (0-50 ppm) and temperatures (5-25 °C). The RCS color changed from purple to New York pink when exposed to H₂S. A colorimeter method was used to develop prediction curves with values of R² > 0.95 for H₂S concentrations at 5-25 °C. The physicochemical properties of fresh and spent RCS were characterized using various techniques (Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy/energy-dispersive X-ray spectroscopy, and thermogravimetric analysis). In addition, when stored at 5 and 25 °C for 90 days, the RCS had outstanding stability. The developed RCS could be applied to food packaging as an intelligent indicator of meat spoilage.

Review of Chemical Sensors for Hydrogen Sulfide Detection in Organisms and Living Cells

As the third gasotransmitter, hydrogen sulfide (H₂S) is involved in a variety of physiological and pathological processes wherein abnormal levels of H₂S indicate various diseases. Therefore, an efficient and reliable monitoring of H₂S concentration in organisms and living cells is of great significance. Of diverse detection technologies, electrochemical sensors possess the unique advantages of miniaturization, fast detection, and high sensitivity, while the fluorescent and colorimetric ones exhibit exclusive visualization. All these chemical sensors are expected to be leveraged for H₂S detection in organisms and living cells, thus offering promising options for wearable devices. In this paper, the chemical sensors used to detect H₂S in the last 10 years are reviewed based on the different properties (metal affinity, reducibility, and nucleophilicity) of H₂S, simultaneously summarizing the detection materials, methods, linear range, detection limits, selectivity, etc. Meanwhile, the existing problems of such sensors and possible solutions are put forward. This review indicates that these types of chemical sensors competently serve as specific, accurate, highly selective, and sensitive sensor platforms for H₂S detection in organisms and living cells.

Parts-per-billion-level detection of hydrogen sulfide based on doubly resonant photoacoustic spectroscopy with line-locking

We report on the development of a highly sensitive hydrogen sulfide (H₂S) gas sensor exploiting the doubly resonant photoacoustic spectroscopy technique and using a near-infrared laser emitting at 1578.128 nm. By targeting the R(4) transition of H₂S, we achieved a minimum detection limit of 10 part per billion in concentration and a normalized noise equivalent absorption coefficient of 8.9 × 10^-12 W cm^-1 Hz^-1/2. A laser-cavity-molecule locking strategy is proposed to enhance the sensor stability for fast measurement when dealing with external disturbances. A comparison among the state-of-the-art H₂S sensors using various spectroscopic techniques confirmed the record sensitivity achieved in this work.

GLAD Based Advanced Nanostructures for Diversified Biosensing Applications: Recent Progress

Glancing angle deposition (GLAD) is a technique for the fabrication of sculpted micro- and nanostructures under the conditions of oblique vapor flux incident and limited adatom diffusion. GLAD-based nanostructures are emerging platforms with broad sensing applications due to their high sensitivity, enhanced optical and catalytic properties, periodicity, and controlled morphology. GLAD-fabricated nanochips and substrates for chemical and biosensing applications are replacing conventionally used nanomaterials due to their broad scope, ease of fabrication, controlled growth parameters, and hence, sensing abilities. This review focuses on recent advances in the diverse nanostructures fabricated via GLAD and their applications in the biomedical field. The effects of morphology and deposition conditions on GLAD structures, their biosensing capability, and the use of these nanostructures for various biosensing applications such as surface plasmon resonance (SPR), fluorescence, surface-enhanced Raman spectroscopy (SERS), and colorimetric- and wettability-based bio-detection will be discussed in detail. GLAD has also found diverse applications in the case of molecular imaging techniques such as fluorescence, super-resolution, and photoacoustic imaging. In addition, some in vivo applications, such as drug delivery, have been discussed. Furthermore, we will also provide an overview of the status of GLAD technology as well as future challenges associated with GLAD-based nanostructures in the mentioned areas.

