Conjugated polymer-based DNA chip with real time access and femtomol detection threshold

A multiplot DNA-biosensor has been realized on a plastic chip, by the controlled electropolymerization of a thin film of an electroactive pyrrole-based copolymer, poly[pyrrole-COOH, pyrrole-ODNprobe], onto eight gold microelectrodes deposited on the chip. The electrochemical signature of these polypyrrole films vary upon hybridisation of the grafted ODN probes with complementary ODN targets present in an aqueous analyte solution. This direct transduction of the recognition process into an electrical signal allows a real time access to the sensing process, bypassing the conventional tagging step required in other biosensors. It is shown that the key factor governing the detection threshold of these biosensors concerns the quantity of ODN probes deposited on the microelectrodes. By varying the pyrrole-ODN/pyrrole-COOH ratio in the film and by tuning it to the quantity of ODN targets present in the analyte solution, a detection threshold value of 2 × 10−15 mol of ODN target in 2 mL hybridisation solution has been experimentally obtained. The discussion of this very low detection threshold led us to propose the existence of an amplification factor in the electrochemical response of a conjugated polymer-based (bio)sensor.