Biomedical Engineering Reference
In-Depth Information
filters, dielectrophoreses, or magnetic bead separations. The latter approach
has been very successfully implemented in commercial systems for chemilu-
minescence assays (reviewed by Richter [1, 2]).
Microfluidics are becoming increasingly used for three particular facets of
optical biosensors:
1. Microfluidic devices facilitate methods for automated sample processing,
including the mixture of the sample with the fluorescent reagents.
2. They provide an e
cient mechanism for manipulating very small volumes,
which saves reagent costs.
3. They can deliver the target more e
ciently to the sensing surface.
Examples of the latter are laminar fluid focusing as described by Hofmann
et al. [42] and Munson et al. [43] and passive mixing to minimize target dep-
letion at the sensing surface as described by Golden et al. [44]. However,
care must be taken to make sure that fluidic channels are su
ciently large
to avoid clogging by complex samples, and that they have the appropriate
surface chemistry to prevent nonspecific adsorption of the target outside the
sensing region. Furthermore, the issue of interrogating a su
cient volume to
include targets present at low concentrations must never be neglected.
Advances in optics offer new opportunities for increased sensitivity and
reductions in size and cost. Silicon technology is producing better and better
integrated optical waveguides for highly multiplexed analysis. Arrays of sin-
gle photon detectors are described by Eduardo Charbon in this volume that
may offer the opportunity to detect single targets if the a
nity of the recog-
nition molecule is su
ciently high and if the background can be su
ciently
reduced. Both scattered excitation light and stray fluorescence from molecules
not bound in the detection complex can generate “noise” beyond that inher-
ent in the optical device itself. The production of devices based on organic
polymers is also very exciting because they should be relatively simple to inte-
grate biological recognition elements and polymer-based microfluidics to form
monolithic, inexpensive, or disposable sensors. Organic LEDs, transistors, and
photodiodes are described in this volume in the chapter by Peter Seitz.
Finally, systems biology at the molecular level is identifying new targets
for analysis that are of importance for medical, environmental, and defense
applications. Furthermore, the understanding of how to make rationally de-
signed molecules for sensing applications offers new approaches to perform
the biorecognition function with appropriate specificity, increased sensitivity,
and enhanced stability during sensor storage and use. New fluorophores also
provide opportunities for interrogating new types of samples and systems and
for generating multiple signals simultaneously.
The future for fluorescence-based optical biosensors will be rich. If there
is a real limitation, it is only on the ability to synthesize all the emerging
technologies into the most useful system for each customer. That ability rests
on the willingness of scientists and engineers in universities, government, and
industry to work together in interdisciplinary teams and the longer term vision
of those that support such efforts.
