Abstract—The use of magnetic and magnetic/gold core/shell nanoparticles in biotechnology or medicine has shown good promise due to their hybrid nature which possesses superior magnetic and optical properties. Some of these potential applications include hyperthermia treatment, bio-separations, diagnostics, drug delivery and toxin removal. Synthesis refinement to control geometric and magnetic/optical properties, and finding functional surfactants for biomolecular attachment, are requirements to meet application specifics. Various high-temperature preparative methods were used for the synthesis of iron oxide and gold-coated iron oxide nanoparticles. Different surface functionalities, such as 11-aminoundecanoic and 11-mercaptoundecanoic acid, were introduced on the surface of the particles to facilitate further attachment of biomolecular functionality and drug-like molecules. Nanoparticle thermal stability, composition, state of aggregation, size and morphology were investigated and the results from techniques such as Fourier Transform-Infra Red spectroscopy (FT-IR), Ultraviolet visible spectroscopy (UV-vis), Transmission Electron Microscopy (TEM) and thermal analysis are discussed. Keywords—Core/shell, Iron oxide, Gold coating, Nanoparticles. I. INTRODUCTION RON oxide nanoparticles are widely studied materials as they occur naturally, are rapidly synthesised artificially, have attractive chemical and magnetic properties, and applications in in vivo magnetic imaging [1]. Iron oxide nanoparticles are inherently biocompatible [2] due to their general stability in air and their ability to be degraded or metabolised in vivo, making them excellent candidates for a large variety of applications [3]. Iron oxide nanoparticles have been extensively studied and applied in the biomedical field and, as a result, several commercial products have been made available for human diagnostics. Commercially available nanoparticles are typically coated by a biocompatible polymer, which improves the colloidal stability in physiological media and significantly reduces toxicity [4]. When surface modification involves a biomolecule like the FDA approved Poly (D,L-lactide-co-glycolide) (PLGA), H. van der Walt, NIC, Advanced Materials Division, Mintek, Private Bag X3015, Randburg, 2125, South Africa (phone: +27 11 709 4757; fax: +27 11 709 4480; e-mail: hendriettep@mintek.co.za). All authors (L. Chown; R.A. Harris, N. Sosibo, R. Tshikhudo) Advanced Materials Division, Mintek, South Africa. surface coverage is critical, as is the ability of the molecule to retain its native conformation and binding profiles [5]. Polymer coating of magnetic nanoparticles have been well- documented as a method to improve the stability of the magnetic particles and to enhance their biological activity [6]. Of special interest are core/shell structured nanoparticles. These structures are not only ideal for studying proximity effects, but are also suitable for structure stabilisation, as the shell protects the core from oxidation and corrosion [7]. Gold coating of magnetic nanoparticles is a very attractive technique, as the magnetic nanoparticles can be both stabilised more effectively in corrosive biological conditions and easily functionalised through well developed Au-S chemistry. The coating also gives plasmodic properties to the magnetic nanoparticles, making them extremely useful for magnetic, optical and biological applications [6]. Our aim was to use the high-temperature solution phase reaction of Fe(acac) 3 to synthesise 11-aminoundecanoic acid (AUA) and 11-mercaptoundecanoic acid (MUA) stabilised Fe 3 O 4 and Fe 3 O 4 @Au nanoparticles for possible further attachment of biomolecular functionalities and drug-like molecules. To elucidate the influence of the various biomolecularly modifiable stabilisers and the gold coating on the nature, stability and size of the iron oxide nanoparticles, FT-IR, TEM, UV-vis and thermal analysis methods were utilised. II. EXPERIMENTAL PROCEDURE A. General All chemicals were purchased from Sigma-Aldrich and used as received. The structures of the surfactants (AUA and MUA) used, are shown in Fig. 1 (a) and (b). (a) (b) Fig. 1 Structures of surfactants: (a) 11-aminoundecanoic acid (AUA) and (b) 11-mercaptoundecanoic acid (MUA). Hendriëtte van der Walt, Lesley Chown, Richard Harris, Ndabenhle Sosibo and Robert Tshikhudo Fe 3 O 4 and Fe 3 O 4 @Au Nanoparticles: Synthesis and Functionalisation for Biomolecular Attachment I World Academy of Science, Engineering and Technology 44 2010 1048