TABLE OF CONTENTS
CHAPTER ONE
INTRODUCTION AND
LITERATURE REVIEW
1.0 INTRODUCTION
1.1 LITERATURE REVIEW
1.2 Nanotechnology
1.3 Physiochemical Properties of Nanoparticles
1.4 Methods of Nanoparticles Synthesis
1.4.1 Chemical
Approach:
1.4.2 Physical Approach:
1.4.3 Biological Approach:
1.4.4 Photo-induced Approach:
1.5 Applications of Nanoparticles
1.5.1 Medical and Pharmaceutical Applications
1.5.2 Biosensing
1.5.3 Optical
Applications
1.5.4 Optoelectronics
1.5.5 Energy and Electronic Applications
1.5.6 Antibacterial Applications
1.5.7 Other Applications of Nanoparticles
1.6 Silver Metal
1.6.1 Some Uses of Silver
1.7 Recent Works on Nanoparticles
1.8 Gnetum
africanum (Afang Leaf)
1.9 Aim of Work
1.9.1 Objective
of the Research
CHAPTER TWO
MATERIALS
AND METHODS
2.1 Materials
2.2 Instruments
2.3 Preparation of the leaf extract
2.4 Synthesis of the silver nanoparticles
2.5 UV-Vis spectrophotometer
analysis
2.6 Preparation of Culture Media
2.6.1 Sorbitol-MacConkey pt. I & II Agar
(exclusive for E. coli)
2.6.2 Salmonella Shigella Agar (exclusive for S. typhi)
2.6.3 Eosin Methylene Blue (EMB) Agar (exclusive
for S. aureus)
2.7 Sensitivity Test
2.7.1 Determination of Sensitivity
of Isolate with Extract
2.8
Determination of MIC
CHAPTER THREE
RESULTS
AND DISCUSSION
3.1 UV-Vis spectrophotometer
analysis
3.2 KINETIC STUDY
3.3 Antibacterial Evaluation
CHAPTER FOUR
CONCLUSION
AND RECOMMENDATION
REFERENCES
CHAPTER ONE
INTRODUCTION AND
LITERATURE REVIEW
1.0 INTRODUCTION
Nanoscience
has been the subject of substantial research in recent years. It has been
explored by researchers in various fields of science and technology (Kholoud et al. 2010). The novel
properties of NPs have been exploited in a wide range of potential applications
such as in medicine, cosmetics, renewable energies, environmental remediation, biomedical
devices (Quang Huy, 2013), electronics, optics, organic catalysis,
vector control, sensor, etc., have drawn extensive attention to this field of
study (Mousavand et al. 2007). Among the metals, silver
nanoparticles have shown potential applications in various fields such as the
environment, bio-medicine, catalysis, optics and electronics (Rao et al., 2000). Silver nanoparticles
are mostly smaller than 100 nm and consist about 20–15,000 silver atoms. In its
nanoscale form, silver exhibits unique physicochemical and biological
activities. This has made them useful as sensor, vector control, antimicrobial,
anticancer, and antiplasmodial agents, catalysts, among others (Elemike et al. 2014; Vinod et al. 2014;
Kathiravan et al. 2014; Saraschandra and Sivakumar 2014; Namita and Soam 2014).
Concerted effort has been made to
synthesize diverse range of silver nanoparticles
varying in size, geometry, and morphology because of their
potential applications,
particularly in electronics (P.
V. Kamat, 2002), electrochemical
sensing (L. M. Liz-Marzán, 2006), catalysis (F. Zhang, Y. Pi et al., 2007), and
antimicrobial properties (T. Sakai et
al., 2006). The size, geometry, dispersion and stability often determine
the suitability of the nanoparticles for certain applications. Synthesis may
involve physical means such as ultraviolet light, microwaves, photo-reduction,
or chemical reduction using hydrazine, ascorbic acid, sodium borohydride,
glucose, and organic stabilizers or biological means using plant extract, microorganism
or plant sap. Several physical and chemical methods have been used to
synthesize and stabilize silver nanoparticles (Senapati et al., 2005, Klaus-Joerger et al., 2001). The most
popular chemical approaches, including chemical reduction using a variety of
organic and inorganic reducing agents, electrochemical techniques,
physicochemical reduction, and radiolysis are widely used for the synthesis of
nanoparticles.
