Biomedical Engineering Reference
In-Depth Information
circumstances this mechanism might be advantageous. This will depend, the authors indicate,
on the particular parameters that characterize a specific device implementation.
Solomon and Paul (2006)
also attempted to analyze the influence of convection on these
types of BioNems devices. Using simple fluid dynamics arguments these authors show that
at the bulk flow velocities used in these devices and for Damkohler (
Da
) numbers less than
unity, capture efficiencies would be dominated by reaction-diffusion mechanisms. In other
words, convection will only play a minor role. They emphasize that for Damkohler numbers
1, the reaction-diffusion-convection coupled equations need to be solved to obtain a better
perspective of analyte-binding kinetics to receptors immobilized on these nanoscale sensors.
2.2.8 Probing the Functional Heterogeneity of Surface Binding Sites Along with
the Effect of Mass Transport Limitation and Its Influence on Binding and
Dissociation of Analytes on Biosensor Surfaces (
Svitel et al., 2007
)
Svitel et al. (2007)
have recently probed the functional heterogeneity of surface binding
sites under the influence of external mass transport limitations. They did this by analyzing
experimental binding traces. These authors point out the need to analyze the binding of
macromolecules to surfaces assuming that the surface binding sites are heterogeneous (
Sips,
1948; Koopal and Vos, 1993; Vijayendran and Leckband, 2001; Lebedev et al., 2006
).
Svitel
et al. (2007)
suggest that that there may be two (or more) reasons for inhomogeneity on the
surface during the interactions of analyte-receptors on the sensor surface: (a) the surface sites
may be intrinsically inhomogeneous in their binding properties, and (b) the receptors may be
rendered heterogeneous by attaching them to the surface.
Yeung and Leckband (1997),
Rabbany et al. (1997), and Kloss et al. (2000)
have pointed out that the immobilization of
chemically homogeneous species frequently results in functionally impaired subpopulations
due to (a) constraints in orientation, (b) variable cross-linking, and (c) the influence of the
microenvironment of the surface. This heterogeneity,
Svitel et al. (2007)
explain, will influ-
ence the application of antibody-based affinity biosensors (
Wilson and Nock, 2002; Taitt
et al., 2005
), and the analysis of protein interactions by SPR biosensors (
O'Shannessy,
1994; O'Shannessy and Winzor, 1996
;
Schuck, 1997
).
Svitel et al. (2007)
explain that evanescent field biosensors have been used to characterize
protein-protein, protein-small molecule, protein-nucleic-acid interactions, and DNA hybrid-
ization reactions (
Cooper, 2002; Livache et al., 2003
). These biosensors have allowed the
kinetic binding traces to be measured with high sensitivity.
Svitel et al. (2007)
, however, also
point out that these binding traces when analyzed kinetically are apparently not consistent
with a simple 1:1 interaction (
Karlsson et al., 1994; Glaser and Hausdorf, 1996; Schuck,
1997; Schuck et al., 1998
).
Svitel et al. (2003)
attempt to interpret these deviations from a
simple 1:1 interaction as a source of information on the homogeneity of the surface
immobilized sites. They have proposed a computational model that assumes that the binding
