Here's a new direction for smartphones in healthcare.
Researchers from the National Institute of Standards and Technology (NIST), Boulder, Colorado, say a smartphone compass could be used to analyze biomarkers in body fluids — blood, sweat, urine, or saliva — to monitor or diagnose disease.
"We're just at this point demonstrating this new way of sensing that we hope [will be] very accessible and very portable," said Gary Zabow, PhD, a group leader in the applied physics division at NIST who supervised the research.
In a proof-of-concept study, the researchers measured glucose levels in sangria, pinot grigio, and champagne. The detection limit reached micromolar concentrations — on par with or better than some widely used glucose sensors, such as continuous glucose monitors. They also accurately measured the pH levels of coffee, orange juice, and root beer.
More tests are needed to confirm the method works in biological fluids, so it could be a while before it's available for clinical or commercial use.
Still, the prospect is "exciting," said Aydogan Ozcan, PhD, a bioengineering professor at the University of California, Los Angeles, who was not involved in the study. "It might enable new capabilities for advanced sensing applications in field settings or even at home."
The advance builds on growing research using smartphones to put powerful medical devices in patients' hands. A new AI-powered app can use a smartphone camera to detect skin cancer, while other apps administer cognitive tests to detect dementia. Smartphone cameras can even be harnessed for "advanced optical microscopes and sensors to the level where we could even see and detect individual DNA molecules with inexpensive optical attachments," Ozcan said. More than six billion people worldwide own a smartphone.
The compass inside smartphones is a magnetometer — it measures magnetic fields. Normally it detects the earth's magnetic fields, but it can also detect small, nearby magnets and changes in those magnets' positions.
The researchers embedded a small magnet inside a strip of "smart hydrogel — a piece of material that expands or contracts" when immersed in a solution, said Zabow.
As the hydrogel gets bigger or smaller, it moves the magnet, Zabow explained. For example, if the hydrogel is designed to expand when the solution is acidic or contract when it's basic, it can move the magnet closer or farther from the phone's magnetometer, providing an indicator of pH. For glucose, the hydrogel expands or contracts depending on the concentration of sugar in the liquid.
With some calibration and coding to translate that reading into a number, "you can effectively read out glucose or pH," Zabow said.
Only a small strip of hydrogel is needed, "like a pH test strip that you use for a pool," said first study author Mark Ferris, PhD, a postdoctoral researcher at NIST.
Like a pool pH test strip, this test is meant to be "easy to use, and at that kind of price," Ferris said. "It's supposed to be something that's cheap and disposable." Each pH hydrogel strip is about three cents, and glucose strips are 16 cents, Ferris estimated. In bulk, those prices could go down.
Next the team plans to test the strips with biological fluids. But complex fluids like blood could pose a challenge, as other molecules present could react with the strip and affect the results. "It may be that you need to tweak the chemistry of the hydrogel to make sure it is really specific to one biomolecule and there is no interference from other biomolecules," Zabow said.
The technique could be adapted to detect other biomarkers or molecules, the researchers said. It could also be used to check for chemical contaminants in tap, lake, or stream water.