Professor David Heskett (physics) and Dr. Michael Briere (Cherry Semiconductor Corp.) have teamed up to study the fundamental mechanisms underlying electromigration. With students Keith Aubin, Andrew Merrdinyan, and Brian Setlik, these researchers have established models that describe electromigration as a function of temperature, current density, and size of the conductor (5). The microscopy laboratory maintained by the SSTP has been especially useful for this study, because the researchers have been able to record a video of a pristine integrated circuit interconnect driven to failure by current flow.

Although many strain sensors are available, all require a DC power supply to function. Because earthquakes almost always cut electrical service, the strain sensor must have a battery, which must be replaced periodically. One solution to this inconvenience is a sensor that records the strain information without the need for power.

This group has designed such a system using polymers: The sensor is sensitive to strain information in an irreversible fashion. Thus, the sensor records the accumulated strain on a structure during the catastrophic event and stores it for recall at a later date (i.e., after the immediate danger is over). Thus, "invisible" damage to a building could be assessed safely by directly measuring the accumulated strain.

Here we describe an acoustically enhanced fluorescence sensor (4). It starts with a standard "sandwich" immunoassay in which a primary antibody captures a pathogen (e.g., Salmonella typhimurium), which, in turn, captures one or more fluorescently labeled antibodies. For efficient pathogen capture, the primary antibodies must be distributed throughout the sample volume; however, for efficient detection of the sandwich complexes, the concentrations must create the correct optical excitation-to-detection volume ratio.

To circumvent this problem, the primary antibodies are immobilized on polystyrene microspheres 5-10 mm in diameter. These microspheres can be distributed throughout the cell initially and then manipulated with an ultrasonic standing wave into the immediate vicinity of a step-tapered optical fiber aligned along the axis of the cell. The detected fluorescence signal can be increased by a factor of 20 this way. This research is led by professors Chris Brown (chemistry), Stephen Letcher (physics), and Garth Rand (food science); students are Sibel Babacan, He Cao, Gi-Ho Kim, James Lyons, John Seelenbinder, and Chongua Zhou.

The U.S. Department of Agriculture provides partial funding for this research.

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