Biomedical Engineering Reference
In-Depth Information
Recently, Zhang et al. reported an alternative mode of UCNPs-based aptamer
sensor (Fig.
13.9
b) [
130
]. Instead of using carbon materials, they utilized an organic
dye as an energy acceptor for FRET-based design. UCNPs were modified with an
ATP aptamer which was hybridized with a cDNA strand labeled with an organic
dye. Upon excitation with a 980 nm laser, both the fluorescence signals of UCNPs
and dye were observed simultaneously as a consequence of FRET. In the presence
of ATP, conformational change of the aptamer induced the dissociation of the
dye-labeled strand from UCNPs, leading to the inhibition of FRET and a change
in the optical readout. With this design, they demonstrated a detection limit of
20
M. Since these kind of nanoparticles are normally capped with hydrophobic
ligands that lack any functional groups for surface functionalization, one drawback
of this application is stringent control over the DNA modification of the UCNPs
for efficient energy transfer. Developing easy and general methods for producing
functionalizable UCNPs is a prerequisite for many biomedical applications of this
class of materials [
114
,
122
].
13.4
Functional DNA-Modified Magnetic Nanoparticles
for Biosensing
Magnetic resonance imaging (MRI) is one of the most powerful medical imaging
techniques that can provide images with excellent anatomical details in living
organisms [
131
,
132
]. Since the sensitivity of MRI can be greatly enhanced by
contrast agents, a key area of research in the MRI field is the development of such
MRI contrast agents [
133
,
134
]. As a new class of MRI contrast agents, super-
paramagnetic iron oxide nanoparticles (SPIOs) hold great potential for biomedical
applications due to their unique magnetic properties, low toxicity, and high chemical
stability [
135
-
137
].
Recently, the applications of SPIOs for target-specific MRI detection caught the
attention of many researchers. It was found that the SPIOs assembly efficiently
decreased magnetic relaxation of surrounding water protons because the aggregation
of SPIOs generated strong local magnetic fields that accelerated the dephasing of
adjacent water protons and resulted in a decreased spin-spin relaxation time (T2)
[
138
,
139
]. This observation has led to the development of magnetic relaxation
switches (MRS), in which the assembly and disassembly of SPIOs could produce
distinct magnetic relaxation properties. Based on this principle, various MRI-based
detections have been reported [
138
-
143
]. For instance, it has been shown that cross-
linked dextran iron oxide (CLIO) nanoparticles can be functionalized with DNA,
and this material can be used for the sequence-specific detection of complementary
oligonucleotides based on the nanoparticles assembly induced changes of the T2
value [
138
,
139
]. In addition to oligonucleotide detection with this principle, it
would be important to expand this nucleic acid-based MRI approach to detect
broader classes of targets.
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