Atmospheric Scanning Electron Microscope Observation of Cells Using a Charged Gold Labeling Technique

Abstract

Optical and electron microscopes are widely used for morphological observation of microbes and cultured cells. However, the small size of microbes (flagella and pili) and cells (filopodia) limits optical microscope observation. An electron microscope has a high resolution. However, lengthy pretreatments such as dehydration or metal evaporation are basically necessary. This may obscure delicate structures in SEM images. For the observation of natural structures in microbes and cells, we have developed an in-liquid gold labeling technique using an atmospheric SEM (ASEM), which observes a sample in liquid in open atmosphere. Sample pretreatment required only simple tasks including fixation, gold labeling, and medium exchange, taking less than one hour in total. ASEM imaging of the bacteria in aqueous solution revealed pili and delicate spiral flagella in natural form. The gold labeling also allowed filopodia as thin as 100 nm in diameter to be clearly visualized.