People have been using pens to jot down their thoughts for thousands of years but now engineers at the University of Illinois have developed a silver-inked rollerball pen that allows users to jot down electrical circuits and interconnects on paper, wood and other surfaces. Looking just like a regular ballpoint pen, the pen's ink consists of a solution of real silver that dries to leave electrically conductive silver pathways. These pathways maintain their conductivity through multiple bends and folds of the paper, enabling users to personally fabricate low-cost, flexible and disposable electronic devices.

While metallic inks have been used to manufacture electronic devices using inkjet printing technology, the silver pen offers users the freedom and flexibility to construct electronic devices on the fly, says Jennifer Lewis, the Hans Thurnauer professor of materials science and engineering at the University of Illinois who led the research team along with Jennifer Bernhard, a professor of electrical and computer engineering.

"The key advantage of the pen is that the costly printers and printheads typically required for inkjet or other printing approaches are replaced with an inexpensive, hand-held writing tool," said Lewis. "This is an important step toward enabling desktop manufacturing (or personal fabrication) using very low cost, ubiquitous printing tools."

The researchers have used the pen to create a flexible LED display on paper, conductive text and three-dimensional radio-frequency antennas. They now plan to expand the palette of inks to enable pen-on-paper writing of other electronic and ionically conductive materials.

While the pen is likely to prove attractive to electrical engineers and hobbyists, the researchers have also highlighted the potential of the device for creating art. Using the pen to sketch a copy of the painting "Sae-Han-Do" by Jung Hee Kim, which portrays a house, trees and Chinese text, the researchers used the ink as wiring for an LED mounted on the roof of the house that was powered by a five-volt battery connected to the edge of the painting.

The University of Illinois team's research appears in the journal Advanced Materials.