Biomedical Engineering Reference
In-Depth Information
Fig. 3.1
Main types for DNA detection.
a
competitive system,
b
sandwich system, and
c
molecular
beacon structure
proximal ground-state acceptor A through long-range dipole-dipole interactions [
1
-
3
].
The acceptor must absorb energy at the emission wavelength(s) of the donor, but does
not necessarily have to remit the energy fluorescently itself. The rate of energy transfer
is highly dependent on many factors, such as the extent of spectral overlap, the relative
orientation of the transition dipoles, and, most importantly, the distance between the
donor and acceptor molecules [
4
,
5
]. FRET is very appealing for bioanalysis because
of its simpleness of building ratiometric fluorescent systems. At the beginning, the
FRET-based sensing systems were designed with organic dye as donors. With the
appearance and development of QDs, more and more QD-based FRET DNA biosen-
sors have emerged. The wide use of QDs as the donors in FRET can be ascribed not
only to their high fluorescence quantum yield, strong resistance to photobleaching,
but also to their broad excitation wavelengths and narrow and symmetric size-tunable
emission spectra. These characteristic properties make their great promise in FRET
assays [
6
]. This method avoided the numerous problems linked to DNA intercalating
dyes commonly used for DNA imaging (photobleaching, photoinduced cleavage, and
modification of the DNA properties). Krull et al. developed a multiplexed solid-phase
nucleic acid hybridization assay on a paper-based platform using multicolor immobi-
lized QDs as donors in FRET, which could reach a detection limit of 90 fmol and an
upper limit of dynamic range of 3.5 pmol. As shown in Fig.
3.2
, the surface of paper
