A hydrogen sulfide sensing detector based on cholesterol-modified lipid perovskite, its preparation method and application

Abstract

This invention discloses a hydrogen sulfide sensor detector based on cholesterol-modified lipid perovskite, its preparation method, and its application, belonging to the field of biotechnology. This invention utilizes highly biocompatible phospholipids and cholesterol to construct a stable protective layer for hydrophobic perovskite nanoparticles, enabling them to emit light stably. This significantly improves the stability of the perovskite and provides an ideal platform for the accurate detection of hydrogen sulfide. The cholesterol-modified lipid perovskite hydrogen sulfide sensor detector provided by this invention significantly improves the detection limit and response speed of hydrogen sulfide, reduces the risk of false negatives, and provides an intuitive and visual detection method for hydrogen sulfide. With a detection limit as low as ng / mL, it helps to promote the development of gas sensing technology, improve the accuracy and efficiency of harmful gas detection, and also provides a new research direction for the application of nanomaterials in environmental monitoring.

Description

Technical Field

[0001] This invention belongs to the field of biotechnology, and in particular relates to a hydrogen sulfide sensor based on cholesterol-modified lipid perovskite, its preparation method and application. Background Technology

[0002] Hydrogen sulfide (H2S) is a highly toxic gas with a distinctive rotten egg odor, known for its ability to bind to iron in mitochondrial cytochrome enzymes, thus blocking cellular respiration. H2S is widely present in many industrial processes, particularly in petrochemicals, coal mining, and wastewater treatment. This gas poses a serious threat not only to human health but also to the environment. Prolonged exposure to H2S can lead to coma, severe poisoning, rapid respiratory arrest, olfactory inactivation (30-40 ppm H2S), and even death (greater than 250 ppm H2S). Based on the widespread toxic effects of H2S (attacking the nervous system and several other systems in the body), the Occupational Safety and Health Administration (OSHA) has set the exposure limit at 10 ppm (8 hours). In addition to its health hazards, hydrogen sulfide's strong corrosiveness causes severe damage to metal equipment. During industrial production, hydrogen sulfide can react with metal surfaces, leading to corrosion and damage. This not only increases maintenance costs but, more importantly, can cause safety accidents, threatening the lives of workers. Hydrogen sulfide's corrosive effects extend beyond metals; it can also damage building materials, pipes, and electronic equipment, thus impacting the stability and reliability of industrial production. Given these hazards, effective detection and control of hydrogen sulfide are crucial. In industrial environments, rapid and accurate monitoring of hydrogen sulfide concentration is essential for preventing poisoning accidents, ensuring personnel safety, and protecting the environment. However, hydrogen sulfide detection faces numerous challenges, such as its concentration fluctuations in the air, cross-interference with other gases, and the performance limitations of the detection equipment itself.

[0003] Therefore, there is an urgent need for a hydrogen sulfide detector with good stability, fast response speed, and low detection limit to solve the above problems. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention proposes a hydrogen sulfide sensing detector based on cholesterol-modified lipid perovskite, its preparation method, and its application.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing a hydrogen sulfide sensing detector based on cholesterol-modified lipid perovskite, comprising the following steps:

[0007] (1) A CsPbBr3 nanocrystal solution was mixed with an organic solvent containing cholesterol and phospholipids, and then rotary evaporated to obtain a green film.

[0008] (2) The green film obtained in step (1) is hydrated by mixing with water, and then subjected to ultrasound and centrifugation to obtain the hydrogen sulfide sensor based on cholesterol-modified lipid perovskite.

[0009] Preferably, in step (1), the mass ratio of CsPbBr3 nanocrystals to cholesterol and phospholipids in the CsPbBr3 nanocrystal solution is (4-8):(5-18):(55-65).

[0010] Preferably, in step (1), the phospholipid includes soybean lecithin.

[0011] Preferably, in step (1), the temperature of the rotary evaporation is 32-37°C and the time is 10 min.

