Mixed Functional\nSiloxane Monolayers Prepared via\nChemical Vapor Deposition

Functionalizing surfaces with self-assembled monolayers\n(SAMs)\nallows to efficiently bind bioreceptors, for instance, by bio-orthogonal\nclick reactions, which is useful in biosensor fabrication. Control\nof the bioreceptor concentration on the surface can be achieved by\ncoating an SAM mixture consisting of a functional SAM, which binds\nthe bioreceptor, and a nonfunctional SAM for dilution. In this work,\na novel vapor-based coating approach for the preparation of mixed\nSAM coatings is presented. Sequential evaporation of the SAM precursors,\ni.e., fluoroalkyl and azidoalkyl silanes, by heating under reduced\npressure leads to the formation of a two-dimensional siloxane monolayer\nnetwork on silicon oxide. The presence of both SAMs in the mixed coatings\nis confirmed by Fourier transform infrared spectroscopy and X-ray\nphotoelectron spectroscopy. As verified by atomic force microscopy,\nthe morphologies of the coatings and the uncoated silicon oxide substrates\nare similar, indicating a conformal coating. Functionality of the\nSAM mixture is demonstrated by a reaction with a fluorescent dye,\nillustrating its potential application in biosensors.