Electrochemical assay for nucleic acids and nucleic acid probes

A method of assay for determining a target nucleic acid sequence comprising:

• (a) providing, (i) an electrode in contact with an enzyme and a substrate of the enzyme, and a mediator compound associated with the enzyme to transfer charge from the enzyme to the electrode as the conversion of substrate into product proceeds, and (ii) a probe nucleic acid sequence complementary to said target sequence which is linked to either the enzyme or the mediator compound;
• (b) measuring a modification in the activity of the enzyme and the mediator compound and hence the quantity of charge being transferred to the electrode resulting from the binding of said target sequence to the probe nucleic acid sequence, and (c) relating said measurement to the determination of said target nucleic acid sequence.

A nucleic acid probe for establishing the presence or copy number of a given target sequence in a single-stranded nucleic acid molecule, said nucleic acid probe being linked to

• (a) either a metallocene mediator compound or an enzyme electrochemically coupled to an electrode by a metallocene mediator compound, and,
• (b) biotin,
• wherein binding of the probe nucleic acid to the target sequence modifies the electrochemical coupling between the metallocene mediator compound and the enzyme.

A nucleic acid probe comprising:

• (a) a nucleic acid strand complementary to a target nucleic acid sequence, and
• (b) a metallocene mediator chemically linked thereto, wherein said mediator transfers charge from a catalytically active enzyme to an electrode.