Controlling the Absorption Spectra of Gold
Nanoparticles Synthesized via Green Synthesis
Using Brown Seaweed (Sargassum crassifolium) Extract
Johnny Jim S. Ouano1,3,a, Mar Christian O. Que4,d, Blessie A. Basilia4,c
and Arnold C. Alguno2,b
1Materials Science Laboratory, Department of Physics
2Primier Reseach Institute of Science and Mathematics (PRISM), Mindanao State University –
Iligan Institute of Technology, A Bonifacio Avenue, Iligan City, 9200, Philippines
3Physics Department, Mindanao State University, Marawi City, 9700, Philippines
4Department of Science and Technology, Industrial Technology Development Institute Bicutan,
Taguig City, 1631, Philippines
firstname.lastname@example.org, email@example.com, firstname.lastname@example.org,
Keywords: gold nanoparticle, green synthesis, UV-Vis spectroscopy, Transmission electron
Abstract. Gold nanoparticles were synthesized using brown seaweed (Sargassum crassifolium)
extract and chloroauric acid solution. This is an easy, cheap and environment friendly synthesis
method for the formation of gold nanoparticles. The gold nanoparticles with varying amount of
seaweed extract was characterized using Ultraviolet-visible spectroscopy. Moreover, Transmission
Electron Microscopy characterization was used to observe the shape and size of gold nanoparticles.
Experimental results revealed that varying the amount of brown seaweed extract can control the
optical absorption spectra of the produced gold nanoparticles. Greater amount of brown seaweed
extract will exhibit peak in the lower wavelength while smaller amount of seaweed extract will
exhibit peak in the higher wavelength. It is believed that the wavelength of free surface electrons
resonance is related to the shift of absorption peak. TEM images revealed a more spherical and
smaller particles as the amount of brown seaweed extract was increased. This simple green
synthesis method of gold nanoparticles will give a cost effective route in the mass production of
gold nanoparticles for biomedical applications.
Synthesis of gold nanoparticles (GNPs) are being studied rigorously because of its various
applications in biomedical field including drug delivery , cancer photodiagnostics and
phototherapy . Likewise it has been reported that GNPs are being utilized as antibacterial  and
anticancer  agents. In addition, gold nanoparticles can be used in industrial applications as
coatings and printings  and as building blocks in nanoelectronics 
Several methods has been developed in synthesizing gold nanoparticles. Such are chemical,
physical and biological methods. These methods aim to reduce HAuCl4 (Chloroauric acid) by
addition of organic or inorganic reducing agents. It was reported that physical method utilize
irradiation technique to enhance the synthesis process of gold nanoparticles. However this method
is quite expensive and sophisticated. On the other hand, chemical synthesis utilizes inorganic agents
and shows an effective reduction process that produces a monodispersed particles . However,
there is an issue of toxicity in the process . To address this problem, green synthesis route can be
a good alternative utilizing biological agents. It offers a straight forward and environment friendly
process . Previous works utilized biological agents like plant extract , bacteria  and fungi
 as reductants and capping agents of gold nanoparticles. In like manner, it was reported that
microbe mediated synthesis is not good for industrial applications due to contamination and
Key Engineering Materials Submitted: 2018-04-12
ISSN: 1662-9795, Vol. 772, pp 78-82 Accepted: 2018-04-25
doi:10.4028/www.scientific.net/KEM.772.78 Online: 2018-07-04
© 2018 Trans Tech Publications, Switzerland
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans
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maintenance issues . It has been reported that plant extracts contain biomolecules such as
terpenoids, flavones, ketones, aldehydes, amides and carboxylic acids . These biomolecules
may act as reduction and capping agent in the synthesis of GNP’s. On the other hand, marine algae
was also used to synthesize GNPs because it is rich in biological compounds . Specifically,
brown seaweeds were used to synthesize gold nanoparticles . However, they were not able to
control the absorption spectra of the synthesized GNPs. Moreover, they failed to correlate the
absorption spectra with respect to size, shape and density of the synthesized GNPs.
In this work, we are going to control the absorption spectra of the synthesized GNP by
controlling the amount of seaweed extract. The size, shape and density of the synthesized GNPs
will be intensively elucidated using Transmission electon microscopy and associate its structural
morphology to its absosrption spectra.
Materials and Methods
Brown seaweeds (Sargassum crassifolium) were collected from the seashore of Biga, Lugait,
Misamis Oriental in the Philippines. The seaweeds were washed with fresh water with final
washing of distilled water. It was then air dried for 5 days then oven dried for 24 hours at 60o C.
