Some ruthenium and osmium complexes and metallopolymers have been synthesised and characterised using viscosity, spectroscopic and electrochemical techniques. The obtained results showed that the photochemical and electrochemical properties of the monomeric complexes, i.e. M(bpy)32+ and M(bpy)2(pic)22+, where bpy is 2,2’bipyridyl and pic is 4-picoline, accurately predict the properties o f the analogous polymeric material, M(bpy)2(PVP)io2+, where PVP is poly-4-vinylpyridine. However, the excited state lifetimes and quantum yield of photoluminescence are considerable lower for the polymeric materials than for the analogous M(bpy)32+ complexes. The Ru(bpy)2(PVP)i02+ polymer is an effective mediator for the oxidation of the DNA base guanine using thin films of these materials on electrode surfaces. The film thickness and electrode potential were systematically varied in both sulphuric acid and PBS electrolyte showing that charge transport through the film is a diffusion-like process and the charge transport diffusion coefficient, DCT is approximately 2 x 10'11 cm V . This charge transport rate is independent of the concentration of the electrolyte, indicating an open porous layer structure. The osmium metallopolymer, Os(bpy)2(PVP)io +, was also shown to be an effective mediator for the oxidation of the biomarker 8-oxoguanine. The characteristics of this metallopolymer as a thin film were also investigated, yielding similar results to the ruthenium analogue. ECL was demonstrated in solution phase via annihilation between the electrogenerated 3+ and 1+ forms of the compounds. The ECL spectrum for Ru(bpy)2(PVP)102+ was similar to the photoluminescence, suggesting that the same orbitals are responsible for the emission, whether the excited state was formed electrochemically or photochemically. The ECL efficiencies (<|>ecl) followed the same order as the photoluminescent efficiencies (4>p). The effects of quenchers and self quenching as well as the temperature dependence of the luminescence was investigated, yielding information on the quenching constant, kq, and the activation energies for both the monomeric and polymeric materials. Electrodes modified with thin films containing one or both of the redox polymers and DNA were used for dual amperometric and electrochemiluminescent detection of DNA damage, either by the formation of adducts by chemically generated damage or oxidative DNA damage, for use as a toxicity screening sensor. This system provides fast and accurate responses to the production of DNA adducts, which cause disruption of the DNA helical structure and to oxidative DNA damage in comparison to the methods already in use. The combined amperometric and electrochemiluminescent detection provided a more sensitive and selective sensor for this type of analysis, immobilisation of the chemiluminescent reagent has a number of advantages over solution-phase ECL-based systems; conserves reagent, is simpler and more cost effective and has an additional level of selectivity. It also allowed for the utilisation of thin films containing both the redox polymers and DNA, which resulted in quick easy analysis of potential toxins.