[0012] Preferably, in step (1), the preparation method of CsPbBr3 nanocrystals in the CsPbBr3 nanocrystal solution includes: mixing PbBr2, CsBr, oleylamine and oleic acid in N,N-dimethylformamide, and stirring to obtain a precursor solution; rapidly adding the precursor solution to ethyl acetate at 32-37°C, and obtaining the CsPbBr3 nanocrystals by stirring and centrifugation.

[0013] Preferably, in step (2), the ratio of the green film to water is 0.064g:6mL.

[0014] Preferably, in step (2), the ultrasound duration is 2-5 minutes and the power is 50W.

[0015] Preferably, in step (2), the centrifugation speed is 12000 rpm and the time is 10 min.

[0016] The present invention provides a hydrogen sulfide sensing detector based on cholesterol-modified lipid perovskite prepared by the preparation method described in the above technical solution.

[0017] The present invention also provides the application of the cholesterol-modified lipid perovskite-based hydrogen sulfide sensor described above in the detection of hydrogen sulfide.

[0018] Compared with the prior art, the present invention has the following advantages and technical effects:

[0019] This invention constructs a stable protective layer for hydrophobic perovskite nanoparticles using highly biocompatible phospholipids and cholesterol, enabling them to emit light stably. This not only significantly improves the stability of the perovskite but also provides an ideal platform for the accurate detection of hydrogen sulfide. The cholesterol-modified lipid perovskite-based hydrogen sulfide sensor provided by this invention significantly improves the detection limit and response speed of hydrogen sulfide, reduces the risk of false negatives, and provides an intuitive and visual detection method for hydrogen sulfide. With a detection limit as low as ng / mL, this invention contributes to the development of gas sensing technology, improves the accuracy and efficiency of hazardous gas detection, and also provides a new research direction for the application of nanomaterials in environmental monitoring. Attached Figure Description

[0020] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0021] Figure 1 This is a schematic diagram of the preparation method of the hydrogen sulfide sensor detector based on cholesterol-modified lipid perovskite in Example 1;

[0022] Figure 2 TEM image of CsPbBr3@PL prepared in Example 1;

[0023] Figure 3 TEM image and elemental mapping of CsPbBr3@PL prepared in Example 1;

[0024] Figure 4 Images of CsPbBr3 n-hexane solution (a) and CsPbBr3@LP aqueous solution (b) under fluorescent light.

[0025] Figure 5 Photoluminescence intensity of CsPbBr3@PL prepared in Example 1 at different time points in PBS;

[0026] Figure 6 Fluorescence intensity diagrams of different concentrations of sodium sulfide after incubation for 10 min with aqueous solutions of CsPbBr3@PL prepared in Example 1;

[0027] Figure 7 The image shows the detection results of hydrogen sulfide content in colorectal cancer cells using CsPbBr3@PL prepared in Example 1. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] This invention provides a method for preparing a hydrogen sulfide sensing detector based on cholesterol-modified lipid perovskite, comprising the following steps:

[0031] (1) A CsPbBr3 nanocrystal solution was mixed with an organic solvent containing cholesterol and phospholipids, and then rotary evaporated to obtain a green film.

[0032] (2) The green film obtained in step (1) is hydrated by mixing with water, and then subjected to ultrasound and centrifugation to obtain the hydrogen sulfide sensor based on cholesterol-modified lipid perovskite.

[0033] In a preferred embodiment, in step (1), the mass ratio of CsPbBr3 nanocrystals to cholesterol and phospholipids in the CsPbBr3 nanocrystal solution is (4-8):(5-18):(55-65). This invention constructs a stable protective layer for hydrophobic perovskite nanoparticles using highly biocompatible phospholipids and cholesterol, enabling them to emit light stably. This not only significantly improves the stability of the perovskite but also provides an ideal platform for the accurate detection of hydrogen sulfide. Controlling the mass ratio of CsPbBr3 nanocrystals to cholesterol and phospholipids within the above range is beneficial for improving the stability of the perovskite; changing the amount of cholesterol and phospholipids will reduce the stability of the CsPbBr3 nanocrystals.

[0034] In a preferred embodiment, in step (1), the phospholipid includes soybean lecithin; more preferably, the phospholipid is soybean lecithin and DSPE-PEG.

