title: Development of X-ray excitable luminescent probes for scanning X-ray microscopy.
abstract: Transmission soft X-ray microscopy is now capable of achieving resolutions that are typically 5 times better than the best-visible light microscopes. With expected improvements in zone plate optics, an additional factor of two may be realized within the next few years. Despite the high resolution now available with X-ray microscopes and the high X-ray contrast provided by biological molecules in the soft X-ray region (lambda = 2-5 nm), molecular probes for localizing specific biological targets have been lacking. To circumvent this problem, X-ray excitable molecular probes are needed that can target unique biological features. In this paper we report our initial results on the development of lanthanide-based fluorescent probes for biological labeling. Using scanning luminescence X-ray microscopy (SLXM, Jacobsen et al., J. Microscopy 172 (1993) 121-129), we show that lanthanide organo-polychelate complexes are sufficiently bright and radiation resistant to be the basis of a new class of X-ray excitable molecular probes capable of providing at least a fivefold improvement in resolution over visible light microscopy. Lanthanide probes, able to bind 80-100 metal ions per molecule, were found to give strong luminescent signals with X-ray doses exceeding 10(8) Gy, and were used to label actin stress fibers and in vitro preparations of polymerized tubulin.
mesh_terms: D000199:Actins / Q000032:analysis; D000818:Animals; D002478:Cells, Cultured; D005347:Fibroblasts / Q000737:chemistry; D005456:Fluorescent Dyes; D008674:Metals, Rare Earth / Q000378:metabolism*; D051379:Mice; D008855:Microscopy, Electron, Scanning / Q000295:instrumentation* / Q000379:methods*; D008856:Microscopy, Fluorescence; D008870:Microtubules / Q000378:metabolism; D015335:Molecular Probes; D011817:Rabbits; D011829:Radiation Dosage; D014965:X-Rays