Sweaty fingers make tidy prints. Beads of perspiration seeping from a person’s pores can leave detailed maps of the fingertips, and a new technique can detect the sweat.
Human finger pores ooze salty drops of water about the size of pinpricks, says materials scientist Jong-Man Kim of Hanyang University in Seoul, South Korea.
He and colleagues created color-changing polymers that snap from blue to red when they touch the tiny droplets. Individual polymer units look like teeny tadpoles, with bulbous heads and skinny tails. When packed tightly together, they form stacked sheets that appear blue. But when water swells the polymers’ heads, the crowded sheets twist apart and absorb shorter wavelengths of light, making the sheets look red.