An innovative alternative to the conventional method of blood typing is based on the application of synthetic antibodies, which are synthesized by imprinting of polymers with native erythrocytes. Simple, low cost monomers can be used. In this way robust materials are generated by this strategy. Polyvinylpyrrolidons, polyacrylates or polyurethanes are suitable for this purpose. The transducers are coated by patterned polymers and combined with a flow system. In this way erythrocytes in blood can be characterized according to the AB0 groups, but also in respect to sub-groups.