Please cite this article as: T.A.Vincent, J.W.Gardner, A low cost MEMS based NDIR system for the monitoring of carbon dioxide in breath analysis at ppm levels, Sensors and Actuators B: Chemical http://dx.doi.org/10. 1016/j.snb.2016.04.016 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.A low cost MEMS based NDIR system for the monitoring of carbon dioxide in breath analysis at ppm levels Highlights  MEMS based NDIR system for ppm CO2 detection with lock-in amplifier.  Fast 1.3 s response time for breath-by-breath analysis.  Portable breath analyser designed for measuring metabolic rate of subjects.  Effect of path length on NDIR system investigated with novel sensor housing.  Silicon on insulator IR emitter used for low power, low cost gas detection. AbstractThe molecules in our breath can provide a wealth of information about the health and well-being of a person. The level of carbon dioxide (CO2) is not only a sign of life but also when combined with the level of exhaled oxygen provides valuable health information in the form of our metabolic rate. We report upon the development of a MEMS-based non-dispersive infrared CO2 sensor for inclusion in a hand held portable breath analyser. Our novel sensor system comprises a thermopile detector and low power MEMS silicon on insulator (SOI) wideband infrared (IR) emitter. A lock-in amplifier design permits a CO2 concentration of 50 ppm to be detected on gas bench rig. Different IR path lengths were studied with gases in dry and humid (25 % and 50 % RH) in order to design a sensor suitable for detecting CO2 in breath with concentrations in the range of 4 to 5 %. A breath analyser was constructed from acetal and in part 3D printed with a side-stream sampling mechanism and tested on a range of subjects with two data-sets presented here. The performance of the novel MEMS based sensor was validated using a reference commercial breath-by-breath sensor and produced comparable results and gave a response time of 1.3 s. Further work involves the detection of other compounds on breath for further metabolic analysis and reducing the overall resolution of our MEMS sensor system from ca. 250 ppm to 10 ppm.

We report here on the results of a study into the response of a tungsten oxide based low power MEMS gas sensor to ppb of nitrogen dioxide at low levels of ambient oxygen. It was found that the resistive gas sensors not only had a high sensitivity to NO 2 (3.4%/ppb vs. 0.2%/ppb obtained for commercial MOX) but can still operate reliably at lower oxygen levels (down to 0.5 %) albeit with slightly longer response and recovery times. The optimal operating temperature was determined to be ca. 350°C and so easily within the range of a MEMS based SOI CMOS substrate. The response was sensitive to significant changes in ambient humidity, but was found to have low cross-sensitivity to CO, hydrogen, methane, and acetone even at much higher ppm levels. We believe that these tungsten oxide gas sensors could be exploited in harsh applications, i.e. with a low oxygen (lean) environment often associated in the exhaust gases from combustion systems.

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The wealth of information concealed in a single human breath has been of interest for many years, promising not only disease detection, but also the monitoring of our general well-being. Recent developments in the fields of nano-sensor arrays and MEMS have enabled once bulky artificial olfactory sensor systems, or so-called “electronic noses”, to become smaller, lower power and portable devices. At the same time, wearable health monitoring devices are now available, although reliable breath sensing equipment is somewhat missing from the market of physical, rather than chemical sensor gadgets. In this article, we report on the unprecedented rise in healthcare problems caused by an increasingly overweight population. We first review recently-developed electronic noses for the detection of diseases by the analysis of basic volatile organic compounds (VOCs). Then, we discuss the primary cause of obesity from over eating and the high calorific content of food. We present the need to measure our individual energy expenditure from our exhaled breath. Finally, we consider the future for handheld or wearable devices to measure energy expenditure; and the potential of these devices to revolutionize healthcare, both at home and in hospitals.

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Highlights Custom sensor module developed for use in harsh environments by rescue personnel High-bandwidth MOX sensors evaluated to plumes of VOCs inside a wind tunnel PdPt SnO2, WO3 and NiO coated MOX sensors produce fast responses to low ppm plumes Pulse broadening of VOC plumes observed and mapped inside tunnel Performance verified in real world, unit is ready for use in hazardous environments

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