Fig. 1

The comparison of P-GERTs and S-GERTs. Schematic diagrams and representative TEM images of GERTs with a petal-like shell (P-GERTs, a, b), and GERTs with a smooth-surface shell (S-GERTs, c, d). Red arrows in panel b, d indicate the internal nanogaps of GERTs. The scale bars are 10 nm. e Representative low-resolution TEM image (top, the scale bar is 50 nm) and high-resolution TEM images (bottom, the scale bar is 10 nm) of P-GERTs. Yellow arrows in panel e indicate the external nanogaps between petal-like structures on the shell of P-GERTs. f Extinction spectra of P-GERTs (red) and S-GERTs (black). The insets in panel f show the corresponding photos of GERTs solution. g SERS spectra of P-GERTs (red) and S-GERTs (black). The insets in panel g show the finite-difference time-domain (FDTD) calculated electric field enhancement distribution of a single P-GERT (top) and S-GERT (bottom) excited by 638 nm. Raman measurements were performed using 638 nm laser, 2 s acquisition time, and ×10 objective lens