In recent years correlative microscopy, combining the power and advantages of light and electron microscopy, has become an important tool for biomedical research.

Light microscopy has the advantage that cellular processes can be observed in life imaging. Cell movements and responses to chemical effectors can be monitored by phase contrast imaging or specific proteins can be labelled by genetically expressed fluorescent proteins, such as GFP^1,2. Next to life cell imaging, light microscopy has the advantage of easily searching large areas, even volumes, for the cells of interest, e.g., a special cell type in tissue, astrocytes in brain,³. Also on thin sections, the low magnification of light microscopy and therefore ease of searching large areas are very beneficial to speed-up the analysis of rare events⁴.

Electron microscopy reveals the cellular ultrastructure a high resolution and individual organelles, even large protein polymers like cytoskeletal filaments or ribosomes can unequivocally identified. Proteins of interest can be labelled with colloidal gold particles and localised to the visible ultrastructural features within the cells. Searching for a few gold particles within a few cells of a large tissue, however, is very cumbersome and can be extremely time consuming.
Seen the advantages of light and electron microscopy suggests that the optimal approach is to combine both techniques for cell biology research. Life cell imaging and the localisation of rare cellular events are followed and identified by (fluorescence) light microscopy, the high resolution data and fine localisation to cellular substructures are done by electron microscopy.
¹Tsien, R.Y., Annl Rev Biochem 67 (1998). p. 509-544.
²Tsien, R.Y., Integrat Biol 2 (2010). p. 77-93.
³Loussert Fonta, C., et al., J Struct Biol 189 (2015). p. 53-61.
⁴Schwarz, H. and B.M. Humbel, Meth Mol Biol 1117 (2014). p. 559-592.

Bruno M. Humbel, PhD, is head of Imaging Group of the Okinawa Institute of Science and Technology, Japan. I got my PhD at the Federal Institute of Technology, ETH, Zurich with Prof. Hans Moor and Dr. Martin Müller, both pioneers in cryo-electron microscopy. My research focuses on sample preparation for optimal, life-like imaging of biological objects in the electron microscope. The main interests are preparation methods based on cryo-fixation applied in Cell Biology. From here, hybrid follow-up methods like freeze-substitution or freeze-fracture are used. I am also involved in immunolabelling technology, e.g., ultra-small gold particles. I teach cryo-techniques and immunolabelling in international workshops and have professional affiliations with Zhejiang University, Hangzhou, People's Republic of China and the Federal University of Minas Gerais, Belo Horizonte, Brazil.