Department of Chemistry Seminar - Plasmon Coupling Enhanced Optical Properties and Their Applications in Biosensing, Imaging and Phototherapy

Speaker: Professor Qing-Hua XU

Institution: Department of Chemistry, National University of Singapore 

Hosted By: Professor Hongkai WU

Abstract

Noble metal nanoparticles (NPs) have been known to display unique localized surface plasmon resonance (LSPR) property, which could be utilized to significantly enhance optical responses of metal NPs themselves and nearby chromophores, such as Surface enhanced Raman scattering (SERS), metal enhanced fluorescence and Plasmon enhanced nonlinear optical (NLO) responses. In this talk, I will present our group’s efforts on various Plasmon enhanced optical properties and their applications. I will focus on aggregation induced enhancement of optical properties of plasmonic metal nanoparticles: aggregation induced two-photon photoluminescence of metal NPs, and aggregation induced emission (AIE) of chromophore conjugated metal NPs. We found an interesting phenomenon that two-photon photoluminescence of metal NPs were significantly enhanced upon formation of aggregates, up to >800-fold in the colloid solution and several orders of magnitude on single particle level. This phenomenon has been further utilized to develop various two-photon-excitation based biomedical applications, such as sensing, imaging and phototherapy. We have also employed ultrafast spectroscopy and single particle spectroscopy to understand the underlying enhancement mechanisms. Taking advantages of giant local electric amplification of plasmon coupled nanostructures, we have developed a new type of AIE based on aggregation of metal-chromophore conjugates. The working principle of this new AIE scheme is based on aggregation induced plasmon coupling of metal NPs that help to enhance the excitation efficiency and emission quantum yield at the same time. We have further developed various schemes that display significantly enhanced photoactivities to allow applications for multimodal imaging and synergistic cancer therapy.

About the speaker

Qing-Hua Xu received his B.S. from Zhejiang University (1993), M.S. from Peking University (1996) and University of Chicago (1997), and Ph.D. from UC Berkeley (2001). He conducted postdoctoral research at Stanford University (2001-2002) and UC Santa Barbara (2002-2005) before he joined NUS Chemistry in 2005 and became a tenured Associate Professor in 2011. His primary research interests focus on optical properties and dynamical processes of novel low-dimensional materials as well as their applications in biomedicine, energy, and environmental areas. His research spans a broad range from materials preparation to practical applications as well as fundamental studies by using single particle spectroscopy and time-resolved spectroscopy, nonlinear optical spectroscopy and microscopy. So far, he has published over 240 peer reviewed articles with total citations of >17,000 times and H-index of 78 (Google scholar).