Supporting Information
Fabrication and magnetic-induced aggregation of Fe3O4-noble metalcomposites for superior SERS performances
Zibao Gana,b,c,, Aiwu Zhaoa,b,c,Maofeng Zhanga, Dapeng Wanga,b, Hongyan Guoa,Wenyu Taoa,b, Qian Gaoa, Ranran Maoa,b , Erhu Liua,b
aInstitute of Intelligent Machines, Chinese Academy of Sciences, Hefei 230031, PR China
b Department of Chemistry, University of Science and Technology of China, Hefei 230026, Anhui, PR China
c State Key Laboratory of Transducer Technology, Chinese Academy of Sciences, Hefei 230031, PR China
*Corresponding author at: Institute of IntelligentMachines, Chinese Academy ofSciences, Hefei 230031, PRChina. Tel.: +86 551 5593360; fax: +86 551 5592420.E-mail address: (A. Zhao).
Fig. S1.The histogram of particle size distribution for ultrafine Fe3O4 nanoparticles (The inset exhibit the magnetic response of dispersion of the ultrafine Fe3O4 nanoparticles).
Fig. S2.XRD patterns of the samples prepared in different solvent (a) DEG, (b)EG.
Fig. S3.(a) Normal Raman spectrum of the bulk R6G, (b) SERS spectrum of 1.0 × 10-8 MR6G adsorbed on themagnetic-induced Fe3O4-Ag aggregates.
Calculation of the SERS enhancement factor
The enhancement factor (EF) values of R6G on the magnetic-induced Fe3O4-Ag aggregates according to the following formula:
where and are the SERS intensity of R6G on themagnetic-induced Fe3O4-Ag aggregates and the normal Raman scattering intensity of R6G, respectively. and are the number of R6G molecules under Laser excitation for the bulk samples, and the number of R6G molecules for SERS, respectively(Cai et al. 1998). According to the changes of Raman intensity of the fingerprint band (614 cm-1) of the R6G molecules (Fig. b), we estimated an approximate saturated adsorption point is 1.0 × 10-8 M of the R6G solution(Huh et al. 2011). We assumed that the R6G molecules were evenly scattered on the SERS substrate, can be calculated according tothe average surface density of R6G and the area of the Laser spot(Zhai et al. 2012). In our experiment, 10 μL of 1.0 × 10-8 M R6G solutionweredropped into the solutions of obtained Fe3O4-Agcomposites (20 μL), sonicating for 30 min. Then, 10 L above mixed solutions were carefully dropped on the specially cleaned monitor tank.Under the induction of an external applied magnetic field, a large number of Fe3O4-Agcomposites with adsorbed R6G molecules were aggregated up to dry to form a circular spot with the radius of ~ 1 mm (Fig. S4). Thus the mean surface density of R6G molecules was calculated as 1.06× 10-20 mol/μm2. According to the diameter of Laser beam (2μm), the area of the Laser spot was estimated to be 3.14 μm2. Therefore, we can conclude that the value of is 3.33× 10-20 mol. For the bulk R6G sample, the volume of Laser radiation = the area of Laser spot × the penetration depth of the Laser beam (2 μm)(Sun et al. 2011). Referring to the density and molar mass of the bulk R6G (0.79 g/cm3, 479.01 g/mol), can be calculated to be 1.04 × 10-14 mol. For the typical band at 614 cm-1, the ratio of is about 3.89 (Fig. S3). Finally, the EF value is calculated to be 1.2×106.
Fig. S4.Optical photo and corresponding SEM image of magnetic-inducedFe3O4-Ag aggregateson the specially cleaned monitor tank.
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