Microcontact Printing Using Poly(dimethylsiloxane) Stamps Hydrophilized by Poly(ethylene oxide) Silanes

Abstract

The patterning of a surface using microcontact printing (μCP) generally employs a hydrophobic micropatterned stamp made from poly(dimethylsiloxane) (PDMS) to place ink molecules on a surface with spatial control. We present a simple procedure to hydrophilize PDMS stamps based on the O2 plasma oxidation of PDMS (referred to as PDMSox) and the grafting of poly(ethylene oxide) silanes (PEO-Si) to the oxidized surface. The wetting properties of a PDMSox surface derivatized with PEO having none, one, or two silanes and having chains with 7-70 EO units are inspected. All PDMSOx surfaces treated with PEO-Si are hydrophilic and have advancing and receding contact angles of ∼40° and ∼30°, respectively. These surfaces remain hydrophilic for periods longer than 7 days, which saves having to hydrophilize stamps freshly prior to their usage. In particular, grafting a PEO having two triethoxysilane end groups and a molecular weight (MW) of 3400 g mol-1 enables inking and microcontact printing a polar Pd/Sn catalyst for electroless deposition (ELD) from a stamp to an amino-functionalized glass surface. The printed pattern of colloids has high accuracy and contrast, as reflected by the selective ELD of NiB in the printed regions of the glass. The same stamp can be reused for many cycles of inking and printing without degradation of the quality of the final NiB patterns. The hydrophilic layer provided by the grafted PEO molecules is, in some cases, not sufficiently thick to incorporate and print enough polar ink to form a complete monolayer of cysteamine, for example, onto printed Au substrates. Oxidizing a planar PDMS surface through a mask permits the patterning of PEO onto PDMSoX. It then becomes possible to ink the stamp with proteins either by depositing proteins from solution onto the areas left underivatized with PEO or by printing proteins in the PEO-derivatized areas only. The proteins on the planar PDMS/PDMSOX-PEO surface in turn are microcontact printed with high accuracy onto glass. This work may help expand μCP to applications in which it is desirable to use polar inks or proteins.