Design and Development of Theranostic Nanomedicines - Nanotechnology for Biomedical Imaging and Diagnostics - page 423

life, route of administration, etc.). The earlier we consider these issues, the more
likely our successful theranostic nanomedicine candidate in the preclinical testing
will reach the clinic.
15.2 soliD nanoparticle systems
15.2.1 iron oxide nanoparticles
iron oxide nanoparticles (ionps) are among the most commonly used nanomaterials
for biomedical applications. in general, ionps have two main components: a magnetic
iron oxide core composed of magnetite (Fe 3 o 4 ) and maghemite (γ-Fe 2 o 3 ) and a hydro-
philic surface coating with dextran, polyethylene glycol (peg), or other polymers.
ionps have many favorable features as a theranostic platform, including:
1. Magnetic resonance imaging (Mri) signature for therapeutic monitoring. small
ionps (typically <20 nm) become superparamagnetic when each particle has a
single magnetic domain and thermal energy is high enough to overcome the
energy barrier of magnetic flipping [5]. such superparamagnetic ionps are
highly magnetic under external magnetic field but show zero magnetism without
it. in Mri, superparamagnetic ionps are effective in reducing T 2 relaxation
time, therefore showing dark contrast in Mri images. This information allows
for the imaging of ionps uptake to monitor treatment efficacy [6].
2. Well-developed surface chemistry for bioconjugation. ionps can be coated
with a large number of functional groups for bioconjugation with therapeutic,
signaling, and targeting molecules. it is therefore possible to use ionps in
target-specific drug delivery and multimodal imaging. For example (Fig. 15.3),
a multifunctional polymeric matrix of poly(acrylic acid) (paa)-coated ionps
were reported to have an encapsulated chemotherapeutic agent for cancer
therapy, a surface folate receptor ligand for cancer targeting, an encapsulated
near-infrared (nir) dye for fluorescent imaging capabilities, and a superpara-
magnetic iron oxide core for Mri [7].
3. Biocompatibility and biodegradability. Unlike many other metallic compounds,
iron oxide is considered suitable for in vivo applications as the iron cell homeo-
stasis is well controlled by uptake, excretion, and storage [8]. Moreover, excessive
iron can be efficiently cleared from the body [9]. in fact, several ionps have
been approved by the FDa for clinical usage, such as Feridex and resovist.
overall, ionps represent an outstanding class of nanomaterials for theranostic
applications.
although Mri provides outstanding anatomical information with good resolu-
tion, it suffers from poor sensitivity [10]. This limitation can be resolved by combining
Mri with other sensitive imaging techniques, such as positron emission tomography
(peT), single-photon emission computed tomography (speCT), and optical imaging
[10]. With large surface area and sophisticated surface chemistry, ionps can serve