Seed-mediated synthesis of acanthosphere-like gold microstructures with tunable LSPR in the NIR region using gemini surfactants as directing agents for SERS applications

Acanthosphere-like gold microstructures (AGMs) were synthesized using a facile, two-step, seed-mediated method and butanediyl-1,4- bis (dimethylhexadecylammonium bromide) (16-4-16) as a structure-directing agent. The morphologies and sizes of the products were controlled during the synthesis process by adjusting the concentrations of 16-4-16, the AgNO 3 feed, HAuCl 4 , ascorbic acid, the amount of Ag seeds and the types of gemini surfactants used through systematic inquiry; particle sizes ranging from 130 to 800 nm were well prepared. Correspondingly, the morphology of the products changed between regular and irregular AGMs, and the products presented a number of new morphologies, such as open-mouthed submicrostructures and ribbon nanowires. In particular, with the increase in the 16-4-16 concentration, the structural morphology of the thorns clearly changed from a tip to a lamellar structure. A UV-vis spectroscopic analysis indicated that the localized surface plasmon resonance (LSPR) peak of the AGMs could be adjusted by changing the above factors, which extended from 500 to 1350 nm in the near-infrared (NIR) region, enabling a tremendous potential for using the AGMs as platforms for various biomedical applications. Based on the intermediate products, we propose a two-stage growth mechanism for the AGMs in which their solid cores and tips are generated successively. Surface-enhanced Raman scattering (SERS) measurements indicate that the AGMs can serve as sensitive SERS substrates; a SERS detection limit of 5 × 10 −7 M is presented for rhodamine B molecules. Graphical abstract