Method of platinum-carbon coating of ultrathin sections for transmission and scanning electron microscopy: an application for study of biological composites

Many biological materials are composites containing two or more components with different mechanical properties. This study is concerned with the application of a method of platinum-carbon coating (Pt/C) of ultrathin sections for TEM and SEM studies of the design of natural composite materials. The changes in profile of the ultrathin resin-embedded sections during different stages of the preparation reflect the material properties of the various components: stiffer regions deform less than softer ones. Such changes in the section profile can be visualized by the Pt/C method and used as evidence of specific material properties in particular regions of composite materials. The method increases the relief contrast, improves the 3D-view of structures, and in combination with standard TEM and SEM procedures can provide clear demonstrations of material design. The distribution of chitin crystallites in the insect cuticle and the ultrastructure of the pore canal system specialized for the transport of epidermal secretions to the cuticle surface were studied here as examples.