High-yield synthesis of multi-branched urchin-like gold nanoparticles

Here, we report on an aqueous room temperature synthesis method for the production of gold nanoparticles that have a number (>4) of branches ultimately resembling the shape of sea urchins. The particles are synthesized in the presence of water soluble thiol terminated molecules, used as ligand molecules. These nano-urchins are produced in high yield and exhibit unique optical properties. The thiolated ligands stabilize the particles, making it possible to dry them and store them for days. When redissolved, the particles show some aggregation but not a loss in shape; their extinction spectrum shows a shift in the plasmon resonance from 585 to 622 nm together with a peak broadening. Large local electromagnetic (EM) field enhancements are expected near the sharp featured branches of the nanourchins. Finite difference time-domain (FDTD) calculations performed on a nanoparticle with four branches show enhancements of the light intensity relative to the incident field of approximately 3000-fold. We reason that these particles will find applications as materials for surface enhanced Raman scattering (SERS).