Biology Reference
In-Depth Information
Figure 6.7.
Electrochemicalimpedancespectroscopycharacteristicsfora
Au electrode with ssDNA and after hybridization.
method the sample-to-sample variability was reduced as compared
to previously reported immobilization methods. The ratio on the
surfacewasapproximatelyequaltothatinthesolutiononlyforDNA
mole fractions lower than 0.3%.
Electrostatic repulsion between the immobilized negatively
charged oligonucleotide probes and negatively charged ferri/
ferrocyanide redox couple in solution results in a modulation of the
charge transfer resistance with probe surface density. The increase
in negative charge at the sensor surface upon hybridization only
results in a modulation of charge transfer resistance at probe
densitiesabove2.5
×
10
12
cm
−
2
[37].Thisthresholdisprobablydue
to counterion screening of the oligonucleotide charge resulting in
channels between probes through which the mass transport of the
ferri/ferrocyanide redox couple is unaffected.
