Surface imprinting of polyurethane with yeasts allows selective and highly sensitive enrichment of microorganisms in flowing conditions. The selectivity of the highly robust sensor allows yeasts, gram positive., and gram negative bacteria to be distinguished. The surface imprinted polymers are truly an alternative to biological recognition layers, such as antibodies, as they operate with a high sensitivity and label-free detection. The results are encouraging to extend the search for artificial recognition sites to the micrometer scale.