With the technology currently available, diabetics have to check their blood sugar by pricking their finger and testing a drop of blood with a glucometer. This unpleasant method could soon be replaced by a non-invasive and painless procedure resulting from a study in progress at the Center for Research and Development of Functional Materials (CDFM), one of the Research, Innovation and Dissemination Centers (RIDCs) supported by FAPESP. The device that scientists are developing there is a sensor similar to a breathalyzer, except that it analyzes not blood alcohol content but rather a key biomarker of diabetes in the patient’s breath.
The principle underlying the device is the sensitivity of silver tungstate (α-Ag2WO4) to acetone (C3H6O). “The development of gas sensors is one of CDFM’s research lines, and we’re paying special attention to silver tungstate. Our main motivation is to use it to detect and measure the acetone vapor in exhaled breath. Everyone’s breath contains acetone vapor, but in diabetics, it’s about double the amount in normal people’s breath. While a non-diabetic exhales 0.3 to 0.9 parts per million, a diabetic exhales over 1.8 parts per million,” physicist Luís Fernando da Silva told Agência FAPESP.
Silvia is a researcher at CDFM and has a postdoctoral scholarship from FAPESP. He studies nanostructured materials used as gas sensors and is the lead author of the article “Acetone gas sensor based on α-Ag2WO4 nanorods obtained via a microwave-assisted hydrothermal route”, published in the Journal of Alloys and Compounds.
The study described in the article brought together researchers at São Paulo State University (UNESP), with which Silva is affiliated, as well as the University of São Paulo (USP), the Federal University of São Carlos (UFSCar) and Piauí State University (UEP) in Brazil; Jaume I University in Castellón, Spain; and Aix-Marseille University in Marseille, France. Besides Silva, the following researchers in the Brazilian group are or have been supported by FAPESP: Ariadne Cristina Catto, Waldir Avansi Junior, Laécio Santos Cavalcante,Valmor Roberto Mastelaro, and CDFM’s principal investigator Elson Longo.
“In 2014, we observed for the first time that silver tungstate could serve as a sensor of ozone gas. We published our finding in an articlein the journal Nanoscale, ‘A novel ozone gas sensor based on one-dimensional (1D) α-Ag2WO4 nanostructures’, which attracted a great deal of attention at home and abroad,” Silva said. “Since then, we’ve focused on acetone detection for use in monitoring diabetes. The same principle can be used to identify other diseases via specific gases in exhaled breath.”
The researchers are now studying the material’s selectivity by testing its response to other gases normally present in exhaled breath, such as water vapor, carbon dioxide, alcohols and aldehydes. “Our interest is silver tungstate’s detection of acetone, and not of these other gases,” Silva explained. “A device that detects several substances at the same time can’t be used for this type of monitoring. We’ve discovered so far that the material’s response to water vapor is low, which is good news because water vapor accounts for a very large proportion of exhaled breath. We’ve also tested its response to ethanol and ammonia. Now we need to see how it responds to carbon dioxide and aldehydes.”
The silver tungstate used as a sensor material is made up of nanoparticles in the form of rods. The rods are deposited on an electrode. The chemical reaction between acetone vapor and the surface of the sensor material reduces the latter’s electrical resistance. When the gas is removed, the resistance returns to the initial value. The variation in resistance detected by the sensor is used to establish a correlation between resistance and the acetone concentration.
“Because the variation doesn’t obey a linear function, the correlation between resistance and concentration has to be obtained experimentally, point by point,” Silva said. “On the basis of these experimental measurements, it’s possible to construct a device with a display screen that directly shows the user’s blood sugar level by breath analysis. We haven’t yet produced this device, but we’re nearly there.”