Gold-silver bimetallic nanoparticles with a Raman labeling chemical assembled on silica nanoparticles as an internal-standard-containing nanoprobe

Surface-enhanced Raman scattering (SERS) has a great potential as a sensitive probe for analytical detection, but the low level of reproducibility remains a challenge for quantitative detection. To enhance the reproducibility, an internal standard that is incorporated between the core and shell structure of metal nanoparticles (NPs) can be employed. However, the unstable sol form of “core-shell” substrates has been unsatisfactory, causing rapid agglomeration. Herein, we prepared a SERS-active core-Raman labeling chemical (RLC)-shell material based on Au-Ag NPs assembled on silica NPs (SiO₂@Au@RLC@Ag NPs) as internal-standard-containing NPs. When 4-mercaptobenzoic acid (4-MBA) was used as a model RLC with a silica template, the Raman intensity of SiO₂@Au@4-MBA@Ag was ∼8-fold higher than that without a silica template (Au@4-MBA@Ag NPs). Concentrations of 4-MBA in the range of 1 × 10⁻⁶ to 1 × 10⁻² M incorporated between the SiO₂@Au core and the Ag shell did not significantly affect the Ag shell coating. Nevertheless, the Raman intensity increased linearly and was proportional to the logarithm of the 4-MBA concentration. When SiO₂@Au@4-MBA@Ag was utilized as internal-standard-containing NPs, the dynamic linear range of thiram detection was 5–50 μM with a limit of detection of 1.2 μM. These results show that our material can be used for the broad dynamic detection of (bio)-chemical traces with high sensitivity.