With support from the Chemical Measurement and Imaging Program in the Division of Chemistry, Professor Xu at University of California, Berkeley, is developing new strategies for super high resolution and super fast chemical imaging. The technique in development will allow him to obtain spectral signatures of individual molecules for identification purposes as well as the spatial location of these molecules. Moreover, his approach collects data at a much faster speed than what currently feasible, e.g positions of millions of single molecules in dense samples can be collected in minutes. The technique, once developed, will be a very powerful approach for the study of single molecules in a complex environment. For example, it can be used to study uneven distribution of molecules at nanometer scales or to monitor molecule-nanostructure interactions in real time, which cannot yet be achieved by existing techniques. This new measurement capability will find many applications in chemistry, biophysics, cell biology, and materials science. Professor Xu is also interested in integrating what he learns from research into his teaching. He is developing new courses on advanced microscopy and single-molecule spectroscopy for students who are interested. He is also passionate in mentoring students, especially those from underrepresented minority groups, by serving as a Faculty Mentor to Regents' and Chancellor's (RC) and Cal Opportunity (CalOp) Scholars on campus. Professor Xu and his graduate students are teaming up with Bay Area Scientists in Schools (BASIS), a local volunteer program, to develop new science demos and teaching materials for local, underprivileged public schools.
Professor Xu is working to overcome the limitations of modern super high resolution optical imaging techniques by bringing together the spatial, temporal, and spectral dimensions of single-molecule spectroscopy. Indeed, current approaches for the measurement of the fluorescence spectra of single molecules are limited by low throughput and spatial resolution. Meanwhile, emerging super-resolution microscopy methods offer outstanding spatial resolution but no spectral information. Through the development of a new scheme to spectrally disperse the fluorescence of single molecules in the wide-field and achieving molecular sparseness via photoswitching, Xu's approach enables concurrent spectral measurement and super-localization of single molecules with ultrahigh throughput (millions of molecules in a few minutes). Such spectrally-resolved super-resolution microscopy capabilities would offer spectral information for large amount of single molecules together with nanometer spatial resolution. It can therefore enable the interrogation of the behavior of single molecules in different chemical environments, modeling lipid bilayers and cell plasma membranes, and revealing, in a spectrally and spatially resolved fashion, the mechanisms of single-molecule fluorescence enhancement by plasmonic nanostructures.
