Bare silicon wafers were also immersed in 10−2 M R6G or 4-ATP solution for comparison. After thoroughly rinsed with ethanol and drying by nitrogen, they were subjected to Raman characterization. The data were obtained by choosing six different spots of the sample to average. The SERS spectra were recorded using a Bruker SENTERRA confocal Raman spectrometer coupled to a microscope with a × 20 EX 527 solubility dmso objective (N.A. = 0.4) in a backscattering configuration. The 532-nm wavelength was used with a holographic notch filter based on a grating of 1,200 lines mm−1 and spectral

resolution of 3 cm−1. The Raman signals were collected on a thermoelectrically cooled (−60°C) CCD detector through 50 × 1,000 μm × 2 slit-type apertures. SERS data was collected with laser power of 2 mW, a laser spot size of approximately 2 μm, and integration time of 2 s. The Raman band of a silicon wafer at 520 cm−1 was used to calibrate the spectrometer. Results and discussion The SEM images of the flower-like Ag nanostructures with different amounts of catalyzing agent NH3•3H2O are shown in Figure  1. All the flower-like Ag nanostructures consisting of a silver core and many rod-like tips protruding out are abundant with higher curvature surface

such as tips and sharp edges compared to the highly branched nanostructures in NVP-BGJ398 solubility dmso previous reports [28, 29]. There is a trend that the constituent rods become smaller in both longitudinal dimension (from about ACY-1215 datasheet 1 μm to dozens of nanometers) and diameter (from 150 nm to less than 50 nm) as the amount of catalyzing agent NH3•3H2O increases. Meanwhile, the rods become abundant; consequently, the junctions or gaps between two or more closely spaced rods turn to be rich. One interesting thing deserving to be mentioned is that there is a turning point in which various kinds

of rods with different length and diameters coexist when the amount of NH3•3H2O is 600 μL (Sample P600) as shown in Figure  1C . Figure 1 all SEM images of the flower-like Ag nanostructures. SEM images of the flower-like Ag nanostructures prepared with PVP and different amounts of catalyzing agent NH3•3H2O: (A) 200 μL, (B) 400 μL, (C) 600 μL, and (D) 800 μL. In solution-phase synthesis of highly branched noble metal nanostructures, the reaction rate and the final morphology can be manipulated by the concentration of the precursor [30], the reaction time [9], the trace amount of salts such as Cu2+, Fe2+, or Fe3+ [31], and so on. In the case of our synthesis, the reaction rate is dominated by the amount of catalyzing agent NH3•3H2O injected. As ammonia is added, the pH value of the solution is raised leading to initiation of Ag+ reduction to Ag0 atoms.