Figure 1.

Schematic illustration of self-assembly of gold nanoparticles and fabrication of AuNPs-ML sample substrate. Briefly, stock solution of gold nanoparticles was added dropwise on the surface of deionized water in the trough. Afterward, a cover with a hole at the edge was covered onto the trough. After evaporation for 24 h, the self-assembled gold nanoparticles were obtained on the surface of deionized water. A steel plate was slowly pulled out of the sub-phase to transfer self-assembled gold nanoparticles.