X-Message-Number: 4873 Newsgroups: sci.cryonics Date: Wed, 13 Sep 1995 21:46:20 +0200 (MET DST) From: Eugene Leitl <> Subject: neurotissue voxel imaging at molecular resolution Message-Id: <> High-resolution (till down to molecular level) 3d scan of cerebral tissue is a long-pursued dream of neuroscience. With relatively recent advent of vitrification and ultrarapid freeze of biotissue specimens at least the long-term stability of "tissue snapshot" has been assured. However, how can a small tissue block be transformed into the according voxel block? Water ice sublimates if exposed to hard vacuum. Vacuum etching of cytosol and a subsequent carbon/platinum shading is a widely used EM contrasting technique. Though high glycerol (and other polyols) levels will reduce cytosol sublimation rate, phospholipid membranes and cytosol embedded proteins remain prominent, however. What to do? A complementary abrasion technique can be the UV (excimer) etching. Short hard UV laser pulses virtually turn a few-nm thin surface layer into an ionized, rapidly expanding gas cloud which get rapidly pumped off by the turbovac (surface must be clean, hence no oildiff (at least without a cryotrap baffle)). The fine details of the exposed (both (cycled) vacuum etch and excimer pulse) surface can be scanned by an AFM (atomic force microscope) at relatively high (audio to video) bitstream rate. UV photoionisation potential background induced problems do not appear unsurmountable. E.g. cryovitrified synapse 3d scan at molecular resolution might be attainable with above abrasive microscopy technique. Since ultrarapid freezing can snapshot few-ms processes this method might feature both high temporal and spatial resolution. The experimental setup would require a small (fist-sized) vacuum chamber with vacuum-tight electrode array, a turbovac (vibration!) or a cryotrap-baffle equipped oildiff, a standard vacuum-proof AFM with an attached computer, a weak pulse excimer laser, a fiber or window UV-clear optics, a copper finger cooled with an appropriate solvent sludge as tissue base and a low-vibration workbench. Extensive earthing might be needed due to UV-induced photopotentials. Discontinous use (vacuum cycling) appears straightforward. Though above equipment list may appear formidable, it can be easily allocated at any well-funded university. Since this is only proof of principle (POP), all gadgets can be recycled after few month's duration. -- Eugene P.S. Joe Strout, the founder of NEL, arrived at the same method independantly. Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=4873