Gas sensing

Storage of cereal crops and other foodstuffs is an essential part of ensuring a sustainable and robust food supply. Cereal crops are typically harvested between mid-July to mid-September but with careful storage can be kept for periods longer than a year. Successful storage of cereals involves the balance of a variety of environmental conditions to ensure the maintenance of quality and the original properties of the grain, including weight and appearance. Ideally, stored grain should be able to match freshly harvested grains in terms of nutrition and appeal.

Poor quality storage not just threatens global food security, a growing concern in a world with expanding populations and energy demands, but also comes with a significant financial cost. Maize crops lost to poor storage conditions account for $500 million to $1 billion of lost revenue for the developing world alone.

These are strong motivations to find reliable methods for the monitoring and optimising of environmental conditions for grain storage. Common reasons for spoilage of stored cereals include water and humidity damage, invasion by insects or microorganisms, or even decomposition. Common approaches to kill invasive species were to fumigate storage silos with toxic chemicals but this only addresses the issue of damage by organisms and has become generally less popular with time due to concerns about the safety of using such chemicals on foodstuffs. However, it has been found that by using modified atmospheric conditions that, not only can temperature and humidity damage be minimised, but the decomposition rate slowed and even the growth rates of microorganisms minimised.

Modified Atmospheres

Modified atmospheric conditions mean an environment that deliberately has its gas composition controlled, often by complete replacement of the local atmosphere with a combination of deliberately chosen gases. These are commonplace in all areas of food preservation, from the packaging on supermarket shelves for meat and vegetables, to their use in storage silos for cereals.

Some of the advantage of using modified atmospheric conditions for cereal storage over traditional physio-chemical methods is that there are fewer safety concerns associated with the use of chemical products and several contributors to cereal spoilage can be tackled with the same process. For example, one of the most common causes of food spoilage in humid areas is the uptake of water by the cereal, which often leads to mold growth and decomposition. Reducing the humidity in the environment does not just have to be done with a physical dehumidifying process, such as using a refrigerant to condense water out of the air, but can be done by increasing the nitrogen concentration. Increased nitrogen and oxygen concentrate can also be used to kill insects and microbes.

One gas that is often carefully controlled in modified atmospheric conditions is carbon dioxide. Carbon dioxide is often used in high concentrations to inhibit insect life in the cereal for preservation, but detection, of carbon dioxide levels can be very useful as an indicator of spoilage of crops.8 As decomposition of the cereal starts to occur, a combination of carbon dioxide, and highly toxic carbon monoxide, are produced and this can be used as a diagnostic for the quality of the storage. One of the issues, if decomposition occurs due to the presence of microorganisms, is if the problem is not rectified quickly, the microorganisms will continue to grow and more of the cereal will be wasted.

Sensitive gas monitors can, therefore, help not just to ensure modified atmospheric conditions are optimal but to check for signs of spoilage, or also the formation of toxic gases. Grain silos will can become anaerobic environments and spoilage can produce large volumes of carbon dioxide, which could lead to the asphyxiation of workers and so gas monitoring is required as part of health and safety legislation.

Many cereal storage facilities are retroactively fitted with modified atmosphere equipment and so easy to install and robust independent gas monitors are the perfect complement for that. To that end, Edinburgh Sensors offer a wide range of OEM gas sensors based on nondispersive infrared (NDIR) technology, a highly sensitive and accurate approach for the detection of many gaseous species such as carbon dioxide and carbon monoxide.

For cereal storage facilities, Edinburgh Sensors‘ GasCard NG is the ideal way to ensure optimal storage conditions for crops. As the device is calibrated in factory, no reference gas is required, (the detector is suitable for use with a series of different gases but one device can detect one gas sat a time), and installation and use is designed to be as straightforward as possible. As in the case of spoilage the change in carbon dioxide levels may be very small, the accuracy of ±2% in measuring carbon dioxide concentrations between 0 – 100 % is ideal.

