A visual tutorial on the synthesis of gold nanoparticles
Medical Radiations, School of Medical Sciences, RMIT University, Victoria, Australia
Many papers have been written on the synthesis of gold
nanoparticles but very few included pictures of the process, and none of them
used video to show the whole process of synthesis. This paper records the
process of synthesis of gold nanoparticles using video clips. Every process
from cleaning of glassware, an important step in the synthesis of metallic
nanoparticles, to the dialysis process is shown. It also includes the
preparation of aqua regia and the actual synthesis of gold nanoparticles. In
some papers, the dialysis process was omitted, but in this paper, it is
included to complete the whole process as it is being used for purification. © 2010
Biomedical Imaging and Intervention Journal. All rights reserved.
Keywords: gold nanoparticles, video tutorial, synthesis
There were many reports in journal articles on the
synthesis of gold nanoparticles (AuNPs) [1-26]. However, very few images were
shown and none of them showed any video clips detailing the whole process of
There were variations in the process of synthesising
AuNPs. Chloroauric acid (HAuCl4) is typically used as the reactant
containing gold atoms [1-26], and most of them reported to use trisodium
citrate [1-4, 8, 17, 19, 23, 25] or sodium borohydride (NaBH4) [5,
7, 9-16], as the reducing agent. In this experiment, NaBH4 was used
as the reducing agent.
This paper attempts to illustrate the process of synthesis
of AuNPs with video clips. As a picture speaks a thousand words, so a video
speaks ten-thousand words.
Methods and Materials
500 mL Milli-Q H2O + 1 mL of 10-1 M HAuCl4
+ 0.05 g NaBH4 ==> 0.2 mM AuNPs
The laboratory consists of glassware, fume cupboard,
deionised water, Milli-Q water, balance, hot plate with magnetic stirrer,
pipette, etc (video 1).
The preparation of aqua regia solution
Aqua regia was prepared by mixing 3 parts hydrochloric
acid (HCl) to 1 part nitric acid (HNO3) by volume [1-6, 24, 25] in a
beaker (figure 1, video 2). Both items were obtained from Merck Pty Limited.
Aqua regia should be prepared just before its use as it will lose its
effectiveness quickly. Aqua regia is corrosive and highly oxidising. It should
be prepared in a well-ventilated fume cupboard with protective clothing,
goggles and gloves. It is used for cleaning glassware as it can dissolve any
residual metallic particles, which may interfere with the synthesis.
The cleaning process
The cleaning of glassware and experiment utensils is a
laborious process before AuNPs can be synthesised. Detergent and aqua regia
were used to clean all the glassware, rinsing was done with deionised water and
final washing in Milli-Q water (video 3, video 4).
The synthesis process
HAuCl4 and NaBH4 were purchased from
Aldrich (America). Milli-Q water was used for the preparation of the solution
for this experiment. Milli-Q water is deionised water, which has been further
purified by Milli-Q purification system [6-8]. However, quite a few reported
just using deionised water instead of Milli-Q water [9-11].
Then, 0.05 g of NaBH4 is added to 10 mL of
Milli-Q water. The centrifuge tube was weighed first followed by NaBH4. In
the process of getting the correct amount of NaBH4, 0.06 g of it was
weighed instead. In order to get the same concentration, 12 mL of water was
added to obtain the same concentration level. The solution in the tube was
shaken to ensure that all the NaBH4 was dissolved (video 5).
In order to obtain 500 mL of 0.2 mM amount of naked gold
nanoparticles, 500 mL of Milli-Q water is poured into a flask. Using a pipette,
1 mL amount of 0.1 M HAuCl4 aqueous solution, yellow in colour, was
transferred to the flask. It was then shaken to mix the solution well (video 6).
NaBH4 was added as a reductant [7, 9-16] to
obtain naked gold nanoparticles. Using a pipette, 10 mL of NaBH4
solution was transferred dropwise to the flask. It was added slowly initially
to prevent aggregation and, subsequently, could be added more quickly. It was
shaken well in the flask for each aliquot of reducing agent added. The solution
in the flask should change from yellowish to ruby red in colour. The ruby red
colour indicates the formation of gold nanoparticles  (figure 2, video 7).
The dialysis process
The dialysis is the last process. Dialysis tubing
cellulose membrane from Sigma Aldrich was used in this dialysis process. In
short, the dialysis tubing cellulose membrane is called the dialysis bag
The outside and inside of the dialysis bag was washed with
20 mL of deionised water and then put in a beaker with a magnetic stirrer to
boil for about 5 minutes. The water was poured out and the step repeated with
another 20 mL of deionised water (video 8).
The boiled water was poured away and the dialysis bag was
washed with Milli-Q water (video 9).
The dialysis bag was pressed between the fingers to remove
as much water in the tubing as possible. One end was folded and clipped with a
peg. A funnel, which was cleaned with aqua regia solution, was used to pour
AuNPs into it. The bag was tested for leakage before further AuNPs suspension
was poured into it. Once all the liquid was transferred, the other end of the
tubing was also folded and clipped. The dialysis bag was then placed in a large
beaker (video 10).
The beaker with the dialysis membrane was filled with
Milli-Q water. The more water is filled, the quicker it would be for the
purification of AuNPs (video 11).
It was boiled for 6-hourly and the water was changed three
times. It will yield 0.2 mM concentration of gold nanoparticles (video 12).
There were variations in the types of water being used in
the synthesis of AuNPs. Some used deionised water throughout the experiments
[8-11], others used doubly distilled water [4, 20, 22], nanopure water [1-3],
ultrapure water , and Milli-Q water [5-7, 15, 19, 21, 23]. In this
experiment, deionised water and Milli-Q water were used.
Dialysis is to purify the resultant solution  and to
remove the extra free small molecules [4, 9]. However, many synthesis AuNPs
without going through the dialysis process [1-3, 5-8, 11-25]. Experiments of
synthesising AuNPs were conducted with and without the dialysis process, and
both AuNPs solutions looked visibly the same after 3 months of synthesising.
The size of the AuNPs could be analysed by transmission
electron microscope [1, 2, 6-9, 15, 17, 21, 22]. However, different sizes of
AuNPs were prepared by altering the ratio of HAuCl4 and the reducing
This paper visually describes each stages of AuNPs
synthesis from the preparation of aqua regia solution to the dialysis of the
final suspension. The purpose of the last process, i.e., the dialysis, was to
demonstrate the complete process of synthesis even though some of the authors
do not find this process necessary.
Figure 1 Aqua regia solution.
Figure 3 Dialysis tubing cellulose membrane.
Movie 1 Laboratory facilities.
Movie 10 Fill dialysis bag with AuNPs.
Movie 11 Submerged dialysis bag with Milli-Q.
Movie 12 Boil for 6-hourly.
Movie 3 Wash with detergent.
Movie 4 Wash with aqua regia and deionised water.
Movie 5 Get NaBH4 concentration.
Movie 6 Prepare HAuCl4 solution.
Movie 8 Dialysis bag wash and boil.
Movie 9 Dialysis bag wash with Milli-Q water.
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|Received 25 June 2009; received in revised form 3 November
2009; accepted 13 November 2009
Correspondence: RMIT University, School of Medical Sciences, Medical Radiations, PO Box 71, Bundoora 3083, Victoria, Australia. E-mail: firstname.lastname@example.org (Albert Low).
Please cite as: Low A, Bansal V,
A visual tutorial on the synthesis of gold nanoparticles, Biomed Imaging Interv J 2010; 6(1):e9