Biochemical Reactions in Biochips - Microfluidics for Biotechnology - page 341

Figure 7.38 Sketch of a functionalized surface in a microchamber where the buffer fluid is at rest.

where d is the vertical dimension of the microchamber. If Da is large the reac-
tion time is larger than the diffusion time and diffusion does not delay the reac-
tion kinetics. On the other hand, if Da is small, the reaction kinetics is limited by
diffusion.
A very interesting observation can be made by analyzing the relation (7.83). If
the vertical dimension of the microchamber is sufficientlty small, the Dammkohler
number becomes large and diffusion does not limit the reaction kinetics. Thus, it is
best to design a microchamber with a vertical size smaller than

D

δ << (7.84)

k G 0

on

Usually, for oligonucleotides, the dimension d should be smaller than 50 to 70 μ m.

Figure 7.39 View under the microscope of a functionalized surface during the process of hybridiza-
tion: the intensity of the laser light diffracted relates to the surface concentration of hybridized DNA.
(Courtesy of CEA-LETI/BioMérieux.)