Bioconjugation of Noble Metal Nanoparticles and Their Applications to Biolabeling and Bioimaging - From Bioimaging to Biosensors: Noble Metal Nanoparticles in Biodetection - page 21

nm Au shells, respectively (Fig. 2.4C). The longitudinal relaxivities,
r 1 , were determined to be 8.60 (12 nm), 7.06 (26 nm), and 2.84
(63 nm) s −1 mM −1 . The r 1 relaxivity depends on the thickness of Au
shells. The thinner Au shell thickness resulted in higher r 1 value,
while thicker Au shell hindered interaction between the protons of
water molecules and Gd 2 O(CO 3 ) 2 ⋅ H 2 O, decreasing the MR contrast
effect.

(A)

a) a)

(B)

b)

400 nm 400 nm

(C) c) c)

12 nm 12 nm

26 nm 26 nm

63 nm 63 nm

Figure 2.4 (A) Schemes for the fabrication of Gd 2 O(CO 3 ) 2 ⋅ H 2 O/silica/
gold hybrid particles. Inset shows the SEM image of the
Gd 2 O(CO 3 ) 2 ⋅ H 2 O/silica spherical particles embedded in
63 nm Au. (B) UV-vis spectra versus the different thicknesses
of Au shells on the Gd 2 O(CO 3 ) 2 ⋅ H 2 O/silica spheres in the same
particle number of 7 × 10 7 per mL. (C) In vitro MR assays of
Gd 2 O(CO 3 ) 2 ⋅ H 2 O/silica/gold hybrid particles in 12, 26, and
63 nm Au shells as a function of Gd 3+ concentration (mM).
[Reprinted with permission from ref. 51. Copyright 2009 Royal
Society of Chemistry].

Recently, pure noble metallic Au 3 Cu 1 with shell-like
nanostructures was fabricated through a reaction of copper
nanoparticles with HAuCl 4 solution. The surface of Au 3 Cu 1 nanoshells
could be modiied with polyelectrolytes (coated with PEI/PAA/PEI)
to form Au 3 Cu 1 nanocapsules (Fig. 2.5A). 54 X-ray absorption near-
edge spectroscopy (XANES) measurements of Au 3 Cu 1 nanoshells
indicated the edge positions ( E 0 ), being sensitive to the oxidation
state of the metals, shifted slightly to lower energy (−0.23 eV) at
the Au L III edge and increased signiicantly (+6.88 eV) at the Cu K
edge. The large E 0 change at the Cu edge relected its high oxidation
state. Here, Cu in Au 3 Cu 1 can be assigned up to +3, where Cu 3+
has an electronic coniguration of d 8 with two unpaired electrons.
Therefore, Au 3 Cu 1 nanocapsules are made of signiicant numbers
of paramagnetic Cu 3+ ions, resulting in bimodal MR contrast agents