PhotoSmart · Photo-switching of smart surfaces for integrated biosensors

Smart surfaces with switchable properties hold great promise for future integrated sensors. Azobenzene molecules have been demonstrated to switch reversibly between the trans and cis isomer with picosecond time constants, when triggered with an external light source. Due to the different molecular geometries and electronic properties of the isomers, these may be used as molecular switches for realizing smart surfaces. The objective of this research proposal is to establish methods for integrating photo-switchable smart surfaces into miniaturized sensors. For efficient switching this requires on-chip light sources providing sufficient intensity at the location of the molecular switch. Ultraviolet and blue organic light emitting diodes will be integrated monolithically onto dielectric substrates with a periodically nanostructured high refractive index layer. This slab photonic crystal allows for resonant excitation of the molecular switches. Two types of smart surfaces will be studied. First, the reversible switching of wettability between hydrophilic and hydrophobic will be investigated, which is of particular importance for reconfigurable microfluidic chips. Second, the switchable surface adsorption of biomaterials is targeted. The periodic switching of the binding sites between an active and an inactive state will cause a periodic measurement signal. This allows for the use of lock-in techniques with superior signal-to-noise ratio and for subtraction of the background at same position. Combining both types of smart surfaces promises reconfigurable, multifunctional, highly-selective future integrated biosensors. The final goal of the proposed project is to demonstrate for the first time an integrated microsystem with smart surfaces switched by on-chip light sources for spatial and temporal control of the surface wettability as well as control of binding sites for biomolecules.