Polydopamine-Coated Co3O4 Nanoparticles as an Efficient Catalase Mimic for Fluorescent Detection of Sulfide Ion

Surface engineering of nanozymes has been recognized as a potent strategy to improve their catalytic activity and specificity. We synthesized polydopamine-coated Co₃O₄ nanoparticles (PDA@Co₃O₄ NPs) through simple dopamine-induced self-assembly and demonstrated that these NPs exhibit catalase-like activity by decomposing H₂O₂ into oxygen and water. The activity of PDA@Co₃O₄ NPs was approximately fourfold higher than that of Co₃O₄ NPs without PDA, possibly due to the additional radical scavenging activity of the PDA shell. In addition, PDA@Co₃O₄ NPs were more stable than natural catalase under a wide range of pH, temperature, and storage time conditions. Upon the addition of a sample containing sulfide ion, the activity of PDA@Co₃O₄ NPs was significantly inhibited, possibly because of increased mass transfer limitations via the absorption of the sulfide ion on the PDA@Co₃O₄ NP surface, along with NP aggregation which reduced their surface area. The reduced catalase-like activity was used to determine the levels of sulfide ion by measuring the increased fluorescence of the oxidized terephthalic acid, generated from the added H₂O₂. Using this strategy, the target sulfide ion was sensitively determined to a lower limit of 4.3 µM and dynamic linear range of up to 200 µM. The fluorescence-based sulfide ion assay based on PDA@Co₃O₄ NPs was highly precise when applied to real tap water samples, validating its potential for conveniently monitoring toxic elements in the environment.

Hydrogen sulfide poisoning in forensic pathology and toxicology: mechanism and metabolites quantification analysis

Historically, hydrogen sulfide (H₂S) poisoning has extremely high and irreparable mortality. Currently, the identification of H₂S poisoning needs to combine with the case scene analysis in forensic medicine. The anatomy of the deceased seldom had obvious features. There are also a few reports about H₂S poisoning in detail. As a result, we give a comprehensive analysis of the related knowledge on the forensic aspect of H₂S poisoning. Furthermore, we provide the analytical methods of H₂S and its metabolite-which may assist in H₂S poisoning identification.

Physiological roles of hydrogen sulfide in mammalian cells, tissues and organs

H2S belongs to the class of molecules known as gasotransmitters, which also includes nitric oxide (NO) and carbon monoxide (CO). Three enzymes are recognized as endogenous sources of H2S in various cells and tissues: cystathionine g-lyase (CSE), cystathionine β-synthase (CBS) and 3-mercaptopyruvate sulfurtransferase (3-MST). The current article reviews the regulation of these enzymes as well as the pathways of their enzymatic and non-enzymatic degradation and elimination. The multiple interactions of H2S with other labile endogenous molecules (e.g. NO) and reactive oxygen species are also outlined. The various biological targets and signaling pathways are discussed, with special reference to H2S and oxidative posttranscriptional modification of proteins, the effect of H2S on channels and intracellular second messenger pathways, the regulation of gene transcription and translation and the regulation of cellular bioenergetics and metabolism. The pharmacological and molecular tools currently available to study H2S physiology are also reviewed, including their utility and limitations. In subsequent sections, the role of H2S in the regulation of various physiological and cellular functions is reviewed. The physiological role of H2S in various cell types and organ systems are overviewed. Finally, the role of H2S in the regulation of various organ functions is discussed as well as the characteristic bell-shaped biphasic effects of H2S. In addition, key pathophysiological aspects, debated areas, and future research and translational areas are identified A wide array of significant roles of H2S in the physiological regulation of all organ functions emerges from this review.

