© Copyright 1998 American Chemical Society
APRIL 28, 1998 VOLUME 14, NUMBER 9
Letters Printing Patterns of Proteins Andre´ Bernard,†,‡ Emmanuel Delamarche,† Heinz Schmid,† Bruno Michel,† Hans Rudolf Bosshard,‡ and Hans Biebuyck*,† IBM Research Division, Zurich Research Laboratory, CH-8803 Ru¨ schlikon, Switzerland, and Biochemisches Institut der Universita¨ t Zu¨ rich, Winterthurerstrasse 190, CH-8057 Zu¨ rich, Switzerland Received January 5, 1998. In Final Form: March 2, 1998 Microcontact printing of proteins proves to be an excellent means of directly patterning biomolecules on solid substrates. Monolayer quantities of protein equilibrated on the surface of a hydrophobic, elastomeric stamp are immobilized there to rinses with buffer. These biomolecules can nevertheless transfer with >99% efficiency from the stamp to a substrate after just 1 s of contact. This capability allows the simple creation of functional patterns of proteins at scales that involve the placement of 85% of closest packing). We used unstructured stamps to deliver IgG to ≈4 cm2 regions on silicon substrates. Ellipsometry measured the average thickness (3-3.5 nm using a refractive index of 1.45 for the protein) of the printed film over this area and showed that it was indistinguishable from a similar film of IgG adsorbed onto silicon from a solution (50 µg/mL) of the protein. Higher
or lower coverage of the surface is possible under different conditions to equilibrate the solution with the surface of the stamp, but this parameter was not explored systematically here. We emphasize that the coverage of the substrate with protein-derived material reflected the occupation of the stamp prior to µCP and that all (>99%) of this material left the stamp after the print. Many of the individual features within stamped regions on the silicon surface had dimensions, in both their spatial extent and height, like those of individual IgGs (≈20 × 25 × 4 nm3). The latter, in particular, reinforced our conclusion that only a single layer of IgG was present on the printed regions. Third, a large fraction of the printed surface was available for specific recognition by polyclonal antibodies having a nanomolar solution avidity for the immobilized antibody. Furthermore, a sandwich-type assay was possible. A third antibody in solution recognized the bound secondaries with excellent specificity as judged by AFM or fluorescence measurements (data not shown). Other related polyclonal IgGs without specificity for the bound antibodies caused no observable changes in the appearance, fluorescence, or activity of the surface at either the first or second stage of recognition. We did not attempt in this work to correlate individual features of the AFM scans with their capacity to bind antibodies, although we generally found a high level of specific binding everywhere (estimates obtained by counting the features in our AFM scans) on the printed parts of the surface. Each of the patterned features in Figure 3 had no more than 1500 IgGs, as could be determined by their direct count. Detection of their placement and immunocompetence was nevertheless easily explored by a number of techniques, even on areas (1 × 0.5 µm2) that corresponded to
