TiN(IV) oxide coated gold nanoparticles: synthesis, characterization and investigation of surface enhanced raman scattering activities

Elçi, Aylin
Noble metal nanoparticles (i.e. gold (Au) and silver (Ag)) have received enormous attention due to their superior optical properties related to localized surface plasmon resonance (LSPR) and their potential applications in sensing, imaging, catalysis and optoelectronic devices. In particular, the ones with anisotropic morphologies have attracted intense interest from the researchers because of their superior optoelectronic properties. High electromagnetic field forms on the nanoparticle surface. The intensity of this field is even higher on the edges and/or tips of the nanoparticles with sharp features. The molecules, which are adsorbed or in close proximity in these regions are polarized. This provides detection of molecules in trace amount by spectroscopic techniques such as surface-enhanced Raman scattering (SERS). Because of all these reasons noble metal nanoparticles with anisotropic morphologies are fascinating candidates as SERS substrates and they are subject of a very active research area. However, agglomeration tendency of noble metal nanoparticles in harsh mediums restrict their application areas. Coating these particles with optically transparent and semiconductive materials (e.g. SnO2, SiO2, and TiO2) make them more durable in harsh conditions while protecting their morphologies and optical properties. In this study, Au nanoparticles in three different morphology (star, rod, sphere) have been synthesized, and coated with tin (IV) oxide (SnO2) layer to obtain hybrid systems in the core-shell structure. Au nanoparticles were synthesized based on a method called “seed-mediated growth method”. The SnO2 coating was performed by using a simple hydrothermal-based method. The synthesized hybrid systems have been fully characterized by a combination of UV-vis spectroscopy, transmission electron microscope (TEM) and energy-dispersive X-ray (EDX) studies, scanning electron microscope (SEM), X-Ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The characterization studies showed that Au nanoparticles with three different morphology were successfully coated with SnO2 layer. Among them, SnO2 coated Au nanostar hybrid system was synthesized for the first time in this study. The potential use of the Au nanostar-SnO2 core-shell system as SERS substrate was also investigated by using crystal violet (CV) as a probe molecule. The SERS studies showed that SERS activity of Au nanostars remains after coating them with SnO2 and the new hybrid system is very promising to be used as a SERS substrate.