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1 Electronic Supplemental Information Laser wavelength- and power-dependent plasmon-driven chemical reactions by single particle surface enhanced Raman spectroscopy Leilei Kang, a Ping Xu* a,b Bin Zhang, a Hsinhan Tsai, b Xijiang Han * a and Hsing-Lin Wang* b a Department of Chemistry, Harbin Institute of Technology, Harbin , China. Fax: ; Tel: ; pxu@hit.edu.cn; hanxj63@yahoo.com.cn b Chemistry Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA. Tel: ; hwang@lanl.gov Experimental: Synthesis of hierarchical Ag microspheres: 1 ml of 1 M AgNO 3 aqueous and 0.1 ml of 0.25 M succinic acid were added to 10 ml of deionized water in a 25 ml beaker with a magnetic stirrer in an ice water bath. 1 ml of ascorbic acid aqueous solution (C 6 H 8 O 6, 1 M) was then quickly injected into the vigorously stirred mixture. The solution became dark immediately, and a large quantity of Ag particles was produced in a few minutes. After 15 min, the particles were collected by centrifugation and repeatedly rinsed with deionized water. Then the Ag particles were dried in a vacuum drier at 60 o C. Single particle surface enhanced Raman spectroscopy: The dried Ag microspheres were immersed in a 1mg/ml p-nitrothiophenol (pntp) ethanol solution for about 1 h. Then the Ag microspheres were rinsed repeatedly with ethanol to remove the pntp residuals. Then the Ag microspheres were re-dispersed into ethanol to make a diluted suspension, and one drop of the suspension was transferred onto a silicon wafer. After air drying, SERS spectra and Raman images of pntp were measured with a Renishaw invia confocal microscope Raman system by focusing on one single Ag particle at different laser excitation time periods. Lasers with wavelengths of 633 and 532 nm were used as the excitation sources. In our Raman experiment, the laser power irradiating the SERS sample was measured at 0.5 mw or 2 mw with a 100X objective. For comparison, p-nitrothiophenol (pntp) ethanol solution was exposed to the 532 nm excitation laser for different time periods. Then, SERS measurements were carried out by putting the laser exposed pntp on Ag microshperes. Characterization: Scanning electron microscopic (SEM) images were taken on a FEI Inspect SEM. The characteristics of the crystallite structure of the Ag microspheres were determined using an XRD-6000 X- ray diffractometer (Shimadzu) with a Cu Kα radiation source (λ= Å, 40.0 kv, and 30.0 ma). UV-Vis spectrum was measured on a Varian Cary 500 Scan UV-Vis-NIR spectrophotometer in the range between nm.

2 Additional Figures: Fig. S1. UV-vis spectrum of the hierarchical Ag microspheres. Fig. S2. Raman spectrum of p, p -dimercaptoazobenzene (DMAB).

3 Fig. S3. SERS spectra of p-nitrothiophenol (pntp) after pntp solution was exposed to 532 nm laser excitation for different time periods. It shows that without the presence of Ag microspheres, pntp would not be converted to p, p -dimercaptoazobenzene (DMAB) under laser excitation.

4 Fig. S4. Raman images collected at the 1335 cm -1 peak of p-nitrothiophenol (pntp) after exposure to 633 nm laser (0.5 mw) for 0 (a), 20 (b), 40 (c), 100 (d), 200 (e), 400 (f), and 500 min (g). Scale bars are in microns.

5 Fig. S5. Raman images collected at the 1440 cm -1 peak of p-nitrothiophenol (pntp) after exposure to 633 nm laser (0.5 mw) for 0 (a), 20 (b), 40 (c), 100 (d), 200 (e), 400 (f), and 500 min (g). Scale bars are in microns.

6 Fig. S6. Raman images collected at the 1335 cm -1 peak of p-nitrothiophenol (pntp) after exposure to 633 nm laser (2 mw) for 0 (a), 1 (b), 2 (c), 4 (d), 6 (e), 10 (f), and 15 min (g).

7 Fig. S7. Raman images collected at the 1440 cm -1 peak of p-nitrothiophenol (pntp) after exposure to 633 nm laser (2 mw) for 0 (a), 1 (b), 2 (c), 4 (d), 6 (e), 10 (f), and 15 min (g).