Plasma enhanced chemical vapour deposition was investigated for the deposition of bioactive surfaces which can be categorised into two functions. The first is in biosensor applications, immunoassay biodevices have been researched considerably but significant problems remain in particular non-specific adsorption. This work demonstrates a new method of reducing the non specific adsorption on the surface of cyclo olefin polymers for use as immunoassay biodevices. PECVD deposition of a silicon oxide bonding layer followed by an acrylic acid functional layer which contains carboxylic acid functional groups on cylic olefin polymers is achieved. The deposited film exhibits low non-specific adsorption of non target analytes and increased covalent attachment of target analytes. A comprehensive characterisation of the deposition is carried out and conclusions of the mechanisms involved in creating the surface are elucidated; surfaces are analysed using a combination of quantitative and qualitative approaches. The mechanisms behind the plasma deposition of acrylic acid are investigated and methods to increase carboxylic retention on the surface are considered, in particular the influence of background gas is investigated. The function of the second surface is in anti-fouling devices. The production of antifouling films is a key element for the development of biomedical materials such as medical devices and implants. Anti-fouling coatings favour the biological integration by limiting the interactions between the implants and physiological fluids. Proteins present in the blood will be the first components to become adsorbed on the surface of the biomaterial. Fibrinogen present in the blood is the major initiator of inflammatory reactions and is involved in blood clotting. By minimising fibrinogen adsorption it is possible to reduce the contribution of the biomaterial surface characteristics to thrombosis and inflammatory reactions. Here in, a method to reduce fibrinogen adsorption is discussed and a characterisation of the plasma phase used to deposit the antifouling coating is investigated and a study on the properties of the surface for antifouling is examined. Using HMDSO and oxygen ‘polymer-like’ and ‘silica-like’ surfaces can be deposited, silica-like depositions when compared to the polymer-like depositions displayed lower fibrinogen adsorption, 42% compared to 23%.