Biomedical Engineering Reference
In-Depth Information
Fig. 11.7.
High-density multianalyte bio-optrode composed of microsphere array on
an imaging fiber. (
a
) Scanning force micrograph (SFM) of microwell array fabricated
by selectively etching the cores of the individual fibers composing the imaging fiber.
(
b
) The sensing microspheres are distributed in the microwell. (
c
) Fluorescence im-
age of a DNA sensor array with
∼
13,000 DNA probe microspheres. (
d
) Small region
of the array showing the different fluorescence responses obtained from the differ-
ent sensing microspheres [20]. Reprinted from [1] with permission from American
Association for the Advancement of Science
a sandwich reaction or a third die, e.g., one that binds to double stranded
DNA. Then only the beads with target have three colors and the identity can
be read from the bead code (Fig. 11.7).
11.6 Planar Biosensors
Planar waveguide biosensors also usually employ evanescent illumination from
a coherent source to excite fluorophores at the surface of the waveguide. The
resulting fluorescence emission can be measured either by a single photode-
tector or by a system capable of imaging, usually a CCD or CMOS camera.
A variety of focusing lenses have been used to improve detector response
[7, 17, 29-32]. The introduction of bandpass and longpass filters was found to
improve the rejection of scattered laser light and hence reduce the background
of the system [7] (Fig. 11.8).
Unfortunately, a side effect of using bulk waveguides and collimated light
is the production of sensing “hot spots” along the planar surface that occur
where the light beam is reflected, illuminating only discrete regions. These
