Several biosensor principles are based on biomolecular interactions on surfaces or in thin sensing layers. One of the most wellknown techniques for the direct elucidation of biomolecular interactions utilizes optical changes in a thin hydrogel (dextran) sensing layer occurring upon the binding of biomolecules to the ligands in the sensing layer. Labelling one of the molecules in an interaction pair with fluorescent groups leads, however, to a large sensitivity, and forms therefore the basis for several detection schemes. Molecular beacons, for example, utilize changes in fluorescence resonance energy transfer or quenching for the detection of structural changes in a biomolecule upon binding to a ligand or upon hybridisation. We are developing synthetic helix-loop-helix polypeptide scaffolds, which show promise as a vehicle for new biosensor principles. Their interesting property is that (arbitrary) ligands can be site selectively introduced in a predetermined order into the scaffold using simple solution chemistry, based on active esters, and without need of protecting groups. The scaffolds are also easily functionalised for covalent binding of them to different types of surfaces and hydrogels. In the talk the use of these versatile scaffolds for biosensing purposes will be described after a short introduction to their chemistry. The coupling of the scaffolds to gold surfaces and to dextran matrices and their use for non-labelling biospecific interaction analysis are touched upon. It will furthermore be shown how the scaffolds can be provided with a binding ligand for a molecule and a (fluorescent) reporter group, indicating that binding has occurred.. In the example an inhibitor, benzenesulfonamide, is used as the ligand for an enzyme, carbonic anhydrase, and dansyl as the fluorescent reporter group. The use of arrays of scaffolds with ligands with different affinities for different biomolecules to enable "diagnostic chips" will finally be discussed.