Three scientists were awarded this year’s Nobel Prize in Chemistry for developing a new generation of optical microscopes that can peer at the processes inside living cells on the nanoscale. Their invention represents a huge leap over the optical microscopes that gave scientists their first glimpse of tiny living organisms starting in the 17th century.
The biological imaging techniques pioneered by Eric Betzig, Stefan Hell, and William Moerner succeeded in overcoming a physical limit defined by half the wavelength of light and first described by microscopist Ernst Abbe in 1873. That limit meant optical microscopy could not reveal biological objects smaller than 0.2 micrometers, such as viruses or proteins. Modern electron microscopes have the resolution to see at such small levels of detail, but their preparation is lethal for cells under observation and prevents scientists from peering at the inner workings of living cells.
One of the first breakthroughs came from Stefan Hell, a physicist at the Max Planck Institute for Biophysical Chemistry, in Göttingen, Germany. In 1993, Hell had his eureka moment while working on fluorescence microscopy, a technique that involved using pulses of light to excite certain molecules in a way that allows scientists to see their glowing locations within cells. The problem was that the microscope resolutions were still too low to see objects such as individual DNA strands.
Hell bypassed the limitation by proposing a method called stimulated emission depletion. After using a laser beam’s pulse of light to excite the fluorescent molecule, a second laser quenches the fluorescent glow except for a nanometer-size volume in the middle. That allows scientists to build a very detailed image of the molecule by sweeping the “nano-flashlight” along the object and continuously measuring light levels, according to a Nobel Foundation explainer. Those small volume images were put together to form a detailed whole image.
By comparison, Eric Betzig and William Moerner, working independently, helped develop a second method called single-molecule microscopy. That method takes several images of the same area while turning the fluorescence of a few individual molecules on and off. Once all the images are superimposed on one another, they form a single “super-image” with details at the nanoscale level.
In 1989, Moerner, a chemist at Stanford University and an IEEE Senior Member, became the first scientist to ever measure the light absorption of a single molecule (he worked at the IBM research center in San Jose, Calif., at the time). He followed up that work eight years later by showing it was possible to control the fluorescence of single molecules, work he described in the journal Nature in 1997.
Such control over single-molecule fluorescence represented the practical solution to a theoretical concept envisioned by Eric Betzig two years earlier. Betzig, a physical chemist at the Janelia Research Campus of the Howard Hughes Medical Institute in Ashburn, Va., developed his ideas in the 1990s while working on a new type of optical microscopy called near-field microscopy.
After leaving his research career for a while (to work at his father’s machine tool company), Betzig returned and eventually demonstrated how the single-molecule fluorescence could help create the highly detailed “super-image” of a specialized cell organelle called a lysosome. His groundbreaking work appeared in the journal Science in 2006.
These advances in optical microscopy have allowed researchers to begin studying the inner workings of living cells in unprecedented detail. Hell has used the technique to peer inside living nerve cells to understand how brain synapses work. Moerner has examined proteins related to Huntington’s disease, an inherited genetic disorder that leads to the malfunction and breakdown of brain cells. Betzig has studied cell division within embryos.