Real-Time Monitoring of Siloxane Monolayer Film Formation on Silica Using a Fiber Bragg Grating

We present a series of experiments to study the silanization of the silica surface of a fiber Bragg grating biosensor. A simple 4-layer attachment model is developed to describe the bonding of 3-aminopropyl triethoxysilane (APTES) or 3-aminopropylethoxydimethylsilane (APMDS) to the silica surface when both APTES and APMDS are dissolved in water or in pure ethanol. An adsorbed water layer is created during the attachment of APTES and APMDS and is necessary to explain the results in water and in ethanol. It is found that a monolayer of APMDS attaches to the silica surface when APMDS is diluted in either water or ethanol. In the case of APTES, it is found that a 1-2 and 5 APTES layers attach to the glass surface when APTES is diluted in water and in ethanol, respectively.