First-row transition metals are required for
all forms of life on earth. The high
reactivity of these elements means that an array of mechanisms has evolved to
regulate key processes governing their transport and binding action. Tracking metals within biological tissue is
non-trivial; tagging approaches suffer from lack of specificity, and can fail
to find strongly-bound species; in addition, tags can interfere with normal
biochemistry. Electron microscopy
provides stupendous resolution, but probes miniscule volumes due to the short
penetration of electrons.
With µM sensitivity, X-ray Fluorescence
Microscopy (XFM) can probe endogenous metal concentrations at resolutions at
the µm length scale. Elemental maps are
quantitative. With penetration depth and
depth of field well matched at around 0.5 mm, the method can be up-scaled to
3-D visualisations via tomography. Here
we report on our application of X-ray fluorescence tomography of Zn, Cu, Fe,
and Mn in C. elegans and discuss
recent progress in developing self-absorption corrections that will enable
accurate mapping of light elements.