The GasCard NG can easily be connected to external data logging devices using a RS232 interface or TCP/IP protocol. As the sensor is provided with logging software, it only needs a connecting cable to be purchased to be up and ready for real-time data logging. With a short warm-up time of a minute and a response time of less than 90 seconds, the GasCard NG is also suitable for high throughput measurements on a rapidly changing and complex environment of a storage silo, ensuring problems can be detected and solved before they evolve any further and significantly reducing food spoilage.

Casella, a leading world expert in monitoring solutions for noise, air sampling and vibration, has announced its schedule for courses and webinars for 2020.

The company has aligned a series of one-day courses on Air Sampling and Noise Monitoring in the Workplace, hosted at its headquarters in Bedford. Delivered by expert trainers, they provide managers and safety practitioners with guides to best practice, compliance and regulations.

The Introduction to Air Sampling course will run in March, June, September and November, and the Introduction to Noise course will be held in February, May, August and October. Both courses offer attendees a pragmatic guide to best practice, current legislation and the practical use of monitoring equipment, suitable for all levels of experience.

In addition, Casella will be running monthly free webinars covering best practices across its core knowledge base and product areas: Introduction to Workplace Noise, Use of SLMs and Noise Dosimeters, Introduction to Personal Dust Monitoring, Setting up Air Sampling Pumps, Introduction to Personal Sampling of Vapours and Gases and Introduction to Hand Arm Vibration.

The full schedule of Casella 2020 webinars is available on the Casella website and, registration is free. To book a place, visit  https://www.casellasolutions.com/uk/en/support/training.html or call +44(0)1234844100

Due to the high demand for medical technology, LASER COMPONENTS Detector Group has switched its production of IR detectors to multi-shift operation. The components manufactured in Arizona are important key elements in the examination of the CO2 level in breath gas analysis. Due to the current situation, production capacities in the medical technology sector must be increased significantly to provide urgently needed equipment.

In spectroscopic breath gas analysis, PbSe detectors can quickly detect the smallest fluctuations in CO2 concentration even without additional cooling. They can therefore be integrated into medical devices in a space-saving manner. In ventilators, the carbon dioxide content of exhaled air is measured to check whether the patient has absorbed the oxygen provided.

LASER COMPONENTS Detector Group’s portfolio includes all common IR technologies. The production facility in the U.S. state of Arizona primarily manufactures (x-)InGaAs-PIN photodiodes, pyroelectric DLaTGS and LiTaO3 detectors, and PbS and PbSe detectors. With many years of experience and employees who are known in the industry as proven experts, LASER COMPONENTS Detector Group has established itself as the global market leader for PbSe technology. In the E.U., LASER COMPONENTS is leading the campaign to extend RoHS exemptions to continue use of this technology in such important industries as medical technology.

LASER COMPONENTS’ IR detectors are supplied to well-known medical technology manufacturers. Coordination with these customers currently determines the international day-to-day business in order to ensure rapid delivery of critical components.

ION Science recently held a two-day service training course for representatives from Norwegian distributor, Vestteknikk AS, at its state-of-the-art facility in Cambridgeshire, UK.

Led by ION Science’s Technical Support Specialist and Trainer, Marcus Wadey-Leblond, the service training provided Vestteknikk’s Joar Nicolaysen and Kenneth Andre Rishaug with a comprehensive learning experience designed to strengthen their knowledge of the company’s full range of high performance photoionisation detectors (PIDs).

Joar and Kenneth were able to get ‘hands-on’ with the Ion Science instruments including Tiger, Tiger Select and TigerLT handheld PIDs, as well as the Falco fixed PID, Cub personal PID and GasCheck G and Tesla gas leak detectors.

Joar Nicolaysen, Service Technician at Vestteknikk AS comments: “We would like to thank Ion Science for providing an enjoyable training session. I’m pleased to say that it has helped make us more confident in the operation of the company’s gas detection instruments, which will enable us to provide faster and better support for the end user.

He continues: “Visiting Ion Science also means we got to know the team better which is invaluable when it comes to having a good in-depth dialogue going forward with our working relationship. The fact that it was just our company attending the training made the dialogue easier and the information we required could be tailored to fit our needs. “All in all it was a very enjoyable and productive trip from start to finish,” he concludes.

