Silanization of glass chips—A factorial approach for optimization

Silanization of glass chips with 3-mercaptopropyltrimethoxysilane (MPTS) was investigated and optimized to generate a high-quality layer with well-oriented thiol groups. A full factorial design was used to evaluate the influence of silane concentration and reaction time. The stabilization of the silane monolayer by thermal curing was also investigated, and a disulfide reduction step was included to fully regenerate the thiol-modified surface function. Fluorescence analysis and water contact angle measurements were used to quantitatively assess the chemical modifications, wettability and quality of modified chip surfaces throughout the silanization, curing and reduction steps. The factorial design enables a systematic approach for the optimization of glass chips silanization process. The optimal conditions for the silanization were incubation of the chips in a 2.5% MPTS solution for 2 h, followed by a curing process at 110 °C for 2 h and a reduction step with 10 mM dithiothreitol for 30 min at 37 °C. For these conditions the surface density of functional thiol groups was 4.9 × 1013 molecules/cm2, which is similar to the expected maximum coverage obtained from the theoretical estimations based on projected molecular area (∼5 × 1013 molecules/cm2).