Although these
means are fast and easy, they are either expensive or toxic particularly the chemical
method and may lead to non eco-friendly byproducts thus the need for
environmental, nontoxic synthetic protocols for nanoparticles synthesis. In the
global efforts to reduce generated hazardous waste, “green” chemistry and
chemical processes are progressively integrating with modern development in
science and industry (Sharma et al., 2009)
leading to the developing interest in biological approaches which are free from
the use of toxic chemicals as by products. Biological methods can be used to synthesize
nanoparticles without the use of any harsh, toxic and expensive chemical
substances. The bioreduction of metal ions by combinations of biomolecules
found in the extracts of certain organisms (e.g., enzymes/proteins, yeast,
fungi, bacteria and plants) is environmentally benign, yet chemically complex (Ankamwar et al., 2005). It has been
elucidated that biomolecules with carbonyl, hydroxyl, and amine functional groups
have the potential for metal ion reduction and capping of the newly formed
particles during their growth processes (Harekrishna
et al., 2009, He et al., 2007). Biomolecules in plants and spices extract are
essential oils (terpenes, eugenols, e.t.c.), polyphenols, carbohydrates, e.t.c.
and can reduce and stabilize Ag+ to Ag0. It provides
advancement over chemical and physical methods as it is cost effective and
environment friendly.
1.1 LITERATURE REVIEW
Disease-causing microbes are becoming
resistant to drug therapy and therefore poses great public health problem. Many researchers are now engaged in developing new
effective antimicrobial reagents with the emergence and increase of microbial
organisms resistant to multiple antibiotics, which will increase the cost of
health care. Colloidal silver has been known for a long time to
possess antimicrobial properties and also to be non-toxic and environmentally
friendly. It has been used for years in the medical field for antimicrobial
applications such as burn treatment (Parikh
et al. 2005; Ulkur et al 2005), elimination of microorganisms on textile
fabrics (Jeong et al. 2005; Lee et al.
2007; Yuranova et al. 2003), disinfection in water treatment (Russell and Hugo 1994; Chou et al. 2005),
prevention of bacteria colonization on catheters (Samuel and Guggenbichler 2004; Alt et al. 2004; Rupp et al. 2004),
etc. It has also been found to prevent HIV from binding to host cells (Sun et al. 2005). The mechanism of the bacterial effect of AgNP as
proposed is due to the attachment of AgNPs to the surface of the cell membrane,
thus disrupting permeability and
respiration functions of the cell (Kevitec
et al. 2008). It is also proposed that AgNPs not only interact with the
surface of a membrane but can also penetrate inside the bacteria (Morones et al. 2005), but
the effects of silver nanoparticles (AgNP) on microorganisms have not been
developed fully. Researchers believe that the potential of colloidal silver is
just beginning to be discovered (Dorjnamjin
et al., 2008).
1.2 Nanotechnology
Nanoparticles are viewed as the fundamental building
blocks of nanotechnology (Mansoori et
al., 2005). They are the starting points for preparing many nanostructured
materials and devices and their synthesis is an important component of the
rapidly growing research efforts in nanoscience and nanoengineering (Mansoori et al., 2007).
In nanotechnology, a nanoparticle is defined as a
small object that behaves as a whole unit in terms of its transport and
properties. Nanoparticles can equally
be called ultrafine particles since
their sizes range from 1 to 100 nm. Fine particles ranges from 100 to 2,500 nm,
while coarse particles are sized between 2,500 and 10,000 nm (Williams, 2008). A nanometer is one billionth of a meter (10-9 m),
roughly the width of three or four atoms, smaller than the wavelength of
visible light and a hundred-thousand the width of human hair.
Nanoparticles can
be made of
materials of diverse
chemical nature, the
most common being metals,
metal oxides, silicates,
non-oxide ceramics, polymers,
organics, carbon and biomolecules.
