Guide to Critical Point Drying (CPD) of Biological Samples
With magnification up to 1,000,000 times and resolution of 1-10 nm, scanning electron microscopy (SEM) is a versatile technique that allows us to gain insights into the morphological structures of surfaces.
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.