Fig. 1. (a) SEM image of the graphene film as-grown on Au substrate. The different contrasts represent the different orientations of Au grains. (b) Optical image of the graphene film transferred on SiO2/Si substrate. (c) Optical transmittance spectrum of the graphene film transferred on quartz. (d) Raman spectra taken from randomly selected 5 positions in (b) and the as-grown graphene film on Au.

Fig. 2. (a) SEM image of PG film grown on Cu substrate. (b) Optical image of the PG film transferred on SiO2/Si substrate. (c) Optical transmittance spectrum of PG film transferred on quartz. (d) Raman spectra taken from randomly selected 5 positions in (b).

Fig. 3. (a, b) Photos of a water droplet on (a) DG and (b) PG. (c, d) Photos of a RhB solution (2 × 10-5 M) droplet on (c) DG and (d) PG.

Fig. 4. (a-c) Raman spectra of DG films that have been soaked in (a) RhB, (b) MB and (c) MO excited with different lasers. (d-f) Raman spectra of bare SiO2/Si that have been soaked in (d) RhB, (e) MB and (f) MO excited with different lasers.

Fig. 5. Comparison of the enhanced Raman scattering effects of DG and PG that have been soaked in RhB solutions with different concentrations. (a) 2 × 10-5 M, (b) 2 × 10-6 M, (c) 2 × 10-7 M, (d) 2 × 10-8 M, and (e) 2 × 10-9 M. (f) I1650/IG vs the concentration of RhB solution for DG and PG. Inset, photograph of a series of RhB solutions with concentration from 2 × 10-5 M to 2 × 10-9 M.

Fig. 6. Raman maps of (a) ID/IG of DG and I1650/IG of DG films that have been socked in RhB solution with a concentration of (b) 2 × 10-7 and (c) 2 × 10-9 M. (d) Photograph of the completely separated PMMA/DG and Au foil. (e) Optical image of the graphene film grown on the reused Au foil and then transferred on SiO2/Si substrate. (f) Raman spectra taken from randomly selected 5 positions in (e).