Electronic DNA hybridisation detection in low-ionic strength solutions

Fast DNA detection remains of great interest in human genetics, medicine, and drug discovery. The detection of DNA hybridisation makes the screening of point mutations in potential cancer genes or DNA fingerprinting for phylogenesis purposes possible (S.W. Yeung, T.M.H. Lee, H. Cai, and I.M. Hsing, A DNA biochip for on-the-spot multiplexed pathogen identification, Nucleic Acids Research 34 (2006), p. e118; P. Liepold, H. Wieder, H. Hillebrandt, A. Friebel, G. Hartwich, DNA-arrays with electrical detection: a label-free low cost technology for routine use in life sciences and diagnostics, Bioelectrochemistry, 67 (2005), pp. 143-150). The speed, cost and reliability of the hybridisation detection is of high importance. Electronic detection of hybridisation events using standard CMOS-fabricated devices such as Field Effect Transistors (FETs) promises fast, label-free and multiplexed read-out systems. Moreover, they hold the advantage of high-throughput and minimalisation, which makes them ideal for implementation in fast diagnostic tools such as lab-on-chip systems. Field-effect devices, however, imply the necessity of low-ionic strength buffer solutions for signal maximisation because of the occurrence of charge screening effects near the electrolyte-oxide interface layer. In this article, we present a surface chemistry-based methodology that allows FET-based recordings of hybridisation events in low-ionic strength solutions. Quartz Crystal Microbalance results show that positively-charged surfaces promote DNA hybridisation, even when performed in lower salt concentrations then commonly used. Fluorescence measurements were performed on the different surfaces to reveal the optimal DNA adsorption conditions on the surface. For proof-of-principle, the surface chemistry was applied on the surface of a floating-gate field-effect transistor, and online recordings of DNA hybridisation events were performed in low-ionic strength solutions.