Preparation of Gold Colloid Using Pyrrole- 2-carboxylic Acid and Characterization of Its Particle Growth
Takeshi Sakura and Yukio Nagasaki*
Tsukuba Research Center for Interdisciplinary Materials Science, University of Tsukuba, Tennoudai 1-1-1, Tsukuba, Ibaraki 305-8573, Japan
, Tel: +81-29-853-5749,Fax: +81-29-853-5749
Time course of UV spectraduring the preparation of gold colloid with PCA in the presence of MeO-PEG-SH
According to the experimental part,we prepared gold colloid with PCA in the presence of MeO-PEG-SH. As described in the main text, the surface plasmon peak shifted from 570 nm to 520 nm and absorbance at the maximum wavelength shifted from 0.08 to 1.83 as shown in Figure S1 (Shimadzu UV2400PC). The spectra were drawn in Figure 1 in the text. The spectra indicated that rather larger particles were formed in the early stage of this reaction, which is consistent with the results of Kreibig, et al. [1-3]. As shown in Figure 2, the spectra are consistent with the TEM image data. Particles larger than 120 μm were formed early in the reaction and gradually disappeared over time.
Fig.S1. λmax (plasmon peak wavelength, ●) and Absmax (absorbance atλmax, □) change as a function of time
Time course of zeta-potentialduring the preparation of gold colloid with PCA in the presence of MeO-PEG-SH
Figure S2 shows the time course of zeta-potential of the obtained gold nanoparticles (ELS-6000 Photal Co., Ltd.), in order to investigate the dispersion stability during the particle growth process. Regardless of the reaction stage, the surface potential was almost neutral and constant (between –3.6 mV and +3.4 mV), indicating that the obtained gold nanoparticles were fully covered by MeO-PEG-SH to form an effective PEG-brush shell on the surface from the initial stage of the reaction. Thus, no electric repulsive force dominated in the dispersion of the obtained gold nanoparticles under the present preparation conditions. We have already reported that the PEG-brush shell layer should improve not only biocompatibility but also stable dispersion in physiological fluids [4].
Fig.S2. Time course of the zeta potential of gold nanoparticles formed during the preparation reaction with PCA in the presence of MeO-PEG-SH measured by ELS 6000 (OtsukaPhotal Co., Ltd.)
Sizes and their distributions analysis by TEM
The size of the obtained gold particles and changes in shape were analyzed by TEM, using a JEOL JEM-2010Fat 200 kV. Histogram distributions of the obtained gold nanoparticles are shown in Figure S3 as a function of reaction time. As can be seen in Figure S3a, large fluffy particles with diameters larger than 100 μm were observedin the early stage of the reaction. Severalproducts were observed as large rectangular parallelepiped shapes. It is interesting to note that the mean particle size decreased with increasing time. Eventually, these large non-round-shaped particles disappeared almost completely, and uniform round-shaped particles with a mean diameter of 10.5 nm became dominant. The sizes and their distribution are summarized in Table S1.
Table S1. Change of particle diameter as a function of time
Time (min) / Dmean (nm) / SD (nm)20 / 25.1 / 20.5
40 / 22.6 / 22.4
60 / 23.3 / 14.5
120 / 23.7 / 15.1
300 / 23.1 / 13.8
540 / 21.4 / 13.0
1320 / 18.0 / 14.8
2940 / 11.4 / 3.4
4320 / 10.6 / 2.3
5820 / 10.5 / 2.6
Dmean: mean particle diameter, SD: standard deviation of particle diameter.
Dmean and SD, calculated using the TEM image data, indicate that the particle diameter decreased and became uniform with increasing time.
Investigation of reaction conditions for suitable gold nanoparticle preparation
In order to investigate the influence of the concentration of MeO-PEG-SH and PCA on the gold nanoparticle preparation, the following reaction conditions were investigated.
