Guide to Critical Point Drying (CPD) of Biological Samples

Due to the high vacuum conditions in SEM, and exposure to an electron beam, biological samples need specialised preparative techniques to ensure accurate and detailed imaging of fine morphological and ultrastructural features. As a result of the high surface tension of water to air (72.86 mN/m at 20 ˚C), the vacuum-induced evaporation of water molecules from biological specimens can lead to structural deformations and image distortions. Consequently, it is imperative to eliminate water from biological samples prior to imaging to ensure accurate results. In this Application Note, we explore the use of CPD in SEM, outline a general workflow for preparing biological samples using CPD, and provide experimental details for selected applications.