The service training programme is part of Ion Science’s on-going commitment to providing its worldwide distributor network with the necessary guidance and support to develop business in its key target markets, and to learn about its gas detection products in a collaborative environment.

ION Science is backed by some 55 distributors from across Europe and the rest of the world and also has offices in France, Germany, Italy, USA, China and India.

In 2018, there were an estimated 1.002 billion head of cattle worldwide, an increase of 6.5 million head over 2017. Global meat production has continued, and is seemingly continuing, to rise and although cattle now accounts for a relatively smaller percentage of overall meat consumption, there were still over 68 billion tonnes of cattle meat produced in 2014. Beef exported from the US alone in 2018 was worth 7.3 billion dollars so cattle farming remains big and profitable business.

However, there have been growing concerns about the environmental impact of cattle farming. This is largely because cattle produce a significant amount of methane gas, between 250 – 500 L per day. Methane is a more efficient and effective heat-trap than CO2, the most abundant greenhouse gas in the atmosphere, and therefore potentially has a large contribution towards global warming.

As livestock is a key source of nutritional and economical sustenance for many communities, cattle farming is unlikely to disappear in the immediate future. Therefore, finding ways to reduce methane production from cows is an important route to improving the sustainability of cattle farming and minimising its environmental impact.

Reducing Methane Production

Finding ways to reduce methane production from cows is currently a highly active area of research. Cows, and other ruminant species, produce methane as part of their digestion process. This is because ruminants are one of the few species that can digest cellulose, which is what the cell walls in plants are composed of. Breaking down cellulose is a multi-step process, involving regurgitation and re-ingestion of the food and the use of a large array of microbes that carry out fermentation of the plant material. The fermentation process is what generates the majority of methane gas, which exits the cow via eructation (burping) or flatus (farts).

Much of the research aimed to reduce this methane production involves finding methods to alter the digestive process and microbes in the cow’s stomach. Some success has been found by either changing the composition of the ruminants’ diets, such as increasing the amount of sugarcane feed or by the introduction of chemicals that act as methane inhibitors. The challenge with using additives is finding chemical species that are non-toxic and do not have unwanted side effects on produce, be it the meat or milk of the animal.

However, all of this research relies on being able to monitor methane production in cattle accurately and unobtrusively. Indirect calorimetry respiration chambers are often considered to be the ‘gold standard’ of methane measurement methods but involve large capital investment, are not ideally suited for use with large numbers of animals and require confinement of the animal, which may make such measurements not truly reflective of normal behaviour.

As changes in methane emission from dietary changes may be small, sensing technologies need to have good sensitivity as well as reproducibility and accuracy. Recent work has shown that non-dispersive infra-red (NDIR) sensor technologies show greater repeatability for measurement of methane concentrations and that the concentrations measured were in line with those measured by other techniques NDIR sensor technologies are particularly effective for methane detection for the same reason it is such an efficient heat trap in the atmosphere, methane strongly absorbs infra-red light.

Gas Sensing

Edinburgh Sensors have thirty years of experience in the development of NDIR gas sensors for the monitoring of hydrocarbons and other gaseous species. Their NDIR devices have already been demonstrating the ability to work well for detecting methane production in cows9 in field environments and are designed to be robust, easy to install and use.

The Guardian NG is an example of a Methane monitor that is ideal for such applications, capable of detecting methane in low concentrations of 0 – 1 %. The Guardian NG has an R323 interface with the option of TCI/IP communications protocol so can be connected to data logging networks to monitor in real-time changes in methane emission levels. The sensor also comes with data logging software, so only requires connection with a cable to a PC to be able to start instantly recording measurements.12

The device is designed to be robust, with minimal installation and set-up time. The zero stability is ±2% of range (over 12 months) with an excellent ±2% accuracy. Important for use on live farm environments, the readouts are also temperature, pressure and humidity compensated and will remain accurate over 0 – 95 % humidity conditions.

