H2S Test Research Articles

Biochemical and Molecular Detection of Aeromonas Hydrophila Isolated from Infected Cyprinus Carpio in Salah Al-Din Governorate

This study aimed to identify the presence of Aeromonas hydrophila bacteria in diseased common carp (Cyprinus carpio) fish collected from Salah al-Din Governorate in Iraq. For this purpose, 128 swabs were obtained from skin, gill and fin lesions of 70 fish showing symptoms of hemorrhagic sepsis, skin ulcers and boils, and fin and gill rot. Through different biochemical tests, the isolates showed negative results for Gram stain, methyl red, lactose fermentation, H2S, and string test, while positive results were recorded for glucose fermentation, oxidase, motility test, catalase, Voges-Proskauer, indole, citrate utilization, and gelatin hydrolysis. Eleven isolates were confirmed as A. hydrophila by amplification of the hemolysin gene fragment (hlyA) by conventional PCR. This study represents the first comprehensive study to characterize A. hydrophila bacteria from infected common carp fish in Salah al-Din Governorate. The findings of this study provide valuable insights for developing genetic diagnostic strategies for A. hydrophila infections in this region.

Cave Bats as Carriers of Extended Spectrum Beta-lactamase Produced by Escherichia coli from the Island of Lombok, Indonesia

Background: Escherichia coli is a Gram-negative commensal bacterium that normally resides in the digestive tract of humans and animals which is used as an indicator of the extended-spectrum beta-lactamase (ESBL) gene in an individual and can carry out gene transfer. Transmission of ESBL E. coli from wild animals has not been given much attention even though wild animals can act as vectors that spread ESBL in the environment so that it can pose a risk to public health. This research aims to identify the blaTEM gene which codes for ESBL in E. coli from bats that live in caves in Lombok, Indonesia. Methods: A total of 135 samples from bat rectal swabs were cultured on Eosin Methylene Blue Agar media and biochemical suspects were identified using the Indole, Methyl red, Voges-Proskauer, Citrate + and H2S (IMVIC) test. The E. coli bacteria obtained were tested for sensitivity using 7 classes of antibiotics, namely amoxicillin, ciprofloxacine, sulfamethoxazole/trimethoprim, tetracycline, gentamicin, cefotaxime and azithromycin. Bacteria that show multidrug resistance are subjected to PCR testing to detect the blaTEM gene. Result: Of the 135 test samples, it was found that 97 (71.85%) samples were positive for E. coli, 12 (12.37%) samples were Multidrug Resistance (MDR) and 2 (2.06%) samples had the blaTEM gene as the ESBL coding gene in bats that live in caves on the island of Lombok, Indonesia. The presence of the blaTEM gene in E. coli from bats can be indicated as a reservoir for MDR and ESBL transmission so that it can have an impact on public health.

Effect of cinnamon bark (Cinnamomum zeylanicum) biomass on organoleptic quality of goat meat during shelf life

Abstract Cinnamon is an herbal spice that contains antioxidants and antimicrobials. The use of cinnamon in the postharvest industry of agricultural products has been widely practised and provides economic benefits. Goat meat is a postharvest product with high protein levels, making it susceptible to damage due to microbial growth during its shelf life. Goat meat also has a distinctive aroma that is less favoured by consumers. Appropriate methods are needed to improve the organoleptic quality of goat meat. This study aims to determine cinnamon’s effect on the organoleptic quality of goat meat. The design used was a factorial, completely randomised design. The factor I is Cinnamon concentration (K0:0%; K1:5%; K2:10%; K3:15%), and Factor II is the length of storage (H1:24 hours, H2:48 hours). The results showed that cinnamon marinade had a very significant effect (P<0.01) on taste and aroma but no significant effect (P>0.05) on texture and colour. The hedonic test showed that marination using 10%-15% cinnamon on goat meat was preferred in terms of aroma and flavour. The H2S test showed that samples marinated in cinnamon and stored for 48 hours did not show spoilage. Cinnamon has the potential to be a sustainable preservative.

