New immobilisation method for oligonucleotides on electrodes enables highly-sensitive, electrochemical label-free gene sensing.

We present a versatile and facile procedure for the immobilisation of bioprobe molecules to an electrochemical sensing element. We eliminate lengthy preparation procedures for direct functionalisation of electrode surfaces by pre-attaching probe molecules to carboxylic acid bearing termonomers of pyrrole phenylenes or thiophene phenylenes. We demonstrate that these conjugates can be electrodeposited at low potentials to form nano-scale porous, electroactive conducting polymer films, exposing the bioprobe and retaining activity and specificity for binding, exemplified here with DNA sensors. The electrochemical reaction impedance for Fe(CN)6 3-/4- on oligonucleotide-modified electrodes showed remarkable (down to aM) detection sensitivity for target DNA sequences present in solution. Cross-sensitivity to non-complementary target sequences is small and multi-target arrays are easily made. There is no need for labelling of either probe or target oligonucleotide.