Iron Oxide Nanoparticles and Derivatives for Biomedical Imaging and Application in Cancer Diagnosis and Therapy - Bioanalysis Advanced Materials Methods and Devices - page 2

1.1 Introduction

Iron oxide nanoparticles have been of interest for biomedical applications due to
their functional versatility. Concrete applications include cellular therapy,
biosensing, tissue repair, drug delivery, hyperthermia therapy, MRI, magnetofection,
etc. [ 11 ] The literature includes numerous reports describing the synthesis of iron
oxide nanoparticles via physical and chemical methods. Among them, wet chemistry
procedures have been widely used, as size, composition, magnetic properties,
and shapes are more controllable with this method [ 12 ]. Iron oxides are generally
prepared by co-precipitation of Fe 2+ and Fe 3+ salts in an aqueous solution.
The anionic salt content (chlorides, nitrates, sulfates, etc.), the Fe 2+ and Fe 3+ ratio,
pH and the ionic strength in the aqueous solution are key elements in controlling the
size of the particles [ 28 ]. One important step in the synthesis is to prevent the
oxidation of the synthesized nanoparticles and protect their magnetic properties,
which is generally established by carrying out the reaction in an oxygen free
environment (under N 2 )[ 10 ]. The co-precipitation process is generally done in the
presence of a surface coating in order to prevent the agglomeration of the iron oxides
into microparticles during the synthesis. There have been several surface coating
materials used for stabilizing iron oxide nanoparticles, among which there are
synthetic and natural polymers, such as polyethylene glycol (PEG), dextran,
polyvinylpyrrolidone (PVP), fatty acids, polypeptides, chitosin, gelatin, etc. [ 11 ].

1.2 Biomedical Applications of Iron Oxide Nanoparticles

The majority of iron oxide nanoparticles are intended for biomedical applications.
Their use as contrast agents for MRI is particularly attractive, due to their high
sensitivity of detection [ 3 ]. MRI is a clinically approved noninvasive medical
imaging method, which allows the collection of three-dimensional information
from the body with excellent tissue contrast. Iron oxide nanoparticles have been
used to observe different in vivo biological events , MRI including determining the
fate of transplanted pancreatic islets [ 6 , 20 ], tumor progression [ 22 ] or lymph node
metastasis [ 13 ], etc.
Establishing target specific contrast agents for MRI presents a great opportunity
for detecting disease at the initial stages when therapeutic intervention has the highest
chances of success. This is possible because molecular targeting of the contrast would
accomplish the detection of the early phenotypic changes that define the pathology.
Combining diagnosis and therapy would be even more interesting, because it would
allow the assessment of therapeutic efficacy as a function of drug delivery. It is
possible to impart all of these functionalities to iron oxide nanoparticles by having
different ligands attached to the surface of the nanoparticles.
There are several methods of preparing iron oxide nanoparticles but the focus of
this chapter is on cross-linked dextran coated superparamagnetic iron oxides, whose