Polypyrrole based DNA hybridization assays: study of label free detection processes versus fluorescence on microchips

In this paper, we present different ways to detect DNA hybridization on a solid support. The grafting chemistry is based on the electro-controlled copolymerization of a pyrrole-modified oligonucleotide and pyrrole. This process allows an easy functionalization of conducting materials. Three kind of devices were studied: silicon chips bearing an array of addressable 50 or 4 microm microelectrodes, quartz crystal microbalance (QCM) and a non patterned gold/glass slide bearing 500 microm spots. Each device is compatible with a specific detection process: a classical indirect fluorescence detection for the microchips, a microgravimetric measurement for the QCM and a surface plasmon resonance imaging process (SPRi) for the gold slides. Both QCM and SPRi are a label-free real time detection process whereas the fluorescence methodology gives end-point data but only the fluorescence and the SPRi give multiparametric results. Although the hybridization experiments show that the detection limit for an oligonucleotide is better for the fluorescence (1-10 pM) than that found for SPRi (10 nM) and QCM (250 nM), the information content of real time measurement techniques such as SPRi is of interest for many biological studies.