Fig. 1. Structure diagram of IP6

Fig. 2. Schematic of IP6@Au NPs as a SERS substrate by adding Fe3+ to increase hot spots

Fig. 3. SEM images of three kinds of nanoparticles. (a) IP6@Ag NPs; (b) IP6@Ag NPs@Au NPs; (c) IP6@Au NPs

Fig. 4. Ultraviolet-visible absorption spectra of three kinds of nanoparticles

Fig. 5. Ultraviolet-visible absorption spectra after adding different concentrations of Fe3+ in IP6@Au NPs

Fig. 6. Raman spectra of RhB (10-7 mol·L-1) with IP6@Au NPs@Fe3+ as SERS substrate. (a) Composite substrate containing different concentrations of Fe3+; (b) substrate without Fe3+; (c) linear fitting chart of Raman intensity between 1100 cm-1 and 1200 cm-1

Fig. 7. Raman spectra of different concentrations of RhB detected with IP6@Au NPs@0.28×10-6 Fe3+ as SERS substrate