BME PhD Prospectus Defense - Yixin Mei

Title: "Plasmon Coupling Based Nanoplasmonic Actuators and Photocatalytic Nanocomposites"

Advisory Committee: Michael Smith, PhD – BU BME, MSE (Chair) Björn Reinhard, PhD – BU Chemistry, MSE (Co-Advisor) Wilson Wong, PhD – BU BME (Co-Advisor) Shyamsunder Erramilli, PhD – BU Physics, MSE, BME

Abstract: Noble metal nanoparticles (NPs) have been of interest due to their localized surface plasmon resonance (LSPR) in the visible range of the electromagnetic spectrum. Under illumination the imaginary component from the dielectric function of metal NPs leads to heating of NPs, which can give rise to a self-thermophoretic force near a metal film with high thermal conductivity. Since the plasmonic NPs can act as heat sources and signal probes at the same time, in aim 1 we investigate the thermophoretic force by a nanoplasmonic actuator consisting of a polymer-tethered 20 nm Ag NP on a 20 nm Au film. The resonance resulted large extinction cross section has shown immense potential in sensing and imaging. While between a NP and a metal film, the plasmonic coupling is also sensitive to the NP-film separation change which allows us to detect the displacement via an Interferometric Scattering (iSCAT) microscopy. The two-color iSCAT imaging enables the use of small NP probes and helps differentiate plasmonic NPs from background scatterers. In the study we’re able to observe a gradual iSCAT signal decrease of NPs which is indicative of an attractive self-thermophoretic force. Understanding self thermophoretic forces of NPs in the vicinity of metal films provide opportunities of characterizing molecular biophysics and mechanical properties as well as manipulating NPs and colloids for nanofabrication. Besides high light harvesting efficiency, the enhanced electric (E-) field and hot electron transfer associated with LSPR on plasmonic hybrid nanostructures also rationalize the possibility of energy conversion as well as photocatalysis. Lipid membrane has been a versatile scaffold of loading photosensitizers around plasmonic metal NPs with a proper separation. In aim 2 we design a porphyrin-based sensitizer incorporated nanocomposite with a 40 nm Ag NP core to catalyze hydrogen evolution reaction (HER). Synergy between NPs and photosensitizers in the vicinal active site enhanced HER with an increased photocurrent under illumination. Overall, our goal is to take advantage of plasmon coupling for single particle level characterization as well as photocatalysis.