Abstract
To
determine the antibacterial sensitivity of silver and gold nanoparticles
chemical reduction method is used in which trisodium citrate (TSC) is a
reducing agent. Optical properties, surface morphology, and structure have been
examined by various characterization techniques i.e., UV-Vis, SEM, and XRD.
These results have shown peculiar behavior of silver and gold nanoparticles i.e.,
face-centered cubic FCC structure with an absorption peak at 405nm and 520nm. It
was found that the size ranges of silver and gold nanoparticles have diameters
from 15 to 40nm. The antibacterial activity properties of all prepared NPs were
examined. The antibacterial activity is tested in the Disk
Diffusion method. Results showed that small size particles of silver are more
resistant to gram-positive and gram-negative bacteria than that large size
gold nanoparticles.
Keywords:
Chemical reduction method; Gold and silver Nano Particles, Antibacterial,
Introduction
Nanotechnology has
emerged in the last decades, which is developed with high speed and is now
undergoing revolutionary. There is no doubt to say nanotechnology is
preparing to play a significant and commercial role in our future society. Gold and Silver nanoparticles have unique electronic and
optical properties. Hence, they have been used in a broad range of fields,
including catalysis, biological labeling, photonics, and surface-enhanced Raman
scattering. Therefore, an efficient, stable, and convenient process for
the production of gold and silver nanoparticles is important. Various
syntheses of gold and silver nanoparticles were reported and reviewed. The
Turkevich method also named the Citrate reduction method is one of the most
classic processes. It is popular and convenient; however, the products’
stability and disparity are often limited. In recent years, this synthesis was
developed to control the process by adjusting the reaction conditions to
present improved results with higher monodisperses and better size control.
Through these investigations, we know these solutions are sensitive to the
changes in PH, the ionic strength of the medium, and the presence of other
organic materials, and this promoted the Turkevich process to be controllable
with certain defined size distribution requirements. Therefore, the Turkevich
process is considered a promising method to be developed as a suitable route
for the quantity production of gold and silver nanoparticles.
Experiments
The
experimental setup is very modest, eco-friendly, and low-cost for the chemical
reduction method for synthesizing silver and gold nanostructures. The material
used for this activity is
§ Silver
Nitrate Molecular mass 99.9%)
§ Tetra-chloroauric Acid, Molecular mass
§ Trisodium citrate Molecular mass
§ Distilled
water (DW)
§
Deionized water (DI)
Synthesis
of silver nanoparticles (AgNPs)
The metallic precursor
used is silver nitrate or silver nanoparticle synthesis using the Turkevich method. The deionized water is utilized in the
whole experiment. The aqueous solution of
.
Synthesis of gold nanoparticles (AuNPs)
AuNPs were also
prepared by the chemical reduction method (Turkevich method). In this research, 30
ml of 38.8mM trisodium citrate was added into 300 ml of 0.5 mM boiled aqueous
solution of HAuCl4 under vigorous stirring. The solution was boiled
on a hot plate with continuously stirring for a few minutes, till its color was
changed from yellow to colorless then dark blue to dark red and at last red
wine color appeared. At this moment, the obtained solution was cooled and stored at
room temperature for further use. The formation of chemically citrate gold
nanoparticles.
Characterization of silver and gold nanoparticles (AgNPs and AuNPs)
Nanostructures
synthesized by chemical reduction are characterized by UV Visible spectroscopy
for optical analysis. The determination of size and morphology is done by SEM
and XRD analysis. The Disk Diffusion technique is utilized for the investigation of
antibacterial action against gram-positive (S.aureus) and gram-negative
microbes (E.coli).
Results and Discussion
UV Vis
Spectroscopy Analysis
The
UV-Vis spectroscopy investigates the optical properties. The formation of
silver Nanoparticles is depicted by the dark yellow color of the solution and that of
gold Nanoparticles is indicated by the red wine color. The absorption peak of
silver nanoparticles indicates unique, sharp, and Localized Surface Plasmon
Resonance (LSPR) at 405 nm which indicates the extent of Ag nanostructures in
the range of 15-30 nm. Similarly, the
absorption peak of gold nanostructures can be dictated by UV-Vis Spectra by
estimating the absorbance band that lies in the visible region of Localized
Surface Plasmon Resonance (LSPR). The absorbance band of Au nanostructures lies in
the range of 500-600 nm. This is because of the particular optical feature of the combined oscillation of electrons in the conduction band. Gold nanoparticles
produced using a chemical method display an absorption peak at 520 nm as depicted.
