The EF Was Defined As Equation S1

Supporting information

The calculation of EF value [1,2]

The EF was defined as equation S1.

EF = (I1 /N1 ) / (I2 /N2 ) (S1)

-1 Where I1 stands for the intensity of the vibrational band at ~1580 cm in the SERS

spectrum of 4-MAB and I2 stands for that of the solid sample. N1 and N2 are the number of 4-MAB molecules adsorbed on the SERS substrate and bulk molecules illuminated by the laser light to obtain the corresponding SERS and ordinary Raman

spectra, respectively. N1 can be obtained according to equation S2.

N1= NaA1A2/δ (S2)

Where Na is the number density of the nanoparticles, A1 is the nanoparticles footprint

area, A2 is the area of the focal spot of laser, and δ is the surface area occupied by an

adsorbed 4-MAB molecule. Na and A1 can be obtained from the SEM images in Fig. 2,

and A2 can be obtained from the diameter of the laser spot (~100 μm). According to the report by Kim [3], δ can be adopted as ~0.22 nm2/molecule. Then the total number

of surface adsorbed molecules (N1) on the composite film within the illuminated laser

11 spot can be obtained at 2.3×10 . N2 is the molecule number of the solid 4-MAB in the laser illumination volume. In our experiment, the laser spot of 100 μm in diameter and the penetration depth (~200 μm) of the focused laser beam are used. Taking the

3 density of the solid 4-MAB (1.2 g/cm ) into account, N2 was calculated to be about

7.3×1015 within the illuminated laser light. The intensity ratio of the band at ~1580 cm-1 in Fig.4b and Fig.4a was measured to be 1.02 and 8.13 for SERS and ordinary Raman, respectively. The EF at the composite film for the band at ~1580 cm-1 can be calculated to be about 1.9×105 at 633 nm excitation.

Reference

1.C. J. Orendorff, A. Gole, T. K. Sau, C. J. Murphy, Anal. Chem. 2005, 77, 3261.

2. S. J Guo, L. Wang, E.K. Wang. Chem. Commu.2007, 3163.

3. K. Kim, J. K. Yoon J. Phys. Chem. B. 2005, 109, 20731. Figure S1 SEM images of hierarchically flowerlike Ag microstructure prepared from different concentration of AgNO3 aqueous solutions: (a) 5 mM; (b) 10 mM; (c) 15 mM.

Figure S2 Raman spectrum of 4-MAB dsorbed on the Ag microstructure as-prepared

Ag microstructure prepared from 20 mM of AgNO3 aqueous solution for 10 min.