| Abstract
| - The development of organic−inorganic composite materials using a two-step aqueous sol−gel processing method is demonstrated, and the effect of processing parameters on the homogeneity of the materials is assessed by various imaging methods.
- The entrapment of biomolecules within organic−inorganic nanocomposite materials derived by a sol−gel method has proven to be a viable route for the development of biosensors and biocatalysts. However,the phase separation behavior within nanocomposite materials formed by a protein-compatible two-stepaqueous processing method is not well-understood. In this study, a range of imaging methods was usedto assess the degree of heterogeneity in a series of dipcast thin films formed with different types andlevels of ormosils in the presence and absence of polyethylene glycol (PEG), using both separate andco-hydrolysis of precursors. Both microscopic (bright-field and fluorescence microscopy) and nanoscale(atomic force microscopy and scanning electron microscopy) imaging demonstrate that short chainmonofunctional ormosils such as methyltrimethoxysiline do not lead to significant heterogeneity whenmixed with TEOS, while disubstituted (dimethyldimethoxysilane) or longer chain (isobutyltrimethoxysilane) ormosils show significant heterogeneity at the microscopic and nanoscopic scale when preparedby a separate hydrolysis method. The addition of PEG can improve the homogeneity in some materials,likely due to the coating of silica sol particles, which reduces microscopic phase separation; however,cohydrolysis of the precursors provides a more general route to create homogeneous materials. Interestingly,the heterogeneity observed by bright-field microscopy, which reflects variations in the refractive index,did not fully correlate with the fluorescence microscopy images of entrapped fluorophores, suggestingthat chemical heterogeneity exists even when samples appear to be homogeneous. The implications ofthese findings for biosensor development will be discussed.
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