Glen E. Southard

Sensors for chemical weapons detection

Many methods can sense and respond to chemical agent release. We evaluate current and near-term sensor options for detecting the most likely threats, currently sarin, cyanide, and pesticides. We also identify sensor technologies that may be capable of responding to additional chemical threats and biological agents and provide options for coping with new threats as they develop. We collate previous research results on background contaminants that have the potential of introducing unwanted false alarms in chemical agent detection systems and suggest techniques that may be capable of reducing the impact of releases of toxic materials.

Molecularly imprinted ion-exchange resin for Fe3+

Abstract Ion exchange resins selective for the sequestration of Fe3+ from aqueous solutions containing citrate were prepared by the molecular imprinting technique. Sorption characteristics of imprinted resins prepared with high (85 mole%) and low (3 mole%) amounts of covalent cross‐linking were examined. Experiments to determine loading capacity and selectivity, relative to several metal ions of physiological significance, were performed. The Fe3+ capacity of the highly cross‐linked resin was larger but the selectivity was lower.

Molecularly Imprinted Polymer Receptors for Sensors and Arrays

Molecular imprinting is a process for making selective binding sites in synthetic polymers. The process may be approached by designing the recognition site or by simply choosing monomers that may have favorable interactions with the imprinting molecule. The successful application of the methodology to biochemical sensing typically requires the designed approach. The process involves building a complex of an imprint molecule and complementary polymerizable ligating monomers. At least one of the molecular complements must exhibit a discernable physical change associated with binding. This change in property can be any measurable quantity, but a change in luminescence is the most sensitive and selective analytical technique. By copolymerizing the complexes with a matrix monomer and a suitable level of crosslinking monomer, the imprint complex becomes bound in a polymeric network. The network may need to be mechanically and chemically processed to liberate the imprinting species and create the binding site. The design of the binding site requires insights into its chemistry. These insights are derived from studies of molecular recognition and self-assembly and include considerations of molecular geometry, size, and shape, as well as molecule-to-ligand thermodynamic affinity.

Molecularly Imprinted Ionomers

Abstract : Ionomers have been defined as copolymers that have a certain proportion of ionic groups. The ionic groups have a significant effect on the mechanical properties of the copolymers. This is generally due to aggregation of ions in a low dielectric medium. The primary result is to restrict chain motion and raise the glass transition temperature. These attributes have relevance to molecular imprinting, since restricted chain motion should help preserve the integrity of the binding site. The connection between ionomers and molecular imprinting has come from the production of metal ion imprinted resins. Metal ions are used in the production of molecularly imprinted polymer ion exchange resins and ionically permeable membranes. The polymers have applications as separations media, sequestering media and as ion selective sensors. Metal ions are also being used to form imprinted polymers based on metal mediated imprint binding. We have prepared ion exchange resins, selectively permeable polymer membranes, ion selective electrodes and ion selective optical sensors using a modified version of the molecular imprinting technique. The modification is a reduction in the amount of covalent crosslinking used to form the polymers. This reduction may be justified by the presence of residual metal ion crosslinking in the immediate region of the imprinted binding site. The effects of metal ions on the thermal and mechanical properties of the polymers, as well their impact on binding selectivity are critical variables.

Optical Transduction Schemes for Molecularly Imprinted Polymer Sensors

Molecular imprinting is a useful technique for making a chemically selective binding site. [1] The method involves building a synthetic polymeric scaffold of molecular compliments containing the target molecule with subsequent removal of the target to leave a cavity with a structural “memory” of the target. Molecularly imprinted polymers can be employed as selective adsorbents of specific molecules or molecular functional groups. Sensors for specific molecules can be made using optical transduction through chromophores residing in the imprinted site. The use of metal ions as chromophores can improve selectivity due to directional bonding. The combination of molecular imprinting and spectroscopic selectivity can result in sensors that are highly sensitive and nearly immune to interferences. [2]