The extent of the particles at these absorption spectra is in the range of 25
to 40 nm.
X-ray Diffraction (XRD) Analysis
The crystalline nature
of silver nanostructures is recognized by X-ray Diffraction Analysis. The
prepared sample is placed under high-energy X-rays. The spectra of XRD inhibit the strong signals of oriented planes of silver nanoparticles. The XRD pattern
reveals four intense peaks with indices (111), (200), (220), and (311) at 2θ 38.5, 44.2, 65.9, and 75.0.
These peaks show the polycrystalline nature of silver nanoparticles. This
indicates the face-centered cubic crystal structure of silver nanoparticles.
Gold nanostructures were also characterized by XRD analysis. The spectra of XRD
inhibit the strong signal of oriented planes of gold nanoparticles. The XRD
pattern reveals four intense peaks with indices (111), (200), (220), and (311)
at 2θ 38.5, 44.2, 65.9, and 75.0). At
the angle (2θ) of 38.5, the strongest diffraction peak of the crystalline structure
has appeared. These planes of diffractions compare to confront the face-centered
cubic crystal structure of gold nanoparticles.
SEM Analysis
The
silver nanostructures are characterized by SEM to determine the surface
morphology. High density and spherical shape nanoparticles have been formed
having an average diameter in the range of 15-30 nm. The size of Ag nanostructures
varies with the molarity of a solution, the quantity of precursor, and the reducing agent.
By using SEM, the
surface morphology of the citrate-prepared gold nanoparticles has been
characterized and illustrates the SEM analysis of gold nanoparticles. The
surface morphology clearly demonstrates well-dispersed AuNPs.
High density and
spherical shape nanoparticles have been formed having an average diameter in the range
of 25-40 nm.
Antibacterial
Analysis by Disk Diffusion method
To estimate the
antibacterial sensitivity of two distinctive Ag and Au nanostructures Disk
Diffusion method has been selected. For the antibacterial response, gram-positive (S.aureus) and gram-negative (E.coli) organisms have been chosen the
effect of silver and gold nanostructures against the bacterium
For the estimation of
antibacterial potential, the Disk Diffusion method has been utilized to evaluate
the antibacterial fallout of Ag and Au nanostructures against human pathogens
bacteria S.aureus, and E.coli. The results of antibacterial potential presented in table 3.1 suggest that all bacteria are vulnerable to these
nanostructures. The zone of inhibition for chemically synthesized silver and
gold nanostructures is clearly visible. No zone of inhibition appears in the control region. The inhibitory zones are measured in mm and have been measured
after 24 hours. The calculated inhibition zone for silver nanoparticles for gram-positive bacteria S.aureus is 12 mm and for gram-negative
E.coli is 10 mm. While the calculated
inhibition zone for gold nanoparticles for gram-positive bacteria S.aureus is 9 mm and for gram-negative
E.coli is 6 mm with an equal dose for
silver and gold nanostructures.
illustrates a graphical representation of the inhibitory zone of S.aureus, and E.coli with an equal
dosage of silver and gold nanostructures. From this antibacterial activity, it
is noted that all bacteria are vulnerable to nanostructures but bacteria are
more resistant to gold nanoparticles. The reason is largely due to the relatively
inert chemical nature of gold. Secondly, the size of nanoparticles contributes
highly to the antibacterial potential. According to the literature survey, small
size nanoparticles are more vulnerable to bacteria. The SEM analysis
depicts the smallest size of silver nanoparticles than that of gold
nanoparticles.
CONCLUSIONS
The
best and easiest way the synthesis of AgNPs and AuNPs is by the chemical reduction
method (Turkevich Method). UV spectroscopy reveals the sharp and prominent
peaks of both nanoparticles. The Surface Plasmon Resonance peak for AgNPs is at
405 nm while for AuNPs is at 520nm. Size and morphology are studied by SEM and
XRD techniques. SEM results depict the size of AgNPs in the range of 15- 30 nm
and that of AuNPs in the range of 25-40 nm. Hence for the synthesis of small-size nanoparticles of silver, the chemical reduction method is the most suitable
technique. XRD pattern reveals the crystalline natures of both the
nanoparticles i.e. face-centered cubic structure (FCC). The antibacterial
activity of Ag and Au nanoparticles is tested against gram-positive bacteria
and gram-negative bacteria. The antibacterial potential is measured by the Zone
of inhibition. Both the nanoparticles are vulnerable to bacteria. Results
declared the antibacterial of silver nanoparticles is more proficient than gold
nanoparticles because of the highly chemical inert nature of gold.
