Controllable Aggregates of Silver Nanoparticle Induced by
Methanol for Surface-Enhanced Raman Scattering
Zhiliang Zhang,1,a)
Yongqiang Wen, 2,b)
1
Research Center of Analysis and Test, Shandong Polytechnic University, Jinan 250353, China.
2
Research Center for Bioengineering & Sensing Technology, University of Science and Technology
Beijing, Beijing 100083, China
a)
Email: zhzhl@iccas.ac.cn
b)
Email: wyq_wen @iccas.ac.cn
Silver acetate, 1-hexadecylamine, phenylhydrazine were purchased from Alfa Aesar.
Methanol and acetone were obtained from Beijing Chemical Co. Rhodamine 6G (R6G) was
used as received from Sigma-Aldrich. All of these chemicals and materials were used as
received without further purification. The water used throughout this work was ultrapure
water (18.2 MΩ) produced by a Milli-Q system.
The extinction spectra of silver nanoparticles were collected using a Hitachi U-4100
spectrophotometer. The aggregation of the silver nanoparticles was characterized by JEOL
JEM-2100F transmission electron microscopy (TEM) operated at 200 kV, and the samples
were prepared by dropping the solution onto a carbon coated copper grid. X-ray
photoelectron spectroscopy (XPS) was recorded on ESCALab 220i-XL electron
spectrometer from VG Scientific using 300 W Al Kα radiation, and the base pressure was
about 3×10-9 mbar. Surface-Enhanced Raman Scattering (SERS) spectra were taken on a
Renishaw invia Raman Microscope using 532 nm laser excitation with a 50 × objective
focusing the laser beam onto a spot with approximately 1 µm in diameter. The Raman light
was dispersed by a diffraction grating with 1800 lines/mm. All of the spectra reported were
the results of a single 20 s accumulation.
The silver nanoparticles used in the experiment were synthesized by a straightforward,
one-phase reaction according to the literature with some modification.1,
1
2
In a typical
synthesis process of silver nanoparticles, silver acetate (0.51 g) and 1-hexadecylamine (1.82
g) in toluene (20 mL) were firstly heated at 60 °C with stirring until silver acetate and
1-hexadecylamine were completely dissolved. A solution of phenylhydrazine (0.31 g) in
toluene (10 mL) was slowly added into the resulting solution with continuous stirring and
reacted at 60 °C for 1 h. Subsequently, before the above solution down to 30°C, acetone (30
mL) was added into to precipitate the silver nanoparticles. The silver nanoparticles were
isolated by centrifugation at 5000 rpm, washed twice with acetone (30 mL), and
vacuum-dried at room temperature to obtain a blue-black solid. The UV-Vis absorbance
spectra and TEM image of synthesized silver nanoparticles (Fig. S1) indicated that this
procedure gave silver nanoparticles in high yield.
The synthesized silver nanoparticles were redissolved into the mixture of cyclohexane and
terpineol, with ultrasonic for 30 min, followed by filtrating through a 0.45µm syringe filter
to form the conductive ink. The final concentration of silver nanoparticles in the ink was
1-2 % by weigh. According to the design, the SERS substrates were fabricated by ink-jetting
the silver nanoparticles ink onto glass substrates using Microfab JetDrive III printer with a
50 µm diameter single nozzle.
The printed SERS substrates were dipped into the methanol solution, and the protective
layers were partially removed and resulted in the silver nanoparticles aggregation due to the
preferential dissolution of hexadecylamine in methanol. R6G solution was diluted to various
concentrations ranging from 1×10-6 to 1×10-12 M, and 20 μL of each solution was dropped
onto the above aggregated silver nanoparticles for SERS experiments.
2
Fig. S1. (a) UV-Vis absorbance spectra and (b) TEM image of the synthesized silver
nanoparticles
FIG. S2. (a) Reproducibility of the printed SERS substrates. SERS spectra were collected
from 15 randomly selected printed spots (b) Intensity distribution of the 1648 cm-1 peak in
the 15 spectra.
References
1
B. S. Ong, Yiliang Wu, Yuning Li, J. Am. Chem. Soc. 127, 3266 (2005).
2
B. S. Ong, Y. Li, Y. Wu, J. Am. Chem. Soc. 128, 4202 (2006).
3