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-controled 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 mum microelectrodes, quartz crystal microbalance (QCM) and a non patterned gold/glass slide bearing 500 mum 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. (C) 2003 Elsevier Science B.V. All rights reserved.