Binding of the Same Analyte to Different Biosensor Surfaces - Biosensors and Biosensor Kinetics - page 157

Suwansara-ard et al. (2009) report that the immunosensors method of detecting CA 125
involves labeling with an enzyme and different steps ( Dai et al., 2003; Bange et al., 2005;
Wu et al., 2006; Fu et al., 2008 ). Suwansara-ard et al. (2009) point out the importance of
label-free detection of CA 125 because it directly permits the detection of changes in the
physical properties involved in the antigen-antibody interactions on the transduction surface.
Tang et al. (2006) have obtained a detection limit of CA 125 of 1.8 units/ml.

Suwansara-ard et al. (2009) report that the SPR biosensors and capacitive immunosensors
have recently attracted substantial attention as direct detection devices ( Berggren and
Johansson, 1997; Limbut et al., 2006; Yin et al., 2006; Dudak and Boyad, 2007; Takamura
and Iwata, 2007; Mazumdar et al., 2008 ). Suwansara-ard et al. (2009) have compared the per-
formance of the SPR biosensor with that of a capacitive immunosensor for the detection of
CA 125. Here only the analysis for the detection of CA 125 by the SPR biosensor is pres-
ented. Anti-CA 125 was immobilized on the gold surface of the SPR biosensor chip using
a self-assembled monolayer. The performance of the different parameters were optimized.
The human serum samples were also analyzed under optimum conditions ( Table 6.12 ).

Figure 6.12 shows the binding of the CA antigen in solution to the anti-CA immobilized on
the SPR sensor chip surface ( Suwansara-ard et al., 2009 ). A single-fractal analysis is ade-
quate to describe the binding kinetics. The values of the binding rate coefficient, k , and the
fractal dimension, D f , for a single-fractal analysis are given in Table 6.2 .

It is of interest to compare the single-fractal analysis binding of the CA antigen in solution
to the anti-CA immobilized on the SPR sensor chip surface ( Suwansara-ard et al., 2009 )
with the binding (cancer monitoring) in mouse 2 and 3 ( Daniel et al., 2009 ). At the outset
it should be noted that the comparison is being made between cancer monitoring in mice
( in vivo ) and the binding of CA in solution to anti-CA immobilized on a SPR biosensor
chip surface. Furthermore, the fractal dimension values obtained for mouse 2 and 3 are
equal to zero. This indicates that the surface acts like a “Cantor-like” dust. The fractal
dimension for the in vitro binding of the CA is 2.1056. As one goes from the in vivo moni-
toring in mice to the in vitro binding of CA, both the fractal dimension and the binding rate

Table 6.12: Binding rate coefficients and fractal dimension for
CA 125 binding to anti-CA 125 immobilized on a surface
prasmon resonance biosensor ( Suwansara-ard et al., 2009 ).

Analyte in Solution/
Receptor on Surface k D f

CA 125/anti-CA 125 2.7070 0.2822 2.1056 0.0892