Bimetallic nano-mushrooms with DNA-mediated interior nanogaps for high-efficiency SERS signal amplification

Uniform silver-containing metal nanostructures with well-defined nanogaps hold great promise for ultrasensitive surface-enhanced Raman scattering (SERS) analyses. Nevertheless, the direct synthesis of such nanostructures with strong and stable SERS signals remains extremely challenging. Here, we report a DNA-mediated approach for the direct synthesis of gold-silver nano-mushrooms with interior nanogaps. The SERS intensities of these nano-mushrooms were critically dependent on the area of the nanogap between the gold head and the silver cap. We found that the formation of nanogaps was finely tunable by controlling the surface density of 6-carboxy-X-rhodamine (ROX) labeled single-stranded DNA (ssDNA) on the gold nanoparticles. We obtained nano-mushrooms in high yield with a high SERS signal enhancement factor of ~1.0 × 10⁹, much higher than that for Au-Ag nanostructures without nanogaps. Measurements for single nanomushrooms show that these structures have both sensitive and reproducible SERS signals.