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.

Credit: J.-M. Kim et al.

The sensor technology could be used to identify people by their fingerprint even if only a small part of it was visible, the authors say.

Nature Commun. 5, 3736 (2014)