Nanoparticles exist in several different morphologies such as spheres,
cylinders, platelets, tubes, flowers, cubes etc. They
possess unique physiochemical, optical and biological properties which can be
manipulated to suit a desired application. Nanoparticles are of great interest
due to their externally small size, and large surface to volume ratio. They
exihibit utterly novel characteristics compared to the large particles of the
bulk material and have been included in fields of science as diverse
as surface science, organic chemistry molecular biology, semi conductor
physics, microfabrication, material science, inorganic chemistry and so on.
The concepts that seeded nanotechnology
were first discussed in 1959 by renowned physicist Richard Feynman in his talk
“There's Plenty of Room at the Bottom”, in which he described the possibility
of synthesis via direct manipulation of atoms. In 1974, “Norio Taniguchi now
used the word nanotechnology to describe precision manufacturing materials at
the nanometer level which refers to the synthesis, manipulation, and control of
matter at nano dimensions that will make most products lighter, stronger,
cleaner, less expensive and more precise.
1.3 Physiochemical Properties of Nanoparticles
·
Nanoparticles also often possess unexpected optical
properties as they are small enough confine their electrons and produce quantum
effects e.g. gold nanoparticles appear deep red in dark solutions.
·
A unique property among nanoparticles is quantum confinement in
semiconductor particles, surface plasmon resonance in some metal particles and
super paramagnetism in magnetic materials. For example, ferroelectric materials
smaller than 10 nm can switch their magnetization direction using room
temperature thermal energy. Thus this property is not always desired in
nanoparticles thus making them unsuitable for memory storage.
·
Suspensions of nanoparticles are possible since the
interaction of the particle surface with the solvent is strong enough to
overcome density differences, which otherwise usually result in a material
either sinking or floating in a liquid.
·
The high surface area to volume ratio of nanoparticles
provides a tremendous driving force for diffusion, especially at elevated
temperatures. Sintering can take place at lower temperatures, over shorter time
scales than for larger particles.
1.4 Methods
of Nanoparticles Synthesis
Currently, many methods have been reported for the
synthesis of nanoparticles which include chemical, physical, biological and
photo-induced approach.
1.4.1 Chemical Approach:
The chemical approach
is the most used method since it for provides an easy way to synthesize
nanoparticles in solution. This consists of the chemical reduction of a metal
salt in solution followed by the crystallization of zero-valence metal
particles. The particle synthesis is usually conducted in the presence of a
stabilizing agent that prevents excessive molecular growth and/or aggregation
of the metal nanoparticles. Hence when nanoparticles are produced by chemical
synthesis, three main components are needed: a salt (e.g. AgNO3), a
reducing agent (e.g. ethylene glycol) and a stabilizer agent (e.g. PVP) to
control the growth of the nanoparticles and prevent them from aggregating.
In
one study, Oliveira and coworkers (2005) prepared dodecanethiol-capped silver
NPs, according to Brust procedure (Brust et al., 2002) based on a phase
transfer of an Au3+ complex from aqueous to organic phase in a
two-phase liquid-liquid system, which was followed by a reduction with sodium
borohydride in the presence of dodecanethiol as stabilizing agent, binding onto
the NPs surfaces, avoiding their aggregation and making them soluble in certain
solvents. They reported that small changes in synthetic factors lead to
dramatic modifications in nanoparticle structure, average size, size
distribution width, stability and self-assembly patterns.
1.4.2 Physical Approach:
In physical processes, nanoparticles are
synthesized by evaporation-condensation, exploding wire technique, chemical
vapour deposition, microwave irradiation, pulsed laser ablation, supercritical
fluids, sonochemical reduction, and gamma radiation with evaporation-condensation and laser
ablation being the most important physical approaches. The absence of solvent
contamination in the prepared thin films and the uniformity of NPs distribution
are the advantages of physical synthesis methods in comparison with chemical
processes.
Siegel and
colleagues (2012) demonstrated the synthesis of AgNPs by direct metal
sputtering into the liquid medium. The method, combining physical deposition of
metal into propane-1, 2, 3-triol (glycerol), provides an interesting
alternative to time-consuming, wet-based chemical synthesis techniques. Silver
NPs possess round shape with average diameter of about 3.5 nm with standard
deviation 2.4 nm. It was observed that the NPs size distribution and uniform
particle dispersion remains unchanged for diluted aqueous solutions up to
glycerol-to-water ratio 1 : 20.
