Electropolymerization as a versatile route for immobilizing biological species onto surfaces - Application to DNA biochips

Biosensors based on electronic conducting polymers appear particularly well suited to the requirements of modern biological analysis-multiparametric a ssays, high information density, and miniaturization. We describe a new met hodology for the preparation of addressed DNA matrices. The process include s an electrochemically directed copolymerization of pyrrole and oligonucleo tides bearing on their 5' end a pyrrole moiety. The resulting poly mer film deposited on the addressed electrode consists of pyrrole chains bearing co valently linked oligonucleotides (ODN). An oligonucleotide array was constr ucted on a silicon device bearing a matrix of 48 addressable 50 x 50 mum go ld microelectrodes. This technology was successfully applied to the genotyp ing of hepatitis C virus in blood samples. Fluorescence detection results s how good sensitivity and a high degree of spatial resolution. In addition, gravimetric stud ies carried out by the quartz crystal microbalance techniq ue provide quantitative data on the amount of surface-immobilized species. In the case of ODN, it allows discrimination between hybridization and nons pecific adsorption. The need for versatile processes for the immobilization of biological species on surfaces led us to extend our methodology. A biot inylated surface was obtained by coelectropolymerization of pyrrole and bio tin-pyrrole monomers. The efficiency for recognition (and consequently immo bilization) of R-phycoerythrin-avidin was demonstrated by fluorescence dete ction. Copolymerization of decreasing ratios of pyrrole-biotin over pyrrole allowed us to obtain a decreasing scale of fluorescence.