IEEE TRANSACTIONS ON MAGNETICS, VOL. 43, NO. 6, JUNE 2007 2445 Engineering Water-Dispersible FePt Nanoparticles for Biomedical Applications Po-Chieh Chiang , Dung-Shing Hung , Jeng-Wen Wang , Chih-Sung Ho ,and Yeong-Der Yao Institute of Physics, Academia Sinica, Taipei 115, Taiwan, R.O.C. Department of Information and Telecommunications Engineering, Ming Chuan University, Taoyuan 333, Taiwan, R.O.C. Department of Chemical Engineering, Tunghai University, Taichung 407, Taiwan, R.O.C. Department of Materials Engineering, Tatung University,Taipei 104, Taiwan, R.O.C. We reported the synthesis and characterization of water-based FePt nanoparticles for biomedical applications. The superparamag- netic and hydrophilic FePt nanoparticles were synthesized by phase transfer method and the particles size were just only 2–4 nm. The functional FePt nanoparticles through ligand exchanging were achieved to bind the specific biomolecules. The streptavidin-biotin binding pair was used to demonstrate that water-based FePt nanoparticles could be further functionalized to provide a biotin moiety for specific interaction with streptavidin protein. Index Terms—Biomedical applications, FePt nanoparticles, phase transfer method, surface modification. I. INTRODUCTION N ANOTECHNOLOGIES based on the new synthesis in nano materials and characterizations for biomedical applications were offered elsewhere with a focus on the mag- netic nanoparticles for many years. Compared with metal-type nanoparticles, magnetic nanoparticles provide a promising characteristic on handling and manipulation by a magnetic force. This advantage improves a relative motion of the nanoparticles with respect to the fluid and enhances exposure of the nanoparticles surface to the surrounding fluid to profit the more biomedical assays [1]. FePt magnetic nanoparticles intrinsically possessing better chemical stability and higher saturation magnetization are potential magnetic nanomaterials for biomedical applications [2]. The aim of this paper is to de- velop and synthesize FePt magnetic nanoparticles with tailored surface chemistry and topography for biomedical purposes. II. EXPERIMENTAL SECTION Self-assembly of FePt nanoparticles were synthesized by the chemical reduction method [3]. This reaction involved simul- taneous chemical reduction of Pt(acac) (acac is acetylaceto- nate) and Fe(acac) by 1,2-hexadecanediol (i.e., the reduction agent) in an argon atmosphere (i.e., standard airless situation). The mixture was then dissolved in octyl ether and then heated to 100 . In the heating process, oleic acid and oleylamine acting as surfactants were injected into the flask to avoid particle ag- glomeration before forming FePt nanoparticles. The mixture was kept maintaining at Ar atmosphere and heated to a higher temperature for forming the FePt nanoparticles. The re- fluxing was continued for 30 min before cooling down to the room temperature and then the 2 4 nm monodispersed FePt Digital Object Identifier 10.1109/TMAG.2007.894341 Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Fig. 1. The TEM images shown the average diameter of the (A) and (B) hy- drophobic and (C) hydrophilic FePt nanoparticles were 2–4 nm. nanoparticles shown in Fig. 1 were obtained in organic solution for phase transfer reaction. Due to the requirement of nanoparticles applications on the biomedical delivery system, the FePt nanoparticles should be dispersed in aqueous phase. The further application on med- ical purpose would need a phase transfer from hydrophobic to water-based solution. Mercaptoacetic acid (C H O S) was an efficient phase transfer reagent widely used in quantum dots [4]. The reagent contained the thiol functional group (SH) was easily accessed to make the surfactant replaced on specific metal sur- face. We first attempted to build the transfer system based on mercaptoacetic acid reagent for FePt nanoparticles. The process was given by placing the FePt nanoparticles in chloroform and reacted with mercaptoacetic acid for several hours in order to ex- change ligand. Deionized water was then refilled to this mixture and the organic and aqueous layers were successfully separated. 0018-9464/$25.00 © 2007 IEEE