This paper presents evidence and some preliminary explanation for the existence of a steric effect in polypyrrole/oligonucleotide (PPy/ODN) nanocomposite film, which may be responsible for the high electrochemical sensing performance of that nanofilm when being used in DNA hybridization detection. When hybridization occurs in this nanocomposite film, the steric effect in the immediate interface of the hybrid film can damp the ion-flux penetrating
through this interface, thus resulting in the signal differentiation on the electrode electrochemical property. Electrochemical cyclic voltammetry (CV) combined with atomic force microscope (AFM) were utilized to clarify the hindering mechanism occurring on such interface. Furthermore, the hybridization reaction of ODN probes in the hybrid PPy/ODN film with
their complementary DNA sequences was measured via CV, with the target ODN concentrations as low as 5310218 mol/L. Under optimized hybridization conditions the sensor response was almost linear, with the logarithm of the target ODN concentration ranging from 1310218 to 1310211 mol/L. These results may be useful in the development of a much simpler labelfree DNA sensor based on the PPy/ODN nanocomposite film.