Ultrafast and nanomolar level detection of H2S in aqueous medium using a functionalized UiO-66 metal-organic framework based fluorescent chemosensor

Here, we present a 4-nitrophenyl functionalized Zr-UiO-66 MOF (MOF = metal-organic framework) and its applications towards the selective, sensitive and rapid detection of H₂S both in the aqueous medium and vapour phase. The MOF material was synthesized using the 2-(nitrophenoxy)terepththalic acid (H₂BDC-O-Ph-NO₂) linker and ZrCl₄ salt in the presence of a benzoic acid modulator. It was carefully characterized by thermogravimetric analysis (TGA), elemental analysis, powder X-ray diffraction (PXRD), FT-IR spectroscopy and surface area analysis. Noticeable thermal stability up to a temperature of 390 °C under air and the considerable chemical stability in different liquid media (H₂O, 1 M HCl, glacial acetic acid, NaOH in the pH = 8 to 10 range) confirmed the robustness of the MOF. The BET surface area (1040 m² g^-1) indicated the porous nature of the MOF. Remarkable selectivity of the MOF towards H₂S over other potential congeners of H₂S was observed in the aqueous medium. A very high fluorescence increment (∼77 fold) was observed after adding an aqueous Na₂S solution to the MOF suspension. The MOF probe displayed the lowest limit of detection (12.58 nM) among the existing MOF-based chemosensors of H₂S. Furthermore, it exhibited a very quick (60 s) response towards H₂S detection. The MOF compound could also detect H₂S in the vapour phase as well as in real water samples. Furthermore, we developed inexpensive MOF-coated paper strips for the naked-eye sensing of H₂S. A thorough investigation was carried out in order to elucidate the fluorescence turn-on sensing mechanism.

Novel Fenton process of Co-catalyst Co9S8 quantum dots for highly efficient removal of organic pollutants

Advanced oxidation processes (AOPs) have been widely accepted as an efficient and promising strategy for treating organic pollutants, is mainly dominated by hydroxyl radicals (•OH); however, its further practical application has been hindered by its low decomposition rate of H₂O₂. Hence, for the first time, we propose an eco-friendly and facile synthesis methodology synthesize water-soluble Co₉S₈ quantum dots (QDs) derived from commercial cobalt disulfide (CoS₂), which can serve as excellent co-catalysts to dramatically enhance the decomposition rate of H₂O₂. It is demonstrated that the conversion rate of H₂O₂ into •OH is ca. 80.02% promoted by Co₉S₈ QDs, whereas the conventional Fenton process is ca. 34.9%. The result shows that unsaturated edged S atoms on the surface of Co₉S₈ play a pivotal role in this enhancement, where the number of protons will react with sulfur atoms to form H₂S and expose reductive metallic active sites to accelerate the Fe³⁺/Fe²⁺ conversion. In addition, to tackle the issue for difficult recovery of liquid quantum dots, the magnetic Co₉S₈ QDs/Fe₃O₄ nanoparticles are particularly synthesized, which show excellent performance for degradation of 20 mg/L Rhodamine B (RhB). Moreover, the TOC degradation rate can remain stable at 80% even after five cycles. It is expected that this work will provide a new pathway of thinking in the Fenton process and impulse the usage of liquid quantum dots in practical AOPs application.

Electroactive Cu2O nanocubes engineered electrochemical sensor for H2S detection

An electrochemical sensor was proposed for the detection of hydrogen sulfide (H₂S) at room temperature, by using electroactive Cu₂O nanocubes (NCs) as an electrochemical beacon. Electroactive Cu₂O NCs were synthesized on the surface of reduced graphene oxide (rGO)/Fe₃O₄ nanosheets (NSs) due to the good electronic conductivity and well-responded magnetic responses. The fabricated rGO/Fe₃O₄/Cu₂O NSs not only showed electrochemical oxidization peak at -0.1 V from Cu₂O NCs, and could be served as sensitive electrochemical beacon for the simple modification on magnetic electrodes in the applications. The unique redox reaction between Cu₂O NCs and H₂S enabled the transformation of Cu₂O NCs to Cu₉S₈ NCs, resulting in decreased electroxidation responses at -0.1 V. The constructed electrochemical platform had a limit of detection (LOD) of 230 pM and a detection range of 500 pM-100 μM. The simple and cheap electrochemical sensor developed in this paper showed potential application for H₂S detection.

