Imaging dynamic biological processes with ESEM – A proof of principle study on plant tissue

The Environmental Scanning Electron Microscope (ESEM) differs from a conventional SEM in that a differential pumping system maintains a pressure of gas (typically H2O) in the specimen chamber whilst the gun remains at high vacuum [1]. Ionizing collisions between electrons and these gas molecules create positive ions which drift down onto the sample providing a mechanism for neutralising specimen charge. It is therefore possible to image insulating samples without the need for a metallic coating. The presence of water vapour in the chamber also means that a high relative humidity can be maintained and therefore samples can be imaged in a hydrated state without the need for dehydration and fixation.