Electrical resistivity dependence of semi-conductive oxide electrode on the label-free electrochemical detection of DNA

The paper reports on the influence of electrical resistivity of bio-modified transparent and conductive oxide (TCO) electrodes on the sensitivity to DNA hybridization in term of impedance variation. We have deposited pure cadmium indate (CdIn2O4) film electrodes on glass substrates by aerosol pyrolysis. By adjusting the film deposition conditions, films with a wide range of resistivity ranging between 4 × 10−4 and 2 × 10−3 Ω cm were obtained. Using electrochemical impedance spectroscopy (EIS), we showed that the behaviour of bare films is typical of semiconductor electrode with flat band potentials depending on the film resistivity. Then we studied the electrochemical behaviour of the biomodified electrodes before and after DNA hybridization. The impedance variation due to DNA hybridization was particularly studied in the low frequency range where large and significant increases were observed. These increases were studied in term of calculated polarisation resistance Rp. For all films, Rp variation is potential dependant and is maximum between −0.1 and 0 V/ref. In this range of potential, the magnitude of this variation increases with the film resistivity. This behaviour is explained by the relationship between the field effect phenomenon, the thickness of the space charge region and the film electrical resistivity. This work shows that, in the case of metallic semi-conductive oxide electrode, the sensitivity to the DNA detection increases with the electrode resistivity.