Antibody meets the microbeam: Or how to find neurofibrillary tangles

In biomedical research the distributions of physiologically or pathologically active elements around or in a certain structure (e.g. tangles, plaques or different cell types) are often of great interest. Therefore, μPIXE analyses are applied to yield quantitative and spatially resolved concentration images of the elements of interest. However, the localisation of the structures to be examined is sometimes scarcely practicable or even impossible. This paper proposes a method of localising the areas of interest for μPIXE analysis. The method is based on the application of a suitable antibody tagged with a single elemental marker (e.g. Ni, Co, Cd, Ag or Au). The antibody then binds selectively to the structures of interest. The elemental marker is detectable via μPIXE, thus, showing finally the structure of interest via the bound antibody. The versatility of the antibodies in combination with the easily applied marker facilitates the localisation of a variety of structures in both light microscopy and μPIXE-imaging. The method is demonstrated on several cellular and subcellular structures in the brain. The elemental concentrations of two consecutive slices, one stained with Ni-enhanced antibody, the other unstained control, are compared to show the feasibility of trace elemental analysis for particular elements in spite if immunohistochemical structure identification. It has to be stated that the proposed technique will not work for free diffusing elements (like Na, Cl, K and Ca) whose concentrations can be altered by wet sample preparation.