Optical Biosensor Detects Biological Toxins and Infectious Agents Synthesis, Structural Characterization and Property Optimization of Novel Antimonides and Bismuthides Svilen Bobev Department of Chemistry and Biochemistry, University of Delaware Newark, DE 19716 The new compound Ba11Cd6Sb12 was synthesized and structurally characterized by single-crystal X-ray diffraction. Its structure features CdSb4 tetrahedra that share corners and form polyanionic sub-structure consisting of one-dimensional ribbons. There also are some short Sb–Sb bonds, which “zip” the corners of two CdSb4 tetrahedra, leading to a unique arrangement that was dubbed “double pentagonal tubes” as shown in the picture. Applying the classic concepts to rationalize the bonding in this structure type appears straightforward and results in the formulation [A2+]11[Cd6Sb12]22–, i.e., Ba11Cd6Sb12 should be a salt-like Zintl phase. However, from analyses of the chemical bonding based on ab-initio calculations, it can be suggested that the simplistic description of the structure is not informative – two of the Cd–Sb interactions are very weak and are inconsistent with the notion of 2-center-2-electron bonding. These findings complement our recent reports on other related Zintl phases with transition metals, suggesting an inadequacy of the classic (empirical) rules for electron counting for understanding the complicated structures of these intermetallic compounds. Optical Biosensor Detects Biological Toxins and Infectious Agents Toxins (poisons produced by living organisms) and disease-causing organisms such as viruses work by binding to specific receptors on the surface of an affected cell. Binding causes the receptors to aggregate, allowing the toxin or invading virus to enter the cell. Our Optical Biosensor uses optically tagged natural receptors embedded in a synthetic cell membrane to mimic a natural chain of events. When a target protein binds, the receptors in the cell membrane are pulled into a cluster by the toxin’s binding sites (shown for cholera toxin in red). The close proximity of the receptors, which are normally further apart, triggers an energy transfer leading to a fluorescent response.