Nanoplasmonics and surface enhanced spectroscopy

Magneto-plasmonic Fe3O4/Au nanocomposites
Mukha Iu.P.1, Pylypchuk Ie.V.1, Vityuk N.V.1, Khodko A.A.2, Stetsenko M.O.3,4, Qu J.4, Chepurna O.M.4, Ohulchanskyy T.Y.4
1Chuiko Institute of Surface Chemistry, NAS of Ukraine, 17 General Naumov Str., Kyiv 03164, Ukraine. E-mail: iu.mukha@gmail.com
2Institute of Physics, NAS of Ukraine, pr. Nauky, 46, Kyiv, 03028, Ukraine.
3V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine, pr. Nauky, 41, Kyiv, 03028 Ukraine
4 College of Physics and Optoelectronic Engineering, Shenzhen University, Shenzhen, Guangdong Province, 518060, P.R. China.

Magneto-plasmonic nanostructures composed of magnetic iron oxide core and gold shell can possess properties inherent to both individual components and be applied in biomedical field for targeted drug delivery and therapy. 
Herein, we report an approach for Fe3O4/Au core-shell nanoparticles synthesis in aqueous medium containing amino acid tryptophan (Trp) – an advantageous reagent for preparation of biocompatible nanosized noble metals. Fe3O4/Au nanoparticles were produced both by chemical and photochemical reduction methods; irradiation by deep ultraviolet light (~278 nm) from light emitting diode was employed in the latter case. Both methods assume the activation of indole ring of Trp in red-ox process. It was shown that temperature of reaction and optical power of UV illumination can affect the rate of reaction and resulting physico-chemical characteristics of nanobjects, e.g., optical properties, size, morphology and assembling of nanoparticles. The position of plasmon resonance band maximum of magneto-plasmonic nanocomposites can be adjusted by varying the temperature of reaction from 25 to 100°C. The obtained Fe3O4/Au colloids possess optical properties of nanosized gold and react on the applied magnetic field (Fig.1). 

Figure 1. Absorption spectra of colloidal water suspensions of magneto-plasmonic Fe3O4/Au nanocomposites and the photographs of colloids with the applied magnetic field.