Color Changes in Ag Nanoparticle Aggregates Placed in Various Environments: Their Application to Air Monitoring

Fresh Ag nanoparticles (NPs) dispersed on a transparent SiO₂ exhibit an intense optical extinction band originating in localized surface plasmon resonance (LSPR) in the visible range. The intensity of the LSPR band weakened when the Ag NPs was stored in ambient air for two weeks. The rate of the weakening and the LSPR wavelength shift, corresponding to visual chromatic changes, strongly depended on the environment in which Ag NPs were set. The origin of a chromatic change was discussed along with both compositional and morphological changes. In one case, bluish coloring followed by a prompt discoloring was observed for Ag NPs placed near the ventilation fan in our laboratory, resulted from adsorption of large amounts of S and Cl on Ag NP surfaces as well as particle coarsening. Such color changes deduce the presence of significant amounts of S and Cl in the environment. In another case, a remarkable blue-shift of the LSPR band was observed for the Ag NPs stored in the desiccator made of stainless steel, originated in the formation of CN and/or HCN compounds and surface roughening. Their color changed from maroon to reddish, suggesting that such molecules were present inside the desiccator.

A Paper-Based Ultrasensitive Optical Sensor for the Selective Detection of H2S Vapors

A selective and inexpensive chemical paper-based sensor for the detection of gaseous H2S is presented. The triggering of the sensing mechanism is based on an arene-derivative dye which undergoes specific reactions in the presence of H2S, allowing for colorimetric analysis. The dye is embedded into a porous cellulose matrix. We passively exposed the paper strips to H2S generated in situ, while the absorbance was monitored via an optic fiber connected to a spectrophotometer. The kinetics of the emerging absorbance at 534 nm constitute the sensor response and maintain a very stable calibration signal in both concentration and time dimensions for quantitative applications. The time and concentration dependence of the calibration function allows the extraction of unusual analytical information that expands the potential comparability with other sensors in the literature, as the limit of detection admissible within a given exposure time. The use of this specific reaction ensures a very high selectivity against saturated vapors of primary interferents and typical volatile compounds, including alkanethiols. The specific performance of the proposed sensor was explicitly compared with other colorimetric alternatives, including standard lead acetate strips. Additionally, the use of a smartphone camera to follow the color change in the sensing reaction was also tested. With this straightforward method, also affordable for miniature photodiode devices, a limit of detection below the ppm scale was reached in both colorimetric approaches.

Emerging analytical tools for the detection of the third gasotransmitter H2S, a comprehensive review

BACKGROUND

Hydrogen sulfide (H2S) is currently considered among the endogenously produced gaseous molecules that exert various signaling effects in mammalian species. It is the third physiological gasotransmitter discovered so far after NO and CO. H2S was originally ranked among the toxic gases at elevated levels to humans. Currently, it is well-known that, in the cardiovascular system, H2S exerts several cardioprotective effects including vasodilation, antioxidant regulation, inhibition of inflammation, and activation of anti-apoptosis. With an increasing interest in monitoring H2S, the development of analysis methods should now follow.

AIM OF REVIEW

This review stages special emphasis on the several analytical technologies used for its determination including spectroscopic, chromatographic, and electrochemical methods. Advantages and limitations with regards to the application of each technique are highlighted with special emphasis on its employment for H2S in vivo measurement i.e., biofluids, tissues.

KEY SCIENTIFIC CONCEPTS AND IMPORTANT FINDINGS OF REVIEW

Fluorescence methods applied for H2S measurement offer an attractive non-invasive and promising approach in addition to its selectivity, however they cannot be considered as H2S-specific probes. On the other hand, colorimetric assays are among the most common methods used for in vitro H2S detection, albeit their employment in vivo H2S measurement has not yet been possible . Separation techniques such as gas or liquid chromatography offer higher selectivity compared to direct spectrophotometric or fluorescence methods especially for suitable for endpoint H2S measurements i.e. plasma or tissue samples. Despite all the developed analytical procedures used for H2S determination, the need for highly selective, much work should be devoted to resolve all the pitfalls of the current methods.

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.