1.4.3 Biological Approach:
As stated earlier
in the chemical method of synthesis, three
main components are needed: a salt (e.g. AgNO3), a reducing agent
(e.g. ethylene glycol) and a stabilizer agent (e.g. PVP) to control the growth
of the nanoparticles and prevent them from aggregating. In biological synthesis
of nanoparticles, the reducing agent and the stabilizer are replaced by
molecules produced by living organisms. These reducing and/or stabilizing
compounds can be utilized from bacteria, fungi, yeasts, algae or plants.
The development of efficient green
chemistry methods for synthesis of nanoparticles has become a major focus of
researchers. In the global effort to
reduce generated waste and toxic materials, “green” chemistry and chemical
processes are progressively integrating with modern developments in science and
industry. They have investigated in
order to find an eco-friendly technique for production of well-characterized
nanoparticles. Various approaches using
plant extracts have been used for the synthesis of nanoparticles. These
approaches have many advantages over chemical, physical, and microbial
synthesis because there is no need of the elaborate process of culturing and
maintaining the cell, using hazardous chemicals, high-energy and wasteful
purifications.
The first successfully reported synthesis
of nanoparticles assisted by living plants appeared in 2002 when it was shown
that gold nanoparticles, ranging in size from 2-20 nm, could form inside
alfalfa seedlings. Subsequently it was shown that alfalfa could form silver
nanoparticles when exposed to a silver rich medium. Other works on plants and plant parts that have been
used for
the synthesis of silver nanoparticles
are Thevetia peruviana latex (Rupiasih et al. 2013), Wrightia tinctoria (Bharani et al. 2011), Solanum
xanthocarpum (Muhammad et al. 2012),
Opuntia ficus (Silva-de-Hoyos et al. 2012), Sphaeranthus
amaranthoides (Swarnalatha et al.
2012), Punica granatum (Naheed et al. 2012) Citrullus colocynthis (Satyavani
et al. 2011), Eucalyptus chapmaniana
(Ghassan et al. 2013), Acacia auriculiformis (Nalawade et al. 2014), Ficus benghalensis, Azadirachta indica (Debasis
et al. 2015), e.t.c.
The biomolecules present in these plants
are responsible for the formation and stabilization of silver nanoparticles (Iravani et al. 2014). Nanoparticles produced by plants are more stable and
the rate of synthesis is faster than in the case of microorganisms. Moreover, this method is simple, cost effective,
energy-saving and reproducible. The nanoparticles
are more various in shape and size in comparison with those produced by other
organisms. The advantages of using plant and plant-derived materials for
biosynthesis of metal nanoparticles have interested researchers to investigate
mechanisms of metal ions uptake and bioreduction by plants, and to understand
the possible mechanism of metal nanoparticle formation in plants.
1.4.4 Photo-induced Approach:
The photo-induced
synthetic strategies can be categorized into two distinct approaches, that is
the photo-physical (top down) and photochemical (bottom up) ones. The former
could prepare the NPs via the subdivision of bulk metals and the latter
generates the NPs from ionic precursors. The NPs are formed by the direct
photo-reduction of a metal source or reduction of metal ions using
photo-chemically generated intermediates, such as excited molecules and
radicals which are known as photosensitization in the synthesis of NPs.
Huang and coworkers (2008) reported the
synthesis of silver NPs in an alkaline aqueous solution of
AgNO3/carboxymethylated chitosan (CMCTS) using UV light irradiation. CMCTS, a
watersoluble and biocompatible chitosan derivative, served simultaneously as a
reducing agent for silver cation and a stabilizing agent for the silver NPs.
The diameter range of produced silver NPs was 2–8 nm, and they can be dispersed
stably in the alkaline CMCTS solution for more than 6 months
The main
advantages of the photochemical synthesis are;
·
It is a clean process, with high spatial resolution, and
convenience of use.
·
It has great versatility; the photochemical synthesis
enables one to fabricate the NPs in various mediums including emulsion,
surfactant micelles, polymer films, glasses, cells, etc.
1.5 Applications of Nanoparticles
There
is wide applicability of nanoparticles due to their interesting optical,
conductive, physio-chemical, electronic, antimicrobial properties.