The Guardian NG only requires connection to a reference gas for set up and has a rapid response time, with a T90 of just 10 seconds. This is ideal for where samples from multiple cattle need to be processed quickly or a large number of samples are being taken per day. It can be set up as an automated gas analyzer installs to minimise the amount of personnel time involved in the monitoring. This is also completely noninvasive monitoring for the cattle and does not require trying to take samples from them, making the Guardian NG a cost-effective and easy solution for methane monitoring of cattle.

Supermarkets all over Australia and New Zealand are benefiting from advanced carbon dioxide monitors as new natural refrigeration systems are installed in the fight against climate change.

The Woolworths Group employs over 205,000 staff and serves 900 million customers each year. As a large and diverse organisation, Woolworths knows that its approach to sustainability has an impact on national economies, communities and environments, and this is reflected in the Group’s Corporate Responsibility Strategy 2020.

The strategy is built around twenty key targets which cover Woolworths’ engagement with customers, communities, supply chain and team members, as well as its responsibility to minimise the environmental impact of its operations. One of the twenty commitments within the strategy is to innovate with natural refrigerants and reduce refrigerant leakage in its stores by 15 per cent (of carbon dioxide equivalent) below 2015 levels.

Carbon dioxide (CO2) is commonly regarded as the ideal natural refrigerant. It is a non-toxic, non-flammable, odourless, colourless gas, however, high concentrations can cause unconsciousness and even death, so accurate, reliable monitoring is necessary for safety reasons and for the rapid detection of potential leaks. Woolworths, and its cold chain partner Emerson, therefore needed an accurate, reliable CO2 monitor that could fulfil this vital role as the Group expands the use of natural refrigerants in its stores.

Over the last 8 years, Vaisala carbon dioxide probes have been employed widely across Woolworths Group stores, delivering a range of benefits and helping the group to achieve its strategic goals.

Global move to natural refrigerants

Synthetic refrigerant gases have been utilised in a wide variety of industries for many decades. However, Chlorofluorocarbons (CFCs) caused damage to the ozone layer and were phased out following the Montreal Protocol in 1987. Production of Hydrochlorofluorocarbons (HCFCs) then increased globally, because they are less harmful to stratospheric ozone. However, HCFCs are very powerful greenhouse gases so Hydrofluorocarbons (HFCs) became more popular. Nevertheless, most HCFCs and HFCs have a global warming potential (GWP) that is thousands of times higher than that of carbon dioxide, so many countries have been lowering the use of HFCs, and the Kigali Amendment (2018) to the Montreal Protocol, will bring about a global phasedown of HFCs. Consequently, there is a strong push for the adoption of natural refrigerants such as carbon dioxide.

In Australia and New Zealand, Woolworths Group is leading the way in the move to refrigerants that have a dramatically lower GWP. Luke Breeuwer, Senior Commissioner at Woolworths, says: “I believe that ultimately all supermarket refrigeration, in store and back of house, will move to transcritical CO2, unless a better method emerges.

“CO2 refrigeration technology has improved markedly in recent years, which is enabling us to roll it out in most regions, except for parts of Queensland where humidity levels currently dictate the deployment of hybrid CO2 systems.”

The move to transcritical CO2 refrigeration systems involves a significant capital outlay, which may limit the speed of implementation at other supermarkets. At Woolworths Luke says: “There is pressure from our finance department to push ahead with the new systems; not just to deliver environmental benefits, but also to ensure that at some point in the future, we are not left with refrigeration assets that cannot be maintained. The capital costs of the initiative are being offset by also utilising this technology for in-store heating.”

Monitoring Carbon Dioxide

To protect the health and safety of customers, staff and contractors, around six CO2 sensors would be necessary in a traditional store. However, those with transcritical CO2 refrigeration would typically require twenty four sensors or more.

Many of the Woolworths stores’ refrigeration and HVAC control systems are supplied by Emerson. Looking back, Shannon Lovett, Senior Business Manager Cold Chain ANZ for Emerson, says: “Around 8 years ago we evaluated a locally sourced CO2 sensor, but it suffered from quality issues and failures, so we equipped one store with the Vaisala sensors as a ‘proof of concept’.

