<p> Supporting information</p><p>The calculation of EF value [1,2] </p><p>The EF was defined as equation S1.</p><p>EF = (I1 /N1 ) / (I2 /N2 ) (S1)</p><p>-1 Where I1 stands for the intensity of the vibrational band at ~1580 cm in the SERS</p><p> 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</p><p> spectra, respectively. N1 can be obtained according to equation S2. </p><p>N1= NaA1A2/δ (S2)</p><p>Where Na is the number density of the nanoparticles, A1 is the nanoparticles footprint</p><p> area, A2 is the area of the focal spot of laser, and δ is the surface area occupied by an</p><p> adsorbed 4-MAB molecule. Na and A1 can be obtained from the SEM images in Fig. 2,</p><p> 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</p><p> of surface adsorbed molecules (N1) on the composite film within the illuminated laser</p><p>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</p><p>3 density of the solid 4-MAB (1.2 g/cm ) into account, N2 was calculated to be about</p><p>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. </p><p>Reference </p><p>1.C. J. Orendorff, A. Gole, T. K. Sau, C. J. Murphy, Anal. Chem. 2005, 77, 3261. </p><p>2. S. J Guo, L. Wang, E.K. Wang. Chem. Commu.2007, 3163.</p><p>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.</p><p>Figure S2 Raman spectrum of 4-MAB dsorbed on the Ag microstructure as-prepared</p><p>Ag microstructure prepared from 20 mM of AgNO3 aqueous solution for 10 min. </p>