Intellectual Merits: Certain metals, including silver and gold, exhibit dramatically altered optical properties when formed into nanostructures. Under specific conditions, referred to as localized surface-plasmon resonances (LSPR), light can be highly concentrated around the nanostructure and strongly absorbed. The wavelength at which this phenomenon occurs is highly sensitive to the local environment; as a result, such structures allow biological and chemical sensing in incredibly small volumes. This research effort addresses the two major challenges preventing LSPR sensors from being widely adopted for environmental monitoring, food safety, point-of-delivery medical care, and defense and security applications. (1) Currently, it is difficult to detect a target chemical in the presence of interfering effects such as solution refractive index changes and non-specific interactions between the nanostructure and other components in solutions. By engineering the size, shape, and material of the nanostructures to support multiple surface-plasmon resonances, the research team will be able to distinguish the presence of a target chemical from these interfering effects. (2) By understanding how to effectively interrogate these sensors using integrated optical chips, the team will lay the foundation for highly manufacturable high-density sensor arrays and for in-vivo applications.
Broader Impacts: This research effort will have broad impact by developing a sensor platform that will better serve society's needs in drug discovery, medical diagnosis, food quality assurance, and bio-chemical defense. From an educational perspective, the project provides undergraduate and graduate training in an inherently interdisciplinary field by incorporating aspects of electromagnetics, micro- and nano- scale fabrication, chemical sensing, and signal processing. The project also contributes to the educational infrastructure required to attract and train future engineers through the development of an interdisciplinary NanoPhotonics course, further development of the University of Kentucky's Nanoscale Engineering Certificate Program (NECP), and enhancement of outreach efforts to underrepresented Appalachian students.
This CAREER development effort integrated research, education, and outreach activities in the area of nanophotonic sensing. The intellectual merit of the work rests on understanding how nanoscale metallic structures that strongly interact with different colors of light can detect (bio)chemical interactions in the presence of interfering effects. For example, one might wish to detect a disease biomarker or study a drug interaction in a complex fluid sample, or detect a contaminant in a complex environmental sample. Key outcomes supporting this goal include differentiating between changes in liquid refractive index and the presence of a target molecule using the surface-plasmon resonances of gold nanorods and nano-slits in a gold film. Furthermore, the resonances of U-shaped gold nanostructures could differentiate between target molecules and non-specific binding of interfering molecules. Specific protocols were developed to use, and re-use, these sensors for immunoglobulin G interactions. The project also laid the groundwork for integrating these structures with optical waveguides to move their use from a benchtop system to a highly portable "lab-on-a-chip" based design. The project had a number of broader impacts. From a scientific perspective, the effort contributed to simulation methods for nanoscale photonic structures, new ways of rapidly prototyping nanoscale structures, new means of patterning materials like Teflon to guide light on a chip, and better understanding of how nanoparticles change shape, and optical response, in the presence of certain chemicals. The project extensively developed the nanotechnology workforce by partially training seven graduate students, four undergraduates, and one high school student in the areas of nanophotonics, biochemical sensing, computational electromagnetics, and nanofabrication. Among these students, six were female and five hailed from traditionally underrepresented groups in the STEM disciplines. The program also contributed to educational efforts by strengthening the University of Kentucky (U.K.) Electrical Engineering and Nanoscale Engineering Certificate Program curricula with a new Nanophotonics course that enrolled more than 50 students during the duration of the award. Moreover, this integrated effort impacted a number of Appalachian high school students through on-campus programs, remote interactions with high-school physics courses, and hands-on workshops at the Center for Rural Development in Somerset, KY.
