Study of DNA hybridization on polypyrrole grafted with oligonucleotides by photocurrent spectroscopy.

Recognition of DNA sequences by biochemical sensor is generally performed by analysis after completion of hybridization. Using a technique able to directly translate the biological event into an electrical signal allows the in situ monitoring of the hybridization kinetics. In this aim, the photoelectrochemical behavior of one electroactive polymeric sensor based on a copolymer of polypyrrole and polypyrrole-oligonucleotide has been investigated in aqueous solution. This sensor has been studied as such (i) and in two other situations: (ii) when the copolymer is in presence of non-complementary oligonucleotides; and (iii) when the copolymer is in presence of complementary oligonucleotides. From the photocurrent spectra obtained at -0.6 V/SCE versus incident energy the allowed direct and indirect transitions for each polymer have been evidenced. The photocurrent evolution during hybridization and adsorption processes has been recorded in real time and the hybridization kinetics has revealed to be comparable with mass variations obtained by quartz crystal microbalance under the same experimental conditions.

Electropolymerisable pyrrole-oligonucleotide: synthesis and analysis of ODN hybridisation by fluorescence and QCM.

Conducting polymer films, such as polypyrrole, appear particularly attractive for the immobilisation of biological molecules by entrapment or covalent grafting. We describe here a new pyrrole phosphorarnidite building block allowing the synthesis of oligonucleotide (ODN) bearing a pyrrole moiety. The electropolymerisable pyrrole moiety was then introduced on the 5' end of the oligonucleotide. The electrosynthesis of a copolymer, from solutions containing pyrrole and pyrrole-ODN, gives in one step strongly adhesive films containing ODN probes at electrode surfaces. In this contribution, we have used such a methodology to verify its feasibility for the modification of quartz crystal microbalance (QCM) electrodes. The obtained biosensors enable the detection of DNA hybridisation in real time by micro-gravimetric transduction. Finally, as DNA targets were previously modified by biotin, we have used the affinity between biotin and avidin to validate the effectiveness of QCM transduction by fluorescence microscopy and to amplify the recorded micro-gravimetric signal.