Consecutive microcontact printing - ligands for asymmetric catalysis in silicon channels

Consecutive microcontact printing ( mu CP) has been developed to enable mul tiple functionalization of silicon surfaces, such as the immobilization of chiral ligands. The technique involves two subsequent printing steps using unstructured poly(methylsiloxane) stamps. The pattern is already defined on the substrate, consisting of etched channels. Hence, no precise alignment is needed between the two printing steps. A carboxylic acid group containin g reagent was initially printed onto the silicon oxide surface and transfor med to an anhydride. hi the second printing step an ester bond was formed w ith the hydroxy-functionalized ligand. The formed molecular layers were eva luated by contact angle measurements, scanning electron microscopy (SEM) an d electron spectroscopy for chemical analysis (ESCA), indicating that the c onsecutive mu CP was successful. Initially, printing was performed on planar silicon surfaces but to realize a flow-through microfluidic device for high throughput screening a mu CP t echnique was developed for etched channels. To verify the technique, hydrop hobic valves consisting of octadecyltrichlorosilane were formed using mu CP in deep reactive ion etched channels (50 mum wide and 50 mum deep). The pr inted hydrophobic patches were visualized by SEM and functioned well. Final ly, the consecutive mu CP technique was applied to immobilize the ligand in the channels. The channels were then sealed with a low-temperature bonding technique using an adhesive PDMS film, which does not destroy the printed ligand. In this study mu CP is used in a novel manner. It enables a convenient meth od for performing complex surface modification of etched structures, which is a frequently appearing problem in biochemical microfluidic systems. (C) 2001 Elsevier Science B.V. All rights reserved.