Sensitive and uniform detection using Surface-Enhanced Raman Scattering: Influence of colloidal-droplets evaporation...

Surface Enhanced Raman Scattering (SERS) has been developed into a powerful vibrational spectroscopy technique for chemical detection. However, the fabrication of colloidal droplets-based SERS substrates with well reproducibility and uniformity still remains challenging. In this paper, colloidal suspensions of hollow Au-Ag alloy nanourchins (HAAA-NUs) and Au nanoparticles (Au NPs) with different morphologies were employed as SERS-active substrates. After evaporation of colloidal suspensions, we evaluated the SERS performance based on the following features: "Coffee Ring Effects", adsorption processes of probe molecule and colloidal NPs, spin coating and morphologies of suspended NPs. The results demonstrated that SERS signals could be enhanced enormously in the marginal region of Coffee Ring patterns. The limit of detection (LOD) for amaranth molecule would be reached 10^-8 M. Moreover, by combining the droplets evaporation of HAAA-NUs suspensions with spin coating, the relative standard deviation (RSD) could be down to 3.5%, showing excellent reproducibility. The investigation here would provide a simple, practical and portable SERS detection method with excellent signal uniformity.