Almost all modern mobile phones have a built-in compass or magnetometer that detects the direction of the Earth’s magnetic field and provides critical information for navigation. Now, a team of researchers at the National Institute of Standards and Technology (NIST) has developed a technique that uses an ordinary cell phone magnetometer for a completely different purpose: measuring glucose concentration, a marker of diabetes, with high precision.
The same technique, which uses the magnetometer together with magnetic materials designed to change their shape in response to biological or environmental signals, could be used to quickly and inexpensively measure a number of other biomedical properties to monitor or diagnose human diseases. The method also has the potential to detect environmental toxins, said NIST scientist Gary Zabow.
In their proof-of-concept study, Zabow and fellow NIST researcher Mark Ferris attached a small well containing the solution to be tested and a strip of hydrogel, a porous material that swells when immersed in water, to a cell phone. . The researchers embedded small magnetic particles inside the hydrogel, which they had designed to react to the presence of glucose or pH levels (a measure of acidity) by expanding or contracting. Changes in pH levels can be associated with a variety of biological disorders.
As the hydrogels enlarged or shrank, they moved the magnetic particles closer or further away from the mobile phone’s magnetometer, which detected corresponding changes in magnetic field strength. Using this strategy, the researchers measured glucose concentrations as small as a few millionths of a mole (the scientific unit for a certain number of atoms or molecules in a substance). Although such high sensitivity is not required to monitor glucose levels at home using a drop of blood, in the future it could allow routine glucose testing in saliva, which contains a much lower concentration of sugar.
The researchers reported their findings in the March 30, 2024, issue of Nature Communications.
Engineered or “smart” hydrogels like those the NIST team employed are inexpensive and relatively easy to make, Ferris said, and can be tailored to react to a number of different compounds that medical researchers may want to measure. In their experiments, he and Zabow stacked individual layers of two different hydrogels, each of which contracted and expanded at different rates in response to pH or glucose. These bilayers amplified the motion of the hydrogels, making it easier for the magnetometer to track changes in magnetic field intensity.
Because the technique does not require any electronic device or power source beyond that of the cell phone nor does it require any special sample processing, it offers an inexpensive way to perform testing, even in relatively resource-poor settings.
Future efforts to improve the precision of such measurements using cell phone magnetometers could enable the detection of DNA strands, specific proteins, and histamines (compounds involved in the body’s immune response) at concentrations as low as a few tens of nanomoles (trillionths). of one mole). .
That improvement could have a substantial benefit. For example, measuring histamines, which are typically detected in urine at concentrations ranging from 45 to 190 nanomoles, would typically require a 24-hour urine collection and sophisticated laboratory analysis.
“A home test using a mobile phone magnetometer sensitive to nanomolar concentrations would allow measurements to be made with much less hassle,” Ferris said. More generally, greater sensitivity would be essential when only a small amount of a substance is available for testing in extremely dilute quantities, Zabow added.
Similarly, the team’s study suggests that a cell phone magnetometer can measure pH levels with the same sensitivity as a thousand-dollar tabletop meter but at a fraction of the cost. A home brewer or baker could use the magnetometer to quickly test the pH of various liquids to hone their craft, and an environmental scientist could measure the pH of on-site groundwater samples with greater accuracy than a test strip could provide. of litmus.
To make mobile phone measurements a commercial success, engineers will need to develop a method to mass produce the hydrogel test strips and ensure they have a long shelf life, Zabow said. Ideally, he added, hydrogel strips should be designed to react more quickly to environmental signals in order to speed up measurements.