Nearly every modern cellphone has a built-in compass, or magnetometer, that detects the direction of Earth’s magnetic field, providing critical information for navigation. Now a team of researchers on the National Institute of Standards and Technology (NIST) has developed a way that uses an unusual cellphone magnetometer for a completely different purpose — to measure the concentration of glucose, a marker for diabetes, to high accuracy.
The identical technique, which uses the magnetometer together with magnetic materials designed to alter their shape in response to biological or environmental cues, may very well be used to rapidly and cheaply measure a number of other biomedical properties for monitoring or diagnosing human disease. The tactic also has the potential to detect environmental toxins, said NIST scientist Gary Zabow.
Of their proof-of-concept study, Zabow and fellow NIST researcher Mark Ferris clamped to a cellphone a tiny well containing the answer to be tested and a strip of hydrogel — a porous material that swells when immersed in water. The researchers embedded tiny magnetic particles inside the hydrogel, which they’d engineered to react either to the presence of glucose or to pH levels (a measure of acidity) by expanding or contracting. Changing pH levels could be related to a wide range of biological disorders.
Because the hydrogels enlarged or shrunk, they moved the magnetic particles closer to or farther from the cellphone’s magnetometer, which detected the corresponding changes within the strength of the magnetic field. Employing this strategy, the researchers measured glucose concentrations as small as a number of millionths of a mole (the scientific unit for a certain variety of atoms or molecules in a substance). Although such high sensitivity just isn’t required for at-home monitoring of glucose levels using a drop of blood, it’d in the longer term enable routine testing for glucose in saliva, which comprises a much smaller concentration of the sugar.
The researchers reported their findings within the March 30, 2024 edition of Nature Communications.
Engineered, or “smart,” hydrogels just like the ones the NIST team employed are inexpensive and comparatively easy to fabricate, Ferris said, and could be tailored to react to a number of various compounds that medical researchers will probably want to measure. Of their experiments, he and Zabow stacked single 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 trace changes in magnetic field strength.
Since the technique doesn’t require any electronics or power source beyond that of the cellphone nor call for any special processing of the sample, it offers a cheap method to conduct testing — even in locations with relatively few resources.
Future efforts to enhance the accuracy of such measurements using cellphone magnetometers might allow detection of DNA strands, specific proteins and histamines — compounds involved within the body’s immune response — at concentrations as little as a number of tens of nanomoles (billionths of a mole).
That improvement could have substantial profit. As an illustration, measuring histamines, that are typically detected in urine at concentrations starting from about 45 to 190 nanomoles, would ordinarily require a 24-hour urine collection and a classy laboratory evaluation.
“An at-home test using a cellphone magnetometer sensitive to nanomolar concentrations would allow measurements to be done with much less hassle,” said Ferris. More generally, enhanced sensitivity can be essential when only a small amount of a substance is out there for testing in extremely dilute quantities, Zabow added.
Similarly, the team’s study suggests that a cellphone magnetometer can measure pH levels with the identical sensitivity as a thousand-dollar benchtop meter but at a fraction of the price. A house-brewer or a baker could use the magnetometer to quickly test the pH of varied liquids to perfect their craft, and an environmental scientist could measure the pH of ground water samples on-site with higher accuracy than a litmus test strip could provide.
With a view to make the cellphone measurements a industrial success, engineers might want to develop a way to mass produce the hydrogel test strips and make sure that they’ve a protracted shelf life, Zabow said. Ideally, he added, the hydrogel strips needs to be designed to react more quickly to environmental cues so as to speed up measurements.
