22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Synthesis of biocompatible gold nanoparticles in liquid phase by atmospheric
pressure glow microdischarge
P. Jamróz, A. Dzimitrowicz, K. Greda and P. Pohl
Wroclaw University of Technology, Faculty of Chemistry, Division of Analytical Chemistry and Chemical
Metallurgy, Wybrzeze Stanislawa Wyspianskiego 27, PL-50370 Wroclaw, Poland
Abstract: The gold nanoparticles were prepared using atmospheric pressure glow
microdischarge generated between a helium microjet and a flowing liquid cathode. The
microdischarge was operated in the open to air atmosphere. As a precursor of the Au NPs,
chloroauric acid was applied. Additionally, to prevent the agglomeration and sedimentation
of the produced nanoparticles, gelatine and other natural capping agents (e.g., starch,
fructose) were tested. The production of the gold nanoparticles was confirmed using UVVis absorption spectroscopy. The size distribution as well as the mean size of the obtained
gold nanoparticles were determined by dynamic light scattering (DLS). Their shape was
assessed using scanning electron microscopy (SEM). The microdischarge system working
in a flowing liquid mode was investigated in reference to its application to the synthesis of
the biocompatible gold nanoparticles.
Keywords: Atmospheric pressure glow discharge, gold nanoparticles, nanoparticle
characterization, UV-Vis optical properties.
1. Introduction
The production of gold nanoparticles is of a great
importance due to their specific properties, e.g., optical,
electrical, therapeutic, and bio-compatibility [1-3]. So far,
different methods have been used for the production of
the gold nanoparticles, including sonochemical [4],
photochemical [5], chemical [2], biochemical [6], laser
ablation [7] and plasma [1,8-10] methods. Among all the
methods, the microplasma reduction is very promising for
the production of the gold nanoparticles due to the
simplicity of the whole process as well as the lack of the
toxic and hazardous reagents (e.g. reductors) and the byproducts [9]. The gold nanostructures produced by the
microplasma may be applied as an excellent candidate for
the production of the biosensors and for the medical
diagnostics, e.g., to detect cardiac troponin I (cTn-I) [10].
The main objective of this work was to elucidate a new
atmospheric pressure glow microdischarge reactor/system
working in a flowing liquid mode. The effect of the
addition of the natural stabilizing agents (gelatine, starch,
fructose) on the granulometric properties of the produced
gold nanoparticles were also investigated. The optical
phenomena of the gold nanoparticles in reference to the
presence of the localized surface plasmon resonance were
characterized by UV-Vis absorption spectrometry. The
morphology of the resultant gold nanoparticles was
investigated by scanning electron microscopy (SEM),
while their size was obtained directly from the dynamic
light scattering (DLS) measurements. The influence of the
various experimental conditions on the production of the
gold nanoparticles was also investigated.
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Experimental section
Direct
current
atmospheric
pressure
glow
microdischarge was generated between a helium microjet
nozzle anode and a small-sized liquid flowing cathode
(see Fig. 1) [11,12].
Fig. 1. The experimental microdischarge reactor/system
with a flowing liquid cathode for the synthesis of the Au
NPs (not to scale).
The internal diameter of the nozzle was 0.5 mm, while
the distance between the electrodes was 5 mm. The
volume of the discharge was estimated to be below 1.5
mm3.
A direct-current high-voltage (dc-HV) power supply
(Dora, Wroclaw, Poland) was applied to ignite and sustain
the discharge between the electrodes. A series of the high-
1
power ballast resistors (5kΩ) was applied to stabilize the
discharge current. dc driven atmospheric pressure glow
microdischarge was stably operated after passing a
miniature flow of helium (range 60-300 sccm at STP)
through the nozzle and applying a high voltage (10001300 V) to the electrodes. The discharge current was in
the range of 15-40 mA. The mean power forwarded to the
discharge was below 40 W.
The working solutions of the Au(III) ions, i.e., 25, 50
and 100 mg L-1, prepared from analytical grade
chloroauric acid (HAuCl 4 ×3H 2 O) (POCh, Gliwice,
Poland), were continuously delivered into the discharge
zone through a quartz-graphite tube (inner diameter 4
mm) by means of a MasterFlex L/S peristaltic pump
(Cole-Parmer, USA). Three natural capping agents, i.e.,
gelatine, starch and fructose, were also added to the
solutions containing the Au(III) ions at a final
concentration of 0.1% (m/V). The flow rate of the
solutions was in the range of 1.2-5.0 mL min-1. The
solutions treated by the microdischarge were collected
into the 10-mL stoppered polypropylene tubes. The Au
NPs produced through the microplasma treatment were
washed with re-distilled water by using the centrifugation
(12 000 rpm, 10 minutes) in a MPW-350 centrifuge
(Medical Instruments, Poland). Three rounds of the
washing were used in each case.
