Magnetic field modulated SERS enhancement of CoPt hollow nanoparticles with sizes below 10 nm

Abstract

It is well known that Pt shows much weaker plasmonic effects in the visible spectrum when compared to Au, Ag and Cu. Therefore, the realization of efficient optical absorption by Pt nanoparticles with sizes below 10 nm in the visible spectrum remains a challenge. One possible way to enhance the optical absorption is to prepare Pt-based bimetallic magnetic nanoparticles. Furthermore, if an external magnetic field is applied, the synergistic effect of both electric and magnetic fields may provide sufficient SERS enhancement. In this paper, CoPt hollow nanoparticles (NPs) with sizes below 10 nm and ultrathin shells (∼2 nm) were synthesized in solution, at room temperature. The NPs have high surface-to-volume ratios and excellent structural stability. The hollow NPs exhibited enhanced light absorption characterized by surface-enhanced Raman scattering (SERS) with 4-mercaptobenzoic acid (4-MBA) as tip molecules. It is noted that the SERS enhancement of these alloyed NPs can be tuned by using an external magnetic field. A synergistic optical effect between these hollow NPs and the Ag film substrate is obtained. Hence, CoPt hollow NPs show promise as SERS substrates and potential for other applications in optical enhancement.