An assay for the determination of diclofenac concentration, in the micromolar range in water, was developed. It is based on the use of a recently developed cyclodextrin-based polymer that possesses an inherent affinity for the target pharmaceutical. This competitive assay is exploiting the possibility to displace a fluorescent dye, adsorbed in the cyclodextrin-based polymer, by the target drug. This displacement is followed by measuring the increase in fluorescence polarization of the dye released in solution. The assay was successfully tested on a real wastewater sample with a limit of detection of 1 mu M. (C) 2015 Elsevier B.V. All rights reserved.