A polymer that is sensitive to sub-nanolitre volumes of water could be used to map sweat pores for fingerprint analysis. Jong-Man Kim and Chan Woo Lee at Hanyang University in Seoul and their colleagues developed a thin film made of caesium polydiacetylene that changes from blue to red in the presence of water. The authors found that a fingertip pressed on the blue film produced a pattern of red dots (pictured) that coincided with sweat pores and was visible using an optical microscope.
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