[0035] In a preferred embodiment, in step (1), the organic solvent is dichloromethane.

[0036] In a preferred embodiment, step (1) involves preparing the CsPbBr3 nanocrystals in the CsPbBr3 nanocrystal solution by: mixing PbBr2, CsBr, oleylamine, and oleic acid in N,N-dimethylformamide and stirring to obtain a precursor solution; rapidly adding the precursor solution to ethyl acetate at 32-37°C, and then stirring and centrifuging to obtain the CsPbBr3 nanocrystals. The CsPbBr3 nanocrystals prepared by the method provided by this invention exhibit good dispersibility.

[0037] In a preferred embodiment, the ratio of PbBr2, CsBr, oleylamine, oleic acid, and N,N-dimethylformamide is 0.367g:0.212g:0.1mL:0.5mL:5.0mL.

[0038] In a preferred embodiment, the stirring temperature is room temperature and the stirring time is 5 minutes.

[0039] In a preferred embodiment, the volume ratio of the precursor solution to ethyl acetate is 0.5:10.

[0040] In a preferred embodiment, the stirring speed in the stirring and centrifugation is 1000 rpm for 10 min; the centrifugation speed is 1000 rpm for 5 min.

[0041] In a preferred embodiment, in step (1), the size of the CsPbBr3 nanocrystals in the CsPbBr3 nanocrystal solution is 10-20 nm.

[0042] In a preferred embodiment, in step (1), the solvent of the CsPbBr3 nanocrystal solution is n-hexane.

[0043] In a preferred embodiment, in step (1), the rotary evaporation temperature is 32-37°C, the time is 10 min, and the equipment is a rotary evaporator; the rotary evaporation is performed under vacuum. This invention removes the solvent hexane and the organic solvent dichloromethane from the CsPbBr3 nanocrystal solution by rotary evaporation, while simultaneously forming a green film. By controlling the rotary evaporation temperature and time within the above-mentioned range, this invention facilitates the removal of organic solvents and prevents the oxidation of CsPbBr3 nanocrystals. Changing the rotary evaporation temperature and time will affect the formation of the green film.

[0044] In a preferred embodiment, in step (2), the ratio of the green film to water is 0.064 g: 6 mL. This invention hydrates the green film by mixing it with water, allowing cholesterol and phospholipids to freely assemble into a shell structure in the solution, thereby encapsulating CsPbBr3 nanocrystals within a lipid layer and enhancing the stability of the perovskite.

[0045] In a preferred embodiment, in step (2), the ultrasound duration is 2-5 minutes and the power is 50W.

[0046] In a preferred embodiment, in step (2), the centrifugation speed is 12000 rpm and the time is 10 min. The present invention uses centrifugation for purification.

[0047] The present invention provides a hydrogen sulfide sensing detector based on cholesterol-modified lipid perovskite prepared by the preparation method described in the above technical solution.

[0048] In a preferred embodiment, the hydrogen sulfide sensor based on cholesterol-modified lipid perovskite has a particle size of 40-110 nm and a spherical morphology.

[0049] The hydrogen sulfide sensor provided by this invention based on cholesterol-modified lipid perovskite has long-term stability, reusability, and applicability under complex environmental conditions, as well as excellent sensitivity and specificity.

[0050] The present invention also provides the application of the cholesterol-modified lipid perovskite-based hydrogen sulfide sensor described above in the detection of hydrogen sulfide.

[0051] In this embodiment of the invention, room temperature refers to "25±2℃".

[0052] In the following examples, cesium bromide (CsBr, 99.5%), lead bromide (PbBr2, 99%), dichloromethane (DCM), oleic acid (OA, 90%), oleylamine (OAm, 80-90%), and N,N-dimethylformamide (DMF, 100%) were purchased from Aladdin Industries, Inc. (Shanghai, China). Soy lecithin and cholesterol were purchased from Meilun Biotechnology (Dalian, China). Hexane was purchased from Shanghai Lingfeng Chemical Reagent Co., Ltd. Phosphate-buffered saline (PBS, pH 7.4) was purchased from Nanjing Bookman Biotechnology Co., Ltd. DSPE-PEG was purchased from Shanghai Yuanye Biotechnology Co., Ltd.

