Joining the dots

Northwestern University researchers have employed a technique called Dip-Pen Nanolithography (DPN) to simultaneously create 55,000 identical one-molecule high patterns.

DPN was invented at Northwestern in 1999. The most recent demonstration used a 55,000-pen, two-dimensional array to draw the patterns with tiny dots of molecular ink on substrates of gold or glass.

To demonstrate the technique’s power, the researchers reproduced the face of Thomas Jefferson from a five-cent coin 55,000 times, which took only 30 minutes. Each identical nickel image is 12 micrometers wide, about twice the diameter of a red blood cell, and is made up of 8,773 dots, each 80 nanometres in diameter.

The parallel process paves the way for making DPN competitive with other optical and stamping lithographic methods used for patterning large areas on metal and semiconductor substrates, including silicon wafers. The advantage of DPN, which is a maskless lithography, is that it can be used to deliver many different types of inks simultaneously to a surface in any configuration. Mask-based lithographies and stamping protocols are extremely limited in this regard.

‘This development could lead to massively miniaturised gene chips, combinatorial libraries for screening pharmaceutically active materials and new ways of fabricating and integrating nanoscale or even molecular-scale components for electronics and computers,’ said Chad A. Mirkin, director of Northwestern’s International Institute for Nanotechnology, who led the research.

‘In addition, it could lead to new ways of studying biological systems at the single particle level, which is important for understanding how cancer cells and viruses work and for getting them to stop what they do,’ he said. ‘Essentially one can build an entire gene or protein chip that fits underneath a single cell.’