Detection of molecules and in particular of biomolecules in liquids is of high economic importance, above all in medical diagnosis and biochemistry. A new development by the Institute of Nanotechnology allows for the production of specific sensors for biological and medical applications in particular. By dip-pen nanolithography (DPN), a periodical optical grating is generated, the sensitivity of which is comparable with conventional grating-structured sensors. In contrast to conventional processes, however, the process steps with the sensitive biomolecules are much smoother. DPN, a surface nanostructurization process, is based on various molecular inks. The structures are generated by applying the molecular ink to a substrate using a scanning force microscope (see also dip-pen nanolithography for biological inks). The ink used is a mixture of phospolipids and any other functional molecule that may serve as specific bonding site for the substance searched for. As the desired functional molecules often cannot be written directly by DPN, phospholipids are used as transfer ink to introduce these molecules into the nanostructures and obtain a functionalized ink.If a liquid containing the target molecule is applied to the substrate and grating structure, optical properties of the grating are changed. To detect the molecules searched for, light diffraction effects of the grating are used. By adding the liquid and modifying the optical grating, light intensity is changed and the molecule searched for can be detected sensitively. A special advantage of the new biosensors is the high sensitivity for substances dissolved in an inhomogeneous serum (high sensitivity, high specificity). As the resources required for sensor production are available at low costs, the process might be used to produce single-use products that are highly suited for biomedical applications.