A versatile electrochemical sensor for the rapid and selective detection of chemical warfare agents, glucose, explosives and for other molecules in the gas and liquid phases is proposed. The sensor is based on arrays of nanometer thick films of metallic LiMo3Se3 nanowires that are dispersed between two or several gold electrodes. Upon exposure to solvent vapors the nanowires undergo large (240%) and reversible changes of their conductivity. The electronic response depends on the nature of the solvent and on the concentration, and it occurs within seconds of the exposure. The selectivity of the nanowires can be controlled by covalently linking receptors to the selenide surface of the nanowires. Upon attachment of propionic acid (a proton receptor) the nanowire film becomes a detection element for protons in aqueous solution. A similar pH sensor also forms by linking 10 nm large gold nanoparticles to the wires, and by subsequently attaching 3-mercaptopropionic acid to the gold nanoparticles. In order to use the LiMo3Se3 nanowires for sensors that will be faster, smaller, more sensitive and versatile and less expensive than sensors based on conventional materials, it is planned to systematically study the structure, physical and electrical properties of LiMo3Se3 nanowires under variable conditions. The conductivity response of the nanowires to molecules or variable charge, polarity and coordinating power will be measured using patterned indium tin oxide microelectrode arrays that allow simultaneous interrogation of up to twenty different nanowire films. The number of molecules/ions that interact with the nanowires under given conditions will be determined with quartz crystal microbalance measurements. Systematic covalent modifications of the nanowires with small molecules and with oligopeptides will be conducted to introduce receptors for the selective detection of chemical warfare agents, for glucose and for explosives. Scanning tunneling measurements on modified nanowires will probe changes of the electronic structures that occur as a result of these modifications and that are due to analyte interactions. Accompanying electronic structure and molecular dynamic calculations will simulate the observed phenomena, and develop models to rationalize the effects. In being able to detect glucose, explosives, and chemical warfare agents, the nanowire based sensors that will be fabricated in this project will directly contribute to health care and national security. In establishing a molecular level understanding of the physical and chemical aspects of molecule-nanowire interactions this project will make also a general impact on the design and understanding of nanowire sensors. Graduate and undergraduate students will be involved in all aspects of the project. They will prepare the materials and characterize them with instruments that they operate independently, and they will present their results at conferences. Collaborations with physical and theoretical chemists and with a physicist will strengthen the communication across disciplines. Results from the project will be incorporated into exhibits at a local science museum and into chemistry demo shows on campus and at local high schools. This K-12 outreach initiative will involve the UC Davis chemistry club, an organization of 20 undergraduate students with different majors which is overseen by the PI. During an open door day undergraduate students will be given the opportunity to visit the lab and to make contact with the respective PIs. An graduate course on "Inorganic Colloids" will be offered as an introduction to the chemistry and physics of colloidal particles and their uses for engineering applications, and in particularly to sensor technology.
