Formation and Microscopic Investigation of Iron Oxide Aligned Nanowires Into Polymeric Nanocomposite Films DESPINA FRAGOULI, 1 * BRUNO TORRE, 2 GIOVANNI BERTONI, 2 RAFFAELLA BUONSANTI, 3 ROBERTO CINGOLANI, 1,2 AND ATHANASSIA ATHANASSIOU 1,3 1 Center for Bio-Molecular Nanotechnologies,CBN, of IIT@UniLe, via Barsanti c/o STAMMS, Arnesano 73010, (LE) Italy 2 Italian Institute of Technology, IIT, via Morego 30, 16152 Genova, Italy 3 National Nanotechnology Laboratory, NNL, of CNR-INFM, Universita ` del Salento, via per Arnesano km 5, 73100 Lecce, Italy KEY WORDS colloidal nanocrystals; polymers; magnetic assembly; magnetic force microscopy ABSTRACT We present a microscopic investigation of nanocomposite films of iron oxide (g-Fe 2 O 3 ) magnetic nanowires (NWs) aligned into polymers, formed upon evaporation of solutions of acrylate polymer/magnetic nanoparticles under magnetic field (MF). The field causes the assembly of the g-Fe 2 O 3 nanoparticles along the direction of the MF lines, resulting in magnetic NWs embedded throughout the entire volume of the polymer film. The scanning electron microscopy and the trans- mission electron microscopy studies show that the cylindrical-shaped NWs have 15-lm average length and are isotropically distributed throughout the film. The study with the MF microscopy tech- nique not only proves that the composed NWs are magnetic but also makes possible the magnetic study of each individual NW in a nondestructive way. In this way it becomes possible for the localized study of the magnetic properties alteration after the binding of various molecules onto individual NWs, opening up the way of using these films in sensor devices applied in various fields ranging from biology to environmental purposes. Microsc. Res. Tech. 73:952–958, 2010. V V C 2010 Wiley-Liss, Inc. INTRODUCTION The magnetic nanoparticles have generated much in- terest nowadays because of their unique properties (e.g., chemical resistance, biocompatibility, electromag- netic properties, and hardness) that are essential in a large range of applications in fields such as biology, magnetic sensors, and microfluidics. For many of these applications, the ordering of the nanoparticles into high density and spatially oriented arrays of nanowires (NWs) is critical, due to the novel collective properties of the latter, evidently different from those of isolated nanoparticles (Tang and Kotov, 2005). For the mag- netic NWs formation, various techniques have been developed, such as the molecularly linked induced as- sembly under or not magnetic fields (MFs) (Goubalt et al., 2005; Singh et al., 2005), templating techniques using polymer–nanoparticles mixtures (Martin and Mijangos, 2009), or the use of controllable external MFs (Lallatone et al., 2004; Park et al., 2007; Sahoo et al., 2004) during evaporation of nanoparticles/ solvent solutions. Especially, the latter technique is an attractive option for the fabrication of 1D magnetic NWs, due to its extreme simplicity, effectiveness, and speed. In parallel, the incorporation of nanoparticles or nanofibers in polymers also attracts particular research attention because of the synergistic and hybrid properties derived from the individual compo- nents (Schmidt and Malwitz, 2003). Specifically, the fabrication of nanocomposites consisting of aligned NWs in polymer matrices results into novel materials with anisotropically enhanced physical properties, combining the intrinsic properties of the polymers with the highly anisotropic properties of the aligned units (Jestin et al., 2008; Kimura et al., 2002), ready to be used in various polymer-based technological applica- tions. In particular, the magnetic NWs-based nanocom- posites have great potentiality in information storage (Weller and Doerner, 2000), sensing (Kaushik et al., 2009), actuation (Fahrni et al., 2009), molecular sepa- ration (Merkel et al., 2002), and electromagnetic wave absorption (Huo et al., 2009). The use of strong MF (10 T) for the alignment of the fillers in the polymers has been used in the past mostly in the field of the car- bon nanotube composites where the tubes are oriented in the matrix during the curing of the polymer or dur- ing the evaporation of the solvent (Kimura et al., 2002). Very few studies have used MFs for the orienta- tion of nanoparticles, in order to form NWs in poly- mers. This technique has been applied mainly on particles of micrometer sizes (Martin et al., 2000). The dispersion of magnetic nanoparticles in polymer/ prepolymer solutions and the subsequent orientation during evaporation/curing under weak MFs resulted only to the formation of oriented aggregates (Fahrni et al., 2009; Jestin et al., 2008). In this work, we present the simultaneous topo- graphic and magnetic study of 1D magnetic NWs, formed by the assembly of iron oxide (g-Fe 2 O 3 ) colloidal nanoparticles in polymer matrices under the applica- tion of MF. The formation of the NWs is done in situ, during the drying of a casted polymer solution mixed with g-Fe 2 O 3 nanoparticles, in a weak homogeneous MF (160 mT). The microscopic investigation of the *Correspondence to: Despina Fragouli, Center for Bio-Molecular Nanotechnol- ogies, CBN, of IIT@UniLe, via Barsanti c/o STAMMS, Arnesano 73010, (LE) Italy. E-mail: despina.fragouli@iit.it Received 11 January 2010; accepted in revised form 30 January 2010 DOI 10.1002/jemt.20848 Published online 15 March 2010 in Wiley Online Library (wileyonlinelibrary.com). V V C 2010 WILEY-LISS, INC. MICROSCOPY RESEARCH AND TECHNIQUE 73:952–958 (2010)