The Analytical and Surface Chemistry (ASC) program of the Division of Chemistry will support the research program of Prof. Andrew Hilier of Iowa State University. Prof. Hilier's research program focuses on the development of highly sensitive surface plasmon spectroscopic methods for quantitative studies of adsorption of analytes to surfaces. Prof. Hilier and his students will perform detailed experimental and modeling studies to better understand and optimize the conditions needed to facilitate maximum enhancement of light transmission through metal-coated gratings. The proposed studies will be directly applicable to the development of a greatly improved surface plasmon spectroscopic technique. The study will provide an excellent educational opportunity for graduate students and postdoctoral trainees to carry out a spectroscopic method development project wit the potential to revolutionize the field of surface plasmon spectroscopy.
Andrew C. Hillier Department of Chemical and Biological Engineering Iowa State University The primary objective of this project was to exploit the recently discovered phenomenon of extraordinary light transmission through nanometer-scale metallic structures in order to create new and highly sensitive analytical measurement tools, including chemical and biological sensors as well as novel spectroscopy measurements. In this work, gold and silver films coated onto surfaces possessing nanostructures in the form of one-dimensional periodic grooves, also known as surface relief gratings, were fabricated out of common sources, such as compact disks (CDs) or digital versatile disks (DVD), or out of elastomeric polymers whose surface could be controllably buckled by coating with a thin, rigid film. These grating sources, when coated with a thin layer of gold or silver, could excite an oscillation of free electrons at the surface of the metal in the form of a surface plasmon resonance, whose properties could then be monitored to detect changes at the metal interface, such as due to the adsorption of a thin film or coating. The benefits of sensing and spectroscopy methods exploiting surface plasmon resonance are that they are simple and can be constructed from relatively inexpensive components. In addition, surface plasmon resonance is a highly flexible platform and is also exceedingly sensitive. In this work, we have focused on exploiting the tunability provided by grating-based nanostructures to excite surface plasmons, both in terms of the geometry of the grating structure and also in terms of the geometrical aspects of the optical system used for analysis. Through a combination of numerical modeling, experimental fabrication, and sample analysis, we have attempted to develop a greater understanding of the role of specific nanoscale surface structures, in terms of height, shape and width, on the resulting optical response. Specific project objectives included the use of optical modeling to determine the optimum shape of the grating surface, Specific outcomes of the research include: (1) the discovery of angle tunability in the surface plasmon-induced optical transmission, (2) demonstration of surface plasmon imaging detection of protein spot arrays, (3) fabrication of a novel "chirped" grating with a variable surface profile the provided up to 900% enhancement in the optical response, (4) development of a new microscope-based diffractive detection method, (5) combining surface plasmon resonance imaging with an electrochemical microarray system, and (6) development of a new spectroscopy that combines surface plasmon resonance with films containing a strongly absorbing dye. This project has supported the training of several undergraduate students through research experiences, plus the education of two graduate students, with one just recently completing their PhD. Training included developing an expertise with a variety of experimental fabrication and measurement tools. Dissemination of the results of this research occurred through a number of journal articles in peer-reviewed archival research publications and research presentations at universities and national technical meetings.
