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Figure 2.7. The electrochemical detection system for oxyteracycline
(OTC)using aptamer-immobilized interdigitated array (IDA)gold electrode
chip. Left: An IDA gold electrode chip and the IDA gold electrode. Right: A
typical electrochemical reaction occurring after aptamer binds to its target
molecole.
A very interesting biosensor was developed based on a similar
principleforthedetectionofcancercells[34].Theaptamerselected
for acute leukaemia cells was fixed onto a gold electrode and elec-
trochemical impedance spectroscopy (EIS) technique was used to
characterizethesurfacewith[Fe(CN) 6 ] 3 / 4 asaredoxprobe.Upon
binding of the aptamer-modified electrode with leukaemia cells,
the electron-transfer resistance of [Fe(CN) 6 ] 3 / 4 on the sensor
surface increased substantially. A linear relationship was observed
between the electron-transfer resistance and the concentration of
the leukaemia cells in a range 1 × 10 4 to 1 × 10 7 cells/mL with a
detection limitof 6 × 10 3 cells/mL and high selectivity.
2.8 Electrochemical Aptasensors Based on the Aptamer
Conformational Changes
Aptamers bind their targets through adaptive recognition; in solu-
tionaptamersareunstructured,butfolduponassociatingwiththeir
molecular targets into molecular architectures in which the ligand
 
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