Chien-Ching Wu

Strategies for patterning biomolecules with dip-pen nanolithography.

Dip-pen nanolithography (DPN) is an atomic force microscopy (AFM)-based lithography technique, which has the ability to fabricate patterns with a feature size down to approximately 15 nm using both top-down and bottom-up approaches. DPN utilizes the water meniscus formed between an AFM tip and a substrate to transfer ink molecules onto surfaces. A major application of this technique is the fabrication of micro- and nano-arrays of patterned biomolecules. To achieve this goal, a variety of chemical approaches has been used. This review concisely describes the development of DPN in the past decade and presents the related chemical strategies that have been reported to fabricate biomolecular patterns with DPN at micrometer and nanometer scale, classified into direct- and indirect DPN methodologies, discussing tip-functionalization strategies as well.

Porous Multilayer-Coated AFM Tips for Dip-Pen Nanolithography of Proteins

A simple and novel method for fabricating nanoporous-structure-coated silicon nitride tips for dip-pen nanolithography (DPN) by using the layer-by-layer (LbL) technique has been developed. The pore sizes can be adjusted by treating the LbL films coated onto the amino-terminated self-assembled monolayer (NH(2)-SAM)-functionalized AFM tip surface with a base solution for different periods of time. This hydrophilic porous material can absorb biomolecules easily and also provides a larger-volume ink reservoir compared with a bare silicon nitride tip. Proof-of-concept of the porous AFM tip is demonstrated by using fluorescent proteins as ink molecules to fabricate protein patterns at the micrometer and submicrometer length scales.

Fabrication and visualization of metal-ion patterns on glass by dip-pen nanolithography.

Fluorescent self-assembled monolayers (SAMs) are used as dip-pen nanolithography (DPN) substrates for the fabrication of patterns of Ca(2+) and Cu(2+) ions. The driving force for the transfer of these ions from an atomic force microscopy (AFM) tip to the surface is their complexation to organic ligands on the monolayer. By means of fluorescent surfaces, the patterns can be visualized under a fluorescence microscope. We use a custom-built atomic force fluorescence microscope (AFFM), a combination of atomic force and confocal fluorescence microscopes, to deposit the metal ions onto the sensing SAMs by DPN and to subsequently visualize modulations of fluorescence intensity in a sequential write-read mode.