Value of exhaled hydrogen sulfide in early diagnosis of esophagogastric junction adenocarcinoma.

Esophagogastric junction adenocarcinoma (EJA) has increased in recent years, and it exhibits a poor prognosis and a short survival period for patients. Hydrogen sulfide (H2S) plays an important role in the pathogenesis of cancer and has been studied as a diagnostic factor in some tumor diseases. However, few studies have explored the diagnostic value of H2S for EJA. In the present study, a total of 56 patients with early-stage EJA were enrolled while 57 healthy individuals were selected as the healthy control group. Clinical features were recorded, and exhaled H2S and blood samples were collected from both groups. Exhaled H2S and serum interleukin-8 (IL-8) expression levels were detected in both groups. The correlation between exhaled H2S and serum IL-8 levels was analyzed using Pearson's correlation method. Receiver operating characteristic (ROC) curve was used to evaluate the diagnostic value of exhaled H2S combined with IL-8 detection in EJA. The results showed that patients with EJA exhaled more H2S than healthy individuals. In addition, exhaled H2S was positively correlated with increased IL-8 expression. The ROC curve revealed that the exhaled H2S test had an acceptable diagnostic effect and could be used to diagnose EJA. The increase in H2S exhaled by patients with EJA indicated that H2S may be related to the occurrence and development of EJA; however, the in vivo mechanism needs to be further explored. Collectively, it was determined in the present study that exhaled H2S was significantly higher in patients with early-stage EJA than in healthy controls and combined diagnosis with patient serum IL-8 could improve diagnostic accuracy, which has potential diagnostic value for early diagnosis and screening of EJA.

Biochemical and molecular characterization of Campylobacter fetus isolates from bulls subjected to bovine genital campylobacteriosis diagnosis in Spain

BackgroundBovine genital campylobacteriosis (BGC) is caused by Campylobacter fetus subsp. venerealis (Cfv) including its biovar intermedius (Cfvi). This sexually transmitted disease induces early reproductive failure causing considerable economic losses in the cattle industry. Using a collection of well-characterized isolates (n = 13), C. fetus field isolates (n = 64) and saprophytic isolates resembling Campylobacter (n = 75) obtained from smegma samples of breeding bulls, this study evaluated the concordance of the most used phenotypic (H2S production in cysteine medium and 1% glycine tolerance) and molecular (PCR) methods for the diagnosis of BGC and assessed possible cross-reactions in the molecular diagnostic methods.ResultsCharacterization at the subspecies level (fetus vs. venerealis) of C. fetus isolated from bull preputial samples using phenotypic and molecular (PCR targeting nahE and ISCfe1) methods showed moderate concordance (κ = 0.462; CI: 0.256–0.669). No cross-reactions were observed with other saprophytic microaerophilic species or with other Campylobacter species that can be present in preputial samples. Whole genome sequencing (WGS) of discrepant isolates showed 100% agreement with PCR identification. For the differentiation of Cfv biovars, comparison of the H2S test (at 72 h and 5 days of incubation) and a PCR targeting the L-cysteine transporter genes showed higher concordance when H2S production was assessed after 5 days (72 h; κ = 0.553, 0.329–0.778 CI vs. 5 days; κ = 0.881, 0.631–1 CI), evidencing the efficacy of a longer incubation time.ConclusionsThis study confirmed the limitations of biochemical tests to correctly identify C. fetus subspecies and biovars. However, in the case of biovars, when extended incubation times for the H2S test (5 days) were used, phenotypic identification results were significantly improved, although PCR-based methods produced more accurate results. Perfect agreement of WGS with the PCR results and absence of cross-reactions with non-C. fetus saprophytic bacteria from the smegma demonstrated the usefulness of these methods. Nevertheless, the identification of new C. fetus subspecies-specific genes would help to improve BGC diagnosis.

