Biomedical Engineering Reference
In-Depth Information
(1)
Freeze dry the AuNPs suspension at −50 °C and 0.05 mbar for more than 8 h.
(2)
Aerosolize the AuNPs powder or suspension through an aerosol generation
system and collect on 25-mm polycarbonate filters (pore size: 0.015 mm,
Whatman, USA) and place on individual stages of a low-pressure impactor
(Dekati, Finland).
(3)
Impregnate portions of the filters loaded with AuNPs over a glass support
for XPS analysis.
(4)
Heat at 500 °C for 1 h in a tubular furnace (Nabertherm Furnace, Bremen,
Germany), with air as carrier gas at a flow rate of 2 L/min.
(5)
Perform XPS measurements in a vacuum of 10
−7
-10
−9
Torr using a mono-
chromatized AlKa X-ray radiation (1486.7 eV photons), at a constant
dwelling time of 100 ms and pass energy of 40 eV. Keep the anode voltage
at 15 mV with a current of 10 mA. Obtain the survey scans and the core-
level spectra at a photoelectron take-off angle of 90° (α with respect to
the sample surface). Survey scans are recorded within a range of 0e1100
eV. All core-level spectra were referenced to the C1s hydrocarbon peak
at 284.5 eV to compensate for surface charging. This process was used to
record high-resolution photoelectron spectra for Au4f. Use the XPSPEAK
software to interpret the binding energy of most prominent peaks based on
a nonlinear least-square regression method.
→ 2Au
0
AuNP
2HAuCl
4
tetrachloro-
auricacid
+ 3Na
3
C
6
H
5
O
7
trisodium
citrate
+ 3Na
2
C
5
H
6
O
5
sodium
ketoglutarate
+ 3NaCl
sodium
chloride
+
5Cl
−
chloride
ion
5H
+
hydronium
ions
+
+ 3CO
2
carbon
dioxide
(2.2)
More than 75% of citrate originally added as a reactant remains in the syn-
thesized AuNP solution, which may help to stabilize the AuNPs.
82
Other side
products found include ketoglutarate and acetate that must be eliminated before
use to avoid interference.
The size of the AuNPs is established using TEM (
Figure 2.7
). About 250
NPs are used to measure size distribution using an imaging software (Image J).
To calculate the average NP mass, density is assumed to be equivalent to that of
bulk gold (19.30 g/cm
3
). As an example, using a particle size of 15.7 ± 1.2 nm,
an average particle mass was calculated to be 2.4 × 107 g/mol.
83
By combin-
ing these data with inductively coupled plasmon atomic emission spectroscopy
(ICP-AES) data and the average particle volume obtained by TEM analysis the
molar concentration of gold particles in a given preparation is about ∼10 nM.
Using the UV-vis absorbance of AuNP solutions at the surface plasmon fre-
quency (520 nm), the calculated molar extinction coefficient is typically 4.2 ×
10
8
M
−1
cm
−1
for 15.7 ± 1.2-nm diameter.
83
