In waste water treatment plants, noxious organic molecules are not completely removed and thus enter surface waters. Hence, the monitoring of these molecules present in the range of ng/L to μg/L is an urgent problem. However, especially the on-site monitoring of such molecules is currently not possible due to the lack of suitable measurement systems. To address this problem, in this volume of the book series „Dresdner Beiträge zur Sensorik“ a biosensor is presented, which in perspective may be used directly in water treatment plants. The sensor uses the non-steroidal anti-inflammatory drug diclofenac as a guiding substance for assessing water quality. This book presents details of the biosensor setup using a gold nanostructure as optical transducer in a simple transmittance setup. Furthermore, for the specific detection of diclofenac molecules, the transducer is surface functionalised and binding events between anti-diclofenac antibodies and the sensor surface are optically detected. The results confirm that, diclofenac concentrations in environmentally relevant ranges can be detected and it, thus, may pave the way for the on-site detection of (polluting) molecules.weiterlesen