Miniaturized Detection Systems - Waterborne Pathogens: Detection Methods and Applications - page 310

Figure 10.2 Microfluidic manufacture. Source: Reproduced from Figure 2 in Ref. 4 . Scan-
ning electron microscope (SEM) micrograph of (a) PDMS mold for plastic casting; (b) the
epoxy chip fabricated by casting. (c) schematic of the casting method showing an elas-
tomer material poured over a molding template, peeled off, and sealed with an appro-
priate substrate, such as glass or silicon, to form microfluidic channels. (For color version
of this igure, the reader is referred to the online version of this topic.)
Therefore, new alternative methods of microfabrication have been devel-
oped that reduce cost by allowing for replication of numerous structures
from one master and offer the ability to use polymeric materials. These
methods are known as soft lithography. The master is produced using con-
ventional microfabrication and is subsequently negatively replicated by rep-
lica molding, hot embossing, or injection molding ( Fig. 10.2 ). 1
Polymers used for microfluidics include, among others, polycarbonate,
polymethylacrylate (PMMA), polyethylene, and PDMS. 6 Rapid prototyping
using replica molding in PDMS was introduced by Whitesides et al. at the
end of the 1990s 7 and since then PDMS has become a key material within
microfluidics. PDMS is extensively used since it is inexpensive, optically
transparent, flexible, biocompatible, impermeable to water but permeable
to gases, and has low electrical conductivity as well as high oxidative and
thermal stability. 8
Irreversible sealing of devices is easily achieved in PDMS without
the need for high temperatures, pressures, or voltages. Exposure to oxy-
gen plasma or coronas 9 creates silanol groups at the PDMS surface