Mixed Functional Siloxane Monolayers Prepared via Chemical Vapor Deposition

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