[0053] Example 1

[0054] A method for fabricating a hydrogen sulfide sensing detector based on cholesterol-modified lipid perovskite:

[0055] (1) Mix 0.367g PbBr2, 0.212g CsBr, 0.1mL OAm and 0.5mL OA in 5.0mL DMF and stir at room temperature for 5min to obtain a precursor solution; at 37℃, quickly add 0.5mL of the above precursor solution to 10mL ethyl acetate, stir at 1000rpm for 10min, and centrifuge at 10000rpm for 5min to obtain CsPbBr3 nanocrystals, denoted as CsPbBr3NCs;

[0056] (2) The CsPbBr3 nanocrystals obtained in step (1) were dispersed in n-hexane to obtain a CsPbBr3 nanocrystal solution; 500 μL of the CsPbBr3 nanocrystal solution was mixed with dichloromethane containing cholesterol, soybean lecithin and DSPE-PEG. The mass ratio of CsPbBr3 nanocrystals to cholesterol, soybean lecithin and DSPE-PEG in the CsPbBr3 nanocrystal solution was 4:5:45:10. Then, the mixture was evaporated in a rotary evaporator under vacuum at 37°C for 10 min to obtain a green film.

[0057] (3) The green film obtained in step (2) was hydrated with deionized water at a ratio of 0.064 g: 6 mL, sonicated at 50 W for 2 min, centrifuged at 12000 rpm for 10 min, filtered, and the precipitate was the hydrogen sulfide sensor based on cholesterol-modified lipid perovskite, denoted as CsPbBr3@PL.

[0058] Figure 1 This is a schematic diagram illustrating the process of preparing the hydrogen sulfide sensor detector based on cholesterol-modified lipid perovskite in Example 1. Figure 1 It can be seen that CsPbBr3 NCs were first synthesized from PbBr2, CsBr, oleylamine and oleic acid and then dissolved in a hexane ring to obtain a CsPbBr3 NCs solution. The CsPbBr3 NCs solution was then mixed with dichloromethane containing cholesterol and phospholipids. The organic solvent was then removed by a thin-film spin-drying method, and deionized water was injected. The cholesterol and phospholipids freely assembled into a shell structure in the solution, thereby encapsulating a large number of CsPbBr3 NCs.

[0059] The CsPbBr3@PL prepared in Example 1 was characterized using transmission electron microscopy (TEM), and the results are as follows: Figure 2 As shown. From Figure 2As can be clearly seen, there are a large number of CsPbBr3NCs (small black dots) in CsPbBr3@PL, proving that CsPbBr3NCs were successfully encapsulated by phospholipids and cholesterol. It can also be seen that CsPbBr3NCs exhibit good monodispersity in CsPbBr3@PL, with a size of approximately 10 nm, and CsPbBr3@PL has a spherical structure of approximately 110 nm. This indicates that CsPbBr3NCs were successfully encapsulated in a lipid layer using a phospholipid and cholesterol free encapsulation method, forming larger composite nanoparticles.

[0060] Figure 3 TEM image and elemental mapping of CsPbBr3@PL prepared in Example 1. Figure 3 As shown, the elemental spectrum reveals a uniform distribution of Cs, Pb, Br, P, N, and O, confirming the presence of CsPbBr3 perovskite nanoparticles and a lipid layer. Cs, Pb, and Br correspond to the constituent elements of perovskite, P likely originates from phospholipid molecules in the lipid layer, and N and O may originate from nitrogen and oxygen elements within the lipid layer. The uniform elemental distribution indicates that CsPbBr3 nanoparticles are uniformly encapsulated within the lipid layer in CsPbBr3@PL, a homogeneity crucial for ensuring the stability and reproducibility of the material's properties.

