Sensitive metal-enhanced photoluminescence and Raman scattering magnetic core–shell nano-particles with tunable size for the detection of methylene blue

The distance between the probe molecule and the metal nano-particle affects photoluminescence (PL) enhancement and surface-enhanced Raman scattering (SERS). On the one hand, magnetic Fe 3 O 4 is introduced into the core–shell structure as a spacer, and the luminous molecules are separated from silver nano-particles (AgNPs) to prevent PL quenching. On the other hand, they are wrapped on the surface of AgNPs to weaken the effect of aggregation on Raman signals. Herein, magnetic core–shell nano-particles (Ag@Fe 3 O 4 ) were successfully synthesised in one step; their size can be controlled by changing the added amount of Fe 3+ . In a series of experiments and comparisons, core–shell nano-particles that can be utilised for PL enhancement and SERS were obtained, and the enhancement factors of particles prepared in different batches were all above 20. In addition, the excellent time stability of Ag@Fe 3 O 4 particles was confirmed, that is, the PL intensity only decreased by 8.6 % within 14 days. Therefore, the core–shell structure can detect methylene blue in aqueous solution by measuring emission spectrum, with a detection concentration as low as 0.1 μM.