Tailored Au@Ag NPs for Rapid Ractopamine Detection in Pork: Optimizing Size for Enhanced SERS Signals

Ractopamine, frequently misused to promote lean meat production, raises significant food safety issues. This study introduces a rapid detection approach for ractopamine in pork using size- turnable Au@Ag NPs core-shell nanoparticles as surface-enhanced Raman scatting (SERS) substrates. By changing the diameter of the gold core and the thickness of the silver shell, the effects of them on the SERS enhancement of ractopamine signals were carefully studied. Interestingly, with the increase of the silver shell thickness, the SERS intensity exhibited a pattern of initially increasing, then decreasing, followed by another increase and subsequent decrease. In contrast, the gold core enlargement displayed a simpler trend: the SERS intensity first rose and then diminished. These phenomena reveal the relationship between SERS signal enhancement effect of ractopamine and local surface plasmon resonance (LSPR) and the contact area between ractopamine molecule and substrate. The most effective SERS enhancement was identified using Au@Ag NPs nanoparticles having a 32 nm Au core coupled with an 18 nm Ag shell. Further quantitative analysis showed the impressive regression correlation coefficient (R2) of 0.99, root mean square error (RMSE) of prediction at 0.012 μg/g, and the limit of detection (LOD) of 19 ng/g for ractopamine detection model spanning concentrations from 0.1 - 10 μg/g.