Significant acceleration of Fe2+/ peroxydisulfate oxidation towards sulfisoxazole by addition of MoS2

Activation of peroxydisulfate (PDS) by Fe²⁺ has been considered as an effective activation method to generate reactive oxygen species (ROS). However, the process is limited for the low production yield of ROS owing to the inefficient Fe³⁺/Fe²⁺ cycle. Herein, we demonstrated that Fe²⁺/PDS system in the presence of molybdenum sulfide (MoS₂) was significantly efficient for the degradation of sulfisoxazole (SIX). As a co-catalyst in the Fe²⁺/PDS system, MoS₂ could greatly enhance the Fe³⁺/Fe²⁺ cycle by the exposed Mo⁴⁺ active sites, which could also improve the PDS decomposition efficiency. As a result, the degradation efficiency of SIX in the MoS₂/Fe²⁺/PDS system could reach to as high as 97.1% within 40 min, which was in distinct comparison with the 45.5% achieved by Fe²⁺/PDS system without MoS₂. Besides, effects of various reaction conditions on SIX degradation were also evaluated during the experiments, including the dosages of MoS₂, Fe²⁺, PDS and initial solution pH and the coexisting inorganic anions. In addition, both of sulfate radicals and hydroxyl radicals were identified as the dominant active species for SIX degradation by the radical scavenging experiments and verified by electron paramagnetic resonance (EPR). This study provides a promising idea for the degradation of organic contaminants in water treatment based on Fe²⁺/PDS process.

Gut microbiota and neuroinflammation in pathogenesis of hypertension: A potential role for hydrogen sulfide

Inflammation and gut dysbiosis are hallmarks of hypertension (HTN). Hydrogen sulfide (H2S) is an important freely diffusing molecule that modulates the function of neural, cardiovascular and immune systems, and circulating levels of H2S are reduced in animals and humans with HTN. While most research to date has focused on H₂S produced endogenously by the host, H2S is also produced by the gut bacteria and may affect the host homeostasis. Here, we review an association between neuroinflammation and gut dysbiosis in HTN, with special emphasis on a potential role of H2S in this interplay.

An accurate and portable colorimetric chemosensor for S2− detection via two complementary mechanisms

A chemosensor based on two complementary mechanisms of color mixing and the recovery of uncoordinated carboxyl groups has been developed, which makes S²⁻ detection in water more accurate.

Rapid measurement of hydrogen sulphide in human blood plasma using a microfluidic method

Hydrogen sulfide (H₂S) is emerging as an important gasotransmitter in both physiological and pathological states. Rapid measurement of H₂S remains a challenge. We report a microfluidic method for rapid measurement of sulphide in blood plasma using Dansyl-Azide, a fluorescence (FL) based probe. We have measured known quantities of externally added (exogenous) H₂S to both buffer and human blood plasma. Surprisingly, a decrease in FL intensity with increase in exogenous sulphide concentration in plasma was observed which is attributed to the interaction between the proteins and sulphide present in plasma underpinning our observation. The effects of mixing and incubation time, pH, and dilution of plasma on the FL intensity is studied which revealed that the FL assay required a mixing time of 2 min, incubation time of 5 min, a pH of 7.1 and performing the test within 10 min of sampling; these together constitute the optimal parameters at room temperature. A linear correlation (with R² ≥ 0.95) and an excellent match was obtained when a comparison was done between the proposed microfluidic and conventional spectrofluorometric methods for known concentrations of H₂S (range 0–100 µM). We have measured the baseline level of endogenous H₂S in healthy volunteers which was found to lie in the range of 70 μM – 125 μM. The proposed microfluidic device with DNS-Az probe enables rapid and accurate estimation of a key gasotransmitter H₂S in plasma in conditions closely mimicking real time clinical setting. The availability of this device as at the point of care, will help in understanding the role of H₂S in health and disease.

