Two novel synthetic routes to formation of gold-magnetite nanoparticles have been designed. Treatment of preformed magnetite nanoparticles with ultrasound in aqueous media with dissolved tetrachloroauric acid resulted in the formation of gold-magnetite nanocomposite materials. The other route involved irradiation of preformed magnetite nanoparticles by UV light in aqueous media with dissolved tetrachloroauric acid. This method resulted in the formation of gold-magnetite nanocomposite materials. These materials maintained the morphology of the original magnetite particles. The morphology of the gold particles could be controlled by adjusting experimental parameters, like addition of small amounts of solvent modifiers such as methanol, diethylene glycol, and oleic acid as well as variation of the concentration of the tetrachloroauric acid solution and time of the reaction. The nanocomposite materials were magnetic and exhibited optical properties similar to gold nanoparticles. Since we were not able to directly synthesize core shell gold magnetite nanoparticles, TiO2 was used as a bridging material. TiO2 nanoparticles with embedded magnetite were suspended in aqueous HAuCl4 and irradiated with ultraviolet light to photodeposit gold. The degree of gold coating and the wavelength of absorbance could be controlled by adjusting concentration of HAuCl4. Absorbance maxima were between 540-590 nm. Particles exhibited superparamagnetic properties (blocking temperature ~170 K) whether or not coated with gold. These particles have potential applications as drug delivery agents, magnetic imaging contrast agents, and magnetically separatable photocatalysts with unique surface properties. Another goal was to synthesize and characterize indium doped magnetite nanoparticles for application as radiotracers for in vivo fate studies. The labeled particles will be useful for determination of pharmacological behavior in biological systems. Indium doped magnetite particles with varying size and surface chemistry were synthesized with wet chemical techniques. The synthesized nanoparticles were characterized in terms of the size and shape with the help of TEM, the elemental composition by ICP and EDS, the crystal structure by XRD and magnetic properties by SQUID measurements. It was found that the indium loading could be controlled even though the magnetic properties were similar to undoped magnetite.