Correlative Tools for in Situ Analysis of Single Nanoparticles and their Ligands

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Designer gold nanoparticles consist of a metallic core surrounded by a molecular shell. Recent advances in nanoparticle growth have produced complicated star-like shapes that exhibit unique physical properties and are about 1/100 the diameter of a human hair. While the formation of the stellated structures is linked to the reaction conditions, controlled formation of particles with specific structural features remains a challenge since the growth mechanism is still unknown. With support from the Macromolecular, Supramolecular and Nanochemistry Program in the Division of Chemistry, Professor Teri Odom of Northwestern University is developing a series analytical tools to achieve higher structural and chemical information of single nanoparticles in their native growth environments. Using this toolkit, Professor Odom and her students are identifying key intermediates in nanoparticle formation that could advance our understanding of how complex nanostructures grow. The project could pave the way to create particles with specified shapes that would have broad implications for a range of technologies, including personalized medicine and single-molecule contaminant detection. The project trains future scientists, with outreach efforts focusing on developing a new general chemistry sequence and developing graduate and junior faculty training initiatives. The project also provides training opportunities for future scientists through programs such as 'Nano Scout Day' at the Alder Planetarium. Professor Odom also actively outreaches to local middle school students targeting underrepresented minority students. This proposal aims to develop correlative tools to study metal nanoparticles and their immediate surrounding environment at the near-in situ, single-particle level. The work combines multiple tools in an integrated strategy to access real-time, statistical, and multi-functional information from individual nanoparticles. Although seedless growth conditions using a gold salt and Good's buffers have been shown to promote distinct curvature regions in nanoparticles that can result in specific, exquisite macroscale properties, identification of intermediates key to nanoparticle formation has not yet been possible. To determine how nanoparticle shape and their ligand distribution interacts with local environments, high-throughput, single-nanoparticle statistical data is required. The research objectives include: (1) repurposing electron paramagnetic resonance spectroscopy to correlate the generation of different radicals with nanoparticle intermediate shapes and final products; (2) visualizing structural evolution of single nanoparticles during growth with wide-field differential interference contrast optical microscopy; and (3) mapping ligand distributions on different particle surfaces with one-of-a-kind tools such as time-of-flight secondary ion mass spectrometry using particle projectiles.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.