Novel Applications of Lead Acetate and Flow Cytometry Methods for Detection of Sulfur-Containing Molecules

Hydrogen sulfide (H₂S) is the most recently established gaseous vasodilator, enzymatically produced from cysteine metabolism, involved in a number of pathophysiological processes. However, its accurate detection in vivo is critical due to its volatility and tendency to form sulfane sulfur derivatives, thus limiting the data interpretation of its biological roles. We developed new applications of the simple and rapid method to measure H₂S release in cell culture systems, based on the lead acetate strip test. This test, previously prevalently used in microbiology, was compared with the agar trap method, applied, in parallel, on both cell cultures and cell-free samples. Sulfane sulfur represents the major species derived from intracellular H₂S. Various fluorescent probes are available for quantitation of H₂S derivatives intracellularly. We present here an alternative to the classic imaging method for sulfane sulfur evaluation, running on a flow cytometer, based on SSP4 probe labeling. Flow cytometry turned out to be more direct, fully quantitative and less time-consuming compared to microscopy and more precise with respect to the fluorescence multi-plate reader assay. The new application methods for H₂S determination appear to be fully suitable for the analysis of H₂S release and sulfane sulfur content in biological samples.

Molybdenum sulfide Co-catalytic Fenton reaction for rapid and efficient inactivation of Escherichia coli

As a typical advanced oxidation technology, the Fenton reaction has been employed for the disinfection, owing to the strong oxidizability of hydroxyl radicals (·OH). However, the conventional Fenton system always exhibits a low H₂O₂ decomposition efficiency, leading to a low production yield of ·OH, which makes the disinfection effect unsatisfactory. Herein, we develop a molybdenum sulfide (MoS₂) co-catalytic Fenton reaction for rapid and highly efficient inactivation of Escherichia coli K-12 (E. coli) and Staphylococcus aureus (S. aureus). As a co-catalyst in the Fe(II)/H₂O₂ Fenton system, MoS₂ can greatly facilitate the Fe(III)/Fe(II) cycle reaction by the exposed Mo⁴⁺ active sites, which significantly improves the H₂O₂ decomposition efficiency for the ·OH production. As a result, the MoS₂ co-catalytic Fenton system can reach up to 83.37% of inactivation rate of E. coli just in 1 min and 100% of inactivation rate within 30 min, which increased by 2.5 times than that of the conventional Fenton reaction. Furthermore, the ·OH as the primary reactive oxygen species (ROS) in MoS₂ co-catalytic Fenton reaction was measured and verified by electron paramagnetic resonance (EPR) and photoluminescence (PL). It is demonstrated an increased amount of ·OH generated from the decomposition of H₂O₂ in the presence of MoS₂, which is responsible for the rapid and efficient inactivation of E. coli and S. aureus. This study provides a new perspective for rapid and highly efficient inactivation of bacteria in environmental remediation.

Enhancement of H2O2 Decomposition by the Co-catalytic Effect of WS2 on the Fenton Reaction for the Synchronous Reduction of Cr(VI) and Remediation of Phenol

The greatest problem in the Fe(II)/H₂O₂ Fenton reaction is the low production of ·OH owing to the inefficient Fe(III)/Fe(II) cycle and the low decomposition efficiency of H₂O₂ (<30%). Herein, we report a new discovery regarding the significant co-catalytic effect of WS₂ on the decomposition of H₂O₂ in a photoassisted Fe(II)/H₂O₂ Fenton system. With the help of WS₂ co-catalytic effect, the H₂O₂ decomposition efficiency can be increased from 22.9% to 60.1%, such that minimal concentrations of H₂O₂ (0.4 mmol/L) and Fe²⁺ (0.14 mmol/L) are necessary for the standard Fenton reaction. Interestingly, the co-catalytic Fenton strategy can be applied to the simultaneous oxidation of phenol (10 mg/L) and reduction of Cr(VI) (40 mg/L), and the corresponding degradation and reduction rates can reach up to 80.9% and 90.9%, respectively, which are much higher than the conventional Fenton reaction (52.0% and 31.0%). We found that the expose reductive W⁴⁺ active sites on the surface of WS₂ can greatly accelerate the rate-limiting step of Fe³⁺/Fe²⁺ conversion, which plays the key role in the decomposition of H₂O₂ and the reduction of Cr(VI). Our discovery represents a breakthrough in the field of inorganic catalyzing AOPs and greatly advances the practical utility of this method for environmental applications.

