Abstract: The present invention relates to a voltammetric sequence-selective sensor for target polynucleotide sequences which essentially comprises: an immobilized polynucleotide probe having one end covalently bound onto an amperometric electrode. The immobilized probe includes a target binding region capable of hybridizing to the target polynucleotide sequences forming an immobilized heteroduplex having at least a hybridized region. The sequence-selective sensor of the present invention also comprises means for voltammetrically detecting immobilized heteroduplexes. There is also provided a method for detecting the presence of a target polynucleotide analyte in a physiological sample, which comprises the steps of incubating the prepared physiological sample with the voltammetric sequence-selective sensor of the present invention; voltammetrically detecting immobilized heteroduplexes; and comparing the resulting voltammogram with a control voltammogram.