Sensors Mag

Nanomix Offers Nanotechnology-Based Hydrogen Sensor

July 1, 2005 By: Peter Adrian

This content is excerpted from Sensor Technology Alert and Newsletter, a sensor intelligence service published by the Technical Insights unit of Frost & Sullivan.

Nanomix Incorporated has launched its first commercial nanosensor product--an ultra low-power, highly specific hydrogen detection device that uses the company's carbon nanotube sensing elements combined with proprietary chemistry and is aimed at monitoring hydrogen gas in industrial environments.

Carbon nanotubes are minute cylindrical forms of carbon that can have key electrical and thermal properties. The carbon nanotubes used in Nanomix's devices are doped with proprietary chemicals and silicon, and are about 1 nm in diameter.

Using highly sensitive carbon nanotube technology purportedly allows the hydrogen sensor to be stable and highly specific to hydrogen, rendering it invulnerable to cross-sensitivity to other analytes (such as hydrogen sulfide and carbon monoxide) and immune to false alarms. The device, which has been in beta site testing since 2004, purportedly requires only nanowatts of power for detection, facilitating its integration into a wireless network and ease of deployment. Nanomix's hydrogen sensor is designed to enhance plant and first-responder safety in industrial settings via long-term monitoring of accidental accumulation of explosive hydrogen gas.

Nanomix has appointed KWJ Engineering as its first distributor. KWJ Engineering has been involved in the evaluation and testing of hydrogen detection device from the prototype stage. Ken Johnson, president of KWJ Engineering, was part of Nanomix's beta test program.

Hydrogen can build up due to over-charging of batteries or other leaks. Current hydrogen detection devices tend to rely on catalytic bead sensors or MOS (metal oxide semiconductor) sensors that have performance limitations, Nanomix has noted. Catalytic bead technology may have difficulty differentiating between hydrogen and other gases, such as propane, isopropanol, or carbon monoxide, opening up the possibility of false alarms. MOS devices can be sensitive to temperature, humidity, or other hydrocarbons, which could limit the deployment of such sensors and potentially lead to false alarms.

Nanomix's carbon nanotubes are combined with silicon microstructures. The nanotube network is coated with the chemical or biological analyte of interest. Interaction between the recognition layer and the analyte generate a measurable change in the electronic characteristics of the detection device. Nanomix has purportedly developed scalable processes for growing uniform, nanoelectronic detection devices directly on silicon wafers. The nanotubes are grown into sensor array patterns using proprietary methods and semiconductor manufacturing techniques. Due to their scalable manufacturing techniques, Nanomix does not envision any limitations in production capacity.

The hydrogen sensor purportedly can respond within a few seconds, and is, therefore suitable for leak detection in battery sheds or similar applications. The company's current hydrogen sensor has an operating range of 2,000 ppm (parts-per-million) to 20,000 ppm levels, which is 5% to 50% of the lower explosive limit for hydrogen. The precision of the hydrogen sensor is plus or minus 15% at full scale. The technology can be tuned to operate in other detection ranges. The device purportedly provides high specificity to hydrogen gas, thereby reducing or eliminating the issue of cross sensitivity or reactivity and resulting problems, such as false alarms. Nanomix's hydrogen sensor could be employed in a wired or wireless configuration. The wireless sensor runs off a 3V battery, while the 4 mA to 20 mA sensor is powered by the current loop.

David Macdonald, Nanomix's president and CEO, explained to Sensor Technology that Nanomix initially developed hydrogen storage technology, using nanomaterials as a storage mechanism for hydrogen. "The hydrogen detection concept was a natural progression from that storage platform," he noted. "Additionally, utilizing the ultra sensitivity of nanoelectronic detection we are able to specifically detect hydrogen with extremely low power requirements. Our platform is an ideal choice for detecting this explosive gas."

The key target applications for Nanomix's hydrogen sensor include room hydrogen monitoring, battery sheds, and laboratory point-of-use monitoring.

Presently, Nanomix is focused on launching their hydrogen detection platform. However, they have various other products under development, including a medical breath carbon dioxide detection device and bio-molecule detection solutions for bio-medical applications.

Nanomix expects its next product launch will be a carbon dioxide detection device applied to emergency respiratory monitoring. This device will take respiratory information currently available in the operating room, and make it available in the ambulance and any other place where respiratory monitoring is needed.

Nanomix's hydrogen detection device is based on the company's Sensation nanostructured detection platform. In May 2005, Nanomix was issued US Patent 6,894,359 for the Sensation detection platform. The patent, entitled Sensitivity Control for Nanotube Sensors, includes claims related to nanostructure sensing devices for detecting an analyte. Such devices include nanostructures connected to conductive elements on a substrate. Contact regions adjacent to points of contact between the nanostructures and the conductive elements are given special treatment. The proportion of nanostructure surface area within contact regions can be maximized to achieve sensing at very low analyte concentrations.

The contact regions can be passivated in order to prevent interaction between the environment and the contact regions for sensing at higher analyte concentrations and for reducing cross-sensing. The contact regions and at least some portion of the nanostructures can be covered with a material that is at least partially permeable to the analyte of interest and impermeable to some other species to tune selectivity and sensitivity of the nanostructure sensing device. The patent also pertains to an electronic system for detecting analytes.

According to Frost & Sullivan's research service on An Assessment on the Future of Carbon Nanotubes--Strategic Analysis of the Market & Potential (published June 2004), world revenues for the carbon nanotube market are projected to reach about $540.0 million in 2007. At that time, the distribution of the overall carbon nanotube revenues by application is anticipated to be: field emission devices--31.2%; electronics (including semiconductor components, memory, sensors, and probes)--35.6%; composites--14.5%; fuel cells--6.0%; batteries--3.8%; and research institutions--8.9%.

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