IOP PUBLISHING NANOTECHNOLOGY Nanotechnology 19 (2008) 245704 (7pp) doi:10.1088/0957-4484/19/24/245704 Surface modification of nanoporous alumina membranes by plasma polymerization Dusan Losic 1 , Martin A Cole, Bj¨ orn Dollmann, Krasimir Vasilev and Hans J Griesser Ian Wark Research Institute, University of South Australia, Mawson Lakes, Adelaide, SA 5095, Australia E-mail: dusan.losic@unisa.edu.au Received 20 February 2008, in final form 26 March 2008 Published 12 May 2008 Online at stacks.iop.org/Nano/19/245704 Abstract The deposition of plasma polymer coatings onto porous alumina (PA) membranes was investigated with the aim of adjusting the surface chemistry and the pore size of the membranes. PA membranes from commercial sources with a range of pore diameters (20, 100 and 200 nm) were used and modified by plasma polymerization using n-heptylamine (HA) monomer, which resulted in a chemically reactive polymer surface with amino groups. Heptylamine plasma polymer (HAPP) layers with a thickness less than the pore diameter do not span the pores but reduce their diameter. Accordingly, by adjusting the deposition time and thus the thickness of the plasma polymer coating, it is feasible to produce any desired pore diameter. The structural and chemical properties of modified membranes were studied by scanning electron microscopy (SEM), atomic force microscopy (AFM) and x-ray electron spectroscopy (XPS). The resultant PA membranes with specific surface chemistry and controlled pore size are applicable for molecular separation, cell culture, bioreactors, biosensing, drug delivery, and engineering complex composite membranes. S Supplementary data are available from stacks.iop.org/Nano/19/245704 (Some figures in this article are in colour only in the electronic version) 1. Introduction As a result of their unique thermal, mechanical, structural, optical and chemical properties, nanoporous membranes have attracted considerable interest for applications in various fields such as separation, adsorption, catalysis, biosensing, photonics, energy storage, and drug delivery [1]. Among them, porous alumina (PA) membranes fabricated by electrochemical anodization are one of the most popular porous materials. Their attractiveness arises from simple, low-cost fabrication, chemical and thermal stability, remarkable hardness, highly organized and uniform pore size and high pore density [2–4]. PA membranes, called ‘Anodisc’ or ‘Anapore’, with a limited selection of pore sizes (20, 100 and 200 nm), have become commercially available. Although these membranes 1 Author to whom any correspondence should be addressed. were initially designed for filtration, they have been used for many other applications including cell culture, biosensing, bioreactors, drug delivery and nanofabrication [5–7]. In the case of their filtration applications, a disadvantage of PA membranes is their relatively large minimum pore diameter (20 nm). This pore size significantly reduces their molecular sieving properties and restricts wider application of PA membranes for the separation of smaller molecular species, metal ions, or gases. Hence, to improve the separation properties of PA membranes, it is desirable to reduce the average diameter of the pores while retaining a narrow pore size distribution. In addition, it is also desirable to modify the surface properties of PA membranes as they are poorly biocompatible and not suitable for applications that involve interaction with biomolecules such as in protein separation devices, cell adsorption/growth, biosensing and drug delivery. Therefore, it is important to modify the surface of PA 0957-4484/08/245704+07$30.00 © 2008 IOP Publishing Ltd Printed in the UK 1