Surface patterning Large-Area, Nanoimprint-Assisted Microcontact Stripping for the Fabrication of Microarrays of Fouling/Nonfouling Nanostructures** Ana Ruiz, Christopher A Mills, Andrea Valsesia, Elena Martinez, Giacomo Ceccone, Josep Samitier, Pascal Colpo, and Franc ¸ois Rossi* Methods for the accurate positioning of nanometric beads on a substrate have been developed over a number of years, and range from serial atomic force microscopy (AFM) techniques for single-bead positioning [1,2] to parallel techniques for the positioning of large populations of beads in monolayer or multilayer architectures, typically from a liquid suspension. For example, topographic cues have been used for bead-based protein array production, although in this case, there is a random distribution of beads within the topography. [3] Bead patterning has also been achieved in capillaries using a micromolding in capillaries (MIMIC) technique. [4,5] Line patterns with micrometer widths are possible with this technique, achieving good multilayer organization. For monolayer bead patterning at micrometer dimensions, electrostatic forces [6] and similar electrostatic assemblies using nanoxerography, [7] as well as patterning by selective chemical functionalization, [8] by transfer of particles from a liquid–liquid interface, [9] and by subtracting top–down processes, [10] are possible. Recently, approaches to the micropatterning of nano- dimensioned beads based on contact printing have appeared. Single-particle resolution has been achieved by directed assembly of the nanobeads on structured poly(dimethyl- siloxane) (PDMS) templates. The beads are then transferred from the filled PDMS template to a substrate by microcontact printing. [11,12] The beads’ surface composition during assembly must be tuned to maximize the bead–surface interaction forces and to avoid strong adherence to the PDMS. Printing of dry nanobeads is, however, hard to realize. On the other hand, selective removal of beads from a surface using PDMS- structured molds has been achieved by lift-off [13] and microcontact stripping. [14] While the former needs a 3 h contact heat treatment to pattern close-packed silica nano- beads, the latter reports on a resolution limitation due to the crystal packing of the beads. Normally, in the reported contact-printing-based methods, the beads have to be loosely attached so that bead transfer or removal will not be inhibited. Here we present a contact-stripping method for micro- patterning nanobead arrays, based on structured poly(methyl methacrylate) (PMMA) stamps and using a nanoimprinter apparatus, which allows careful control of the temperature and pressure during the contact stripping. Scheme 1 represents the patterning method. PMMA stamps, produced by nanoimprint lithography, are placed on the top of the nanobead-coated substrate with the structured parts of the stamp in contact with the beads inside the nanoimprinter chamber. Then pressure and temperature are applied for a few minutes. Afterwards, the stamps are carefully separated from the substrate. As a result, the particles in contact with the stamp are removed from the substrate, producing nanobead-patterned regions that reproduce the structure of the stamp. Microcontact Scheme 1. Scheme of the nanoimprint-assisted contact stripping. The PMMA stamp is put in contact with a substrate coated with nanopar- ticles inside the nanoimprinter chamber. The contact is maintained at 323 K and 5  10 6 Nm 2 of pressure for 200 s. Then, the stamp is lifted up from the substrate, producing a selective removal of the nanopar- ticles in the contact areas. [  ] Dr. F. Rossi, Dr. A. Ruiz, Dr. A. Valsesia, G. Ceccone, Dr. P. Colpo European Commission, DG-JRC Institute for Health and Consumer Protection TP 203, Via Enrico Fermi 2749, 21027-Ispra (Italy) E-mail: francois.rossi@jrc.it Dr. C. A. Mills, Dr. E. Martinez, Prof. J. Samitier Nanobioengineering group Institute for Bioengineering of Catalonia (IBEC) Barcelona Science Park C/ Josep Samitier 1-5, 08028 Barcelona (Spain) Dr. C. A. Mills, Dr. E. Martinez, Prof. J. Samitier Networking Research Center on Bioengineering Biomaterials and Nanomedicine (CIBER-BBN) Barcelona (Spain) Prof. J. Samitier Electronics Department, University of Barcelona C/ Marti i Franques 1, 08028 Barcelona (Spain) [  ] The authors would like to thank M. J. Lopez-Bosque of the Nanotechnology Platform, Barcelona Science Park, for recording the SEM images. The work was supported by the European Commission Joint Research Centre Action ‘‘NanoBiotechnology for Health’’ and the Nano2Life Network of Excellence. CAM acknowledges support from the Spanish Ministry of Science and Technology via the Ramon y Cajal program. : Supporting Information is available on the WWW under http:// www.small-journal.com or from the author. DOI: 10.1002/smll.200801454 small 2009, 5, No. 10, 1133–1137 ß 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1133