"As the size of the capillaries or channels in devices shrinks, the movement of liquid becomes very difficult to control," said Antonio Garcia, bioengineering professor at Arizona State University. "The everyday use of mechanical valves and pumps becomes difficult in nanotechnology because making them tinier is a manufacturing challenge. Also, any real-life application would be prone to operational problems, such as clogging of the pump or valve by small molecules."

The researchers produced photocapillarity by attaching light-responsive molecules to the surface of the nanotubes. "When we shine light just beyond the visible range [onto the nanotube] the light-responsive molecules attract water and trigger the advancement of water through the channel," added Garcia.

The scientists, who reported their work in Langmuir, say that the technique may one day find a use in the targeted distribution of medicine in the human body.