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are at the confluence of the smallest of human-made devices and the largest
of these biomolecules, and the controlled synthesis followed by the directed
assembly of nanoscale synthetic components can lead to nanostructured sub-
strates that interact with cells at the molecular level.
One example of a hybrid nanostructured substrate/whole-cell device comes
from the field of biomedical devices in the area of transplanted cells for the
treatment of hormone deficiencies arising from diseases such as Type I dia-
betes. The transplant of islet cells from other animals into human diabetics
(xeno-transplantation) is seen as a promising approach to the careful control of
blood sugar levels; these cells can both sense glucose and respond by producing
insulin in a closed-loop system. For this strategy to work, the transplanted cells
must be isolated from the patient's immune response to maintain their viability.
Recent work has focused on the development of biocompatible nanoporous
capsules that allow the free flow of glucose, insulin, and other essential nutri-
ents for the islets, yet inhibit the passage of larger entities associated with an
immune response [38]. The result is a hybrid device where all the information
processing and actuation are performed by the cells, and a synthetic nanostruc-
tured substrate manipulates the molecular communication with these cells to
allow their functionality while maintaining their viability.
In the example above, the genetic circuits of the cells were evolved to per-
form the required functions, and the nanostructured portion of the synthetic
device was only required to manipulate molecular communication through size
discrimination. To use the complex functionality of the cells as envisioned
here, a more complete molecular connection between the cells and substrate is
required. Toward this goal, luminescent semiconductor quantum dots have been
derivatized with biomolecules and used as fluorescent probes in intracellular
assays [10, 13]. Although this enhances communication from the molecular
processes of cells, it does not allow communication to or control of these pro-
cesses. However, electronic control over the local hybridization behavior of
DNA molecules by inductive coupling of a radio-frequency magnetic field to
metal nanocrystals covalently linked to DNA was recently reported [28]. To
move further along this path of controlling molecular processes and bidirec-
tional communication between cellular components and nanostructured sub-
strates requires the controlled synthesis of nanoscale elements that interface
with cells and their integration into microscale devices.
We have recently begun investigating the controlled synthesis of individu-
ally addressable, vertically aligned carbon nanofiber (VACNF) elements (Figure
8.6), focused on the synthesis, surface modification, and chemical derivitization
of these nanoscale structures. VACNFs are synthesized in a plasma-enhanced
chemical vapor deposition process and grow perpendicular to the substrate from
metal catalyst particles. We have demonstrated that VACNF synthesis is an ex-
tremely flexible method for the directed assembly of nanoscale features within
