In the present study, a sunflower-like nanostructure array composed of a series of synaptic nanoparticles and nanospheres was manufactured through an efficient and low-cost colloidal lithography technique. The primary electromagnetic field contribution generated by the synaptic nanoparticles of the surface array structures was also determined by a finite-difference time-domain software to simulate the hotspots. This structure exhibited high repeatability and excellent sensitivity; hence, it was used as a surface-enhanced Raman spectroscopy (SERS) active substrate to achieve a rapid detection of ultra-low concentrations of Alpha-fetoprotein (AFP). This study demonstrates the design of a plasmonic structure with strong electromagnetic coupling, which can be used for the rapid detection of AFP concentration in clinical medicine.

Ag–SiO₂ nanomace arrays were prepared on a two-dimensional ordered colloidal (2D) polystyrene sphere template by co-sputtering Ag and SiO₂ in a magnetron sputtering system. The lateral size of the nanomaces and the distance between the neighbor nanomaces were controlled by adjusting the etching time of the 2D template. The nanomaces were composed of SiO₂-isolated Ag nanoparticles, which produced surface-enhanced Raman scattering (SERS) enhancement, and 3D hot spots were created between the neighbor nanomaces. When the distance between the nanomaces was sufficiently large, triangle-shaped nanostructures on silicon substrate were observed, which also contributed to the enhancement of the SERS signals. The finite-difference time-domain (FDTD) method was used to calculate the electromagnetic field distributions in the Ag–SiO₂ nanomace arrays, which generated physical reasons for the change of the SERS signals.