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Figure 8.3 The integrated circuit portion of the BBIC. This integrated circuit was
fabricated in a 0.5- µ m, bulk, complementary, metal-oxide-semiconductor (CMOS)
process. The chip measures approximately 2.2 mm on each side.
Bioreporter Entrapment
Entrapment of the bioreporters to the light-sensing portion of the integrated
circuits presents unique challenges. The entrapment matrix must have mechan-
ical strength, long shelf-life, resist dehydration, be nontoxic to the entrained
cells and the environment, be nonpolluting, and have maximum cell retention.
Further, the entrapment matrix must be porous to facilitate mass transfer of
analytes, oxygen, and other essential nutrients. Because of the optical mode
of communication common to many whole-cell devices, the matrix must be
transparent or at least translucent and adhere to the light-sensing portion of the
IC. The following subsection highlights the more widely used matrices.
Natural Polysaccharides
Alginates, agarose, and
-carrageenan are natural polysaccharides. Alginates,
produced by brown algae and certain bacterial species [11, 21, 22], are linear
polymers of
κ
(1,4)-L-guluronic acid monomers.
Alginates, depending on the algal source, vary in their composition, chain
length, and arrangement and thus have variable properties. A cross-linking
network is formed by the process of ionic gelation, bonding of Ca + 2 ions with
polyguluronic moieties of the polymer strands [11]. Sr + 2 can be substituted for
the Ca + 2 , improving the mechanical stability of the matrix [31]. Alginates with
a higher guluronic acid content bind more Ca + 2 resulting in a stronger ma-
trix. Ionic bonding occurs immediately and is usually complete in 30-60 min
depending on the cell, alginate, and Ca + 2
β
(1,4)-D-mannuronic acid and
α
concentrations [24]. Ionic gelation
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