The dried seaweeds were pulverized using an analytical mill then sieve thru a 0.5 mm strainer. Fifty
grams of fine grain biomass was added to 500 ml deionized water and was stirred to disperse the
powder. The mixture was set aside for 24 hours before it was filtered. The seaweed broth was kept
in refrigerator at 4o C for future use. Preparation of 1 milli molar (mM) Chloroauric acid was done
by mixing 1470 ml of deionized water and 0.5 grams of Gold chloride hydrate (from Aldrich Sigma
with 99.995% trace metal base). The synthesis of GNPs was done by preparing four vials filled with
20 ml of 1 mM cloroauric acid then 10 ml, 12 ml, 14 ml and 16 ml of the seaweed extracts were
added to each vial respectively. The reactants were shaked until the color changes from brown to
purple and were set aside for 24 hours to complete the reaction process. Samples in cuvettes were
characterized using Perkin Elmer Lambda 35 UV-Vis Spectrometer in order to measure the
absorption spectra of synthesized GNPs and to observe the effect of the variation of the seaweed
extract. On the other hand, Transmission Electron Microscopy (TEM) measurement was also
performed using JEOL JEM-2100F to observe the size, shape of GNPs and the changes in its
morphology due to variation of seaweed extracts. In addition, the selected area of electron
diffraction (SAED) was also performed in the TEM to observe the crystallinity of the synthesized
Results and Discussion
Fig. 1. UV-vis spectra of gold nanoparticles showing an increase in absorbance and decrease in wavelength
peak when the amount of seaweed (Sargassum crassifolium) extract was increased.
Key Engineering Materials Vol. 772 79
The UV-Vis spectra shown in Fig. 1 revealed that the peaks of the absorption spectra shifted to
lower wavelength as the amount of seaweed extract was increased. It has been reported that the
wavelength of free surface electron resonance of GNPs is related to the absorption peaks. UV-Vis
spectra revealed that blue shifts of absorption peaks occurred when the amount of seaweed extract
was increased. This blue shifts of absorption peaks of synthesized GNPs can be associated to the
increase of the amount of seaweed extract and probably triggered by smaller sizes of GNPs. The
absorption peak was maintained at 536 nm for 14 ml and 16 ml of seaweed extract maybe because
the biomolecules cease to act as reducing and capping agent of GNPs.
The TEM images of the synthesized GNPs with varied amount of seaweed extract is shown in
Fig. 2. It is very apparent that polydisperse GNPs are present. Sizes of GNPs approximately ranges
from 25 nm to 200 nm in various shapes such as triangles, pentagons, hexagons and colloids.
Moreover, the distribution is nearly monodisperse and spherical in shape as the amount of seaweed
extract was increased. These various formations of GNP’s might be triggered by the presence of
different biomolecules in the seaweed extracts. In fact, it was reported that seaweed extracts contain
sulphated polysaccharides and monosaccharide groups, polyphenol, sodium-aliginate and secondary
metabolite such as flavonoids, tannins, phenolics, sterols and terpenoids that maybe serve as
nucleation centers to commence the formation of GNP’s. These biological compounds present
in seaweed extract might be responsible for the reduction and capping of the synthesized GNPs.
Fig. 2. TEM image of GNPs with varied seaweed extracts (a) 10 ml, (b) 12 ml, (c) 14 ml and (d) 16 ml.
80 Composite Materials Science and Technology
The crystallinity of the synthesized GNPs are shown in Fig 3 in which the fringe spacing is ~
0.17016 nm (a) which corresponds to the spacing of (111) plane of the face centered cubic GNPs.
The typical Selected area electron diffraction (SAED) patterns (b) with bright circular rings may
correspond to the (111), (200), (220), (311) and (222) planes showed the high crystallinity of GNPs.
Fig. 3. (a) Fringe spacing of (111) plane and (b) SAED ring patterns of GNPs.
The absorption spectra of gold nanoparticles synthesize via green synthesis route using
Sargassum crassifolium extract can be controlled by controlling the amount of seaweed extract.
This change in absorption spectra of GNPs may be attributed to the change in morphological
structure of GNPs resulting in the change of resonance wavelength of GNPs. This easy and cost
effective synthesis process may be utilized in the mass production of gold nanoparticles for
industrial and medical applications.
DOST-PCIEERD is acknowledged for the equipment grant. Dr. Drexel Camacho is also
acknowledged for scientific discussions.
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