1.5.1 Medical and Pharmaceutical Applications
Nanoparticles can be made to control and
sustain release of the drug during the transportation and as well as the
location of the release since the distribution and subsequent clearance of the
drug from the body can be altered. An increase in the therapeutic efficacy and
reduction in the side effects can also be achieved. Targeted drugs may be
developed.
The
surface change of protein filled nanoparticles has been shown to affect the
ability of the nanoparticles to stimulate immune responses. Researchers are
thinking that these nanoparticles may be used in inhalable vaccines. Researchers
are developing ways to use carbon nanoparticles called nanodiamonds in medical
applications. For example, nanodiamonds with protein molecules attached can be
used to increase bone growth around dental or joint implants.
Other medical and pharmaceutical applications
include; tissue engineering, bio detection of pathogens, tumour destruction via
heating (hyperthermia), drug and gene delivery, separation and purification of
biological molecules and cells.
1.5.2 Biosensing
A biosensor
is an analytical device used for the
detection of an analyte, which combines
a biological component with a physicochemical
detector (Florinel-Gabriel, 2012). The sensitive
biological element can be tissues, microorganisms,
organelles, cell receptors, enzymes, antibodies,
nucleic acids, e.t.c. or a
biologically derived material or biomimetic component
that interacts, binds or recognizes the analyte
under study. Nanomaterials are exquisitely
sensitive chemical and biological sensors. Their large
surface area to volume ratio can achieve rapid and low cost
reactions, using a variety of designs (Gerald,
2009).
Biosensing can have the following applications;
- Environmental
applications e.g. the detection of pesticides
and river water contaminants
such as heavy metal ions.
·
Determining the presence of pathogen and food toxins in
food analysis.
- Determining
levels of toxic substances
before and after bioremediation.
- Determination
of drug residues in food, such as antibiotics
and growth promoters.
- Drug
discovery and evaluation of
biological activity of new compounds.
1.5.3 Optical
Applications
The optical properties of noble metals
nanoparticles have been of great interest because of many applications in
optical devices (optical limiters, solar cells, medicals imaging, surface
enhanced spectroscopy, surface plasmonic devices) and bio-applications (Haglund et al. 1993).
1.5.4 Optoelectronics
Optoelectronics is the study and
application of electronic devices that source, detect and control light. The
light includes invisible forms of radiation such as gamma rays, X-rays,
ultraviolet and infrared, in addition to visible light. Optoelectronic devices
are electrical-to-optical or optical-to-electrical transducers, or instruments
that use such devices in their operation. It can function as an emitter of
optical radiation, such as a light-emitting diode (LED), or as a photovoltaic
(PV) device that can be used to convert optical radiation into electrical
current, such as a photovoltaic solar cell.
In optoelectronics;
·
Nanoparticles can be applied in the production of optocouplers,
a component that transfers electrical signals between two isolated circuits by
using light. They prevent high voltages from affecting the system receiving the
signal.
·
Nanoparticles are also applied in optical fibers which are
used most to transmit light between the two ends of the fiber and find wide
usage in fiber-optic communications. They are also used for illumination, and
are wrapped in bundles so that they may be used to carry images, thus allowing
viewing in confined spaces e.g. fiberscope.
1.5.5 Energy and Electronic Applications
Quantum Dots;
A quantum dot
(QD) is a nanocrystal made of semiconductor
materials that is small enough to exhibit quantum mechanical properties.
Specifically, its excitons are
confined in all three spatial dimensions. The electronic properties of these materials
are intermediate between those
of bulk semiconductors and of discrete molecules (Brus, 2007, Norris, 1995, Murray et al.,
2000).
Quantum
dots are applied in;
In textile technology, various
kinds of organic dyes are
used but
more flexibility is
being required of these dyes, and the traditional dyes are often unable to meet the expectations
(Walling et al., 2009). To this end, Quantum dots have quickly filled
in the role, found to be
superior to traditional organic dyes on several counts. One of the most immediately
obvious being brightness (owing
to the high extinction co-efficient combined with a comparable quantum yield to
fluorescent dyes (Michalet et al., 2005) as well as their stability (allowing much less
photobleaching).
