As not all markers appropriate for LM can survive the harsh processes involved in sample preparation, a number of CLEM techniques use cryogenic methods. Though these techniques preclude to observe the dynamics of live cells, in 2008 a method was found to combine live-cell data with EM. To make CLEM more user-friendly it is important to stain the structure in a manner suitable for both LM and EM. Several approaches have been developed, including the first genetically encoded fluorescent protein available for EM examinations. Further effort has been invested in finding ways to get accurate image alignment to ensure that the exact same cell is observed under LM and EM. To speed up the CLEM process, mainly caused by the problems to transfer samples from LM to EM for analysis, several automated methods have been proposed. Presenting three case studies the Essential Knowledge Briefing shows how the challenges of CLEM have been met.
Despite the progress in establishing CLEM some major problems remain: The difficulty of locating the region of interest when shifting the sample from LM to EM, further the challenge of how to grow the cells, the lack of compatibility of probes and techniques and the risk of contamination and damage due to the time-consuming handling.
In future, CLEM will probably be complemented by the new super-resolution microscopy techniques as these are easier to integrate with EM. The scope of correlative techniques will broaden and include other complex microscopy techniques. Currently researchers are trying to develop a single probe for CLEM. A significant step forward would be the development of a commercially available all-in-one solution for CLEM.