Sol-gel-derived glasses have emerged as a new class of materials well suited for the immobilization of biomolecules. As a consequence, they are also finding new applications as platforms for chemical sensors. Room temperature (or lower) processing conditions, chemical inertness, negligible swelling effects, tunable porosity, and the high purity of sol-gel-derived glasses make them ideal for many types of sensor applications. We

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Low temperature processed, porous sol-gel glasses represent a new class of materials for immobilization of biomolecules. The ability to form these materials into films, monoliths, and fibers to produce high-purity, porous glasses and the fact that they are optically transparent and chemically inert make them an intriguing platform for the development of chemical biosensors. In this paper, we report on the first attempt to encapsulate an intact antibody in a sol-gel glass matrix. Specifically, we present results on the affinity of solgel-encapsulated polyclonal antifluorescein. The results demonstrate that the sol-gel-encapsulated antibody retains an affinity for fluorescein; the affinity constant (Kt) for antibody-hapten complex is on the order of 10* 1234567 *M-1. The encapsulation process decreases Kt by about 2 orders of magnitude compared to the native system in buffer solution. The effect of aging and drying on the Kt for sol-gel-encapsulated antifluorescein is reported. Finally, we demonstrate that the intact antibody affinity can be maintained using simple storage protocols.

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Recent work from our Photonics Research Laboratory has shown that a new class of hydroxy amino styryl pyridinium derivatives exhibit both one- and two-photon pumped lasing. Because of the exciting prospect of up-conversion lasing by direct two-photon excitation, we have conducted a thorough study of the spectroscopic and lasing properties of a group of related compounds with the objective of understanding the structure−spectroscopic properties relationship. These dyes were found to have two mesomeric forms, one predominant in the ground-state and the other in the excited-state, leading to a large Stokes shift. A low fluorescence quantum yield was observed for all the studied dyes and could be possibly attributed to two factors:  (1) the presence of a counterion, iodide, which increases the singlet-to-triplet intersystem crossing transition, and (2) a twisted intramolecular charge-transfer (TICT) geometry derived from the rotation of the amino moiety. However, significant lasing efficiencies were observed under pulse pump conditions possibly because the dyes are being stimulated to emit at a faster rate than the nonradiative processes. From the one-photon pumped laser loss calculations, we found that the losses are only due to the cavity effect. Solvent effect studies for the hydroxy amino styryl pyridinium derivatives showed that the chromophore is very sensitive to hydrogen bonding donor (HBD) solvents. In addition, the dye-doped sol-gel:PMMA composite glass solid matrix exhibits a behavior close to the dye dissolved in water, suggesting a microenvironment of pure silica. These results indicate that the dye is attached to the silica skeleton of the composite glass through hydrogen bonding.

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A newly synthesized hemicyanine dye, trans-4-[p-[N-ethyl-N-(hydroxyethyl)amino]styryl]-N-methylpyridinium tetraphenylborate (ASPT), has recently been shown to be an excellent dye for both one- and two-photon-pumped lasing and for applications in optical power limiting. We report on the absorption, one- and two-photon-induced emission, quantum yield, and the excited-state lifetime of ASPT in different solvents of varying polarity. We also present the spectral characteristics of ASPT within a reverse-micelle and β-cyclodextrin cavity. Our results demonstrate that ASPT is one of the few dyes which exhibits highly solvent-polarity-dependent fluorescence in the useful orange-red region of the spectrum (560−620 nm). Therefore, it offers many applications in the biomedical field as a fluorescent probe molecule. In addition, ASPT is fluorescent upon excitation with an infrared (IR) source (two-photon-induced emission) making it even more attractive, since the background fluorescence from biological fluids upon IR excitation is highly reduced compared to ultraviolet or visible excitation. The solvatochromic effect of ASPT is proposed to be due to a change in the dipole moment and reduced hydrogen bonding effects of the dye upon excitation. On the basis of our results, we propose that ASPT exists in two mesomeric forms. One is predominant in the ground-state and the other in the excited-state. We observe a low quantum yield of the dye (<10%) in all the investigated solvents. The excited-state lifetime of ASPT is also observed to be solvent-dependent (30−400 ps). The calculated radiative decay rate is observed to remain constant but the nonradiative decay rate increases in solvents of increasing polarity. Finally, we report on the spectral feature of ASPT within a reverse-micelle cavity with varying water loadings and upon binding to a β-CD cavity.

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