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    In Situ X-ray Scattering Studies of Protein Solution Droplets Drying on Micro- and Nanopatterned Superhydrophobic PMMA Surfaces

    Year: 2010

    Journal: Langmuir, 2010, 26 (18), pp 15057–15064, 20111221

    Authors: Angelo Accardo,†,‡,§ Francesco Gentile, †,§ Federico Mecarini, †,§ Francesco De Angelis, †,§ Manfred Burghammer, ‡ Enzo Di Fabrizio, †,§ and Christian Riekel ‡

    Organizations: † Center of Bio-Nanotechnology and Engineering for Medicine, University Magna Græcia, Viale Europa, Catanzaro 88100, Italy, ‡ European Synchrotron Radiation Facility, B.P. 220, F-38043 Grenoble Cedex, France, and § Italian Institute of Technology, Via Morego, Genova 13163, Italy

    Superhydrophobic poly(methyl methacrylate) surfaces with contact angles of 170° and high optical and X-ray transparencies have been fabricated through the use of optical lithography and plasma etching. The surfaces contain either a microscale pattern of micropillars or a random nanofibrillar pattern. Nanoscale asperities on top of the micropillars closely resembleNelumbo nucifera lotus leafs. The evolution of the contact angle of water and lysozyme solution droplets during evaporation was studied on the micro- and nanopatterned surfaces, showing in particular contact-line pinning for the protein solution droplet on the nanopatterned surface. The microstructural evolution of lysozyme solution droplets was studied on both types of surfaces in situ under nearly contact-free conditions by synchrotron radiation microbeam wide-angle and small-angle X-ray scattering revealing the increasing protein concentration and the onset of precipitation. The solid residuals show hollow sphere morphologies. Rastermicrodiffraction of the detached residuals suggests about a 1/3 volume fraction of ≥17 nm lysozyme nanocrystalline domains and about a 2/3 short-range-order volume fraction. About 5-fold larger nanocrystalline domains were observed at the attachment points of the sphere to the substrates, which is attributed to particle growth in a shear flow. Such surfaces represent nearly contact-free sample supports for studies of inorganic and organic solution droplets, which find applications in biochips.