Molecular depth profiling on rat brain tissue sections prepared using different sampling methods.

Brain imaging using time-of-flight secondary ion mass spectrometry (ToF-SIMS) has been reported to produce the distorted biomolecular distributions due to the cholesterol-induced matrix effect when cholesterol migrates to the surface, particularly in white matter, which contains a high level of cholesterol. Frozen-hydrated analysis has been used to inhibit the movement of cholesterol in the brain. In this paper, the authors propose new sample preparation and drying methods that can be used to obtain accurate biomolecular images at room temperature, instead of frozen-hydrated analysis using liquid-nitrogen, which must be continuously supplied to maintain the sample at -160 °C during the experiment. The rat brain prepared by the tape-supporting method on a precooled (-20 °C) stainless steel plate was freeze-dried in a load-lock chamber of ToF-SIMS for about an hour and moved directly to the main chamber. Using this preparation method, the authors found that cholesterol did not migrate to the surface in the corpus callosum (white matter) of the rat brain and sulfatide-related signals obtained from the cerebellum were not reduced in white matter. Our tape-supporting and freeze-drying sampling method for brain tissues could be a useful tool to study important metabolites of neurodegenerative diseases.