Biochips – fundamentals and applications - Electrochemical Sensors, Biosensors and Their Biomedical Applications - page 361

z

100 m

y

x

(a) P

75 m

D ~ 10 nm

(b) E

FIGURE 11.32 Flow profi les in microchannels. (a) A pressure gradient, ∆ P , along a channel generates
a parabolic or Poiseuille fl ow profi le in the channel. The velocity of the fl ow varies across the entire cross-
sectional area of the channel. On the right is an experimental measurement of the distortion of a volume of
fl uid in a Poiseuille fl ow. The frames show the state of the volume of fl uid 0, 66, and 165 ms after the creation
of a fl uorescent molecule. (b) In electroosmotic fl ow in a channel, motion is induced by an applied electric
fi eld E . The fl ow speed only varies within the so-called Debye screening layer, of thickness λ D . On the right

is an experimental measurement of the distortion of a volume of fl uid in an electroosmotic fl ow. The frames
show the state of the fl uorescent volume of fl uid 0, 66, and 165 ms after the creation of a fl uorescent molecule
[165]. Source: http://www.niherst.gov.tt/scipop/sci-bits/microfl uidics.htm (see Plate 12 for color version).