October 19, 2021

I, Science

The science magazine of Imperial College

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The Story of a Molecule

16 November, 2015 @ 6:00 pm - 7:00 pm


More than 25 years ago, low temperature experiments aimed at establishing the ultimate limits to optical storage in solids led to the first optical detection and spectroscopy of a single molecule in the condensed phase.

At this unexplored ultimate limit, many surprises occurred where single molecules showed both spontaneous changes (blinking) and light-driven control of emission, properties that were also observed in 1997 at room temperature with single green fluorescent protein variants.

Super-resolution microscopy has opened up a new frontier in which biological structures and behavior can be observed in fixed and live cells with resolutions down to 20-40 nm and below.  Examples range from protein superstructures in bacteria to details of the shapes of amyloid fibrils and much more.

Current research addresses ways to extract more information from each single molecule such as 3D position and orientation, and both of these can be obtained by proper point-spread function engineering of a wide-field microscope. It is worth noting that in spite of all the current focus on super-resolution, even in the “conventional” low concentration, single-molecule tracking regime where the motions of individual biomolecules are recorded rather than the shapes of extended structures, much can still be learned about biological processes. For example, my laboratory has explored the motions of single Smoothened proteins in the primary cilium, where the molecular motions show clear evidence of binding sites at the ciliary base whose affinity is modulated by Hedgehog pathway activation.

Outside of cells, using a special trap for single molecules in solution, we can measure not only the brightness of each, but also its lifetime, spectrum, polarization, and even its radius and charge.  This approach allows a detailed exploration of photodynamics for single antenna proteins and enzymes, and enables exploration of DNA hybridization and oligomer distributions.


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