A circular dichroism sensor for selective detection of Cd2+ and S2- based on the in-situ generation of chiral CdS quantum dots

We demonstrate an advance in the fabrication of circular dichroism (CD) sensors for detection of Cd²⁺ and S^2- based on chiral CdS quantum dots (QDs) generated by a facile in-situ reaction. The chiral quantum dots are generated in solutions composed of Cd²⁺, S^2-, cysteamine (CA) and L-penicillamine (L-PA), with the number of the generated particles limited by either the Cd²⁺ or S^2- concentration. We show that the magnitude of the CD signal produced by the QDs is linearly related to the initial concentration of Cd²⁺ and S^2-, with excellent selectivity over other ions. Our sensor functions over concentration ranges of 65-200μM and 7-125μM with detection limits of 59.7 and 1.6μM for Cd²⁺ and S^2-, respectively. The sensor is applied in real water samples with results comparing favorably with those obtained from ICP-OES (for Cd²⁺) and HPLC (for S^2-).

Colorimetric detection of endogenous hydrogen sulfide production in living cells

Hydrogen sulfide (H₂S) has received great attention as a third gaseous signal transmitter, following nitric oxide and carbon monoxide. In particular, H₂S plays an important role in the regulation of cancer cell biology. Therefore, the detection of endogenous H₂S concentrations within biological systems can be helpful to understand the role of gasotransmitters in pathophysiology. Although a simple and inexpensive method for the detection of H₂S has been developed, its direct and precise measurement in living cells remains a challenge. In this study, we introduced a simple, facile, and inexpensive colorimetric system for selective H₂S detection in living cells using a silver-embedded Nafion/polyvinylpyrrolidone (PVP) membrane. This membrane could be easily applied onto a polystyrene microplate cover. First, we optimized the composition of the coating membrane, such as the PVP/Nafion mixing ratio and AgNO₃ concentration, as well as the pH of the Na₂S (H₂S donor) solution and the reaction time. Next, the in vitro performance of a colorimetric detection assay utilizing the silver/Nafion/PVP membrane was evaluated utilizing a known concentration of Na₂S standard solution both at room temperature and at 37°C in a 5% CO₂ incubator. As a result, the sensitivity of the colorimetric assay for H₂S at 37°C in the incubator (0.0056Abs./μM Na₂S, R²=0.9948) was similar to that at room temperature (0.0055Abs./μM Na₂S, R²=0.9967). Moreover, these assays were less sensitive to interference from compounds such as glutathione, l-cysteine (Cys), and dithiothreitol than to the H₂S from Na₂S. This assay based on the silver/Nafion/PVP membrane also showed excellent reproducibility (2.8% RSD). Finally, we successfully measured the endogenous H₂S concentrations in live C6 glioma cells by s-(5'-adenosyl)-l-methionine stimulation with and without Cys and l-homocysteine, utilizing the silver/Nafion/PVP membrane. In summary, colorimetric assays using silver/Nafion/PVP-coated membranes can be simple, robust, and reliable tools for the detection of H₂S that can avoid the complicated and labor-intensive analytical approach used in conventional biology. In addition, we expect that this assay will demonstrate a powerful ability to study pathophysiological pathways that involve H₂S.

Endpoint or Kinetic Measurement of Hydrogen Sulfide Production Capacity in Tissue Extracts

Hydrogen sulfide (H₂S) gas is produced in cells and tissues via various enzymatic processes. H₂S is an important signaling molecule in numerous biological processes, and deficiencies in endogenous H₂S production are linked to cardiovascular and other health complications. Quantitation of steady-state H₂S levels is challenging due to volatility of the gas and the need for specialized equipment. However, the capacity of an organ or tissue extract to produce H₂S under optimized reaction conditions can be measured by a number of current assays that vary in sensitivity, specificity and throughput capacity. We developed a rapid, inexpensive, specific and relatively high-throughput method for quantitative detection of H₂S production capacity from biological tissues. H₂S released into the head space above a biological sample reacts with lead acetate to form lead sulfide, which is measured on a continuous basis using a plate reader or as an endpoint assay.

