Chapter 1 of this thesis serves as a general introduction to electrode processes and to some of the electrochemical techniques used for the characterisation and development of amperometric sensors. A brief review of recent applications of modified electrodes in the field of electroanalysis is also presented. The remainder of the thesis is divided into three sections. The first of these comprises chapters 2 and 3. Chapter 2 describes the synthesis and characterisation of a series of polymers based on ruthenium-bound 4-vinylpyridine/styrene copolymers. An investigation into factors that affect charge transport rates and processes through thin films of these polymers on glassy carbon electrodes, using cyclic voltammetry, chronoamperometry and sampled current voltammetry, is also presented. Chapter 3 describes the optimisation of the performance of these polymer modified electrodes as sensors for the nitrite ion, using the rotating disk electrode and flow-injection amperometric detection techniques. The second section of this thesis comprises the development of ruthenium dioxide-based modified electrodes for the electrocatalytic detection of alcohols and selected saccharide antibiotics. The ruthenium dioxide modifier is also confined in a graphite-epoxy matrix to yield a stable, polishable sensor for the saccharide antibiotics. Finally, chapter 5 describes the development of, and investigation into, two sensors for the detection of glucose. The first of these is based on the electrocatalytic oxidation of glucose at a ruthenium dioxide-modified graphite-epoxy electrode surface, while the second involves a novel one-step fabrication of a glucose sensor based on the entrapment of the enzyme glucose oxidase within a poly(ester sulfonic acid) coating.