“Happily, the Vaisala probes performed extremely well, and have been rolled out in the Woolworths Group stores in Australia and New Zealand. We have also utilised Vaisala humidity and temperature sensors in a variety of similar applications. In comparison with some other CO2 sensors, the Vaisala monitors were more expensive, but they were very popular with our contractors and we found that Vaisala’s product reliability lowered the cost of ownership.”

Luke Breeuwer agrees with Shannon on the longer term benefits of investing in higher quality instruments, adding: “The MODBUS communications capability of the Vaisala Indigo200 Transmitter with the GMP252 probe is also a major advantage for us; it means that the amount of wiring required is substantially reduced, which lowers both complexity and costs.”

Commenting on the reliability of the Vaisala probes, Luke says: “We have large numbers of these sensors in operation but there have been no breakdowns or urgent call-outs, so the ongoing costs have been negligible. We are required to check sensor calibration every two years, but they are so stable that this check always shows the sensors to be within specification, which is great.”

Luke does recall one occasion when the accuracy of a Vaisala CO2 sensor was called into question. An installed probe was providing readings that were abnormally low, so a site visit was necessary. However, such was their faith in the sensors that an alternative explanation was sought, and after a period of speculation a Google search solved the mystery by revealing the propensity of (nearby) curing concrete to absorb CO2 through a process known as carbonation.

Advanced sensor technology

The Vaisala CARBOCAP Carbon Dioxide Probe GMP252 is an intelligent carbon dioxide sensor designed for harsh and humid environments where stable and accurate CO2 measurements are required. Importantly, the probe features second generation CARBOCAP technology. In addition to measuring CO2, an electrically tunable micromechanical filter enables a reference measurement at a wavelength where no absorption occurs. The reference measurement compensates for any potential changes in the light source intensity, as well as for contamination in the optical path, which means that the sensor is extremely stable over time. The probe also automatically compensates for temperature, pressure, oxygen and humidity, and with an operating temperature range from -40 to +60 °C, the sensor is able to measure CO2 accurately from 0 to 10,000 ppm, and up to 30,000 ppm with reduced accuracy.

Benefits of the Vaisala technology

From Woolworths’ perspective Luke says: “The main advantages are reliability, low maintenance and MODBUS communications. However, flexibility is important because we also utilise the Vaisala probes in-store to ensure that CO2 levels do not rise excessively. We achieve this by using monitoring data to automatically control and optimise fresh air intake.”

Emerson integrates the probes within its building management systems and Shannon highlights the facility to utilise a dual relay output for local alarms as a particularly useful feature. “Reliability is of course the main advantage for us,” he adds. “But the negligible maintenance requirement, the two year calibration check and MODBUS comms provide us with competitive advantages.”

Looking forward

By identifying the role of natural refrigerants in its Corporate Responsibility Strategy, Woolworths has made a very clear statement of intent. Two years ago, there were no transcritical CO2 stores in the group, but seven stores have now been converted and up to a dozen largely metropolitan stores will be converted in the coming year.

Summarising Luke says: “By utilising CO2 in our refrigeration systems we are helping to lower greenhouse gas emissions whilst also lowering operational costs. However, reliable CO2 monitoring plays a vitally important role; protecting staff and the public, while helping to identify and reduce leakage – a win win situation!”

Engineers have developed a new scanning technique inspired by the natural world that can detect corroding metals in oil and gas pipelines.

By mimicking how bats use differing wavelengths of ultrasound to detect objects, hunt, and avoid predators, engineers have developed a new system that combines two separate types of radiation, fast neutrons and gamma rays, to detect corrosion – a major cause of pipeline leaks.

With thousands of kilometres of pipelines used to transport oil and gas over huge distances globally, leaks are a major issue costing millions annually and have the potential to cause accidents and injuries as well as significant environmental damage.

Typically, corrosion in oil pipelines is measured with ultrasonic or electromagnetic techniques. However, these are not practical for underground pipelines, or for pipelines covered with insulating layers of concrete or plastic.

The new system, developed by Engineers from Lancaster University, the National Physical Laboratory, and a technology company, Hybrid Instruments Ltd, exploits the reflected signals, known as ‘backscatter’, of a combination of isolated fast-neutron and gamma radiation.