Target-induced nanocatalyst deactivation facilitated by core@shell nanostructures for signal-amplified headspace-colorimetric assay of dissolved hydrogen sulfide

Colorimetric assay platforms for dissolved hydrogen sulfide (H2S) have been developed for more than 100 years, but most still suffer from relatively low sensitivity. One promising route out of this predicament relies on the design of efficient signal amplification methods. Herein, we rationally designed an unprecedented H2S-induced deactivation of (gold core)@(ultrathin platinum shell) nanocatalysts (Au@TPt-NCs) as a highly efficient signal amplification method for ultrasensitive headspace-colorimetric assay of dissolved H2S. Upon target introduction, Au@TPt-NCs were deactivated to different degrees dependent on H2S levels, and the degrees could be indicated by using a Au@TPt-NCs-triggered catalytic system as a signal amplifier, thus paving a way for H2S sensing. The combination of experimental studies and density functional theory (DFT) studies revealed that the Au@TPt-NCs with only 2-monolayer equivalents of Pt (θPt = 2) were superior for H2S-induced nanocatalyst deactivation owing to their enhanced peroxidase-like catalytic activity and deactivation efficiency stemmed from the unique synergistic structural/electronic effects between Au nanocores and ultrathin Pt nanoshells. Importantly, our analytical results showed that the designed method was indeed highly sensitive for sensing H2S with a wide linear range of 10-100 nM, a slope of 0.013 in the regression equation, and a low detection limit of 7.5 nM. Also the selectivity, reproducibility, and precision were excellent. Furthermore, the method was validated for the analysis of H2S-spiked real samples, and the recovery in all cases was 91.6-106.7%. With the merits of high sensitivity and selectivity, simplification, low cost, and visual readout with the naked eye, the colorimetric method has the potential to be utilized as an effective detection kit for point-of-care testing.

Chemical probes for molecular imaging and detection of hydrogen sulfide and reactive sulfur species in biological systems

Hydrogen sulfide (H2S), a gaseous species produced by both bacteria and higher eukaryotic organisms, including mammalian vertebrates, has attracted attention in recent years for its contributions to human health and disease. H2S has been proposed as a cytoprotectant and gasotransmitter in many tissue types, including mediating vascular tone in blood vessels as well as neuromodulation in the brain. The molecular mechanisms dictating how H2S affects cellular signaling and other physiological events remain insufficiently understood. Furthermore, the involvement of H2S in metal-binding interactions and formation of related RSS such as sulfane sulfur may contribute to other distinct signaling pathways. Owing to its widespread biological roles and unique chemical properties, H2S is an appealing target for chemical biology approaches to elucidate its production, trafficking, and downstream function. In this context, reaction-based fluorescent probes offer a versatile set of screening tools to visualize H2S pools in living systems. Three main strategies used in molecular probe development for H2S detection include azide and nitro group reduction, nucleophilic attack, and CuS precipitation. Each of these approaches exploits the strong nucleophilicity and reducing potency of H2S to achieve selectivity over other biothiols. In addition, a variety of methods have been developed for the detection of other reactive sulfur species (RSS), including sulfite and bisulfite, as well as sulfane sulfur species and related modifications such as S-nitrosothiols. Access to this growing chemical toolbox of new molecular probes for H2S and related RSS sets the stage for applying these developing technologies to probe reactive sulfur biology in living systems.

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.

Optical analysis of biological hydrogen sulphide: an overview of recent advancements

In this review we provide an overview of recent advancements in optical analysis of biological hydrogen sulphide, with a focus on fluorescence and non-fluorescence optical strategies for sensing and imaging subcellular hydrogen sulphide in living biosystems.