Abstract: Complexes of the general formula I ##STR1## wherein R.sub.1, R.sub.2 and R.sub.3, which may be the same or different, each represent a straight or branched alkyl radical having 1 to 5 carbon atoms or together with the adjacent nitrogen atom a heterocyclic radical having 5 to 7 carbon atoms; "alk" represents a straight or branched alkylene radical having 1 to 5 carbon atoms; R.sub.4 to R.sub.8, which may be the same or different, represent hydrogen, or a hydroxy, alkoxy, aryloxy or primary secondary or tertiary amino group, or the group -alk-N.sup.+ (R.sub.1 R.sub.2 R.sub.3) wherein "alk", R.sub.1, R.sub.2 and R.sub.3 have the meanings given above; M represents a transition metal such as Fe, Ru or Os; X represents an anion and n is an integer corresponding to the number of positive charges of the complex.

Abstract: Mono, bis and tris(substituted 2,2'-bipyridine) complexes of iron, ruthenium, osmium or vanadium are described wherein the bipyridine is substituted by a hydroxy or alkoxy group, or a primary, secondary or tertiary amine group.

Abstract: A sensor for measuring the amount of a component in solution is disclosed. The sensor has a measuring electrode with at least one current collector, electrically connected to one of the electrical contacts and coated with a mixture comprising at least one oxidation-reduction enzyme specific to said component and at least one mediator transferring the electrons between said enzyme and said current collector wherein the mediator is a transition metal complex with at least one bipyridine, terpyridine or phenanthroline ligand substituted by at least one electron donor group. This sensor is particularly useful in the detection of glucose.