Materials: Gold (III) chloride trihydrate (HAuCl
4
.3H
2
O ≥ 99.9% trace metals basis), sodium citrate dihydrate (≥99%) were purchased from Sigma-Aldrich. 5,5’-6,6’-tetrachloro-1,1’diethyl-3,3’-di(4-sulfobutyl)benzimidocarbocyanine (TDBC) was purchased from FEW
Chemicals GmbH. De-ionized water (DI) was obtained through.
Characterization of the particles: Nanoparticles were characterized by TEM and UV-visible spectroscopy. Transmission electronic microscopy was performed on TOPCON EM-002B operation at 200 KV. The extinction spectra were performed on a SAFAS instrument.
Synthesis of citrate stabilized gold nanoparticles (518nm to 548nm Plasmon resonance):
An aqueous solution of HAuCl
4
.3H
2
O was heated to boiling under magnetic stir in a flask.
Then an amount of sodium citrate of aqueous solution was to the boiling solution. The solution is allowed to stay under boiling and stirring for 30minutes and then cooled down at room temperature. The synthesis of different sizes gold nanoparticles is achieves by the changing of the concentration of the gold (III) chloride trihydrate with respect to the sodium citrate.
Preparation of 5.10
-5 M aqueous solution of TDBC: 49.5mL of de-ionized (DI) water and
0.5mL of 10
-3
M NaOH were added to 1.9mg of TDBC. The solution were mixed under magnetic stir for 5 minutes and then placed in an ultrasonic bath for 15 minutes. The mixture was keep from light and can be used directly for the coating of gold nanoparticles.
Preparation of the TDBC-coated gold nanoparticles: This was performed simply by mixing equal quantities of colloidal gold nanoparticles and TDBC aqueous solution, the mixture was left undisturbed. After about 24 hours the particles were washing by a three times series of centrifugation to remove the excess of TDBC and disperse in DI water. Three times of centrifugation at different rpm (depending on the particles size) are necessary to remove the excess of TDBC.
The table 1 represents the maximum wavelength of the extinction spectra of the figure 1 versus the gold nanoparticles sizes measured by transmission electron microscopy.
1