Biomedical Engineering Reference
In-Depth Information
pathways. Several types of microarray have been developed for different tar-
get materials, which can be DNA, cDNA, mRNA, protein, small molecules,
tissues, or any other material that can be quantitatively analyzed. A DNA
array consists of a large number of DNA molecules in an orderly arrange-
ment on a solid substrate to form a matrix of sequences in two dimensions.
cDNA microarrays and oligonucleotide microarrays are used for microarray
expression analysis, and to determine the level or volume of expression of a
given gene. Single nucleotide polymorphism microarrays detect mutations
or polymorphisms in a gene sequence [80]. This technology is used to test
an individual for disease expression patterns, and to determine whether or
not individuals are susceptible to a disease.
Nanotechnology has produced advances in imaging diagnosis, develop-
ing novel methods and increasing the resolution and sensitivity of existing
techniques. These systems include positron-emission tomography (PET),
single-photon-emission CT (SPECT), fluorescence reflectance imaging,
fluorescence-mediated tomography (FMT), fiber-optic microscopy, optical
frequency-domain imaging, bioluminescence imaging, laser-scanning confo-
cal microscopy and multiphoton microscopy [81]. The main benefits of mo-
lecular imaging for in vivo diagnosis lie in the early detection of disease and
the monitoring of disease stages, supporting the development of individu-
alized medicine and the real-time assessment of therapeutic and surgical
efficacy. MRI, CT, PET and SPECT are the most widely used and studied
modalities in cancer patients. Overall, nuclear imaging by PET or SPECT
offers greater sensitivity, but is limited by the lack of anatomical context,
whereas MRI provides accurate anatomical detail but no data on cell vi-
ability and shows poor sensitivity [82]. Although none of these modalities
is ideal, MRI is the preferred option for cellular tracking. Detecting proton
relaxations in the presence of a magnetic field yields tomographic images
with excellent soft tissue contrast, and can locate the cells of interest in the
context of the surrounding milieu (oedema or inflammation) without the
use of harmful ionizing radiations. In addition, MRI offers a longer track-
ing window in comparison to PET and SPECT, which are limited by the
decay of the short-lived radioactive isotopes. New contrast agents, used to
increase the sensitivity and contrast of imaging techniques are increasingly
complex and formed by synthetic and biological NPs. NPs possess certain
size-dependent properties, particularly with respect to optical and magnetic
parameters, which can be manipulated to achieve a detectable signal. The pri-
mary event, in most nanoparticle-based assays is the binding of a nanopar-
ticle label or probe to the target biomolecule that will produce a measurable
signal characteristic of the target biomolecule. A probe that is to function
in a biological system must be water-soluble and stable and have mini-
mal interaction with the surrounding environment. Although remarkable
achievements have been made in nanodiagnostics during recent years, most
of these techniques are still under laboratory investigation. Nida et al. [83]
