Which fixative is considered the best solution for long-term storage of tissue, preserving routine and immunohistochemical staining properties?

• A. 70% alcohol
• B. 10% neutral buffered formalin
• C. Zenker solution
• D. Helly solution

Answer: (A)

When tissues are stored for the long term, the goal is to stabilize structure while keeping antigens accessible for staining. 70% alcohol fixes by coagulation and dehydration, causing less cross-linking than aldehyde fixatives. This preserves epitopes better over time, making immunohistochemical staining more reliable after storage, while also preventing rapid autolysis. In contrast, formalin-based fixatives create cross-links that can mask epitopes and hinder antigen detection after long storage, and mercury-containing fixatives (like Zenker or Helly) pose safety issues and can be less compatible with modern IHC workflows. For these reasons, 70% alcohol is the best choice when long-term storage needs to maintain routine staining quality and immunohistochemical properties.