Chemistry Reference
In-Depth Information
synthesis, dodecylamine (DDA)-capped gold nanoparticles (~3.7 nm) were first
synthesized through a modified Brust-Schiffrin method, and toluene solution of
gold nanoparticles was then mixed with phosphate buffer (pH) aqueous solution
containing thiol ligands (2-(dimethylamino) ethanethiol, DMAET) to form
two-phase mixture. After 3 days of stirring, the characteristic purple of gold
nanoparticles disappeared completely and both the toluene and water phases
became transparent. MALDI-TOF mass spectrometry showed an intense peak at
m/z
2,256.4, which can be assigned to the Au
8
nanocluster with a formula of
[Au
8
C
36
H
82
N
5
S
3
]
+
.
3.3 Au
10
Nanoclusters
Recently, through an ultra-facile one-step reaction, Yang et al. [
54
] successfully
synthesized water-soluble, monodispersed, and bluish-green-emitting Au
10
nanoclusters. Briefly, an aqueous solution of HAuCl
4
was mixed with an aqueous
solution of histidine at room temperature. After incubated for 2 h, monodispersed
Au
10
nanocluster was formed. In this preparation protocol, the histidine serves as
both reducing agent and protecting ligand. From the UV-Vis spectrum, the charac-
teristic SPR peak of gold nanoparticles was not observed; instead, the absorption
rises sharply below 300 nm with a band edge of 450 nm, indicating the molecular-
like properties of formed gold clusters [
55
]. From the ESI mass spectrometry of the
as-synthesized Au nanoclusters, the major peak at
m/z
1,760 was assigned to the
[Au
10
His
10
]
2
, while the major peaks at
m/z
1,139 and 1,449 were assigned to
the [Au
10
His
2
]
2
and [Au
10
His
6
]
2
, respectively. The MS results clearly suggested
that the cluster is composed of 10 gold atoms. X-ray photoelectron spectroscopy
(XPS) result further indicated that the products are exclusively gold clusters
consisting of Au
0
atoms rather than bulk gold or gold thiolates. With the proposed
method, Au
10
nanoclusters can be produced at a relatively wide pH range from
2 to 12 and the fluorescence intensity of clusters changed with the pH and the
concentration ratio of histidine to Au
3+
ions. Yu et al. [
56
] studied the temperature-
dependent fluorescence of the histidine-protected Au
10
nanoclusters and it was
found that with temperature increasing, the fluorescence intensity decreased due
to the thermal activation of nonradiative trapping, the energy band gap exhibited a
small blue shift due to the lattice torsional fluctuation, and the fluorescence band-
width showed a broadening because of the electron-electron interactions.
¼
3.4 Au
11
Nanoclusters
In earlier studies, the Au
11
nanoclusters were always synthesized by using phosphine
or amino-substituted triarylphosphine as protecting ligands [
5
,
57
]. For example,
Bartlett et al. [
5
] have reported the synthesis of Au
11
nanoclusters (
d
¼
0.8 nm)
