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Wellcome Image of the Month: Super resolution microscopy

14 Oct, 2011

Microscopes let us view really small things at bigger scale, opening up a fascinating scientific world normally invisible to the human eye. They have completely transformed cell biology, uncovering an array of complex internal structures and emphasising biological differences across multiple organisms.

The earliest microscopic device invented by Zacharias Jansen in 1595 was pretty simple; a tube with two glass lenses at one end using light to give a magnification ten times the actual size. During the 17th Century magnification and image quality of light microscopes improved, but were ultimately limited by the wavelength and diffraction properties of visible light.

The optical resolution of light microscopy is about 250 nanometers, anything smaller appears blurred in the microscope image. The invention of the electron microscope (EM) in 1931 greatly improved image quality, but even today’s sophisticated EM machines are limited to imaging chemically fixed samples and cannot visualise multiple structures very easily within a single specimen.

However, the innovation of fluorescence microscopy over the last 10 years has totally transformed how scientists use light microscopy to study cell structure. In fluorescence microscopy your specimen is labelled with fluorescent stains or proteins. When light of a specific wavelength (matching the fluorescent tag) illuminates the sample, electrons within the specimen become excited and emit energy as detectable light. Down the microscope, these fluorescing areas are seen in bright colours against a contrasting dark background.

Fluorescence microscopy is a highly sensitive technique and an extremely powerful tool in cell biology, but standard microscopes are still limited by their optical resolution. Recently, however, it was discovered that by imaging individual fluorescent molecules separately over time (using special photoactivatable dyes), a fluorescently tagged specimen can be imaged at much higher resolution than previously possible. Termed super resolution microscopy, this technique made it possible to identify single molecules to an accuracy of 25 nanometers inside live cells for the first time.

But what does this actually look like? Our Image of the Month for October shows fluorescently labelled actin filaments imaged using super resolution microscopy. Because the dye molecules emit photons at random when excited, individual actin molecules are identified over time and this reconstructed image shows their precise location within a cell. If the same sample was imaged using standard fluorescence we would only see the cell and not individual molecules within it.

The image was taken by Dr Colin Rickman at Heriot Watt University, Edinburgh. Colin is a founding member of the Life Science Interface Laboratory, part-funded by the Wellcome Trust, which specialises in molecular imaging and brings together researchers from a range of scientific backgrounds including physics, maths, engineering, chemistry and biology through molecular imaging. Colin is an expert in fluorescence microscopy. His research interest lies in the field of exocytosis, or secretion, a process central to cell communication. His team are currently concentrating on the organisation and tracking of proteins, such as actin, at the single molecule level using super resolution microscopy.

References

  • McEvoy AL, Greenfield D, Bates M, & Liphardt J (2010). Q&A: Single-molecule localization microscopy for biological imaging. BMC biology, 8 PMID: 20707882
  • Schermelleh, L., Heintzmann, R., & Leonhardt, H. (2010). A guide to super-resolution fluorescence microscopy The Journal of Cell Biology, 190 (2), 165-175 DOI: 10.1083/jcb.201002018
  • Ruth Milne, Wellcome Images

    Wellcome Images is one of the world’s richest and most unusual collections, with themes ranging from medical and social history to contemporary healthcare and biomedical science. All our images are available in digital form so please click the link above if you would like to use the picture that features in this post, or to quickly find related ones. Many are free to use non-commercially under the terms of a Creative Commons licence and full details of the specific licence for each image are provided.

    Image credit: Colin Rickman, Wellcome Images
    2 Comments leave one →
    1. 17 Oct, 2011 9:53 am

      Superresolution microscopy is indeed a suite of techniques that have dramatically increased our ability to visualise life at near to molecular resolution. The image shown here does not look like any actin filaments I have seen before and it would be interesting to know what type of filaments these are, i.e. sub-cortical etc.?

    2. Ruth Milne permalink
      25 Oct, 2011 12:09 pm

      According to the researcher, the image was acquired using total internal reflection fluorescence microscopy which illuminates a thin sample at the base of the cell. The image is of cortical actin over an approximately 150 nm depth in to the cell.

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