Cellulose has many desirable properties, such as being renewable, biodegradable, abundant and inexpensive. The cellulose can be treated by sulfuric acid hydrolysis, during which cellulose nanocrystals (CNCs) are obtained. CNCs have a high surface to volume ratio resulting in high fraction of hydroxyl groups that can be used for functionalization in different applications. The anionic sulfate groups, resulting from the sulfuric acid hydrolysis, provide colloidal stability to CNC dispersions, that are otherwise prone to aggregate. However, the site of a sulfate group represents the absence of a hydroxyl group. Desulfation, which is the process where sulfate groups are removed and replaced by hydroxyl groups, can be used to enhance the access to the hydroxyl groups on CNC surfaces. Important parameters are both density and the specific site on the CNC surface. Considerable research has been dedicated to the functionalization of the hydroxyl groups on the CNC surface for tailoring properties. A crucial step in the functionalization is to control the removal of sulfate groups.
Chemical hydrolysis has been reported as a desulfation method. However, when chemical hydrolysis is preformed, there is no control or selectivity in how many or from which site the sulfate groups are removed. In contrast, enzymatic hydrolysis has the potential of controlling both the number and site specificity. Electron microscopy is used to determine the enzymatic reaction mechanisms on the CNC surface. 
The specimen preparation for electron microscopy is a crucial step. To enhance the imaging contrast, the sulfate groups are labelled with silver and gold. The Ag/AuCNC dispersions are diluted to 0.01 wt% and drop casted onto silicon wafers for scanning electron microscopy (SEM), see Figure 1, and on holey carbon films for transmission electron microscopy (TEM). 
Figure 1: SEM image using secondary electrons, illustrating Ag (white dots) bound to sulfate groups on CNCs.