Synthesis and evaluation of time dependent optical properties of plasmonic–magnetic nanoparticles

Magnetic–plasmonic nanostructures were synthesized and their optical properties investigated based on experimental results and theoretical calculations. Magnetite nanoparticles with diameter of 9.5 ± 1.4 nm were fabricated using coprecipitation method and subsequently covered by a thin layer of gold to obtain 15.8 ± 3.5 nm nanoshells measured by TEM micrographs. Crystalinity, surface chemistry, magnetic and optical properties were also studied by XRD, FT-IR, VSM and UV–Vis spectroscopy, respectively. The plane indices data from XRD and calculated unit cell parameter proved the purity of the prepared magnetite nanoparticles. Magnetic saturation of synthesized magnetite nanoparticles reduced from 46.94 to 11.98 emu/g after coating with a thin layer of 5.8 ± 3.5 nm gold but still is high enough to be used as contrast agents in magnetic resonance imaging (MRI). FT-IR results showed a successful functionalization of magnetite nanoparticles which was followed by gold coating. The changes of the optical properties of gold nanoshells during the shell growth based on self-assembly were studied by UV–Vis spectroscopy. In our case, a red Doppler shift of about 15% corresponding to 12 nm in surface plasmon resonance wavelength (λSPR) position was observed within the first minute of growth phase. This was followed by 45% of blue Doppler shift corresponding to 5 nm in 2 min. A good agreement between the UV–Vis spectra and calculated absorption efficiency was observed. The calculated scattering and absorption efficiencies and cross sections of prepared nanoshells have made them an efficient agent for photothermal cancer therapy.

► The shell thickness of synthesized nanoshell was stabilized after 5 min at 531 nm.
► Prepared nanostructure can be used for excitation using 532 nm wavelength such as Nd:YAG laser second harmonic.
► The high value of calculated absorption cross section makes the nanostructure a good candidate for laser thermal therapy.
► High saturation magnetization of synthesized nanostructure makes it suitable for MRI application.