WIN Seminar Series: Professor Qing-Hua Xu

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 two-photon photoluminescence of metal NPs and aggregation induced emission (AIE) of chromophore conjugated metal NPs. Our group 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 demonstrated to be universal for Plasmonic metal NPs, which has been further utilized to develop various two-photon-excitation based biomedical applications. 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 photosensitizer conjugated gold NPs that display significantly enhanced fluorescence, singlet oxygen generation and photothermal response, which allow applications for multimodal imaging and synergistic photothermal and photodynamic cancer therapy below the skin tolerance threshold.