Biomedical Engineering Reference
In-Depth Information
2.2 GOLD AND SILVER NM
s
Gold nanoparticles (AuNPs) are among the first NPs in colloidal suspen-
sion, smaller than 10 nm that have been produced by chemical processes.
65,66
AuNPs are one of the most widely used engineered NMs for biomedical
applications
67,68
because of facile modification with thiols, amines, and silane
that allows conjugation with biomolecules such as proteins, peptides, and
DNA.
69,70
Usually, AuNPs are synthesized through reduction of Au(III) derivatives.
71
The citrate reduction process involves a simple procedure, yielding stable and
reproducible production of AuNPs with narrow size distribution that was pio-
neered by Turkevich et al.
65
It involves the reduction of HAuCl
4
via trisodium
citrate to produce 20-nm gold and was modified by Frens
72
to generate 16-150
nm by adjusting the ratio between the gold and citrate concentration. Excess
unused reagents are removed by centrifugation,
73
ion exchange,
74
solvent
extraction,
75
dialysis,
76
and filtration.
77
2.2.1 Protocol for Citrate AuNP Synthesis
The following protocol for the synthesis of citrate AuNPs is described by
Turkevich et al.
65
The process produces 20-nm AuNPs.
(1)
Clean all glass thoroughly and rinse with DI water 3×.
(2)
Place 5 mg of high purity tetrachloroauric acid (HAuCl
4
) in DI water to a
final volume of 95 mL.
(3)
Boil for 20 min with mechanical stirring.
(4)
Add 50 mg of trisodium citrate dihydrate (5 mL of 1% solution in water
78
)
and boil for additional 20 min.
(5)
Allow it to cool down at RT. Gold atoms that are released from the HAuCl
4
during the synthesis form the AuNPs that continue to grow until all the
HAuCl
4
is reduced.
(6)
Take a TEM scan to establish shape and size.
AuNPs now come in various shapes such as nanorods and nanostars
9,10,17
. Each
of these differently shaped AuNPs come as a result of the synthesis protocol
used. The nanospheres that are about 15 nm in diameter are synthesized using a
trisodium citrate reduction method.
79
This process involves the following protocol:
(1)
Take trisodium citrate (2 mL, 1 wt%) and add to a boiling aqueous solution
of HAuCl
4
·3H
2
O (50 mL, 0.4 mM).
(2)
Continue to boil the solution for 30 min to form a wine-red solution.
(3)
Cool the solution down and store at 4 °C.
(4)
Establish the concentration of the nanospheres based on the UV-vis absorp-
tion spectroscopy by applying the Beer-Lambert law using a molar extinc-
tion coefficient of 1 × 10
8
M
−1
cm
−1
.
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