Rapid Diagnosis of Methanol Poisoning with a Handheld Detector

Abstract

Introduction Over 800 people died this year in Iran alone as a result of methanol poisoning [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 to rapidly respond to disasters. Currently, methanol poisoning is detected directly through blood analysis by gas chromatography or indirectly through blood gas analysis [3]. 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 (Figure 1a), analogous to ethanol as widely applied by law enforcement [4]. However, current chemical sensors cannot distinguish methanol from the usually much higher ethanol background in the breath of poisoned victims. Here, we present an inexpensive and handheld detector for rapid and highly selective methanol detection. Method The handheld detector is shown in Figure 1b. It consists of a capillary inlet for sampling from Tedlar bags, a separation column consisting of a packed bed of Tenax TA polymer sorbent to separate the breath mixture [5], a chemoresistive Pd-doped SnO2 microsensor to quantify the methanol and ethanol concentrations, and a rotary vane pump (SP 135 FZ 3 V, Schwarzer Precision, Germany) drawing the sample through the column to the sensor. A microcontroller (Raspberry Pi Zero W, Great Britain) with integrated circuits on a custom-designed printed circuit board (PCB) is used for autonomous sensor heating, film resistance readout, pump flow control as well as wireless communication with a computer or smartphone [6].The detector was validated with methanol-spiked breath of drunken volunteers (0.1% blood ethanol) [7]. Late expiratory breath was sampled into Tedlar bags and subsequently spiked with 10–1000 ppm methanol on a dynamic gas mixing setup to simulate poisoning without intoxicating volunteers. Samples were then measured by the detector and a high resolution proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF-MS). Results and Conclusions The main challenge for chemical sensors is the selective detection of breath methanol over high ethanol concentrations present after consumption of contaminated beverages or during methanol poisoning treatment where ethanol is even used as an antidote. The present detector (Figure 1b) achieves this with a compact separation column, where ethanol absorbs stronger (and thus is retained longer) than methanol, analogous to GC. A downstream chemoresistive microsensor based on Pd-doped SnO2 nanoparticles quantifies the methanol and ethanol sequentially with high sensitivity. Figure 1c shows the sensor response to breath (green) after consumption of an alcoholic beverage and when spiked with 23 (blue), 66 (purple) and 148 ppm (red) methanol. These methanol levels correspond to endogenous (0–10 ppm), harmless exogenous (10–52 ppm) and toxic concentrations (>52 ppm), respectively. Most importantly, the sensor detects no significant methanol concentration in the original breath (PTR-TOF-MS, <1 ppm) with sensor response below the LOD, as expected from physiological breath methanol concentrations (median 0.26 ppm), while the spiked concentrations are recognized distinctly at 1.8 min.In total, 105 methanol-spiked breath samples from 20 volunteers after consumption of water, beer, liquor or wine were evaluated and the measured methanol concentrations of the detector and PTR-TOF-MS are shown in Figure 2a. Indicated also are the concentration ranges where antidote (>52 ppm, grey shaded) and hemodialysis (>131 ppm, red shaded) treatments are recommended from the corresponding blood methanol concentrations. The detector shows excellent agreement with PTR-TOF-MS (R2 = 0.966) over the entire concentration range (14–1079 ppm) and in the presence of 0–316 ppm ethanol.As a result, this device is promising to screen methanol poisoning and classify severity. This detector can be equipped with a disposable mouthpiece, as for commercial breath alcohol testers, and readily applied as a point-of-care diagnostic tool for fast screening of methanol poisoning by first responders and clinicians.