There is a pressing requirement for compact, reliable, ultra-sensitive and cost-effective chemical sensors for emergency response and threat detection. A major problem in persistent sensors has been the size and power consumption requirements. The technology proposed answers this problem with a proposed network of nano-wires that will be used as selective point sensors, utilizing a combination of electronic and optical responses. Detection of an adsorbed chemical on individual wires will use both current voltage curves and surface-enhancde Raman scattering spectra. Nano-wires are grown and assembled into networks using surface tension and magnetic forces. Making the junctions of the networks reproducible and coupling with electronic sensors will enable design of a multi-modal sensor. This will enable low cost sensors for detection of biological and chemical agents to be built. The group has engaged with local high schools in an active mentoring and internship program, as well as outreach to teachers. An additional university-level laboratory course will be enhanced to deal with the new nano-fabrication requirements of nano-wire networks. The development of the sensors will have a broad impact in medicine and environmental monitoring, as well as national security.
PHS 398 (Rev. 9/04), Continuation Page This project was directed at the development of compact, reliable, ultra-sensitive and cost-effective chemical sensors for early detection of toxins and chemical agents. The focus was on developing strategies to detect chemicals using changes observed in nanoscale elements for enhanced sensitivity. Due to the small overall size of these elements, a small change that occurs on binding of the chemical produces a discernible response in the properties of the element. We fabricated nanowire sensors and demonstrated spectroscopic detection of chemical simulants such as malathion, dicrotophos and dimethyl methylphosphonate. The cores of the sensors were rough nanowires synthesized in large batches using an inexpensive electrochemical technique. Our optical device, in which detection was based on surface enhanced raman spectroscopy (SERS), was shown to have a much higher sensitivity than existing surface acoustic wave (SAW) devices. About three orders of magnitude fewer molecules could be detected which demonstrates significantly enhanced sensitivity. Additionally, the optical signal allows a fingerprint detection of the analyte. This dramatically increases the utility of the sensor, as the analyte can be identified very precisely. This is in contrast to SAW devices which typically only detect a class of analytes. Furthermore, methodologies to array nanowire sensors using electrical fields were developed to enable parallel detection with multiple sensing elements. Our methodologies of nanowire growth and electric field assisted self-assembly of nanowire networks were shown to be inexpensive and compatible with present day wafer scale microchip fabrication; hence the methods can be used to fabricate large numbers of sensor network chips inexpensively. A significant effort was also made to enhance education and training of K-12, undergraduate, graduate and post-doctoral students including those from underrepresented groups in science and engineering by involving them in different aspects of the research in the science and engineering of these sensors.