Also in biology, the usage of quantum dots
for highly sensitive cellular imaging
has seen major advances over the past decade (Spie., 2014). Another application that takes advantage of the
extraordinary photostability
of quantum
dot probes is the real-time tracking
of molecules and cells over extended periods of time (Dahan et al., 2003).
In light emitting devices, because Quantum
dots naturally produce monochromatic
light; they can be more efficient
than light sources which must be color filtered. They are used
to improve existing light-emitting
diode (LED) design.
1.5.6 Antibacterial Applications
Silver
nanoparticles serves as an inorganic antibacterial powder and play a critical
role in the suppression and killing of pathogenic microorganisms such as S. aureus, E. coli, etc. This innovative anti-infective products has broad
spectrum, non-resistance, durable, has a non-oxidized appearance and is
unaffected by pH effects. Ag-Nps are incorporated in apparel, foot wears, paints,
wound dressings, appliances, cosmetics and plastics for their antibacterial
properties. The colloidal silver is capable of disinfecting water through
sterilization.
1.5.7 Other Applications of Nanoparticles
Generally,
nanoparticles are used or being evaluated for use, in many fields. The list
below introduces several of the other uses under development. They include;
Applications in
Manufacturing and Materials: Titanium
dioxide and zinc oxide nanoparticles are commonly used in sunscreen, cosmetics and
some food products while silver nanoparticles are used in food packaging, clothing, disinfectants and
household appliances. Nano silver and carbon nanotubes are
used for stain-resistant textiles; and
cerium oxide as a fuel catalyst.
Zinc oxides nanoparticles can be dispersed in industrial coating to prevent
wood, plastic and textile from exposure to UV rays.
Applications in
Water Purification: Nanotechnology is
also being applied to or developed for application to a variety of industrial
purification processes. Purification and environmental cleanup applications
include the desalination of water, water filtration, wastewater treatment,
groundwater treatment, and other nanoremediation.
Applications in the Environment: Researchers are
using photocatalytic copper tungsten oxides nanoparticles to break down oil
into biodegradable compounds. The nanoparticles are in a grid that provides
high surface area for the reaction. It is activated by sunlight and can work in
water, making them useful for cleaning up oil spills.
1.6 Silver Metal
Silver is a chemical element with symbol
Ag (Latin name; argentum). It has its electronic configuration as [Kr] 4d10
5s1 (no. of electron per shell; 2, 8, 18, 18, 1) and has an atomic
number 47. It is very ductile, malleable metal (slightly less so than gold),
with a brilliant white metallic luster that can take a high degree of polish.
The electrical conductivity of silver is the highest of all metals, even higher
than copper. Pure silver has the highest thermal conductivity of any metal.
The most common oxidation state of silver
is +1 (e.g. silver nitrate, AgNO3), other
oxidation states include; +2 compounds (e.g.
silver (II) fluoride, AgF2), +3 (e.g. potassium tetrafluoroargentate
(III), KAgF4) and even +4 compounds (e.g. potassium
hexafluoroargentate (IV), K2AgF6) (Riedel et al., 2009).
Silver is found in a native form as an
alloy with gold (electrum), and in ores containing sulphur, arsenic, antimony
or chlorine. Some ores include; argentite (Ag2S), chlorargyrite
(AgCl) and pyrargyrite (Ag3SbS3). The metal is primarily
produced as a byproduct of electrolytic copper refining, gold, nickel, and zinc
refining. Naturally occurring silver is composed of two stable isotopes, 107
Ag and 109 Ag, with 107 Ag being slightly more abundant
(51.8% natural abundance).
1.6.1 Some Uses of Silver
Silver is used to make solder and brazing
alloys, and as a thin layer on bearing surfaces can provide a significant
increase in resistance and reduce wear under heavy load, particularly against
steel. It is used in photography, in the form of silver nitrate and silver
halides, for the development of coloured films. Some electrical and electronic
products use silver for its superior conductivity, even when tarnished. Small
devices, such as hearing aids and watches, commonly use silver oxide batteries
due to their long life and high energy-to-weight ratio. Silver, in the form of
electrum (a gold–silver alloy), was coined to produce money. Silver coins and
bullion are also used as an investment to guard against inflation and
devaluation.
