Sol-gel encapsulation has recently surfaced as a successful approach to biomolecule immobilization. Proteins, including enzymes, are trapped in the pores of the sol-gel derived glass while retaining their spectroscopic properties and biological activity. Our current work extends the unique capabilities of biomolecule-doped sol-gel materials to the detection of glutamate, the major excitatory neurotransmitter in the central nervous system. We are developing an in vivo fiber optic biosensor for glutamate along with methods to achieve continuous monitoring. In our research to date we have encapsulated GDH in a silica sol-gel film on the tip of an optical fiber. GDH catalyzes the oxidative deamination of glutamate to α-ketoglutarate and the simultaneous reduction of NAD+ to NADH. To quantify the glutamate concentration, we observe the rate of change of NADH fluorescence as a function of time. An important consideration for continuous in vivo monitoring is the incorporation of a selfsustaining NAD+ source. We have adopted a photochemical means of regenerating NAD+ from NADH, by irradiating thionine (3,7-diaminophenothiazin-5-ium) which we incorporate into the sol-gel sensor material. When excited with visible light (λabc∼ 596 nm), thionine undergoes a reaction with NADH resulting in a non-fluorescent form of thionine and NAD+. We have characterized the kinetics of this reaction in the sol-gel matrix, and have shown that the reaction results in regenerated co-factor that is usable by GDH for the oxidation of glutamate.

This paper describes the preparation of hybrid surfactant-templated thin films functionalized with rare-earth (Eu3+ and Tb3+) organic complexes. 2-D hexagonally ordered films are obtained by a one-pot synthesis process based on an acid-catalyzed approach. Ln3+ ions are coordinated to bis-silylated ligands that co-polymerize with TEOS, which enables one to incorporate the fluorescent centers within the silica framework. Luminescent properties of the organic-inorganic mesostructured films are discussed and compared to those of amorphous samples with similar composition.

The proteins copper-zinc Superoxide dismutase (CuZnSOD), cytochrome c, myoglobin, hemoglobin, and bacterio-rhodopsin are encapsulated in stable, optically transparent, porous, silica glass matrices prepared by the sol-gel method such that the biomolecules retain their characteristic reactivities and spectroscopic properties. The resulting glasses allow transport of small molecules into and out of the glasses at reasonable rates but retain the protein molecules within their pores. The transparency of the glasses enables the chemical reactions of the immobilized proteins to be monitored by means of changes in their visible absorption spectra. Silica glasses containing the immobilized proteins have similar reactivities and spectroscopic properties to those found for the proteins in solution. The enzymes glucose oxidase and peroxidase were also encapsulated in transparent silica glass matrices. Upon exposure to glucose solutions, a colored glass is formed that can be used as the active element in a solid state optically based glucose sensor. Likewise, gels containing oxalate oxidase and peroxidase exhibit spectroscopic changes upon exposure to aqueous solutions containing oxalic acid.

Copper-zinc superoxide dismutase (CuZnSOD), myoglobin, hemoglobin and glucose oxidase are encapsulated in stable, optically transparent, porous, silica glass matrices synthesized under mild conditions using novel sol-gel synthetic techniques. The biomolecules retain their characteristic reactivities and spectroscopic properties. The porous glasses allow transport of small molecules into and out of the glasses at reasonable rates but retain the protein molecules within the pores. The chemical reactions of the immobilized proteins are monitored by means of changes in their visible absorption spectra. Four encapsulated proteins are studied: CuZnSOD reacts with CN−; metmyoglobin is reduced to its deoxy form and then reacts with O2 to make the oxy form and CO to make the carbonyl form; methemoglobin is reduced to its deoxy form and reacted with CO to make the carbonyl form; and glucose oxidase is reacted with glucose to make gluconic acid.

The sol-gel derived ORMOSIL (organically modified silicate) composed of copolymerized tetramethylorthosilicate (TMOS), methylmethacrylate (MMA), and 3-(trimemoxysilyl)-propylmethacrylate (TMSPM) is a stable host for organic molecules. Due to the ORMOSILs utility as an optical host matrix, it is important to obtain a more detailed understanding of the changes that occur during gelation, aging and drying. A useful probe molecule for this purpose is ReCl(CO)3-2,2'-bipyridine. The emission band of this molecule shows a large blue shift as the medium is changed from fluid to rigid. In this paper the changes that occur during the gelation, aging, and drying of a sol-gel derived ORMOSIL are studied. The emission maximum shifts gradually from 615 ran in the sol to 575 nm in dried gels. The final wavelength is indicative of an environment that is not fully rigid, and suggests that the molecule is in a flexible organic site. The properties of the ORMOSIL are contrasted with those of silicate and aluminosilicate sol-gel matrices.

The red/near-infrared emission spectra of alizarin (1,2-dihydroxyanthraquinonone), the potassium salt of alizarin and the aluminum and zinc complexes of alizarin in the solid state are reported. The emission is assigned to an alizarin localized transition from an in-plane nonbonding orbital delocalized over the anthraquinone rings to a predominantly π* C=O acceptor orbital (nπ* ligand localized excited state). The cobalt, nickel and copper complexes do not emit from their nπ* excited state. In these complexes, metal centered d-d excited states which lie lower in energy than the ligand localized state effectively deactivate the luminescence.

A wide variety of natural resins, waxes, gums, drying oils and proteinaceous materials used on paintings are photoluminescent. The photoluminescence spectra of these materials are reported and discussed. The application of this technique towards the identification of these materials is considered. Both bulk materials and films prepared from selected bulk materials were studied and a comparison is made between the bulk and film samples. Temperature and excitation wavelength studies are reported and discussed for several of the samples.