Reagentless amperometric biosensors were prepared using a variety of nitrogen donor groups containing co-polymers. The polymers were coordinated with Os-bis-N,N-(2,2'-bipyridil)-dichloride via a ligand exchange reaction thus assuring an efficient electron-transfer pathway between the polymer-entrapped horseradish peroxidase and the electrode surface by means of a sequence of electron-hopping steps. The impact of structural features of the polymer such as spacer length between the Os-complex and the polymer backbone or the ratio of 4-vinylpyridine and butylmethacrylate in a co-polymer on the activity of the horseradish peroxidase biosensors was investigated. (c) 2006 Elsevier Ltd. All rights reserved.