Selection of a diagnostic tool for microbial water quality monitoring and management of faecal contamination of water sources in rural communities

The aim of the current study was to evaluate, validate and select microbial water quality monitoring tools to establish their suitability and feasibility for use in rural communities. The monitoring of water quality was performed at three different levels: i) basic level focusing on sanitary inspection and hydrogen sulphide (H2S) test; ii) intermediate level via enumeration of faecal indicator bacteria (faecal coliforms, Escherichia coli, Enterococcus spp. and Clostridium perfringens); and iii) advanced level based on qPCR detecting host-associated genetic markers (BacHum, BacCow, Cytb, Pig-2-Bac, and BacCan) and pathogens (Vibrio cholerae, Escherichia coli O157:H7, and Shiga toxin-producing Escherichia coli). A positive correlation was recorded between sanitary risk and faecal coliforms (r = 0.613 and p < 0.002), E. coli (r = 0.589 and p < 0.003), and Enterococcus spp. (r = 0.625 and p < 0.003). The H2S test showed positive correlations with sanitary risk score (r = 0.623; p < 0.003), faecal coliforms (r = 0.809; p < 0.001), E. coli (r = 0.779; p < 0.001) and Enterococcus spp. (r = 0.799; p < 0.001). Similar correlation patterns were also found with advanced techniques used for detecting host-associated genetic markers, excepted between Clostridium perfringens, and Pig-2-Bac (pig), BacCan (dog), and V. cholerae. The H2S test and sanitary inspections are therefore suitable and cost-effective tools to capacitate rural areas at household level for the monitoring of faecal contamination and management of water sources.

Storage conditions, microbial quality, and transport costs of drinking water from alternative sources in a South African municipality.

Makana Local Municipality is located in the Eastern Cape Province of South Africa. The area is water-scarce and has been undergoing aridification in recent years, ie, there has been a 7-year long drought. At the same time, there has been a breakdown in provision of municipal services, such as drinking water, to the population since at least 2008. Mi-crobial water quality has been a result of this, and monitoring has been a challenge. Given the drought and the prob-lems with drinking water delivery, it was necessary to conduct this study to investigate the microbial quality of alterna-tive water resources that the Makana population can use during the municipal water outage. The microbial water quality of alternative sources of drinking water in the Makana Local Municipality was examined using the H2S test kit and enumeration of the fecal coliforms. Storage of the collected water was examined for potential factors influencing the microbial water quality of the alternative sources of drinking water. The costs of the water provision from the most suitable alternative sources of potable water were calculated. There was a general correlation between the H2S test kit results and the fecal coliform concentrations, with the latter values ranging from <0 to 23 ± 7 colony-forming units/100 mL. The bottled water from two retail outlets was provided the best alternative source of potable/drinking water, which is microbially safe, for the Makana population. If the consumption of the drinking water from an alternative source takes place within 24 hours of collection, then the Fairview spring could also be used as a source of drinking water for Maka-na residents. The total cost per 1 L of drinking water from alternative sources was estimated to be from 1.51 to 5.81 ZAR. Therefore, the maximum cost of daily provision of drinking water from alternative sources would account for a maximum of 0.88 percent of the monthly household expenditure in the middle-to-high-income household. However, the daily costs of such provision of drinking water would account for a maximum of 8.11 percent of the monthly household expenditure in the low-income household. Provision of the drinking water from the alternative sources would have a minor impact of the monthly ex-penditure in the middle-to-high-income households. However, it is likely that the low-income households would not be able to sustain their water supply from alternative sources for longer than 24 hours, during a municipal outage in the drinking water supply.

ZnO nanowires based e-nose for the detection of H2S and NO2 toxic gases

In this work, a novel ZnO NWs based e-nose has been developed and demonstrated successfully for its ability to discriminate H2S and NO2 test gases. For this, a MS was fabricated by modifying the surface of the ZnO NWs with suitable sensitizers (∼<10 nm) namely Ni, Au, Cu, and MgO. A post deposition annealing in oxygen environment results in the formation of ZnO–CuO, ZnO–Au, ZnO–NiO and ZnO–MgO heterojunctions. The data repository was formed by measuring the response curves for different set of gas, concentration and operating temperature. The gas sensing results were subsequently interpreted employing both graphical analysis (3D bar chart) and multivariate data analysis (principal component analysis) techniques. For better understanding, the steps involved in the PCA have been explained and discussed elaborately. Our result indicate that the e-nose is capable for producing the qualitative as well as quantitative discrimination of two test gases namely H2S and NO2.

