Biomedical Engineering Reference
In-Depth Information
surrounding the magnetic core, their photoluminescence is not quenched by the
iron oxide nanoparticles. In one example, three colors of QDs were assembled on
paramagnetic microspheres, followed by an outer shell of silica nanoparticles, as
shown in Figure 2.9b. The latter - which are completely transparent at all excitation
and emission wavelengths - were subsequently silanized and functionalized with
an antigenic surface for use in multiplexed immunoassays for serum proteins. In
these immunoassays, three sets of microspheres were incubated with the sample
(as shown in Figure 2.10a), and results were determined by decoding the particles
and detecting molecules bound to them with a fl uorescence reader (Figure 2.10b).
By combining solution-phase kinetics and magnetic separation the immunoassays
could be completed in less than 30 min.
(a)
(b)
Figure 2.10
(a) Scheme of multiplexed
competitive immunoassay for serum proteins.
Stage I, three sets of magnetic particles, each
with a different color code and a different
antigenic surface, are incubated with the
corresponding antibodies and the sample; in
this example the sample contains bovine
serum albumin (BSA); Stage II, the magnetic
particles are precipitated and the sample is
removed; Stage III, the magnetic particles are
incubated with fl uorescent Cy - 5 - labeled
antibodies; Stage IV, the particles are
precipitated and washed; Stage V, the
particles are imaged with a fl uorescence
reader; (b) Fluorescence images showing
colors of the encoding QDs and Cy-5
fl uorescence, for one particle from each set at
the end of the immunoassay. Particles with a
code of red and green QDs are not
fl uorescent in the Cy-5 (cyanine-5) window
because BSA was present in the sample.
However, particles with other codes are
fl uorescent because OVA (ovalbumin) and
HSA (human serum albumin) were not
present in the sample. Reproduced with
permission from Ref. [53] ; © American
Chemical Society.
