A team of researchers here has created a stretchable and transparent sensor that could help robots read human facial expressions -- from smiling and frowning to brow-furrowing and eye-rolling.

Nae-Eung Lee from the Sungkyunkwan University, Seoul and colleagues developed the ultra-sensitive and wearable sensor by layering a carbon nanotube film on two different kinds of electrically-conductive elastomers.

They found it could tell whether people were laughing or crying and where they were looking.

'In addition to applications in robotics, the sensors could be used to monitor heartbeats, breathing, dysphagia (difficulty swallowing) and other health-related cues,' Lee said.

The new sensor detect facial movements, including slight changes in gaze.

'One way to make interactions between people and robots more intuitive would be to endow machines with the ability to read their users' emotions and respond with a computer version of empathy,' Lee added.

The technology, reported in the journal ACS Nano, can help robot developers make their machines more human.