Seedless, size and shape controlled synthesis of gold mesoscopic particles and their excellent SERS applications

Development of facile synthesis strategies for complex-shaped gold nanostructures have great significance owing to their prospective applications. Herein, we demonstrate a remarkably simple single-step recipe for the synthesis of micrometer sized gold particles with tailored nanostructured surfaces. We demonstrate that gold micro-particles (GMPs) can be synthesized simply by mixing HAuCl4, cetyltrimethylammonium bromide (CTAB), AgNO3 and ascorbic acid (AA), without the seed particles. This is contrary to the conventional belief that HAuCl4 cannot be completely reduced by AA in the presence of high concentration of CTAB. The surface morphology of GMPs can be tuned by changing the concentration of AA, whereas the size of the GMPs can be controlled by tuning the concentration of CTAB in the reaction medium. The GMPs have shown excellent potential for SERS applications. The simulation results show that each GMP has high concentration of intraparticle hotspots. The finite element simulation shows maximum enhancement factor in excess of 109, while the average experimental enhancement factor can be as high as 4 × 107. The simulation results also indicate that the presence of branches of different lengths enable GMPs to show efficient SERS sensing for multiple excitation sources. Therefore, GMPs have the capability to become universal SERS platforms.