CeNS Colloquium

Prof. W.E. Moerner
Stanford University

Since the first optical detection and spectroscopy of a single molecule in condensed matter (PRL (1989)), much has been learned about the ability of single molecules to probe local nanoenvironments and individual behavior in biological and nonbiological materials in the absence of ensemble averaging that can obscure heterogeneity. Single-molecule fluorescence imaging enables biophysical measurements in cells without ensemble averaging, but also yields enhanced spatial resolution beyond the diffraction limit when combined with optical control of the single emitters to maintain sparse concentrations.   Using the native photoinduced blinking and switching of EYFP (Dickson et al., Nature (1997)) we achieve sub-40 nm super-resolution imaging of protein structures in the bacterium Caulobacter crescentus: the actin-like protein MreB (Biteen et al., Nat. Meth. (2008)), the DNA binding protein HU (Lee et al., Biophys. J.Lett. (2011)), and the ParA division spindle (Ptacin et al., Nat. Cell Biol. (2010)).  A new photoactivatable small-molecule emitter can be targeted to specific proteins in living cells to provide super-resolution images of protein superstructures (Lee et al., JACS (2010)).  In terms of methods, a new scheme for 3D imaging based on a double-helix point spread function enables quantitative tracking of single mRNA particles in living yeast cells with 15 ms time resolution and 25-50 nm spatial precision (Thompson et al., PNAS (2010)), and this approach has been used to define the 3D spatial structure in bacterial (Lew et al., PNAS (2011)) and mammalian cells (Lee et al., Appl. Phys. Lett. (2012)).

To study a single biomolecule in solution without surface attachment or confinement, a machine called the Anti-Brownian ELectrokinetic (ABEL) trap provides real-time suppression of Brownian motion, and this device has been used to explore the photodynamics of single copies of the antenna protein allophyocyanin (Goldsmith et al., Nature Chem. (2010)), to extract ATP number distributions for single multi-subunit enzymes (Jiang et al., PNAS (2011)), and to explore the action of single redox enzymes (Goldsmith et al., PNAS (2011)).  The examples provided here illustrate some of the frontiers where single-molecule spectroscopy and imaging are yielding new insights into the behavior of complex systems.