Overcoming Adsorption Limitations for Surface Enhanced Spectroscopy Measurements

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New biological, chemical, and radiological agents threaten the environment and human safety every day. While significant advances in small molecule detection have been made, challenges still exist in providing flexible detection methodologies for accurate chemical identification and sensitive and selective detection of some molecules. With support from the Chemical Measurement and Imaging Program in the Division of Chemistry, Professor Haes at the University of Iowa focuses on developing surface sensitive techniques such as surface enhanced Raman scattering (SERS) as a tool molecular detection. SERS is a light-based technique that is used to identify and quantify molecules that adsorb onto metal surfaces. Most molecules do not stick to metal surfaces, limiting the utility of SERS and similar methods. Professor Haes and her group use both experimental and modeling methods to develop the SERS technique so that it can be used to provide accurate chemical identification with high selectivity and sensitivity. Through this research, Professor Haes provides opportunities to graduate and undergraduate students to work on practical problems. The Haes research group performs outreach activities with K-12 students that are focused on the "Size of Things". This project helps students learn about the implications of size on the properties of nanoscale and macroscale objects through hands-on activities. Underrepresented minority students are recruited through the University of Iowa's Center of Exemplary Mentoring. In addition, all personnel participate in educational development and outreach activities geared towards introducing science to Iowa's students in grades K-12. Specifically, Dr. Haes develops a "Size of Things" exhibit for display with a learning game for the size of nanoscale and macroscale objects. They build off of educational activities developed by Public Television (DragonTV on Nano)and provide interactive activities related to (1) What is a nanometer? How big is one billion meters? How small is one-billionth of a meter?; (2) Why is "nanogold" red and "nanosilver" yellow?; and (3) My nanosilver socks do not smell but should I be worried that the nanosilver will get into my body? This project seeks answers regarding how and why some molecules are difficult to detect using SERS. Despite many successful examples of direct small molecule detection using SERS, at least three issues remain including: (1) unpredictable properties of nanomaterials that arise from aggregation, (2) inefficient binding of some classes of molecules to surfaces, and (3) low signals associated with targeted molecules. The two research questions are answered by varying nanoparticle morphology and solution conditions. Research tasks focus on quantifying molecular binding metrics and SERS enhancements and evaluating how solution conditions impact binding metrics, nanoparticle stability, and SERS activity. Key experimental design features are identified so adsorbate-surface interactions are rationally and reproducibly promoted thus facilitating direct detection of molecules using surface-enhanced spectroscopies. Students are trained in the areas of nanoscience, spectroscopy, and measurement science. Through the supported research, the Haes research group is developing design rules that overcome current measurement challenges thus expanding the utility of SERS in a variety of applications.