Dip Pen Nanolithography (DPN) was first demonstrated by Chad Mirkin’s group at Northwestern University in 1999 (Piner, R. D.; Jin, Z.; Feng, X.; Hong, S. H.; Mirkin, C. A. Science 1999, 283, 661-663.) DPN uses an atomic force microscope to pattern molecules on specific areas of a surface. DPN is most commonly used to pattern self-assembled monolayers (SAMs) of long chain alkane thiols, such as octadecanethiol (SH-(CH2)17-CH3; ODT) and mercapatohexadecanoic acid (SH-(CH2)15-COOH; MHA), on Au surfaces. Patterns can be imaged with Lateral Force Microscopy (LFM) which maps the frictional forces of the surface. LFM shows the differing the surface properties of the SAMs patterned by DPN as compared to the surrounding gold surface. The “X” image is an LFM image, made by patterning ODT on Au with DPN. By surrounding the DPN patterned features with a SAM of a shorter molecule (such as Octanethiol, (SH-(CH2)7-CH3; OT)) height images of the patterns can be obtained. The “MIT” image was made by patterning MHA on a Au surface with DPN, surrounding the MHA with an OT SAM and imaging the feature with contact mode atomic force microscopy.

The Sunmag group uses DPN to pattern molecules which can direct the assembly of ligand-coated Au nanoparticles through chemical binding between the patterned molecules and the ligands surrounding the nanoparticle. The “SUNMAG” images show the increase in height of the features before and after the directed assembly of 4 nm Au nanoparticles on top of the patterned features. Directed assembly was achieved here by using the electrostatic attraction between negatively charged carboxylate group (COO-) and Cu2+ ions.