Biomedical Engineering Reference
In-Depth Information
Fig. 13 UV-vis spectrum of
ODA-AOT-capped gold
nanoparticle solutions with
decreasing concentrations of
ODA: (
a
) 0.5, (
b
) 0.1, and
(
c
) 0.05 M.
Inset
shows the
corresponding gold
nanoparticle solutions.
(Adapted from [
66
])
nanoparticles to the toluene layer, indicated by a vivid transfer of color from the
aqueous phase to toluene, then proceeds quickly and completely to leave a colorless
aqueous solution behind. The phase transfer method for preparation of the
alkylamine-stabilized nanoparticles of other noble metals, including Ag, Pd, Rh,
Ir, and Os, has been investigated by Yang et al. [
67
].
For the preparation of alkylamine-stabilized noble metal nanoparticles using the
phase transfer method, typically 0.8 mL of 40 mM aqueous tri-sodium citrate
solution is added to 10 mL of 1 mM aqueous metal salt solution (0.1 mL of
concentrated HCl solution was added for the dissolution of PdCl
2
in the aqueous
environment). Under vigorous stirring, different amounts of 112 mM aqueous
NaBH
4
solution are introduced dropwise upon the metals to prepare a metal
hydrosol in which sodium citrate serves as the stabilizer. The molar ratio of
NaBH
4
to the valence of the noble metal in their salts is kept above 1.5 to ensure
the reduction of the metal to zerovalent state. The hydrosol is then mixed with
10 mL of ethanol containing 200
m
L of dodecylamine and the mixture stirred for
2 min. A 5-mL volume of toluene is added and stirring continued for another 3 min.
Dodecylamine-stabilized noble metal nanoparticles rapidly extract into the toluene
layer, leaving behind a colorless aqueous solution [
67
]. This general phase transfer
protocol for synthesizing alkylamine-stabilized nanoparticles of noble metals has
been reported by Yang et al. [
67
]. TEM images of alkylamine-stabilized Ag and Pd
nanoparticles are shown in Figs.
14
and
15
, respectively.
Copolymer-stabilized nanoparticles based on Au (HAuCl
4
sol), Ag (AgNO
3
),
Pt (Na
2
PtCl
6
6H
2
O), and Rh (Na
3
RhCl
6
) have been prepared using a 0.01 wt%
solution of the appropriate salt and a 1.0 M aqueous solution of NaBH
4
as the
reducing agent (molar ratio of NaBH
4
:dithioester end groups was 25:1). A portion
of the reaction mixture was centrifuged for 1 h at 13,000 rpm, and the supernatant
removed. The resulting aggregates were re-dispersed in deionized water by agita-
tion. The centrifugation and re-dispersal process was repeated several times to
ensure that only covalently bound polymers remained in the colloidal solutions of
the stabilized nanoparticles.
