Handheld Sensor for Point-of-Care Methanol Detection in Breath and Liquor (2020)

Introduction “Over 90 Killed in India by Toxic Homemade Liquor” read the headline in The New York Times on Feb. 23, 2019 [1]. In fact, such outbreaks are quite common with thousands of victims each year [2]. However, no inexpensive and fast point-of-care method exists for diagnosis of methanol intoxication or screening of laced alcoholic beverages to rapidly respond or even prevent such disasters. Currently, methanol poisoning is detected directly through blood analysis by gas chromatography or indirectly through blood gas analysis [3]. However, both require trained personnel, are expensive and rarely available in developing countries where most outbreaks occur. Blood methanol levels can also be determined non-invasively in exhaled breath, analogous to ethanol as widely applied by law enforcement [4]. However, current chemical sensors cannot distinguish methanol from the much higher ethanol background. Here, we present an inexpensive and handheld detector for rapid and highly selective methanol detection. It consists of a separation column (Tenax) separating methanol from interferants like ethanol, acetone or hydrogen and a chemoresistive gas sensor (Pd-doped SnO 2 nanoparticles) to quantify the methanol concentration. This way, methanol is precisely quantified in vivo in the breath of an ethanol-intoxicated subject and in liquor headspace without interference of much higher ethanol levels. Method The methanol detector consists of a separation column placed upstream of a chemoresistive microsensor. The separation column is a packed bed of 150 mg Tenax TA (60–80 mesh, ~35 m 2 g -1 ) inside a Teflon tube (4 mm inner diameter). The sensor consists of Pd-doped SnO 2 (1 mol% Pd) nanoparticles produced by flame spray pyrolysis (FSP) and directly deposited by thermophoresis onto micromachined free-standing membrane type sensor substrates (1.9 x 1.7 mm 2 ). The sensing film is heated to 350 °C through the back heater of the sensor substrate, while a miniature vane pump draws the sample through the column to the sensor at 25 mL min -1 . The detector is characterized with synthetic gas mixtures in a mixing setup adapted from [5] and tested directly on methanol-spiked liquor (Indonesian Arrack) and breath of a drunken volunteer. Results and Conclusions Figure 1 shows the separation column and the micromachined metal-oxide gas sensor of the handheld methanol detector. Breath or the headspace of a beverage is drawn by a pump through the separation column to the sensor. The separation column separates analytes based on their interaction with the Tenax particles, as in chromatography, although much more compact (4.5 cm long and 4 mm inner diameter) and simpler in design. The sensor is micromachined, offering small size and minimal power requirement (76 mW at 350 °C) readily suitable for integration into a battery-driven device. In combination, the resulting detector senses methanol within 2 min in a wide concentration range of 1–918 ppm and can differentiate normal from toxic breath methanol levels (Figure 2). Most importantly, due to separation of analytes in the column, it is not interfered irrespective of much higher ethanol concentrations, as well as other possible interferants (e.g., hydrogen, acetone). Figure 3a shows the response of the detector when sampling the headspace of methanol-laced liquor (Arrack). Thereby, concentrations down to 0.3 vol% are detected and distinguished from the pure liquor. Even small differences between 0.3, 0.4 and 0.5 vol% (i.e., close to the legal limit [6]) are clearly resolved with high signal-to-noise ratio &gt;100. As first proof-of-concept, the detector was also tested on breath of a volunteer after consumption of ethanol. Figure 3b shows the response of the detector to normal and methanol-spiked breath with a methanol concentration of 135 ppm, indicative for a serious intoxication (&gt;133 ppm [2]). Thereby, the added methanol is clearly detected separated from the ethanol background at its specific retention time with high signal-to-noise ratio &gt;1000. In both applications (liquor headspace and breath) the detector fully recovers within 15 min by flushing with ambient air. As a result, this detector shows great promise for quick and non-invasive screening of methanol poisoning from breath and laced alcoholic beverages. Based on its compact size and low price, it could be used by locals, tourists and first responders in developing countries, where most outbreaks occur.[7] References [1] K. Schultz, H. Kumar. The New York Times: Over 90 killed in India by toxic homemade liquor . 2019 March 6, 2019; Available from: https://www.nytimes.com/2019/02/23/world/asia/india-poison-alcohol.html . [2] The American Academy of Clinical Toxicology Ad Hoc Committee on the Treatment Guidelines for Methanol Poisoning:, D.G. Barceloux, G. Randall Bond, E.P. Krenzelok, H. Cooper, J. Allister Vale, American Academy of Clinical Toxicology practice guidelines on the treatment of methanol poisoning , Journal of Toxicology: Clinical Toxicology. 40 (2002) 415-446. [3] J.A. Kraut, Diagnosis of toxic alcohols: limitations of present methods , Clinical Toxicology. 53 (2015) 589-595. [4] A.T. Güntner, S. Abegg, K. Königstein, P.A. Gerber, A. Schmidt-Trucksäss, S.E. Pratsinis, Breath sensors for health monitoring , ACS Sensors. 4 (2019) 268-280. [5] J. van den Broek, A.T. Güntner, S.E. Pratsinis, Highly selective and rapid breath isoprene sensing enabled by activated alumina filter , ACS Sensors. 3 (2018) 677-683. [6] A.J. Paine, A.D. Dayan, Defining a tolerable concentration of methanol in alcoholic drinks , Human &amp; Experimental Toxicology. 20 (2001) 563-568. [7] J. van den Broek, S. Abegg, S.E. Pratsinis, A.T. Güntner, Highly selective detection of methanol over ethanol by a handheld gas sensor , Nature Communications. 10 (2019) 4220. Figure 1