1.1.2 Synthesis
Concentrated HCl and concentrated HNO3 were combined in
a 3:1 volume ratio to create aqua regia, which was used to clean all
glass flasks before the synthesis.
A stock aqueous solution of 0.5 mL 1% HAuCl4 was added
into a flask containing 49.5 mL Milli-Q water. The mixture was
vigorously stirred (600 rpm) while being heated to 250 °C on a hotplate.
Aluminium foil was utilised to cover the flask during the synthesis to
prevent contamination and solvent evaporation. 0.45 mL of 1% Na₃C₆H₅O₇
was rapidly added into the HAuCl4 solution flask after
it had boiled under atmospheric pressure. The mixture was continuously
heated and stirred for 20 min. After the heat was turned off, it was
stirred for an additional 10 min. The main variable controlled to
achieve the required particle size is the molar ratio (MR) of Na₃C₆H₅O₇
to HAuCl4. The sample then was cooled naturally to room
temperature and stored in the fridge at 4 °C.
Gold nanostars
preparation (AuNS)
1.2.1 Reagents
1% HAuCl4, silver nitrate (AgNO3), and
L-Ascorbic acid
(C6H8O6), HCl and
HNO3 solutions were purchased from Sigma-Aldrich
(Sydney, Australia). Milli-Q water (18.2 MΩ ⋅ cm at 25 °C) was used for
all aqueous solutions.
1.2.2 Synthesis
Concentrated HCl and concentrated HNO3 were combined in
a 3:1 volume ratio to create aqua regia, which was used to clean all
glass beakers before the synthesis.
AgNO3 and
C6H8O6 solutions were
freshly prepared before synthesis. Briefly, 400 µL of 1%
HAuCl4 were mixed with 600 µl of Milli-Q water to make 1
mL of 10 mM HAuCl4. 10 mL of 10 mM AgNO3solution and 1 mL of 100 mM
C6H8O6 solution were
prepared by dissolving 17.2 mg of solid AgNO3 in 10 mL
of Milli-Q water and 17.6 mg of solid
C6H8O6 in 1 mL of
Milli-Q water, respectively.
In a glass beaker 10 mM AgNO3 was mixed with 10 mM
HAuCl4 in 1:18 ratio for 30 sec. The solution colour was
slightly yellow, due to presence of yellow coloured gold salt ions. This
was followed by the slow dropwise addition of 100 mM
C6H8O6 with a 1:6 ratio
(AgNO3:
C6H8O6) and then
stirring for another 30 sec, during which the colour of the solution
turned blue. The synthesized particles were stored in the refrigerator
at 4 °C until further use.
Gold nanoparticle characterization
1.3.1 Morphology: Transmission electron microscopy (TEM)
TEM (Philips CM10 TEM, Eindhoven, The Netherlands) was used to estimate
the size and morphology of nanoparticles. TEM samples were prepared by
the following method: a 10 µL drop of nanoparticle suspension was placed
on top of the carbon side of the carbon-coated copper grid
(Zhongjingkeyi Film Technology, Beijing, China), the drop was then
removed with filter paper after it had settled for 3 minutes. This was
then repeated three times, after which sample was then allowed to dry
overnight.