Neutrons and gamma rays have useful complementary characteristics. Neutrons interact mainly with low-density materials like plastics. In addition, fast neutrons have a high penetrating power, so they are suitable for probing thick materials. Gamma rays interact mainly with metals and not always are able to penetrate very thick materials of high density.

The two radiation types produce a different electronic signal. This means researchers can retain data on both types of radiation simultaneously using a novel detecting device called a ‘Mixed Field Analyser’, previously developed by Lancaster University and Hybrid Instruments Ltd.

The system produces a pencil-like beam of probing radiation, of neutrons and gamma, which is directed at the steel section being inspected.

The team tested the two imaging techniques in real time in a laboratory on samples of carbon-steel of different thicknesses.

The researchers were able to see differences in steel thickness. The sensors also worked when an insulating layer was replicated, with concrete or plastic, indicating the likelihood that defects in steels, as well as corrosion and rust, would produce variations in the backscatter.

These results indicate that if used on real pipelines then potential issues could be more easily detected and resolved before oil and gas is able to escape.

“The combined beams of neutrons and gamma rays in parallel bouncing back to an array of detectors yield a comprehensive and fast representation of the inner structure of steel,” said Mauro Licata, PhD researcher on the project from Lancaster University.

“This system works a bit like the chirps made by bats. These chirps are a superposition of different ultrasound wavelengths, which bounce back to the bats’ ears. As well as highlighting the benefits of combining multiple reflection sensing techniques to detect for problems such as corrosion, our work further illustrates the significant potential that can be had from taking inspiration from, and mimicking, systems that have evolved in the natural world.”

“Isolating neutrons and gamma rays backscattered from a steel surface in real time, in a way analogous to the way bats’ brains isolate backscatter ultrasound and thus avoid confusion with their own chirps, could help us isolate flaws in pipe walls more quickly and effectively,” said Professor Malcolm Joyce of Lancaster University and Hybrid Instruments Ltd. “This is a great example of NPL’s world-leading neutron facilities being used for innovative science with a positive impact,” said Neil Roberts of the National Physical Laboratory.

The intention is that the detector system would be further developed and used to detect faults by pointing it at sections of pipeline from the outside. However, the investigators say more research is needed in the field of neutron detectors to make the system faster.

The researchers suggest the technology could also be used in other applications, such as inspecting the integrity of structures such as bridges.

The research has been outlined in the paper ‘Depicting corrosion-born defects in pipelines with combined neutron/γ ray backscatter: a biometric approach’, which has been published by the journal Scientific Reports.

Research at Oregon State University has pushed science closer to developing an electronic nose for monitoring air quality, detecting safety threats and diagnosing diseases by measuring gases in a patient’s breath.

Recently published research led by Cory Simon, assistant professor of chemical engineering in the OSU College of Engineering, in collaboration with chemical engineering professor Chih-Hung Chang focused on materials known as metal-organic frameworks, or MOFs.

The research took aim at a critical yet understudied hurdle in using MOFs as gas sensors: Out of the billions of possible MOFs, how do you determine the right ones for building the optimal electronic nose?

MOFs have nanosized pores and selectively adsorb gases, similar to a sponge. They are ideal for use in sensor arrays because of their tunability, enabling engineers to use a diverse set of materials that allows an array of MOF-based sensors to deliver detailed information.

Depending on which components make up a gas, different amounts of the gas will adsorb in each MOF. That means the composition of a gas can be inferred by measuring the adsorbed gas in the array of MOFs using micro-scale balances.

The challenge is that all MOFs adsorb all gases – not to the same extent, but nevertheless the absence of perfect selectivity prevents an engineer from simply saying, “let’s just dedicate this MOF to carbon dioxide, that one to sulfur dioxide, and another one to nitrogen dioxide.”

“Curating MOFs for gas sensor arrays is not that simple because each MOF in the array will appreciably adsorb all three of those gases,” Simon said.

