A series of novel, surface-active, inorganometallic complexes of osmium were synthesized and then characterized (using electrochemical techniques) as electron transfer mediators for glucose oxidase (EC 220.127.116.11, GOD) from Aspergillus niger. The mediators contain a dipyridylamine ligand bearing (on the amine nitrogen) a saturated alkyl chain (typically C5 to C12), ω-terminated with either a methyl group or a functional group such as carboxyl or hydroxyl. Such compounds displayed subtle differences in their interactions with GOD. The presence of a ω-functional group tended to diminish a mediator's micelle-forming activity, but also concomitantly decreased the denaturing action of the mediator towards the protein structure of GOD. However, the presence of an ionised carboxyl group slowed GOD mediation relative to that of similar mediator bearing a methyl-terminated long alkyl chain, probably because of the additional negative charge. The ω-carboxyl functionality allowed covalent coupling of mediators to NH2-bearing graphite electrodes. GOD was co-immobilized and the resulting, reagentless, glucose-sensitive electrodes were characterized. Immobilization of the mediator did not appear to affect unduly the ability to mediate GOD. Additionally, complexes were directly coupled to lysine groups of GOD to give a self-mediating enzyme.