Nobel Lecture: Single-molecule spectroscopy, imaging, and photocontrol: Foundations for super-resolution microscopy

Abstract

The initial steps toward optical detection and spectroscopy of single molecules in condensed matter arose out of the study of inhomogeneously broadened optical absorption profiles of molecular impurities in solids at low temperatures. Spectral signatures relating to the fluctuations of the number of molecules in resonance led to the attainment of the single-molecule limit in 1989 using frequency-modulation laser spectroscopy. In the early 90's, many fascinating physical effects were observed for individual molecules, and the imaging of single molecules as well as observations of spectral diffusion, optical switching and the ability to select different single molecules in the same focal volume simply by tuning the pumping laser frequency provided important forerunners of the later superresolution microscopy with single molecules. In the room temperature regime, imaging of single copies of the green fluorescent protein also uncovered surprises, especially the blinking and photoinduced recovery of emitters, which stimulated further development of photoswitchable fluorescent protein labels. Because each single fluorophore acts a light source roughly 1 nm in size, microscopic observation and localization of individual fluorophores is a key ingredient to imaging beyond the optical diffraction limit. Combining this with active control of the number of emitting molecules in the pumped volume led to the super-resolution imaging of Eric Betzig and others, a new frontier for optical microscopy beyond the diffraction limit. The background leading up to these observations is described and current developments are summarized. The early days Introduction and early inspirationsI want to thank the Nobel Committee for Chemistry, the Royal Swedish Academy of Sciences, and the Nobel Foundation for selecting me for this prize recognizing the development of super-resolved fluorescence microscopy. I am truly honored to share the prize with my two esteemed colleagues, Stefan Hell and Eric Betzig. My primary contributions center on the first optical detection and spectroscopy of single molecules in the condensed phase(1), and on the observations of imaging, blinking and photocontrol not only for single molecules at low temperatures in solids, but also for useful variants of the green fluorescent protein at room temperature (2). This lecture describes the context of the events leading up to these advances as well as a portion of the subsequent developments both around the world and in my laboratory.In the mid-1980's, I derived much early inspiration from amazing advances that were occurring around the world where single nanoscale quantum systems were detected and explored for both scientific and technological reasons. Some of these were (i) the spectroscopy of single electrons or ions confined in vacuum electromagnetic traps (3-5), (ii) scanning tunneling microscopy (STM) (6) and atomic force microscopy (AFM) (7), and (iii) the study of ion currents in single membrane-embedded ion channels (8). But why not optical detection and ...

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