Richard A. Dunbar

Aerosol-generated sol-gel-derived thin films as biosensing platforms

We have incorporated an antibody into a sol-gel-derived thin film composite and demonstrated that it retains affinity for its hapten. An inexpensive apparatus to produce and deposit, aerosol-generated sol-gel-derived thin films was also developed. The antibody antifluorescein (AF) was entrapped between two sol-gel thin films (0.62 ± 0.05 μm) in a sandwich architecture. The fluorescent hapten 5-(-and 6-)-carboxy-4′,5′-dimethylfluorescein (Me2F) was used to determine the accessibility and viability of the entrapped AF. Results demonstrate that a population of the entrapped antibodies recognizes and binds Me2F for up to 13 weeks when stored in pH 8 phosphate buffer at 4 °C. An intriguing result is that the response times of these AF-doped thin films actually improve as a function of storage time. We explain this observation in terms of decreased viability of AF molecules sequestered between the upper and lower films of the sandwich. Partial regeneration (40–50%) of the biosensor was obtained using a mild chaotropic reagent (NaCl) and the AF-doped films could be reset/regenerated up to six times.

Chemical Sensor Based on an Artificial Receptor Element Trapped in a Porous Sol-Gel Glass Matrix

A synthetic organic receptor, dansyl-tethered β-cyclodextrin, is doped into an inorganic sol-gel matrix and spin cast as a film on fused-silica plates. The entrapped receptor exhibits changes in its fluorescence in the presence of borneol. Thus, this new material can be used as a reversible sensor. Various aspects of a sol-gel matrix as a host for recognition molecules were explored. This system demonstrates the possibility of using artificial receptors and sol-gel porous glass films for chemical sensing purposes.

Comparison of inter- and intramolecular cyclodextrin complexes

Abstract We present the first comparative steady-state and time-resolved fluorescence studies of inter- and intramolecular cyclodextrin complexes. Specifically, we report equilibrium and kinetic results for dansyl-glycine complexed with β-cyclodextrin (intermolecular) and the dansyl-glycine-β-cyclodextrin adduct (intramolecular). The fluorescence intensity decay profile for the intermolecular system is best described by a discrete triple exponential decay law. This is consistent with stepwise 1:1 and 2:1 (β-cyclodextrin:guest) inclusion complexation. Equilibrium constants are in line with previous results on similar species. In contrast, we found that the intramolecular case was described by a doubly exponential decay law—consistent with a single intramolecular inclusion complex. Displacement experiments, with borneol, confirm the simplicity of the intramolecular complex. In all cases, continuous distribution models failed to fit the experimental data.

New fiber-optic-based high-pressure cell for fluorescence measurements in near- and supercritical solvents

Studies of fluorescent molecules in supercritical fluids have done much to improve our understanding of solute-fluid, as well as solute-solute, interactions. However, most of the current high-pressure optical cells used in this field are cumbersome to work with and difficult or tedious to clean. Our group previously reported on a fiber-optic interface based on a bifurcated fiber probe which allowed spectroscopic measurements in supercritical solvents.

On the Local Environment Surrounding Pyrene in Near- and Supercritical Water

We use steady-state and time-resolved fluorescence spectroscopy to probe local solvent–solute interactions between pyrene (the solute) and supercritical water (SCW). Toward this end, we have developed a new fiber-optic-based titanium high-pressure optical cell which can withstand the temperatures and pressure needed to generate supercritical water. Static fluorescence measurements indicate that there is an increase in the local water density surrounding the pyrene molecules (clustering) up to five times the bulk fluid density. This extent of clustering is most prevalent at about one-half the critical density. Consistent with previous work on more mild supercritical fluids (e.g., CO2, CF3H, C2H6), the extent of this solute–fluid clustering decreases as the system temperature and pressure are increased. Time-resolved fluorescence measurements show that the excited-state decay kinetics are exponentially activated and not themselves affected by this solute–fluid clustering process.

Characterization of a sol-gel-entrapped artificial receptor

We report on the development, characterization, and photophysics of a new fiber-optic-based sensor which uses a sol-gel entrapped recognition element. The recognition element is modified (beta) -cyclodextrin to which we have added a short tether (glycine) and a fluorophore (dansyl). This recognition element forms an intramolecular complex, and the dansyl group can include within the cyclodextrin cavity. Non-fluorescent analytes, that bind to the cyclodextrin cavity, can effectively displace the included dansyl group and result in a measurable change in signal. We report on the detection limits, dynamic range, and photophysics (i.e., transduction mechanism) of this new sensor.