Concave Star-Shaped Au Nanocrystals Exhibit Exceptional SERS Activity

ISERS and Inormal represent the intensity of CV at 1617 cm-1 obtained from SERS and normal Raman spectra, respectively. CSERS and Cnormal correspond to the concentration in the SERS and normal Raman measurements, respectively. The calculated AEF values for each nanocrystal, determined using the equation, are listed in Table S1 (Supporting Information). Among the five shapes of Au nanocrystals, concave star-shaped Au nanocrystals exhibited an AEF of 1.22 × 105, approximately 12 times higher than that of Au NSs. This finding clearly demonstrates that concave star-shaped Au nanocrystals possess the most outstanding SERS activity. This exceptional performance can be attributed to the presence of a large number of sharp apexes and edges, which act as hot spots due to the significant electromagnetic field enhancements.