Silver salts have been used since the
middle ages to produce a yellow or orange color to stain glass. Using a process
called sputtering, silver, along with other optically transparent layers, is
applied to glass, creating low emissivity coatings used in high-performance
insulated glazing. Silver can be alloyed with mercury at room temperature to
make amalgams that are widely used for dental fillings. Silver and silver
alloys are used in the construction of high-quality musical wind instruments of
many types. Flutes, in particular, are commonly constructed of silver alloy or
silver plated both for appearance and for the frictional surface properties of
silver. Brass instruments, such as trumpets and baritones, are also commonly plated
in silver.
1.7 Recent Works on Nanoparticles
Though much work
have been done on silver nanoparticles but greater works are underway as this
field of study has proved to enhance the applicability of nanoelectronics,
photonics, biomarker, bio-diagnostic, biosensors and related materials used in
polymers, textiles, fuel cell layers, composites and solar energy materials.
High surface areas can be achieved using solutions and using thin film by
sputtering targets and evaporation technology using pellets, rod and foil.
Caixia
and coworkers 2009, investigated the fabrication of novel Pd-Cu bimetallic nanocomposites
with hierarchically hollow structures
through a simple galvanic replacement reaction using dealloyed nanoporous
copper (NPC) as both template
and reducing agent. The reaction process was monitored by UV-Vis
absorbance spectra and X-ray diffraction
(XRD), which clearly demonstrated a structure evolution from NPC precursor
to a Pd-rich PdCu alloy structure
upon the completion of the reaction. Structural characterization by use of
SEM and TEM revealed that the replacement
reaction between NPC and [PdCl4]2− solution results in a nanotubular
mesoporous structure with a nanoporous
shell, which comprised interconnected alloy nanoparticles with size around
3 nm.
Omid Akhavan and Elham Ghaderi 2009,
investigated the effect of an electric field on the antibacterial activity
silver nanorods against E. coli bacteria. It was found that the grown
silver nanorods show strong and fast antibacterial activity. Applying an
electric field in the direction of the nanorods (without any electrical
connection between the nanorods and the capacitor plates producing the electric
field) promoted their antibacterial activity.
In
another experiment, Elemike et al 2014, investigated silver nanoparticles for
antibacterial activities using pineapple leaf extract. The synthesized
pineapple leaf nanoparticles were reddish brown in aqueous solution and
susceptible to the growth of S. aureus,
S. pnuemoniae and E. coli which showed great antibacterial
properties thereby placing the agents in broad spectrum plane.
1.8 Gnetum
africanum (Afang Leaf)
Gnetum africanum is a vine gymnosperm species found natively
throughout tropical Africa. It has numerous common names most notably, ukase or
afang in Nigeria. It is also referred to as a form of ‘wild spinach’ in
English.
It is traditionally a wild vine and is considered to
be a wild vegetable. It is a perennial plant that grows approximately 10m long,
with thick papery-like leaves growing in groups of three.
Gnetum africanum is found mainly in the humid tropical forest regions
of Central African Republic, Cameroon, Gabon, Democratic Republic of the Congo
and Angola. In Nigeria, it is mostly found in the southern part of the country
(Calabar and Akwa Ibom) and used in preparing special delicacies.
Primarily, the leaves are used as vegetable for soups
and stews, commonly afang soup. The leaves may further be used as a remedy for
nausea, sore throats, or as a dressing for warts. The stem of the plant may
also be eaten for medicinal purposes, including the reduction of pain during
childbirth. It is a good source of protein and is strong in essential and
non-essential amino acids. The plant is also used medicinally as
anti-inflammatory, anticarcinogenic and antioxidant.
1.9 Aim of Work
The
aim of this research is to synthesize silver
nanoparticles from Gnetum africanum
leaf extract and evaluate its antibacterial
function.
1.9.1 Objective
of the Research
The
objectives of the research
are:
·
To synthesize
silver
nanoparticles using Gnetum africanum aqueous
leaf extract.
·
To characterize
the synthesized nanoparticles.
·
To
study the antibacterial properties of the nanoparticle and the ordinary aqeous
leaf extract.
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