The Device Science of Whole Cells as Components in Microscale and Nanoscale Systems - Cellular Computing - page 78

Information processing: what are the information processing pathways,
and how can these be manipulated to produce a desired result?
Communications: what are the modes of communication (interconnec-
tivity, input/output), and how can they be manipulated to allow for the
realization of complex functionality through high interconnectivity?
Fabrication and integration: how can the components be physically ar-
ranged, packaged, and their functionality maintained or even enhanced
within micro- and nanostructured substrates?
Design, modeling, and simulation: how can the devices be modeled in a
way that allows the simulation required for complex system design?
Apart from the scientific pursuit of elucidating cell function, the answers to
these questions, from the point of view of the device designer, define the device
science of whole cells as components in microscale and nanoscale systems.
Cells as Bulk and Discrete Components
The cellular components in whole-cell devices can be used as bulk components
that rely on the average activity of groups of cells. Such devices usually per-
form a chemical or biological sensing function where the bulk reaction of cells
to a particular stimulus is detected by a synthetic system. Cell-based sensing
systems often couple a molecular-sensing element to a reporter gene through
gene fusion, thereby allowing the use of regulatory proteins and promoter se-
quences of chromosomal or plasmid DNA as the molecular-sensing elements
[18]. The specificity of these elements produce system selectivity and analytical
sensitivity, while the reporter gene product, in combination with the synthetic
transducer, determine system sensitivity and detection limits.
An alternate approach would be to use individual or small groups of cells as
discrete components in engineered systems. This would include larger collec-
tions of cells, such as biofilms or tissues, where individual or small groups of
cells perform information processing that lead to group behavior through inter-
connection of these discrete elements. The information transport path shown in
Figure 5.1 illustrates the contrast between cells as bulk and discrete components.
The use of whole cells as bulk or discrete components greatly affects the func-
tional density (i.e., amount of information processing per unit area), the noise
performance, input/output strategies, packaging, and through these, the ultimate
application space of particular cell-based systems. To this point the dominant
use of whole cells in microscale systems has been as bulk components, the
major exception being tissue- or biofilm-based devices. Therefore, many of the
technological challenges such as packaging and integrating cells into these mi-
croscale systems have been addressed in the context of bulk whole-cell devices.