Semiconductor oxide based electrodes for the label-free electrical detection of DNA hybridization: Comparison between Sb doped SnO2 and CdIn2O4

First results are reported regarding the design, fabrication and operation of a DNA biochip based on a semiconductor oxide electrode that employs label-free electrical detection of the DNA hybridization. The same process of DNA functionalisation, including hydroxylation and silanization steps, was performed on two types of semiconductor oxide: Sb doped SnO₂ and CdIn₂O₄ thin films. These oxide electrodes were laboratory-made films deposited on glass substrates using a chemical vapour deposition method, i.e. the aerosol pyrolysis technique. After having characterized some physico-chemical properties of the bare films, the label-free electrical DNA hybridization detection, without redox couple labelling, was performed using electrochemical impedance spectrometry (EIS) before and after hybridization. On both oxides, over a large frequency range, a significant increase in the impedance modulus was obtained. The increase in the case of CdIn₂O₄ was by a factor of 2.1 ± 0.5 and in the case of Sb doped SnO₂ was by a factor of 1.6 ± 0.1. This phenomenon was especially marked on CdIn₂O₄ thin films, which exhibit a higher sensitivity to the surface event. The DNA hybridization to complementary DNA targets labelled with fluorescent markers was confirmed using fluorescence microscopy.