The optical properties of the colloidal gold
nanoparticles were measured by an UV-Vis absorption
spectrometer, model Specord 210 Plus (Analytik-Jena
AG, Germany) in the range of 300-1100 nm and using a
1-cm quartz cuvette. The morphology of the gold
nanostructures was determined using a SEM instrument,
model JSM-6610LVnx (Jeol, Japan) after the evaporation
of the solutions. Finally, the distribution size and the
mean size of the gold nanoparticles in addition to the poly
dispersion index (PdI) were obtained from DLS
measurements carried out with a Zetasizer Nano-ZS
(Malvern Instruments, UK) using a helium-neon 633 nm
laser and the detection angle of 173º.
2. Results and discussion
It was found that the solutions treated by the
microdischarge changed their colour from pale yellow to
ruby red and bluish. Moreover, the intensity of the colour
of the solutions treated by the microdischarge was
dependent on the experimental conditions and changed
with the post discharge time up to 24h. The observed ruby
red and bluish colour of the microdischarge treated
solutions indicated the formation of the gold nanoparticles
in these solutions [13].
The typical UV-Vis absorption spectra of the solutions
treated by the microdischarge are given in Fig. 2
(spectrum 1 and 2). The first broad absorption band in the
range within 520-550 nm (the spectrum 1), with an
intensive peak at around 540 nm, was associated to the
presence of the localized surface plasmon resonance band
and indicated the formation of the gold nanoparticles [3].
The next broad peak in the range of 800-1000 nm (the
2
spectrum 2) was present due to the longitudinal surface
plasmon band and could be assigned to the formation of
the gold nanorods [3,13].
Fig. 2. The typical UV-Vis absorption spectra of the
solutions treated by the microdischarge.
It should be noted that the position, shape and
magnitude of the localized surface plasmon resonance
band were strongly dependent on the experimental
conditions, the concentrations of the Au(III) ions in the
initial solutions and the added capping agents. For
example, the strongest localized surface plasmon
resonance (LSPR) band was observed for the highest
discharge current and the concentration of the Au(III) ions
in the solutions, i.e., 40 mA and 100 mg L-1, respectively.
On the other hand, the flow rate of the solutions was
established to have a little influence on the shape and the
intensity of the localized surface plasmon resonance band.
The UV-Vis absorption spectra of the gold
nanoparticles obtained from the solutions containing the
natural capping agents (gelatine, fructose, starch) are
presented in Fig. 3.
As can be seen, the best protective properties of the
gold nanostructures was observed for gelatine. In this
case, the localized surface plasmon resonance band had a
symmetrical structure and a high absorbance value.
Moreover, the position of the localized surface plasmon
resonance band acquired for the obtained gold
nanoparticles was shifted to short wavelengths (i.e., 536
nm), confirming the formation of the relatively small gold
nanoparticles [3,14]. In the case of fructose and starch
used as capping agents, the position of the localized
surface plasmon resonance band was higher wavelengths,
i.e., 555 and 560 nm, respectively.
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size below 150 nm. However, the production of the gold
nanorods (nanowires) using the described microplasma
reduction method was also possible (see Fig. 4b),
particularly in the case of the solutions containing the
relatively high concentration of the Au(III) ions (100 mg
L-1).
(a)
Fig. 3. The effect of the addition natural capping agents
(gelatine, fructose, starch) on the UV-Vis absorption
spectra of the gold nanoparticles.
(a)
(b)
(b)
Fig. 5. The distribution of the size of the gold nanoparticles obtained from the solutions containing
a) gelatine and b) fructose
Fig. 4. The SEM images of a) the spherical gold
nanoparticles and b) the gold nanorods.
The SEM images of the gold nanoparticles are
presented in Figs. 4a and 4b. As can been seen, the
synthesized nanoparticles were spherical with the mean
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The resultant histograms of the size distribution of the
gold nanoparticles obtained by the DLS measurements are
presented in Figs. 5a and 5b. The mean size of the
produced nanoparticles was 64 nm and 118 nm using
gelatine and fructose as capping agents, respectively. The
solutions containing starch were not measured using DLS
due to the bad quality of the obtained gold nanoparticles.
The values of the PdI were changed from 0.1 to 0.4 and
indicated a homogenous character of the synthesized
nanoparticles obtained with the microdischarge method
applied in the present contribution.
.
3
Conclusions
The spherical gold nanoparticles as well as the gold
nanorods were produced by the microdischarge reduction
processes using the natural capping agents. In each case,
the localized surface plasmon resonance band in the UVVis spectra of the solutions treated by the microdischarge
were observed. Among the studied protective agents,
gelatine was established to exhibit the best protective and
stabilizing properties for the gold nanoparticles produced.
The mean size of these gold nanoparticles was below 120
nm, while the PdI index was changed from 0.1 to 0.4.
Nevertheless, for the superior performance of the
produced gold nanoparticles and its applicability in the
bioanalysis and biochemistry, additional experiments
should be performed and such a study is in progress.
Acknowledgement
The work was financed by a statutory activity subsidy
from the Polish Ministry of Science and Higher Education
for the Faculty of Chemistry of Wroclaw University of
Technology.
The project supported by Wroclaw Centre of
Biotechnology, the programme The Leading National
Research Centre (KNOW) for years 2014-2018 was also
acknowledged.
We would like to thank Marcin Nyk for acquiring SEM
images.
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