Smartphone Magnetometer Uses Magnetized Hydrogel to Measure Biomarkers for Disease Diagnosis

Almost every modern smartphone incorporates a compass or magnetometer, which senses Earth's magnetic field, crucial for navigation purposes. Now, a newly developed technique uses an ordinary cellphone magnetometer to precisely measure glucose levels, an important diabetes indicator. This approach, combined with magnetic materials that change their shape in reaction to biological or environmental stimuli, can be employed to assess a wide array of biomedical properties crucial for human disease monitoring or diagnosis, as well as detecting environmental pollutants.

In their proof-of-concept study, a team of researchers at the National Institute of Standards and Technology (NIST, Gaithersburg, MD, USA) attached a tiny well filled with the test solution and a hydrogel strip, to a smartphone. This hydrogel, a porous material that swells when immersed in water, was embedded with tiny magnetic particles engineered to respond to glucose presence or pH changes by swelling or contracting. Changing pH levels is associated with various biological disorders. When the hydrogels enlarged or shrank, they forced the magnetic particles to come closer to or go farther from the cellphone’s magnetometer, which detected the corresponding changes in the strength of the magnetic field. Utilizing this innovative approach, the team succeeded in measuring glucose concentrations as small as a few millionths of a mole levels. Although such high sensitivity is not needed for home glucose monitoring using blood tests, it could pave the way for saliva-based glucose testing, where sugar concentration is notably lower.

The method's simplicity, without the need for any additional electronics or power sources except for the smartphone or requirement for sample processing, presents an economical solution for widespread testing, even in resource-limited areas. Future potential improvements in measuring accuracy through smartphone magnetometers could lead to detection of DNA, specific proteins, and histamines — key immune response elements — at extremely low concentrations. For example, accurately measuring histamines, typically found in urine at concentrations ranging from about 45 to 190 nanomoles, would usually require a 24-hour urine collection and complex lab analyses. Similarly, the team found that a cellphone magnetometer can measure pH levels with sensitivity equal to a thousand-dollar benchtop meter but at a substantially lower cost. To make smartphone-based measurements a market success, engineers will have to devise a mass-production strategy for the hydrogel test strips and ensure their long shelf life.

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