Synthesis of Au@Ag core–shell nanocubes with finely tuned shell thicknesses for surface-enhanced Raman spectroscopic detection

Abstract

In this work, we describe a facile method for generating monodisperse Au@Ag core–shell nanocubes with well-controlled size and fine-tuned Ag shell thicknesses. In this synthesis method, Au nanocubes were prepared via the seed-mediated growth method. Then, Au@Ag nanocubes with the core–shell structure were prepared separately by reducing AgNO₃ with AA using as-prepared Au nanocubes as seeds. The thickness of Ag shells could be finely tuned from 3.6 nm to 10.0 nm by varying the concentration of the AgNO₃ precursor. By investigating the localized surface plasmon resonance (LSPR) properties of Au@Ag nanocubes in relation to the thickness of the Ag shell, we found that the intensity of the characteristic peak of Ag gradually increases and that of Au gradually decreases as the thickness of the Ag shell increases. Additionally, surface-enhanced Raman scattering (SERS) properties of Au@Ag core–shell nanocubes were evaluated using rhodamine 6G (R6G) as the probe molecule. Interestingly, Au@Ag nanocubes exhibit efficient SERS intensities compared to the Au nanocubes, and Ag shell with a thickness of about 8.4 nm exhibits the optimal SERS activity. In addition, our results also demonstrated that Au@Ag nanocubes with an Ag shell thickness of 8.4 nm exhibited high SERS sensitivity and are capable of probing the analyte down to 10⁻¹² M. The results obtained here suggest that Au@Ag core–shell nanocubes might serve as a nanoprobe for SERS-based analytical and biosensing applications.