Human noses navigate this same problem by relying on about 400 different types of olfactory receptors. Much like the MOFs, each olfactory receptor is activated by many different odours, and each odour activates many different receptors; the brain parses the response pattern, allowing people to distinguish a multitude of different odours.

“In our research, we created a mathematical framework that allows us, based on the adsorption properties of MOFs, to decide which combination of MOFs is optimal for a gas sensor array,” Simon said. “There will inevitably be some small errors in the measurements of the mass of adsorbed gas, and those errors will corrupt the prediction of the gas composition based on the sensor array response. Our model assesses how well a given combination of MOFs will prevent those small errors from corrupting the estimate of the gas composition.”

Though the research was primarily mathematical modeling, the scientists used experimental adsorption data in real MOFs as input, Simon said, adding that Chang is an experimentalist “who we are working with to make a real-life electronic nose to detect air pollutants.”

“We are currently seeking external funding together to bring this novel concept into physical realisation,” Simon said. “Because of this paper, we now have a rational method to computationally design the sensory array, which encompasses simulating gas adsorption in the MOFs with molecular models and simulations to predict their adsorption properties, then using our mathematical method to screen the various combinations of MOFs for the most accurate sensor array.”

Meaning that instead of an experimental trial-and-error approach to decide which MOFs to use in a sensor array, engineers can use computational power to curate the best collection of MOFs for an electronic nose.

Another exciting application of such a nose could be diagnosing disease. The volatile organic compounds humans emit, such as through our breath, are filled with biomarkers for multiple diseases, and studies have shown that dogs — which have twice the number of different olfactory receptors as humans — can detect diseases with their nose.

Marvelous though they are, however, dogs’ noses aren’t as practical for widespread diagnostic use as a carefully crafted and manufactured sensor array would be.

A highly sensitive, wearable gas sensor for environmental and human health monitoring may soon become commercially available, according to researchers at Penn State and Northeastern University.

The sensor device is an improvement on existing wearable sensors because it uses a self-heating mechanism that enhances sensitivity. It allows for quick recovery and reuse of the device. Other devices of this type require an external heater. In addition, other wearable sensors require an expensive and time-consuming lithography process under cleanroom conditions.

Hand and arm showing sensor applied to inner write with moble phone sized read beside it.

“People like to use nanomaterials for sensing because their large surface-to-volume ratio makes them highly sensitive,” said Huanyu Cheng, assistant professor of engineering science and mechanics and materials science and engineering, Penn State. “The problem is the nanomaterial is not something we can easily hook up to with wires to receive the signal, necessitating the need for something called interdigitated electrodes, which are like the digits on your hand.”

Cheng and his team use a laser to pattern a highly porous single line of nanomaterial similar to graphene for sensors that detect gas, biomolecules, and in the future, chemicals. In the non-sensing portion of the device platform, the team creates a series of serpentine lines that they coat with silver. When they apply an electrical current to the silver, the gas sensing region will locally heat up due to significantly larger electrical resistance, eliminating the need for a separate heater. The serpentine lines allow the device to stretch, like springs, to adjust to the flexing of the body for wearable sensors.

The nanomaterials used in this work are reduced graphene oxide and molybdenum disulfide, or a combination of the two; or a metal oxide composite consisting of a core of zinc oxide and a shell of copper oxide, representing the two classes of widely used gas sensor materials — low-dimensional and metal oxide nanomaterials.

“Using a CO2 laser, often found in machine shops, we can easily make multiple sensors on our platform,” Cheng said. “We plan to have tens to a hundred sensors, each selective to a different molecule, like an electronic nose, to decode multiple components in a complex mixture.”

The U.S. Defense Threat Reduction Agency is interested in this wearable sensor to detect chemical and biological agents that could damage the nerves or lungs, according to the researchers. A medical device company is also working with the team to scale up production for patient health monitoring, including gaseous biomarker detection from the human body and environmental detection of pollutants that can affect the lungs.

Ning Yi, a doctoral student in Chen’s lab and co-lead author of the paper posted online in the Journal of Materials Chemistry A, said, “In this paper, we showed that we could detect nitrogen dioxide, which is produced by vehicle emissions. We can also detect sulfur dioxide, which, together with nitrogen dioxide, causes acid rain. All these gases can be an issue in industrial safety.”

