Liquid based techniques are widely used for the surface functionalization of biosensors, e.g. to produce protein-resistant (i.e. antifouling) coatings or to covalently and site-specifically bind biomolecules. A major problem associated with solution-based coatings, concerns incomplete wetting of high aspect ratio structures, e.g. when trying to functionalize the interior surface of microfluidic channels. In this project, we propose to explore Atomic Layer Deposition (ALD), Molecular Vapor Deposition (MVD) and Molecular Lyar Deposition (MLD) as novel and versatile vapor-based approaches for the conformal deposition of bio-functional coatings onto 3D substrates. We target conformal deposition both of functional layers for the selective and covalent binding of biomolecules and of antifouling layers to prevent analyte depletion. For the latter, we will probe the direct vapor deposition of poly-ethylene oxide moieties as well as use a completely novel strategy, namely the deposition of protein resistant MLD-metalcones. To demonstrate the key concepts developed in this PhD, and to showcase the potential of vapor-based surface functionalization in high-aspect ratio structures, we envision to perform an affinity based assay within a closed microfluidic channel with a bioreceptor area inside the channel and anti-fouling functionality on the channel walls.