Sensory characteristics and putrefaction test of broiler chicken meat dipping in Syzygium polyanthum infusion with different storage time

This study aims at evaluating the sensory characteristics and putrefaction testing of broiler chicken meat dipping in Syzygium polyanthum infusion with different storage time. Observations were made on sensory quality of raw meat (color and aroma), cooked meat (color, aroma, flavor, and tenderness), and putrefaction testing of the eber test. The study considered two treatments, namely Syzygium polyanthum infuse concentrations (0 vs. 15%) during 30 minutes and different storage times at 4°C (0, 2, 4, 6, and 8 days) where each treatment repeated three times. The sensory characteristics test of chicken meat is performed by the panelist method. The collected data were analyzed by analysis of non-parametric with the Kruskal Wallis test. The results of the rot test were analyzed descriptively qualitatively. Data showed that the concentration of Syzygium polyanthum infusion and storage time could reduce the color and improve the aroma of raw meat and also tenderness and the smell of cooked meat. The initial rot of control chicken meat and bay leaf on day 4 with positive parameters used the Postma test and control chicken meat using the H2S test.

Novel naphthalimide derived fluorescent probe based on aggregation-induced emission for turn-on detection of hydrogen sulfide

Abstract Two novel aggregation-induced emission (AIE) based fluorescent probes, TPANI-DNs and PCZNI-DNs, have been designed and synthesized for “turn-on” detection of H2S. Chromophore napthalimide fused triphenylamine (or phenylcarbazole) unit as fluorophore in combination with 2,4-dinitrobenzenesulfonyl as recognition moiety constructed probes. The design strategy of the twisted D-π-A structure can efficiently transform the aggregation-caused quenching (ACQ) system into the AIE system by strengthening the restriction of intramolecular motion and preventing the intermolecular π-π stacking. The consequences showed that both TPANI-DNs and PCZNI-DNs displayed large stokes shift (135 nm and 120 nm, respectively), high selective and sensitive detection. The response mechanisms and fluorescent properties were further investigated through the time-dependent density functional theory (TDDFT). Importantly, since the strong AIE properties, a H2S test board has been prepared and used to detect H2S onsite easily and sensitively, displaying potential practical applications.

Modification of the H2S test to screen for the detection of sulphur- and sulphate-reducing bacteria of faecal origin in water

AbstractThe H2S test was created to assess the microbial quality of drinking water in low-resource settings, but the original version of the H2S test lacks sensitivity and specificity for faecal indicator bacteria. There is evidence that a modified media formula of the H2S test may be more sensitive and specific for the faecal indicator bacterium Escherichia coli (E. coli) and less sensitive to organisms of non-faecal origin. This research established the detection threshold and operational range of the H2S test, to increase its sensitivity and specificity for E. coli. A total of 20 modifications of the H2S test, and the original test, were assayed against 20 confirmed and pure culture bacteria of faecal and non-faecal origin at varying concentrations. Additionally, some of the H2S test modifications were evaluated against standard methods for drinking-water analysis. Results indicate that using a modified version of the H2S test containing L-cystine and 2-mercaptopyridine, and bile salts or penicillin G, E. coli will produce H2S. In addition, this research reveals which organisms react positively to the original and modified versions of the H2S test. The modified versions of the H2S test can be promoted as a simple screening test for microbial drinking-water safety in low-resource settings.

