Page 39 - Optofluidics Fundamentals, Devices, and Applications

20 Cha pte r T w o

1 cm
(a)

Solenoid valves
Screw valves

Pneumatic valve

1 cm
(b)
FIGURE 2-5 (a) A photograph of a strip of prefabricated screw valves. A single
valve has been separated from the strip using a razor blade. (b) A photograph of
a microfl uidic gradient generator containing two embedded solenoid valves, two
embedded screw valves, and one embedded pneumatic valve. (S. E. Hulme,
S. S. S., and W. G. M., “Incorporation of prefabricated screw, pneumatic, and
solenoid valves into microfluidic devices,” Lab Chip, submitted. Reproduced
by permission of the Royal Society of Chemistry.)

2-6-3 Mixers
Mixing of fluids in microchannels is important for many biological and
chemical applications. Mixing in simple microchannels can be slow, as
discussed in the preceding section. Mixers are therefore essential in
enhancing mixing efficiency and in homogenizing reagents rapidly.
All mixing ultimately occurs due to molecular diffusion. The basic
idea behind mixers is reducing the distance over which mixing must
occur [32].