Binding of the Same Analyte to Different Biosensor Surfaces - Biosensors and Biosensor Kinetics - page 133

Abu-Rabesh et al. (2009) point out that biosensors have been used for the detection of pathogens
including E. coli ( Ivnitskii et al., 1999; Leonard et al., 2003; Tokarsky and Marshall, 2008 ).
Electrochemical biosensors have also been used previously to detect E. coli ( Abdel-Hamid
et al., 1999a,b; Mittelmann et al., 2002; Palenzuela et al., 2004; Lin et al., 2008a,b,c ).
Abu-Rabesh et al. (2009) indicate that the number of electrochemical platforms for E. coli
detection by biosensors has grown rapidly ( Bakker, 2004; Mehavir and Abidi, 2004 ).

Abu-Rabesh et al. (2009) have developed an alternative immunosensing approach for the
amperometric detection of E. coli . Their method is based on electropolymerization and coat-
ing of GCEs with polypyrole-amine (Pyy-NH 2 ). Figure 6.1a shows the binding of 10 7 CFU
E. coli with lysozyme to the amperometric immunosensor with PAPG. A single-fractal anal-
ysis is adequate 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 6.1 .
Figure 6.1b shows the binding of 10 7 CFU E. coli without lysozyme (control experiment) to
the amperometric immunosensor with PAPG. Once again, a single-fractal analysis is ade-
quate to describe the binding kinetics. It is interesting to note that as the fractal dimension
decreases by a factor of 3.2 from a value of D f equal to 1.6998 to 0.5270, the binding rate
coefficient for E. coli decreases by a factor of 1.74 from a value of k equal to 0.8083 to
0.4647. Note that changes in the degree of heterogeneity or the fractal dimension and in
the binding rate coefficient are in the same direction.

Lee et al. (2009) have developed a method to detect E. coli based on immunomagnetic sepa-
ration and real-time PCR amplification of aptamers. These authors indicate that aptamers are
single-stranded DNA or RNA molecules, which can bind to their targets with high specificity
and affinities ( Ellington and Szostak, 1990; Hermann and Patel, 2000). Lee et al. (2009) point

3

2.5

2

1.5

1

0.5

0

0 2 4

Time (min)

Figure 6.1
Binding of 10 7 CFU/ml E. coli to the amperometric biosensor with PAPG as a substrate
( Abu-Rabesh et al., 2009 ).