Alginate gel embedding preserves antigenicity in free-floating brain sections

Free-floating cryosections are widely used in neuroanatomical and immunohistochemical studies due to their superior antigen preservation and unrestricted antibody penetration. However, long-term storage of these sections is vulnerable to freezer failures, often resulting in irreversible loss of irreplaceable material. To address this limitation, we developed an alginate gel embedding method designed to protect free-floating brain sections after cryotome cutting and maintain antigenicity during extended storage at -40°C. Using a mouse model of ischemic stroke, we evaluated antigen stability under simulated freezer accident conditions by analyzing immunofluorescence for CD68, GFAP, Iba1, and NeuN in consecutive sections exposed to room temperature for 0, 1, or 2 days. CD68 and Iba1 signals showed partial decline by day 2, whereas GFAP and NeuN immunoreactivity remained largely preserved, with only minor reductions in intensity. These results demonstrate that antigen stability varies across markers but can be substantially maintained when sections are embedded in alginate gel. Our findings highlight a simple and effective strategy for long-term preservation of free-floating cryosections and support its use as a safeguard against tissue degradation during storage interruptions. This method offers a practical solution for laboratories relying on extended experimental timelines and repeated immunohistochemical analyses.