An Optical Tweezer Darkfield Plasmon Ruler Microscope for Single Molecule Charge Transport Measurements

This project will advance the understanding of how electrons move through molecular materials by developing a new all-optical technique for single molecule manipulation and conductance measurements in solution. Molecules are the fundamental building block of any material and are smaller than state-of-the-art transistor elements powering modern electronics, which are based on bulk crystalline silicon. To further shrink electronics down in size, approaches to probe and understand electron flow through single molecules are required. Increasing evidence from biological systems points to the ability of organisms to conduct electricity using molecular structures, motivating the adoption of biotechnology to achieve miniaturization of electronics. However, current methods for measuring currents across single biological molecules can destroy the weak bonds that enable their 3D structure and properties. This project will develop a technique for manipulating single molecules and for probing their ability to conduct electricity and transmit electric fields without exerting high forces that can lead to biomolecule disintegration. The technique will use a single molecule manipulation approach known as optical tweezers to suspend a single molecule between two gold nanoparticles in solution as if by a pair of microscopic tweezers made out of light and use optical signals to infer how electrons distribute and flow across the molecular bridge under illumination. By employing graduate and undergraduate students from chemistry, physics and material science, the proposal will contribute to interdisciplinary training of the next generation STEM workforce. The project will develop a new all-optical method in solution for assessing charge transport and transfer across single molecules, including biological molecules such as nucleic acids and protein nanowires, bridging two plasmonic nanoparticles. Building on the optical tweezer methodology, this work will develop tools to manipulate nanoparticle dimers and alter the inter-particle gap, enabling real-time study of charge transport across molecular monolayers and single molecules. Darkfield spectroscopy, surface enhanced Raman and ab initio simulations will be used to characterize the electronic properties of the molecular materials in the dimer junction at optical frequencies. These studies will allow greater understanding of the relationship between nanoscale geometry, electronic properties of molecular spacers and overall optical response, filling in important knowledge gaps about charge transfer and transport processes in single molecular wires and soft materials. 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. NSF Award ID: 2603896 | Program: 01002627DB NSF RESEARCH & RELATED ACTIVIT | Principal Investigator: Maria Kamenetska | Institution: Trustees of Boston University, BOSTON, MA | Award Amount: $570,000 View on NSF Award Search: https://www.nsf.gov/awardsearch/show-award/?AWD_ID=2603896 View on Research.gov: https://www.research.gov/awardapi-service/v1/awards/2603896.html