The invention provides a method of probing for a nucleic acid comprising: contacting a nucleic acid solution with an oligonucleotide probe labelled with an electrochemically active marker, providing conditions at which the probe is able to at least partially hybridize with any complementary target sequence which may be present in the nucleic acid solution, selectively degrading either hybridized, partially hybridized or unhybridized nucleic acid probe, and electrochemically determining information relating to the electrochemically active marker. The invention further provides novel molecules with use in methods of the invention.