Inducing order using nanolaminate templates
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Peter T. Beernink Children’s Hospital Oakland Research Institute, Oakland, California 94609 (Received 3 May 2010; accepted 25 August 2010)
Technological progress in the synthesis and characterization of nanometer-scale structures has improved understanding of molecular and colloidal aggregation, self-assembly, and crystal growth. While substrates are commonly used to control nucleation and growth in metal and semiconductor crystals, their use in protein epitaxy has been limited by the lack of substrate structures commensurate with protein sizes. In this paper we describe the use of polished cross sections of amorphous alumina–silica nanolaminates whose periods varied from 8 to 200 nm in the formation of self-assembled monolayers of the protein macromolecule aspartate transcarbamoylase (ATCase). Scanning force microscopy images of rapidly deposited ATCase demonstrates one-dimensional protein ordering along 13.5 nm wide silica nanolaminate. Numerical studies of irreversible adhesion indicate that patterning can induce a higher degree of ordering by varying the substrate periodicity. We expect this to have implications for nucleation and growth of both two-dimensional crystalline layers and bulk protein crystals.
I. INTRODUCTION
Creating ordered, crystalline structures is essential for a broad range of materials research. One standard means to achieve this is by using an appropriate substrate that serves both to concentrate the crystallizing molecules and also to impart order.1 For small growth units (0.1–1 nm) such as metals and semiconductors, epitaxial substrates are widely used to grow films. In this case, “patterning” is created by employing crystalline materials with the same, or similar, lattice spacing. In this size regime, the driving force for crystallization is dominated by the molecule– molecule and molecule–substrate interatomic potentials. For large growth units (100–5000 nm), such as found in colloidal crystallization, patterning is based on lithography, which has been used to create morphological and compositional surface variations. Such substrates have been used for colloidal epitaxy2 to create ordered structures typically composed of silica and PMMA spheres.3 Because of the large particle sizes, entropic terms stemming from excluded volume effects play a larger role during materials assembly.4 The intermediate regime, between inorganic crystalline structures and the capabilities of lithography, remains a challenge. This size range between 1 and 100 nm is of considerable interest for the ordering of proteins, viruses, dendrimers, and nanoparticles. This scale is also of interest for fundamental crystallization studies because Address correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2010.71 194
J. Mater. Res., Vol. 26, No. 2, Jan 28, 2011
http://journals.cambridge.org
Downloaded: 13 Mar 2015
the magnitude of the interaction potential and the entropic terms cross over within this range. Within the intermediate regime, protein crystallization
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