[0061] 0.011 g of CsPbBr3 nanocrystals from Example 1 were dispersed in 2 mL of n-hexane solution to obtain a CsPbBr3 n-hexane solution. 0.011 g of CsPbBr3@PL prepared in Example 1 was dispersed in 2 mL of deionized water to obtain a CsPbBr3@PL aqueous solution. The CsPbBr3 n-hexane solution and the CsPbBr3@PL aqueous solution were irradiated under fluorescent light. The results are shown in [Figure number missing]. Figure 4 . Figure 4 Images show CsPbBr3 n-hexane solution (a) and CsPbBr3@LP aqueous solution (b) under fluorescent light. Figure 4 As can be seen, both the CsPbBr3 n-hexane solution and the CsPbBr3@LP aqueous solution exhibit a bright green color, further demonstrating the better stability of the CsPbBr3 nanocrystals encapsulated in the lipid cholesterol layer. This is likely because the lipid layer provides additional protection, preventing the nanoparticles from reacting with the aqueous solution and reducing the formation of surface defects. In biomedical applications, the stability of nanoparticles is crucial. Stable nanoparticles can ensure their function in vivo, reduce potential toxicity and immune responses, and improve their effectiveness in diagnostics and treatment.

[0062] Figure 5 Photoluminescence intensity of CsPbBr3@PL prepared in Example 1 at different time points in PBS. Figure 5As can be seen, the photoluminescence spectrum of CsPbBr3@PL exhibits obvious luminescence characteristics, indicating that CsPbBr3 nanocrystals possess excellent optical properties. Even after co-encapsulation of CsPbBr3 nanocrystals with phospholipids and cholesterol, the photoluminescence spectrum remains unchanged. This may be because the encapsulation of the lipid layer alters the local environment of the nanoparticles, affecting the band structure and luminescence centers. With increasing time, its photoluminescence spectrum still shows obvious luminescence characteristics, and the fluorescence intensity remains unchanged, indicating that co-encapsulation of CsPbBr3 nanocrystals with phospholipids and cholesterol does not significantly affect the luminescence performance of CsPbBr3 nanocrystals.

[0063] Add 100 μg / mL sodium sulfide standard solution (as S) 2- The sodium sulfide solution was serially diluted (unit: 10, 20, 30, 40, 50 nmol / L) to obtain sodium sulfide diluents with concentrations of 10, 20, 30, 40, and 50 nmol / L. 10 μL of each sodium sulfide diluent was placed in a separate EP tube, and 100 μL of an aqueous solution of CsPbBr3@PL prepared in Example 1 (concentration: 0.17 mg / mL, based on CsPbBr3 content) was added. After gentle shaking for 10 min, the fluorescence value of each well was immediately detected using a fluorescence microplate reader under excitation light at 365 nm. The test results are shown in [Figure number missing]. Figure 6 .

[0064] Figure 6 The fluorescence intensity graphs are shown for different concentrations of sodium sulfide after incubation for 10 min with an aqueous solution of CsPbBr3@PL prepared in Example 1. Figure 6 It can be seen that as the sodium sulfide concentration increases, the photoluminescence intensity of CsPbBr3@PL also decreases and shows a linear change, indicating that the CsPbBr3@PL prepared in this invention can be used to detect the concentration of hydrogen sulfide.

[0065] Detection of hydrogen sulfide content in colorectal cancer cells using CsPbBr3@PL prepared in Example 1: HCT-116 cells were seeded into confocal culture dishes. After 24 hours, the cells were treated with 100 μM H2S cell culture medium for 2 hours, then washed twice with 1×PBS, and then suspended in 100 μL of 1×PBS containing 1% BSA. 100 μL of CsPbBr3@PL prepared in Example 1 was added, and the cells were incubated at room temperature for 20 min. Then, 1 mL of 1×PBS solution was added, and the cells were washed three times at room temperature. The results were immediately detected using a high-resolution spectrophotometer. (See attached table for details.) Figure 7 .

[0066] Figure 7The figures show the detection results of hydrogen sulfide content in colorectal cancer cells using CsPbBr3@PL prepared in Example 1. Figure A shows HCT116 cells, and Figure B shows HCT116 cells pre-treated with 100 μM H2S for 2 hours. Figure 7 As can be seen, the cells in Figure A exhibit green fluorescence, while the fluorescence in HCT116 cells treated with high concentrations of hydrogen sulfide is quenched, indicating that CsPbBr3@PL can detect the hydrogen sulfide content in colorectal cancer cells.

