206 P. Y. J. Yeh, J. N. Kizhakkedathu and M. Chiao
Figure 9.1. Schematic diagram of the proposed piezoelectric membrane as an implantable
sensor coating. The membrane is composed of two driving electrodes with a piezoelectric
material in between. Adsorbed protein can be desorbed by an electric field and carried
away by acoustic flow generated by the vibration. Reproduced with the permission from
Yeh et al. (2007).
MEMs fabricated device is evaluated by the criteria of protein quantity on the
surface. Figure 9.1 shows the schematic diagram of an antibiofouling mechanism
which is able to integrate an implant, such as, biosensor. Three steps of this
mechanism shown in the Fig. 9.1 are: (1) protein adsorption, (2) protein desorption
by surface charges, and (3) the desorbed proteins swept by the flow.
9.2 PROTEINS VISUALIZATION
There are many methods to identify or visualize the protein adsorbed on the
surface, to name a few, silver stain, radioactive labeling, reverse stain, fluorescence,
chemiluminescence,
41
AC impedance, quartz crystal nanobalance,
42
and so on.
Mainly the fluorescence detection and the electrochemical impedance measure-
ment are used to investigate the adsorption of proteins In this chapter. Fluores-
cence detection can determine the relative amount of adsorbed proteins,
10,43,44
the
advantage of this method is its linearity (intensity vs quantity) and sensitivity. It
is a relatively convenient method to detect proteins. By attaching fluorescence
dyes of emitting different colors, it is easy to identify different proteins on the
surfaces.
45
But it is not the best method to quantify adsorbed proteins especially
if the substrate has a fluorescence background. The electrochemical impedance
spectroscopy (EIS), on the other hand, is sensitive to the adsorption on interface.
It also can be used to investigate the dynamic adsorption behavior of protein and
the thickness of adsorbed proteins.
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