PENDUGAAN UMUR SIMPAN IKAN ASAP MENGGUNAKAN JENIS ASAP TEMPURUNG KELAPA DAN JENIS IKAN AIR TAWAR

The purpose of this research was to find out the shelf life of smoked fish produced from different types of freshwater fish, namely bawal fish, tawes fish and nilem fish using different types of coconut shell smoke, first grade liquid smoke, second grade liquid smoke and direct smoke.This research was conducted using Arrhenius Method on smoked fish using different coconut shell smoke and different freshwater fish species and stored at 25oC for 6 days. The responses in this research is organoleptic response (color, texture, flavour), microbiological response (Total Plate Count) and H2S test and Indol test. The method of this research consists of a preliminary research conducted to obtain a panelist acceptance limit on smoked fish products. The main research was conducted to find out the shelf life of smoked fish using different types of coconut shell smoke with different freshwater fish using microbial parameters also analyzed H2S test and Indol test to determine the overall quality degradation in smoked fish. Based on the parameters of total microbes treated using Arrhenius method, the shelf life of smoked fish was 5.75 days for bawal with garde 1 liquid smoke, 5.91 days for bawal with grade 2 liquid smoke and 3.97 days for bawal with smoke directly. For tawes with grade 1 liquid smoke that is 6.33 days, 3.90 days for tawes with grade 2 liquid smoke and 4.45 for tawes with direct smoke. Nilem fish with grade 1 liquid smoke is 5.72 days, 6.09 days for nilem with grade 2 liquid smoke and 4.25 day for nilem with direct smoke.

Citizen science based monitoring of microbial water quality at a single household level in a South African local municipality during the COVID19 lockdown

Personal hygiene and access to potable water, which is safe for human consumption, are critical to containing the COVID19 pandemic. Here monitoring results are reported for microbial quality of water samples from the municipal supply in Makana Local Municipality in the Eastern Cape Province, South Africa. Access of the human population to sufficient volumes of potable water of required (microbial) quality has been a problem in this local municipality. Samples were taken just before and during 30 days of the strictest phase of the nation-wide lockdown, related to COVID19 in South Africa. Aim of this short communication was to perform the water quality testing with limited to no access to laboratory facilities and using the principles of citizen science. The H2S test kit was used as the basis for the microbial testing, while a cell phone app was used for the temperature monitoring. Five H2S test kit were used per sampling at the author’s house and the kits was developed for the microbial water quality assessment in isolated settings such as those for the lockdown. During the study, the ambient temperature ranged from 17 to 29 °C, with decreases below 18 °C occurring on three out of 12 sampling occasions. Thus the results of the H2S test kit might have been slightly influenced by the fluctuations of the ambient temperature. On 8 sampling occasions between 1 and 4 H2S test kits were positive for faecal contamination. Three samples or 25 % were free of faecal contamination. One sample had all five H2S test kits were positive for faecal contamination. Results of statistical testing indicated that potable water in Makana Local Municipality was probably microbially contaminated at the author’s household on an intermittent basis. Ongoing monitoring of microbial drinking water quality is necessary and continuing at the sampled location.

The efficiency of a low-cost hydrogen sulphide (H2S) kit as an early warning test for assessing microbial rainwater quality and its correlation with standard indicators microorganisms

AbstractTesting microbial quality of the harvested rainwater remains a challenge in many countries. The H2S test kit is a low-cost microbiological field-based test which can be used in areas where water testing facilities are limited. This study compares its efficiency with the standard indicators microorganisms in the detection of faecal contamination of rainwater in South Africa. A total of 88 rainwater samples were collected from various tanks in the Eastern Cape, South Africa over three months in 2016. The collected samples were analysed for faecal bacterial contamination using the H2S test kit, Colilert-18/Quanti-tray®/2000 and the membrane filtration technique for faecal coliforms (MFT). The correspondence rate of the H2S test kit with MFT was 88 %, while for the Colilert®it was 76 %. The H2S test kit confirmed faecal contamination when concentrations of standards indicators microorganisms were 5 most-probable number of cells/100 cm3or higher. Overall, the best correspondence of the H2S test kit with Colilert®was observed atE. coliconcentrations above 50 most-probable number of cells/100 cm3. Results of the H2S test kit correlated better with MTF, while the medium used has strongly influenced the enumeration of faecal contamination. Results point to strong effect of media used and revealed the need to calibrate the correspondence between the standard indicator microorganisms and the H2S test kit under local conditions for specific settings.