An aliquot (9.6 ml) of PCA in aqueous solution (99% purity; Aldrich) was added to a 76.8-ml aliquot of MeO-PEG-SH (Mn 5,200, Mw/Mn = 1.02; NOF Co., Ltd.).Concentrations of PCA and MeO-PEG of this water solution are listed in Table S2. The pH values of these two solutions were adjusted to 10 and 13, respectively, by adding NaOH before mixing. To this mixture, 9.6 ml of an aqueous solution of 10 mM TCA was added with vigorous agitation at room temperature.
The detailed study in the main text was in the case of r = 6.25 and q= 5.0, respectively (Table S2b). Black precipitants were produced in the absence of either MeO-PEG-SH or PCA. With an increasing in MeO-PEG-SH concentration, the size of the gold nanoparticles tended to increase.
Table S2. Influence of concentration of MeO-PEG-SH and PCA.
[MeO-PEG-SH] (mM)0
r = 01 / 5
r = 3.13 / 10
r = 6.25 / 32
r = 20 / 64
r = 40 / 128
r = 80
[PCA]
(mM) / 0
q = 02 / ↓
2
q = 0.2 / (f)
10
q = 1.0 / (g)
50
q = 5.0 / ↓3 / (a)4 / (b) / (c) / (d) / (e)
100
q = 10.0 / (h)
200
q = 20.0 / (i)
1: r = [MeO-PEG-SH] / [HAuCl4], 2: q = [PCA] / [HAuCl4], 3: Samples marked with arrows(↓)showed precipitation, 4: Letters in parentheses correspond to the images in Figure S4.
Fig. S4. Transmission electron micrographs of the obtained colloids, under various ratios of [MeO-PEG-SH] / [HAuCl4] and [PCA] / [HAuCl4].
The influence of pH of the reaction solution was also investigated when r and q were kept at 6.25 and 5.0, respectively. pH was varied as shown in Table S3.
An aliquot (9.6 ml) of 50 mM PCA in aqueous solution was added to a 76.8-ml aliquot of 10 mM MeO-PEG-SH. The pH values of these two solutions were adjusted to 10 and 7, respectively, by adding NaOH before mixing. To this mixture, 9.6 ml of an aqueous solution of 10 mM TCA was added with vigorous agitation at room temperature. pH was adjusted to the value listed in Table S3, by adding 10 M NaOH or 10 M HCl soon after TCA was added to the above mixture.
Goldenagglomerates were observed at up to pH 10. Triangle-shape particles were observed at pH 11. Uniform round particles were observed only at pH 13.TEM image data of the three different pH reaction conditions, pH11, pH12, pH13, are shown in Figure S5.
Table S3. Influence of reaction pH condition
pH2
4
6
8
10
11
12
13 / ↓1
↓
↓
↓
↓
(a)2
(b)
(c)
1: Samples marked with arrows (↓) showed precipitation.
2: Letters in parentheses correspond to the images in Figure S5.
Fig. S5. Transmission electron micrographs of the colloid obtained under various reaction pH conditions. (a)pH 11, (b)pH 12, (c)pH 13.
Conclusions
From the preparation of gold colloid by PCA in the presence of MeO-PEG-SH, the following conclusions are drawn:
1.The spectral change in Fig. S1 showed good agreement with the tendency of particle size change in Fig.4 observed by TEM, according to Kreibig’s theory.
2.The production of aggregate in the absence of MeO-PEG-SH during the reduction process of aurate ion and the result that the surface potentialremained almost neutral indicate that MeO-PEG-SH adsorbed on the particle surface playsan essential role in the growth process of nano-size particles and dispersion stability.
References
1. U. Kreibig, C. v. Fragstein (1996) C. Z. Phys. 224: 307
2. H. C. van de Hulst, “Light Scattering by Small Particles” (1981) Dover, New York
3. D. Fornasiero, G. Grieser (1991) J. Colloid. Interface Sci. 141: 168
4. H. Otsuka, Y. Akiyama, Y. Nagasaki, K. Kataoka (2001) J. Am. Chem. Soc.123: 8226
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