Credit: © 2007 AIP

Dip-pen nanolithography is a patterning technique in which the tip of an atomic force microscope can be used to 'write' on a surface by transferring the material or 'ink' with which it is coated to a substrate. However, although dip-pen is convenient and direct, the existing 'dipping' procedure is limited to picking up large numbers of ink particles. Now, Jun Hu and co-workers1 at the Chinese Academy of Sciences in Shanghai have found a way to use the dip-pen method to pick up and place individual nanoparticles.

Initially, gold nanoparticles are deposited from solution onto a mica substrate. With the microscope tip, the team then identifies a small region on the substrate containing only one nanoparticle and lowers the tip, in 1 nm steps, to pick it up. Once the tip has grabbed the nanoparticle, it can be deposited at a new position using the same set of operations.

In addition to gold, Hu and co-workers can also manipulate single quantum dots and magnetic particles and show that the nanoparticles can be moved on a number of different surfaces. This straightforward approach may have applications in the design of quantum-dot devices.