“As the hydrogels enlarged or shrunk, they moved the magnetic particles closer to or farther from the cellphone’s magnetometer, which detected the corresponding changes in the strength of the magnetic field.”
NIST clamped a well of liquid and a strip of magnetized hydrogel to a phone and used its compass to read glucose at a few millionths of a mole. No extra electronics, no power source, no lab. The team says the same trick measures pH as well as a thousand-dollar benchtop meter. Diagnostics vendors charging lab prices for this kind of test should be nervous.