Self-assembly of biomolecules: AFM study of F-actin on unstructured and nanostructured surfaces Marina Naldi 1 , Elena Vasina 2 , Serban Dobroiu 2 , Luminita Paraoan 3 , Dan V. Nicolau 2 , Vincenza Andrisano 1* 1 Department of Pharmaceutical Sciences, Università di Bologna, Via Belmeloro 6, 40126 Bologna, Italy; 2 Department of Electrical and Electronic Engineering, Liverpool University, Brownlow Hill L69 3GJ, Liverpool, UK; 3 School of Clinical Sciences, Liverpool University, Royal Liverpool University Hospital, L69 3GA, Liverpool, UK 1. ABSTRACT Advanced nanofabrication is capable of producing structures in the vicinity of the size of large biomolecules or their aggregates. Some of these protein aggregates emerge as having deleterious medical effects, e.g., degenerative diseases, or essential for biological processes, e.g., actin, cytoskeleton formation. Therefore it became possible, and important, to think of ways of interacting nanostructured surfaces with biomolecular aggregates in a designed manner. Along this line of thinking, we report on a preliminary atomic force microscopy (AFM) investigation of the behavior of F-actin on unstructured surfaces (mica, silicon) and nanostructured surface (13 nm height nanostructured silicon surface). Keywords: Atomic force microscopy, actin, nanostructures, self-assembly 2. INTRODUCTION The development of advanced nanofabrication, through both bottom-down (lithography) and top-up (self-assembly) approaches, led to the capacity of producing structures in the vicinity of few 10nm range or below, which is not far from the dimensions of –large- biomolecules, e.g., 4nm lysozyme to 50nm myosin. In a very separate development, it has been discovered that some biomolecules, in particular, aggregate in large, self-assembled architectures, some with deleterious medical effects (e.g., degenerative diseases) or essential for biological processes (e.g., actin, cytoskeleton formation). It appears then, as a rather unexpected possibility that one can design, fabricate and interface biomimetic nanostructured surfaces, which possibly control the self-assembly of biomolecules in long-range architectures. Along this line of thinking, we report on a preliminary atomic force microscopy (AFM) investigation of the behavior of F- actin on unstructured surfaces (mica, silicon) and nanostructured surface (13 nm height nanostructured silicon surface). Actin is one of the principal structural proteins in eukaryotic cells and is an ideal biopolymer for investigations of new modes of higher order self-assembly. The actin cytoskeleton dynamically maintains the structural integrity of the plasma membrane and plays important roles in a number of membrane-associated events, such as cell adhesion, cell motility, and regulation of integral membrane protein distributions 1 . G-actin consists of 375 amino acid residues with molecular weight 43 kD and is a highly conserved protein expressed in most living organisms 2 . Actin monomer can be polymerized into long right-handed double helical filaments (F-actin) whose formation is induced by Mg 2+ , K + , Na + , and ATP 3, 4 . F-actin can be considered as a semiflexible and highly charged polyelectrolyte, with diameter DA ~ 80 Ǻ, persistence length ξ A ~ 10 ȝM, and anionic liniar charge density of Ȝ A ~ e/2.5 Ǻ 5-7 . This study focused on the visualization of the different morphologies of pre-formed actin filaments when adsorbed on surfaces which are characterized by different geometries and physical-chemical properties. Specifically, mica and silicon were used as flat surfaces; and platinum on silicon was used as for nanostructured surfaces, were employed as solid supports on which F-actin was deposited. Mica was selectively pretreated with agents capable of modulating its surface chemical properties, whereas the rest of the surfaces were used without treatment. Nanoscale Imaging, Sensing, and Actuation for Biomedical Applications VI edited by Alexander N. Cartwright, Dan V. Nicolau, Proc. of SPIE Vol. 7188, 71880Q © 2009 SPIE · CCC code: 1605-7422/09/$18 · doi: 10.1117/12.822800 Proc. of SPIE Vol. 7188 71880Q-1