Biomedical Engineering Reference
In-Depth Information
but also biological structures.
10
In this technique, AFM is combined with a
confocal Raman microscopy, where laser light is focused onto the AFM tip
coated with gold. Molecular level information from a sub-100 nm region can
be obtained with the technique.
The type of material used is the second parameter for decision making
for which spectroscopic technique should be used for characterization. For
example, if it is a polymer with a fluorescing property, fluorescence based
microscopic techniques such as fluorescence and confocal microscopy
should be used to confirm the coating. Upon attachment of a nanomaterial
with a high density, either SEM or TEM should be used for the localization.
The visualization of AuNPs and AgNPs attached onto S. cerevisiae cells and
T. asperellum conidia with TEM can be given as an example.
11
For clarity, the
steps of the coating procedure of yeast cells are provided in Figure 5.1.
During the first step (1), the intact cells are coated with a triple layer of either
PAH/PSS/PAH or BSA/DNA/BSA. In the second step (2), the polyelectrolyte-
coated cells are further coated with either AuNPs or AgNPs and finally in the
last step (3) the polyelectrolyte and metal NP-coated cells were treated with a
double layer of PAH/PSS or BSA/DNA. Although a color change upon coating
the cells with AuNPs or AgNPs due to the scattered light from the noble
metal NPs is observed, indicating the presence of metal NPs in the sus-
pension containing cells, it is necessary to confirm the metal NPs in this
particular case, and nanomaterials in general, are on the cell surface and
cannot be released in the suspension or leaked into the cells. Figure 5.2
shows the TEM images of a S. cerevisiae cell coated with AuNPs and AgNPs.
As seen from the TEM images, AuNPs or AgNPs are clearly attached onto the
d
n
8
y
4
n
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0
.
Figure 5.1
Schematic representation of the coating of S. cerevisiae cells and
T. asperellum conidia with the polyelectrolyte shells and AuNPs or AgNPs.
(Reprinted with permission from ref. 11. Copyright 2009 the American
Chemical Society.)
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