Modification of silicon nitride with oligo(ethylene glycol)-terminated organophosphonate monolayers

Due to its unique properties, silicon nitride has found a wide variety of applications in nanodevice fabrication and biosensing. Self-assembled monolayers of phosphonic acids (SAMPs) can be applied to prepare well-defined organic interfaces suitable to anchor bioreceptor probes with a high surface density on different substrates. In this work, we report on the fabrication of SAMPs functional interfaces on silicon nitride. By using several surface analysis techniques, including contact angle (CA) measurements, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS), we present a detailed characterization of the morphology, composition, and stability of the functional interface. In addition, we investigate the protective properties of organophosphonate functional interfaces containing only a few ethylene glycol (EG) units per SAMPs building block against non-specific surface binding of charged biomolecules by means of fluorescence spectroscopy.