Biomedical Engineering Reference
In-Depth Information
resolution, magnetic resonance imaging (MRI) is the most used visualisation
technique because it gives better images than do tomography and 3D
imaging. The development of new “dual-modality” contrast agents, capable
of being monitored through their magnetic properties, can solve the problem
of good imaging systems for both optical imaging and MRI. 4 In this context,
nanoparticles are really fundamental. In fact optical and electronic properties
are size dependent and can be tuned by changing particle size. In vivo imaging
with superparamagnetic oxide nanoparticles have already been used as
contrast agents in MRI, 5 because they change the spin-spin relaxation times of
closed water molecules. 7 Quantum dots (QDs) are also promising candidates
in the imaging ield and in the monitoring of cellular events because of their
unique tunable luorescence emission, their great photostability and signal
intensity and their large absorption coeficient, 7 thereby achieving high
sensitivity in the detection of small tumour masses. 4
Early detection of tumour is essential for patient cure, but at the onset of
the disease, the masses are too small to be eficiently identiied by imaging,
considering the problems of spatial resolution and deinition. At this stage,
contrast agents cannot be suficient to overcome this drawback and it is
necessary to amplify the signals, by means of multifunctional nanosystems.
Biosensors can be a good means for early detection but pose some problems,
related to the blood concentration of signiicant pathological biomarkers
and to the sensitivity of detection systems. For example, prostate-speciic
antigen (PSA) concentration can give an indication of the health state with
respect to prostate cancer, but it has widely different baseline expression in
the population and is non-speciic. Although nanotechnology cannot be really
helpful to overcome this problem, it can play an important role in increasing
the sensitivity of sensors.
Many detection platforms have been studied and are under development,
such as the well-known DNA microarrays. In this context, the nanoscale is the
key to improve detection sensitivity. Micro- and nano-cantilevers are examples
of this technology, 3 where, by using both the surface functionalisation and
the cantilever oscillation properties, it is possible to detect the presence of
biomarkers using Hook's law (which relates bending, oscillation frequency
and weight). These systems are the so-called MEMS or NEMS (micro- or
nano-electrical mechanical sensors).
Thanks to the multi-functionalisation, nanosystems can be employed as
biosensors by exploiting their peculiarity, such as paramagnetism. QDs have
been used in the contemporary detection of four different biomarkers to
provide spatial information. 4 Nanowires, nanobarcodes and nanotubes play
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