ABSTRACT
Chemical and physical methods for the synthesis of magnetic
nanoparticles for cancer detection and treatment often involve toxic
chemicals, high cost and the formation of non-stable nanoparticles. This
prompted the development of fundamental understanding of the synthesis
of magnetic nanoparticles, which are biocompatible, cost effective,
stable, localized and environmentally friendly in the presence of
magnetotactic bacteria.
In this work, fundamental understanding of the underlying mechanisms
involved in the formation of magnetic nanoparticles by magnetotactic
bacteria are unraveled. Soil dwelling microbes that respond to magnetic
pull were cultured in the presence of ferrous salts in a magnetic spirillum growth medium (MSGM). A comparative analysis was made whereby a positive control Magnetospirillum magneticum and
an indigenous isolated strain were used in the biosynthesis of magnetic
nanoparticles. The dependence of particle shape and size on pH and
time, were elucidated using a combination of transmission electron
microscopy (TEM) and UV-visible spectrophotometry. The implications of
the results are discussed for the development of magnetic nanoparticles
for the detection and treatment of cancer.
CHAPTER ONE
1.0 INTRODUCTION
1.1 Background and Motivation
Nanotechnology has provides solutions to some critical problem in the
areas of energy generation [1, 2], information storage [3],
environmental remediation [4, 5] and biological application [6] to
mention but a few. In the recent years, there has been increasing
interest in the development of nanoparticles for potential and emerging
applications in medicine [7]. These include potential emerging
applications in disease detection and treatment [8, 9], biological
labelling [10], biosensors [11] and drug delivery [12].
In the case of magnetic nanoparticles (MNPs), there have been
significant efforts to develop magnetic nanoparticles for application in
cancer detection via magnetic resonance imaging (MRI) [13] and
treatment by hyperthamia [14]. In MRI, the current spatial resolution of
detection is of the order of a few millimeters [15]. MNPs have been
produced largely from Iron, cobalt, iron oxide (Fe3O4) and Fe3CoO4 (Yang
et al 2006). Their potential has also been explored for use as contrast
enhancement agent during MRI of tumour tissue [16] and localized
hyperthamia [14] during cancer treatment. Magnetic nanoparticles have
been reported to have the ability of binding to drugs, proteins,
enzymes, antibodies, or nucleotides and can be directed to an organ,
tissue, cells or tumors using an external magnetic field or can be
heated in alternating magnetic fields for use in hyperthermia.
Fe3O4 MNPs are heat-generating nanoparticles which have the ability
to convert electromagnetic energy to heat energy. These MNPs have been
found to be efficient in the detection and treatment of cancer by MRI
and simple radiation therapy. In this case of radiation therapy, energy
produced is used to destroy the cancer cells and reduce the size of
tumours effectively when a cyclic external magnetic field is applied.
In most cases, there are several physicochemical methods that are
used for the synthesis of MNPs. These include: microemulsion, sol-gel
synthesis, hydrothermal reactions, flow injection synthesis,
electrochemical synthesis, pyrolysis, laser pyrolysis, microwave
assisted, carbon arc, combustion synthesis, vapour deposition and
chemical co-precipitation method [7, 17]. However these synthesis
methods often involve the use of toxic chemicals that can have harmful
effects on the environment.
There is therefore a need for environmentally friendly methods for
the synthesis of magnetic nanoparticles, that has stimulated the recent
interest in the biological synthesis of magnetic nanoparticles from
magnetotactic bacteria. There is also a need to understand the
underlying mechanisms of magnetic nanoparticle formation in the presence
of magnetotactic bacteria. To this end, most work in this field has
been done in improving the biocompatibility of the materials, but only a
few scientific investigations and developments have been carried out to
develop a fundamental understanding of the synthesis of magnetic
nanoparticles, which are biocompatible, cost effective, stable,
localized and environmentally friendly in the presence of magnetotactic
bacteria. The need to understand the underlying mechanisms involved in
the formation of magnetite nanoparticles by these bacteria will
contribute positively in improving the quality of magnetic particles,
their size distribution, their shape and surface under certain
preexisting conditions. This would lead to characterizing them to get a
protocol for the quality control and commercialization of these
particles in cancer detection and treatment.