Biomedical Engineering Reference
In-Depth Information
protein. The relative intensities of the ion fragments detected in static SIMS
are sensitive to the orientation of the protein on the surface and its degree
of conformational alteration.
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As protein adsorbs to the NM surface it may
undergo changes in its conformation or orientation allowing new regions of
the protein with different amino acid compositions to be more exposed to the
SIMS sampling depth.
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2.6.4 Colorimetric Methods
Colorimetric methods are used to establish the optical characteristics of NMs as
well as their concentrations. Furthermore, colorimetric methods are also used
to establish the concentrations of proteins. When the wavelengths of maximum
absorption for the NMs and the proteins do not overlap, these can be used to
establish the identity and quantity of both the NMs and the proteins from the
same sample. These properties can be used when controlling tissue regeneration
on NMs that serve NMs as scaffold surfaces. The bicinchoninic acid (BCA)
method is an effective approach to determine the amount of adsorbed protein on
NM surface and kits are commercially available for this purpose.
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However,
the BCA method cannot be used when protein concentration is lower than its
detection limit.
2.6.5 AFM
One of the earlier methods of characterizing NMs is through AFM. AFM can
be used to qualitatively determine the topography of NMs. AFM technique is
based on surface analysis through a precise small-scale movement of a piezo-
electric scanner against a sharp tip mounted at the end of a cantilever. AFM
is advantageous because of minimal sample preparation in comparison with
other imaging techniques (such as SEM or TEM). Unlike SEM or TEM, AFM
can produce detailed three-dimensional rather than two-dimensional images
without the need for a vacuum providing a potential to image samples in ambi-
ent air or liquid.
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Because of this, AFM is used to view and scan samples in
their quasi-native environment for real-time imaging of live biological samples.
AFM provides distinct topographic contrast with direct height measurements
and a direct view of surface features for nonconductive materials (such as poly-
mers and biological tissues)
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but the depth of the field of view for AFM is
limited by the travel distance of the piezoelectric tube as well as the cantilever
tip size and geometry.
2.6.6 DLS for Zeta Potential
Zeta potential can be measured by dynamic light scattering (DLS) using
a Zetasizer Nano ZS instrument (Malvern). One example of this process is
to measure the zeta potential of Si nanocrystals. The average hydrodynamic
