Poly(ethylene glycol) interfaces for the control of biofouling in silicon-based microsystems

Silicon has been extensively employed as a material for the development of microsystems for analytical and separation technologies. However, biofouling that mainly arises due to the charged surface of silicon has been observed to limit the long-term functioning of these microsystems. Surface biofouling can be controlled by engineering the silicon substrates with poly(ethylene glycol) (PEG), a water-soluble, nontoxic, and nonimmunogenic polymer. PEG interfaces on silicon substrates can be created either by physical adsorption or by covalent immobilization such as grafting and chemical coupling. Nevertheless, covalently coupled PEGs are considered to be more stable due to strong forces of adhesion. Furthermore, PEG interfaces are needed, that are ultrathin, uniform, conformal and stable in in vivo-like environments. In the present research effort, we examine PEG interfaces of various chain densities created by a covalent coupling reaction scheme. Unmodified and PEG-modified silicon samples have been analyzed using the techniques of ellipsometry, contact angle measurement, X-ray photoelectron spectroscopy, atomic force microscopy, and fluorescence microscopy. Furthermore, we have investigated the stability of PEG films in dry and aqueous conditions up to four weeks in order to assess their ability to control biofouling on continuous basis.