Locally produced hydrogen sulphide detecting water quality test kits increase household level monitoring in rural Tanzania.

In developing countries, rural water sources have the highest levels of faecal contamination but are the least monitored. Affordable field-based water quality tests are needed. The presence of faecal indicator bacteria can be determined with hydrogen sulphide (H2S) detecting tests, that are inexpensive and simple to make locally. In rural Tanzania, a non-governmental organisation (NGO) designed, produced and evaluated a new H2S water quality test kit. The H2S test results correlated with log10 Escherichia coli densities from conventional water quality tests. The production cost was US$ 1.10 and the test retailed for US$ 1.37. In total, 433 tests were sold through local pharmacies and NGOs. Additionally, 165 WaSH education meetings, reaching 3,408 community members, were conducted with the H2S test demonstrated in over half the meetings. Pre- and post-surveys of 294 meeting participants saw an increased reporting of household level water treatment by 24%. The H2S test was widely accepted, with 94% of those surveyed willing to buy the test in the future. International and national guidelines for drinking water monitoring need to be amended to include locally produced H2S water quality tests. This will enable households to monitor their own water sources and make informed choices about water safety and treatment.

Availability of infrastructure and manpower for primary health centers in a district in Andhra Pradesh, India.

Background:India has a vast public health infrastructure with 23,391 primary health centers (PHCs) and 145,894 subcenters providing health services to 72.2% of the country's population living in rural areas. Although the numbers look impressive, their functional status needs to be studied in terms of physical infrastructure, manpower, equipment, drugs, and other logistical supplies that are greatly needed for ensuring quality services. This work aims to study the infrastructure facilities and manpower in a sample of PHCs in the district of Nellore in the state of Andhra Pradesh in India.Methods:Randomly selected samples of 15 PHCs have been studied using structured and pretested performance standard questionnaire. Data have been analyzed with reference to the Indian Public Health Standards (IPHS) of the Government of India.Results:Many deficiencies were identified in infrastructure and manpower in the PHCs studied. Some of the important findings were that the deficiency of AYUSH medical officers was 86.6% and the deficiency of health workers (female) was 13.33%. Some of the important drugs such as antihypertensives, anticonvulsants, emergency drugs, drops, ointments, and solutions were available in less than 50% of the PHCs. Only 47% of the PHCs had Typhidot tests and H2S test strips, and in the labor rooms only 20% of the PHCs have a Standard Surgical Set for episiotomies in accordance with IPHS.Conclusion:PHCs lack the manpower and vital infrastructure that are necessary for the effective day-to-day functioning and provision of primary healthcare to the population.

Effectiveness of the Hydrogen Sulfide Test as a Water Quality Indicator for Diarrhea Risk in Rural Bangladesh.

.Microbiological water quality is usually assessed by the identification of Escherichia coli (E. coli), a fecal indicator. The hydrogen sulfide (H2S) test is an inexpensive, easy-to-use, and portable alternative field-based water quality test. Our study evaluated the H2S test’s effectiveness as a water quality indicator for diarrhea risk. Field workers collected stored drinking water samples for H2S analysis and detection of E. coli by membrane filtration and measured caregiver-reported diarrhea among children < 5 years in the same households 1 month later. We assessed the association between the H2S test (incubated for 24 hours and 48 hours) and diarrhea prevalence, with 2-day and 7-day symptom recall periods (N = 1,348). We determined the sensitivity, specificity, and positive and negative predictive value (PPV, NPV) of the H2S test compared with E. coli (N = 525). Controlling for potentially confounding covariates, H2S-positive water (at 24 or 48 hours) was not associated with 2-day diarrhea prevalence (24-hour prevalence ratio [PR] = 1.03, 95% confidence interval [CI]: 0.63–1.69; 48-hour PR = 0.89, 95% CI: 0.58–1.38) or 7-day diarrhea prevalence (24-hour PR = 1.17, 95% CI: 0.76–1.78; 48-hour PR = 1.21, 95% CI: 0.81–1.80). The sensitivity, PPV, and NPV of the H2S test was significantly higher when the H2S test was incubated for 48 versus 24 hours whereas specificity showed the opposite trend. H2S test sensitivity, PPV, and NPV increased with increasing E. coli levels, consistent with previous evidence that the H2S test is a useful water quality tool in high-contamination settings. However, our results suggest that the H2S test is not an effective indicator for waterborne diarrhea.

