Sample preparation utilizing sputter coating increases contrast of cellulose nanocrystals in the transmission electron microscope.

Cellulose nanocrystals (CNCs) are prepared for transmission electron microscopy (TEM) using positive or negative stains in an effort to increase the contrast between the specimen and background. When imaging CNCs, conventional stains have been shown to induce particle aggregation and produce artifacts. In this study, we report on methods used to image CNCs. To increase contrast and decrease artifacts and aggregation, sputter coating was used to coat the samples. CNCs were loaded onto copper grids and sputter coated with one of four different metals: iridium, carbon, gold, and titanium. The final layer was deposited at 5 nm to ensure surface homogeneity. The thin layer of conductive metal atoms deposited onto the specimen surface significantly increased contrast and improved image quality. The results presented here demonstrate the advantages of using sputter coating for imaging of highly crystalline cellulose materials with TEM.