Direct Deposition of Nanomaterials onto Cells - Cell Surface Engineering: Fabrication of Functional Nanoshells - page 40

receptor proteins with a high anity to Ca 21 -ions serve as binding sites for
Ca 21 -Au nanoparticles. Interestingly, it was found the deposition of Ca 21 -
AuNP depended on the generation of the yeast cells. The younger cells
showed a denser deposition of nanoparticles on their surfaces whereas older
cells were less prone to Ca 21 -Au immobilization resulting in a poor coating
by Ca 21 -AuNP. This effect can be explained by the higher metabolic activity
of younger cells. Mg 21 ions were also utilized in this immobilization strategy
and showed a similar uniform deposition of Mg 21 -Au on yeast cells. How-
ever, no age discrimination was observed. It is proposed that both younger
and older cells possessed a similar Mg 21 ions uptake rate. Thus, using
biologically important ions as mediators represents another attractive route
for selective deposition of nanoparticles onto cells due to its biocompati-
bility, low toxicity, and specificity.
The development of nanotechnology enables scientist to create new smart
materials with controllable properties particularly with high anity to the
cell surface. Janus nanoparticles, called nanocorals, were engineered using
nanosphere lithography techniques for specific attachment to the cells and
sensing via surface-enhanced Raman spectroscopy (SERS). This polystyrene-
based nanocoral is divided into two distinct parts with different function-
alities. One half of the nanocoral serves for antibody mediated cell targeting
while the other half, coated with a gold layer, enhances the SERS signal. As a
result, anti-HER-2 antibody-modified nanocorals were able to specifically
target breast cancer cells that overexpress human epidermal growth factor
receptor 2 (HER-2). 31
New strategies to control the deposition and orientation of nanomaterials
onto the cell are relevant for the development of two fields. The functiona-
lization of the cell surface to create cell-nanomaterial hybrids and ecient
drug delivery. Though these two fields have different goals, they are con-
nected by the cell surface because the interaction and orientation of nano-
materials on the cell surface can drastically alter their internalization into
the cytoplasm. Cellular backpacks 32 and polymeric microtubes 33 are new
smart materials that are able to specifically attach to the cell membrane and
further promote delivery of their active agents into mammalian cells. De-
signed by photolithographic techniques, layer-by-layer assembly, and spray
deposition the cellular backpacks represent multilayered disk-shaped
structures doped with magnetic nanoparticles to provide mechanical rigidity
and loaded with fluorescein-labeled bovine albumin as a prototype of an
active agent or a drug. The final layers of hyaluronic acid and chitosan
mediate the backpack's deposition onto a macrophage's cell membrane due
to specific interactions of hyaluronic acid with CD44 cell receptors. As a
result, the obtained cellular backpacks showed strong attachment to
macrophages surfaces without internalization and were able to release a
model protein in a controllable manner in vitro, thus providing a promising
new tool for ecient drug delivery. 32 Extending this approach, nanometer
thickness films were folded into microtubes using a sacrificial track-etched
membrane as a template. Three types of chemically nonuniform microtubes

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