A sensitive presence/absence test kit for detection of coliforms in drinking water

Coliforms are the most widely accepted bacterial indicator of fecal pollution in water. Several commercially available portable kits make it possible to carry out on-site water quality testing, but are usually costly and often require technical expertise to operate. In developing countries like India, presence/absence test kits like the H2S test kits are commonly used for routine microbiological water quality examination. H2S test kits require an incubation time of more than 24 hours and often gives false positive results. In this research work, we have developed a low-cost and sensitive test kit (ColiPAT) for the detection of coliforms including Escherichia coli in drinking water. The kit can detect very low contamination levels down to 2 coliforms/100 mL within 18 hours at 35 °C. The ColiPAT kit does not lose its sensitivity in the typical indoor temperature range of 27 °C to 35 °C. ColiPAT is also affordable and easy to perform so that local populace can conduct the test independently. This paper presents the results of sensitivity and specificity analysis of a ColiPAT kit and its comparison with the H2S test kits as standardized using Colilert method.

Bismuth-Based, Disposable Sensor for the Detection of Hydrogen Sulfide Gas.

A new sensor for the detection of hydrogen sulfide (H2S) gas has been developed to replace commercial lead(II) acetate-based test papers. The new sensor is a wet, porous, paper-like substrate coated with Bi(OH)3 or its alkaline derivatives at pH 11. In contrast to the neurotoxic lead(II) acetate, bismuth is used due to its nontoxic properties, as Bi(III) has been a reagent in medications such as Pepto-Bismol. The reaction between H2S gas and the current sensor produces a visible color change from white to yellow/brown, and the sensor responds to ≥ 30 ppb H2S in a total volume of 1.35 L of gas, a typical volume of human breath. The alkaline, wet coating helps the trapping of acidic H2S gas and its reaction with Bi(III) species, forming colored Bi2S3. The sensor is suitable for testing human bad breath and is at least 2 orders of magnitude more sensitive than a commercial H2S test paper based on Pb(II)(acetate)2. The small volume of 1.35-L H2S is important, as the commercial Pb(II)(acetate)2-based paper requires large volumes of 5 ppm H2S gas. The new sensor reported here is inexpensive, disposable, safe, and user-friendly. A simple, laboratory setup for generating small volumes of ppb-ppm of H2S gas is also reported.

Effects of violet-, green-, and red-laser illumination on gas-sensing properties of SnO thin film

We examined the gas-sensing properties of a 10-nm-thick SnO thin film under the illumination of violet, green, and red laser beams at room temperature. A comparison of the gas-sensing outputs of the device after operation in the dark at elevated temperatures (100, 150, and 200°C) and when illuminated by a laser beam at room temperature indicated that this metal-oxide film had good gas-sensing performance and excellent stability under the illumination of the violet beam. When exposed to several target gases, including NO2, SO2, H2S, and NH3, the SnO thin film was most sensitive to H2S with a minimum concentration of 5ppm. During the H2S test, a two-step response of the sensor was recorded, which provided information for understanding the effects of chemisorbed and photo-induced oxygen species on the gas-sensing properties of the illuminated sensor. A possible light-induced gas-sensing mechanism of the SnO thin film was proposed and investigated in detail.