RESEARCH PAPER One-pot synthesis and characterization of rhodamine derivative-loaded magnetic core–shell nanoparticles Jin Zhang • Jiaxin Li • Fereidoon S. Razavi • Abdul Md. Mumin Received: 30 January 2010 / Accepted: 20 April 2010 / Published online: 4 May 2010 Ó Springer Science+Business Media B.V. 2010 Abstract A new method to produce elaborate nano- structure with magnetic and fluorescent properties in one entity is reported in this article. Magnetite (Fe 3 O 4 ) coated with fluorescent silica (SiO 2 ) shell was pro- duced through the one-pot reaction, in which one reactor was utilized to realize the synthesis of super- paramagnetic core of Fe 3 O 4 , the formation of SiO 2 coating through the condensation and polymerization of tetraethylorthosilicate (TEOS), and the encapsula- tion of tetramethyl rhodamine isothiocyanate-dextran (TRITC-dextran) within silica shell. Transmission electron microscopy (TEM), energy dispersive X-ray (EDX) analysis, and X-ray diffraction (XRD) were carried out to investigate the core–shell structure. The magnetic core of the core–shell nanoparticles is 60 ± 10 nm in diameter. The thickness of the fluo- rescent SiO 2 shell is estimated at 15 ± 5 nm. In addition, the fluorescent signal of the SiO 2 shell has been detected by the laser confocal scanning micros- copy (LCSM) with emission wavelength (k em ) at 566 nm. In addition, the magnetic properties of TRITC-dextran loaded silica-coating iron oxide nano- particles (Fe 3 O 4 @SiO 2 NPs) were studied. The hys- teresis loop of the core–shell NPs measured at room temperature shows that the saturation magnetization (M s ) is not reached even at the field of 70 kOe (7T). Meanwhile, the very low coercivity (H c ) and remanent magnetization (M r ) are 0.375 kOe and 6.6 emu/g, respectively, at room temperature. It indicates that the core–shell particles have the superparamagnetic prop- erties. The measured blocking temperature (T B ) of the TRITC-dextran loaded Fe 3 O 4 @SiO 2 NPs is about 122.5 K. It is expected that the multifunctional core– shell nanoparticles can be used in bio-imaging. Keywords Nanoparticles Á One-pot reaction Á Superparamagnetics Á Fluorophore Á Bio-imaging Introduction Magnetic nanoparticles (NPs) with diameter in 1–100 nm normally have high magnetic susceptibility and show superparamagnetic behavior, which are of great interest for molecular diagnosis and alternative disease treatment (Wagner et al. 2006; Kobayashi and Brechbiel 2005). Various polymers, surfactants, and engineered nanoshells have been studied to modify the surface of superparamagnetic NPs to avoid the J. Zhang (&) Á J. Li Á A. Md. Mumin Department of Chemical and Biochemical Engineering, University of Western Ontario, London, ON N6A 5B9, Canada e-mail: jzhang@eng.uwo.ca URL: http://www.eng.uwo.ca/people/jzhang/ F. S. Razavi Department of Physics, Brock University, St. Catharines, ON L2S 3A1, Canada 123 J Nanopart Res (2011) 13:1909–1916 DOI 10.1007/s11051-010-9942-1