Osmium tagged probes for nucleic acid detection

An osmylated single-stranded oligonucleotide probe molecule for use in detecting a target nucleic acid molecule, the osmylated-probe comprising at least one thymidine (T) residue covalently bonded to an Osmium tetroxide (OsO4)-2,2′-bypyridine group (OsBp group) and comprising a sequence that is at least partially complementary to the sequence of the target nucleic acid molecule sufficient to create a hybridized double-stranded complex:

• (i) wherein the osmylated probe comprises at least three adjacent thymidine (T) residues located at the 5′-end of the probe or wherein the osmylated probe comprises at least three adjacent thymidine (T) residues located at the 3′-end of the probe, wherein one or more of said 5′-end or 3′-end adjacent T residues does not hybridize to the target nucleic acid molecule;
• (ii) wherein T residues in the probe sequence, other than the adjacent T residues located at the 5′-end or the 3′-end of the probe, are replaced in the probe molecule by uridine (U), 2′-OMe-Uridine (mU), or deoxyuridine (dU);
• and
• (iii) wherein the osmylated probe further comprises one, two, three, four, five, or six adenosine residues (dA or A) at the 5′-end of the probe or at the 3′-end of the probe, wherein one or more of said 5′-end or 3′-end adenosine residues (dA or A) does not hybridize to the target nucleic acid molecule.