Credit: ©2008 AAAS

The ability to reproducibly print regular patterns of chemicals on a surface is an important goal in many disciplines, from miniaturized analytical techniques to integrated circuits. Producing multiple copies of a predefined pattern to cover a large area, or producing a small number of unique patterns, is relatively straightforward, but methods for reproducing multiple copies without using a predefined pattern are rare. Similarly, producing patterns with features on multiple length scales — from nanometre to millimetre — in a single experiment is complex, as the chosen method is usually optimized to produce features on a particular scale.

Now, Chad Mirkin and colleagues from Northwestern University have introduced polymer pen lithography1. The technique is similar to dip-pen nanolithography (DPN), which is a widely used technique that delivers 'ink' via an atomic force microscope cantilever. But, rather than hard silicon cantilevers, polymer pen lithography uses tips made from the elastomer polydimethylsiloxane (PDMS). Arrays containing many thousands of polymer pens were formed using conventional photolithography. Producing patterns with such a system is not only much less expensive than using large cantilever arrays, but the size of the pattern produced can be controlled by the contact force between the pen array and the surface — higher forces causing flattening of the pen tips and generate larger feature sizes.

The soft nature of the PDMS pens is a key feature of this technique. Not only does this give the force-dependant size character of the patterning, but it also means that the system is self-levelling — Mirkin and colleagues found that the pens themselves were not significantly deformed until the entire array was in contact with the surface. The technique was used to produce 15,000 replicas of a pattern with nanometre and micrometre features in just 40 minutes.