Biomedical Engineering Reference
In-Depth Information
Up to now, displacement reactions have been less sensitive than sandwich reac-
tions, but their performances are steadily increasing.
7.5 Conclusion
The most important application of biochips is biorecognition, and biorecognition
is based on key-lock type of reaction. To this regard, we have investigated the phys-
ics of biochemical reactions and determined the kinetics of the most important
reactions such as DNA hybridization and enzymatic reactions for proteins. These
kinetics, however, can be modified by the concentration of reacting species (analytes
or targets) and the coupling between biochemical reaction and advection-diffusion
of reagents in the biochip is essential. Finally, we have distinguished between two
types of reaction, the “sandwich” reaction that derives directly from the key-lock
approach, and the displacement reactions that are more complex and require the
use of an analog to the target.
It is essential to point out that detection is an important part for the conception
of any biochip. It is not sufficient to have a very efficient capture—by hybridization
or immunorecognition—if there is no sensitive detection associated with it. The read-
ing of the biochip reactive surface should be at least as sensitive as the reaction itself.
Detection is not the subject of this topic; let us just mention that the research on detec-
tion for biochip recognition is the topic of an abundant literature and is a field that
is constantly improving. Developments are aimed in two directions: first, improve-
ments in the detection method itself, such as improving the fluorescence by using new
fluorophores (quantum dots, for example), or developing enzymatic amplification for
detection, and so forth; and second, improvements of the design and materials, such
as improved waveguide in the case of detection by fluorescence, or the use of CMOS
detectors for photons emitted by the fluorophores or by the enzymatic revelation.
References
[1] http://www.cheng.cam.ac.uk/research/groups/laser/Teaching/metrology/immuno_label.
pdf.
[2] Harlow, E., and D. Lane,
Using Antibodies: A Laboratory Manual
, New York: Cold Spring
Harbor Laboratory Press, 1988.
[3] Atkins, P. W.,
Physical Chemistry
, Oxford, U.K.: Oxford University Press, 1998.
[4] Laidler, K. J.,
Chemical Kinetics
, New York: Harper and Row, 1987.
[5] Berthier, J., P. Combette, and L. Blum, “Numerical Calculation of a Microfluidic Protein
Reactor: Is the Classical Michaelis-Menten Integral Relation Sufficiently Accurate?”
Lab-
on-a-Chip and Microarrays Conference
, Zurich, Switzerland, January 14-16, 2002.
[6] Berthier, J., P. Combette, and L. Blum, “A Model for the Kinetics of Heterogeneous Enzy-
matic Reaction in a Protein Microreactor,”
4th LETI Annual Review
,
CEA Grenoble
, June
2002.
[7] Sharov, A. A., Virginia Tech., http://www.gypsymoth.ento.vt.edu/~sharov/PopEcol/lec10/
lotka.html.
[8] Lotka, A. J.,
Elements of Physical Biology
, Baltimore, MD: Williams & Wilkins Co,
1925.