[0067] Comparative Example 1

[0068] The difference from Example 1 is that in step (2), rotary evaporation is performed under vacuum at 27°C, while the other steps and process parameters are the same as in Example 1.

[0069] Comparative Example 2

[0070] The difference from Example 1 is that in step (2), the rotary evaporation is carried out at 37°C under vacuum for 5 minutes, while the other steps and process parameters are the same as in Example 1.

[0071] Comparative Example 3

[0072] The difference from Example 1 is that in step (3), the green film obtained in step (2) is hydrated with deionized water at a ratio of 0.084g:6mL, and the other steps and process parameters are the same as in Example 1.

[0073] Comparative Example 4

[0074] The difference from Example 1 is that in step (2), 500 μL of CsPbBr3 nanocrystal solution is mixed with dichloromethane containing soybean lecithin and DSPE-PEG, while other steps and process parameters are the same as in Example 1.

[0075] Add 10 μL of 100 μg / mL sodium sulfide standard solution (as S... 2- The samples were placed in different EP tubes, and then 100 μL of the aqueous solution of CsPbBr3@PL prepared in Example 1 and Comparative Examples 1-4 (based on the content of CsPbBr3) was added. After gently shaking for 2 min, the fluorescence value of each well was immediately detected by a fluorescence microplate reader under excitation light of 365 nm. The results are shown in Table 1.

[0076] Table 1. Performance of CsPbBr3@PL prepared in Example 1 and Comparative Examples 1-4

[0077] Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 fluorescence value 24226 35978 38189 38920 40029

[0078] As can be seen from Table 1, the hydrogen sulfide sensor detector based on cholesterol-modified lipid perovskite provided by the present invention has excellent sensitivity.

[0079] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for preparing a hydrogen sulfide sensing detector based on cholesterol-modified lipid perovskite, characterized in that, Includes the following steps: (1) A CsPbBr3 nanocrystal solution was mixed with dichloromethane containing cholesterol and phospholipids, and then rotary evaporated to obtain a green film; the phospholipids were soybean lecithin and DSPE-PEG; the rotary evaporation temperature was 32-37℃ and the time was 10min. (2) The green film obtained in step (1) is hydrated by mixing with water, and then subjected to ultrasound and centrifugation to obtain the hydrogen sulfide sensor based on cholesterol-modified lipid perovskite; the ratio of green film to water is 0.064 g: 6 mL.

2. The method for preparing a hydrogen sulfide sensing detector based on cholesterol-modified lipid perovskite according to claim 1, characterized in that, In step (1), the mass ratio of CsPbBr3 nanocrystals to cholesterol and phospholipids in the CsPbBr3 nanocrystal solution is (4-8):(5-18):(55-65).

3. The method for preparing a hydrogen sulfide sensing detector based on cholesterol-modified lipid perovskite according to claim 1, characterized in that, In step (1), the preparation method of CsPbBr3 nanocrystals in the CsPbBr3 nanocrystal solution includes: mixing PbBr2, CsBr, oleylamine and oleic acid in N,N-dimethylformamide and stirring to obtain a precursor solution; at 32-37°C, rapidly adding the precursor solution to ethyl acetate, stirring and centrifuging to obtain the CsPbBr3 nanocrystals.

4. The method for preparing a hydrogen sulfide sensing detector based on cholesterol-modified lipid perovskite according to claim 1, characterized in that, In step (2), the ultrasound duration is 2-5 minutes and the power is 50W.

5. The method for preparing a hydrogen sulfide sensing detector based on cholesterol-modified lipid perovskite according to claim 1, characterized in that, In step (2), the centrifugation speed is 12000 rpm and the time is 10 min.

6. A hydrogen sulfide sensing detector based on cholesterol-modified lipid perovskite prepared by the preparation method according to any one of claims 1-5.

7. The application of the cholesterol-modified lipid perovskite-based hydrogen sulfide sensor as described in claim 6 in the detection of hydrogen sulfide.

Images