Controlling the Material Properties and Biological Activity of Lipase within Sol−Gel Derived Bioglasses via Organosilane and Polymer Doping

The development of optical biosensors based on sol−gel entrapped proteins requires a detailed understanding of the evolution of the physicochemical properties of the material, their affects on protein function, and how these factors can be tailored by processing conditions. In this study, the polymer additives poly(vinyl alcohol) (PVA) and poly(ethylene glycol) (PEG) were dispersed into sol−gel processed materials derived from tetraethyl orthosilicate (TEOS) alone or copolymerized with methyltriethoxysilane (MTES) or dimethyldimethoxysilane (DMDMS), and their effects on the chemical and physical properties of the materials were monitored. In general, the physical properties, including transmittance and resistance to cracking, improved with increasing PEG concentration, but deteriorated with PVA content. The spectroscopic data obtained from entrapped 7-azaindole and 6-propionyl-2-(dimethylamino)naphthalene suggested that the inclusion of polymers and organic moieties into the matrix affected both the homogeneity of the materials and the polarity of the internal environment, with PEG reducing and PVA increasing the internal polarity. In light of these results, preliminary studies were performed on the effects of organic and polymer content on the initial and long-term activity of entrapped lipase. Concomitant with the material data, PVA tended to have a detrimental affect on lipase activity, while PEG provided a concentration-dependent enhancement of the enzyme activity. This study demonstrates for the first time that durable, optically transparent materials with significant lipase activity can be prepared and that optimal materials are produced with TEOS as a precursor and a few weight percent of low molecular weight PEG as an additive, with no need for organosilane precursors.