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Optically clear sol-gel-derived organic-inorganic hybrid materials were prepared by a sonication method suitable for entrapment of biological compounds. Sonication at pH 2.5 hydrolyzed mixtures of tetraethyl orthosilicate (TEOS) and one of the organosilanes methyltriethoxysilane (MTES), propyltrimethoxysilane (PTMS), or dimethyldimethoxysilane (DMDMS). Buffer solutions containing 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 °C over several months. The optical clarity, hardness, and degree of cracking were examined, in conjunction with solid-state 29 Si and 13 C NMR of the materials and fluorescence spectra 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 characteristics, thus allowing control over the hydrophobicity and cross-linking within the matrix. Materials with more than 20% MTES, or incorporating PTMS or DMDMS at levels above 5%, showed significantly poorer physical characteristics, indicating phase separation. Proteins entrapped into these hybrid materials could be examined by optical methods. Both entrapped HSA and lipase showed improvements in function with increased ormosil content, indicating that such materials are suitable for encapsulation of lipophilic proteins for optical sensor development.

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13C and 29Si spin-lattice relaxation in nitrogen-doped 6H-polytype silicon carbide is highly site-dependent. Not only do carbon sites relax much more rapidly than the corresponding silicon sites, but also there are unprecedented differences in relaxation efficiency among the different carbon, and among the different silicon, sites, that can be related to much higher unpaired electron density in the conduction band at the higher-symmetry (types A and B) sites than at the lowest-symmetry (type C) site. In contrast, all sites relax at equivalent rates in most other 6H silicon carbide samples, including both commercial abrasive grade material with high levels of impurities and high-purity aluminumdoped and undoped samples. The nature of the relaxation process differs as well, from stretched exponential in lowerpurity to exponential in high-purity samples.

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