Fluorescence and NMR characterization and biomolecule entrapment studies of sol-gel-derived organic-inorganic composite materials formed by sonication of precursors

Optically clear sol-gel-derived organic-inorganic hybrid materials were pre pared by a sonication method suitable for entrapment of biological compound s. Sonication at pH 2.5 hydrolyzed mixtures of tetraethyl orthosilicate (TE OS) and one of the organosilanes methyltriethoxysilane (MTES), propyltrimet hoxysilane (PTMS), or dimethyldimethoxysilane (DMDMS). Buffer solutions con taining the fluorescent probes 7-azaindole or prodan, or the proteins human serum albumin (HSA) or lipase, were then added to promote gelation and the resulting materials were aged at 4 degrees C over several months. The opti cal clarity, hardness, and degree of cracking were examined, in conjunction with solid-state Si-29 and C-13 NMR of the materials and fluorescence spec tra of the entrapped probes. These studies revealed that MTES can be added to TEOS up to a level of 20% (v/v) with retention of good physical characte ristics, thus allowing control over the hydrophobicity and cross-linking wi thin the matrix. Materials with more than 20% MTES, or incorporating PTMS o r DMDMS at levels above 5%, showed significantly poorer physical characteri stics, indicating phase separation. Proteins entrapped into these hybrid. m aterials could be-examined by optical methods. Both entrapped HSA and lipas e showed improvements in function with increased ormosil content, indicatin g that such materials are suitable for encapsulation of lipophilic proteins for optical sensor development.