The researchers said their next step is to create high-density arrays and try some ideas to improve the signal and make the sensors more selective. This may involve using machine learning to identify the distinct signals of individual molecules on the platform.

Geo-environmental consultancy, IGE Consulting, is using a TigerLT handheld photoionisation detector (PID) from Ion Science to provide comprehensive risk assessments of on-site contamination. Supplied by UK-based distributor, Shawcity, the instrument was chosen for its flexible lamp design options that target different ranges and types of gases, and is monitoring potentially dangerous volatile organic compounds (VOCs) in soils which may cause harm to human health or compromise safety.

Manchester-based IGE Consulting undertakes desk studies and intrusive site investigation works on sites to be developed into residential or commercial developments. The company operates across the UK and provides a tailored service to meet client requirements such as pre-acquisition / planning development, abnormal costing evaluations, site investigation works and construction efficiency savings.

Molly Brown, Geo-environmental Engineer at IGE Consulting comments: “We previously hired the Ion Science TigerLT for monitoring VOCs in soils so have used it numerous times with great success. To save costs in the long term, it made sense to purchase one of the instruments. It also adds value to our site investigations and reports as we are able to provide a more comprehensive risk assessment.”

Molly continues: “One of the most appealing features of the TigerLT for us is the different options for lamps which allow various VOC gases to be detected. For example, we can choose lamps that give us a wide range or target specific ranges if we need to look for a particular type of VOC gas.”

Ion Science’s TigerLT, which offers worldwide Intrinsic Safety (IS) certification for use in potentially explosive atmospheres, is a streamlined, low-cost version of Ion Science’s well proven Tiger PID model.

Like all Ion Science PID instruments, the TigerLT incorporates the company’s market-leading PID technology with advanced patented fence electrode system. This three-electrode format ensures increased resistance to humidity and contamination for ultimate reliability and accuracy in the field.

With a detection range of 0.1 – 5,000 ppm utilising a standard two-point calibration protocol, Ion Science’s robust TigerLT also offers an unrivalled industry response time of just two seconds and equally quick clear down.

Both simple to operate and service, the TigerLT offers easy access to the lamp and sensor with batteries that can be safely replaced in hazardous environments. The intrinsically safe instrument also meets ATEX, IECEx, North American and Canadian standards.

Molly continues: “The TigerLT instrument is working well and enables us to provide a more comprehensive risk assessment of on-site contamination and the associated human health risk.

“In fact, the TigerLT PID instrument has already reduced costs for one of our clients by locating a VOC hotspot and proving blanks elsewhere on site meaning they did not have to install a VOC barrier on proposed plots. This client now only has to install VOC barriers on four out of 54 locations.”

The key advantage of TigerLT over other similar, low-cost handheld PID instruments is its market-leading accuracy and run time due to its anti-contamination and humidity-resistant design. Another attribute is its global Intrinsic Safety certification. Although the accreditation process can differ from country to country, the TigerLT can be used in explosive hazardous areas such as within petrochemical plants that are located anywhere in the world.

The TigerLT six pin MiniPID detector cell with anti-contamination design dramatically extends run time in the field. Low cost filters and lamps can be easily changed in minutes, minimising downtime.

It features long life rechargeable Li-ion batteries which give up to 24 hours usage. Fast battery charging allows the instrument to be fully charged in 6.5 hours, while eight hours of use can be achieved from 1.5 hours of charging time.

TigerLT features a protective, removable boot for harsh environments while a large, clear back-lit display allows for easy viewing in any light condition. It is IP65 rated against water ingress. An integrated torch is designed for directing the instrument’s probe into dimly lit areas. Other features include a loud 95 dB audible alarm and multiple language support.

Ready to use, straight out of the box, the TigerLT does not require complicated set-up procedures via a PC to perform basic functions.

“The Tiger LT is performing well and as expected from our previous experience. The service provided by Shawcity was good with fast delivery. Overall, we are very happy and would recommend the instrument to other environmental and geotechnical consultancies,” Molly concludes.