Thermal energy, also known as heat, flows naturally from hot objects to cold objects. One consequence of this heat flow is that it is difficult to create objects with localized "hot spots," even when heat is applied to a single spot. When touching a hot pan on the stove, the temperature of the lid on top of the pan is not much different than the bottom where the heat is applied. Depositing and maintaining thermal energy in a small region of space becomes even more challenging as the object's size approaches the tens to hundreds of nanometers, or about 1,000 times smaller than a human hair. Yet, the ability to control heat flow and thus temperature at nanoscopic dimensions has important implications for applications ranging from data storage and the local control of chemical reactions to photothermal therapies for disease treatment and pain management through ion channel stimulation. With support from the Designing Materials to Revolutionize and Engineer our Future (DMREF) Program in the Division of Chemistry (CHE) and the Division of Chemical, Bioengineering, Environmental, and Transport Systems (CBET), Professor David J. Masiello from the University of Washington, Professor Katherine A. Willets from Temple University, and Professor Stephan Link from Rice University are developing methods to theoretically design and experimentally realize a new class of materials capable of controllably directing temperature increases to nanoscale regions of space. Beyond impacting a wide variety of applications, the project is also facilitating the interdisciplinary training of students and postdoctoral researchers through student exchange between the three research groups.
Together, the researchers and their students are designing plasmonic nanostructures that exploit Fano interferences to focus and convert optical radiation into precise nanoscopic temperature profiles that are actively tunable from the far-field. They are developing computer simulations to solve the coupled Maxwell-heat diffusion equations and using them to design novel plasmonic nanostructures with Fano interferences that are capable of localizing spatial temperature profiles at dimensions below the diffraction limit. The best candidates are then created in the laboratory and characterized using optical microscopies. Diffraction-limited, single-nanoparticle photothermal absorption spectroscopy techniques measure the heat power absorbed as well as the associated temperature change induced in the target material. Fluorescently-labeled stem-loop DNA structures are used to achieve super-resolution imaging of the nanoscopic temperature profile. The imaging results are then input into the design of the next generation of structures, providing the iterative feedback that is critical to the project's success.
