Biomedical Engineering Reference
In-Depth Information
[50]. Unfortunately, this is a time-consuming procedure, and results in a progres-
sive loss of microsphere cores as more layers are assembled. In one study, 80%
of the microspheres were found to be lost when centrifugal washing was used
during the assembly of 20 polyelectrolyte layers on nonmagnetic microspheres
[51]. However, Wilson and colleagues overcame this problem by using magnetic
separation to perform the washing steps, as shown in Figure 2.9a [52, 53], as this
allows many layers of QDs to be assembled on magnetic cores, without any sig-
nifi cant loss of microspheres and in less than one-quarter of the time required
when centrifugal precipitation is used. Because the QDs are assembled in a shell
(a)
(b)
Figure 2.9
(a) Simplifi ed scheme of LBL
self-assembly of photoluminescent QDs on
magnetic cores. Step I, mix magnetic particles
and QDs; Step II, precipitate magnetic
particles and remove excess QDs; Step III,
assemble new layer of QDs; (b) By combining
LBL self-assembly and magnetic separation,
sophisticated nanoscale architectures can be
constructed. In the scheme on the left, a
magnetic core is surrounded by an inner shell
of QDs and an outer shell of silica
nanoparticles (SiNPs). The latter is
functionalized with an immunosorbent
antigenic surface (AS) for use in multiplexed
immunoassays. The TEM image on the right
shows a thin section though a magnetic
microsphere, with the architecture shown in
the scheme on the left. The encoding QDs are
visible as a dark line between the magnetic
core and outer shell of SiNPs. The TEM
image was reproduced from Ref. [53];
© American Chemical Society.
