The water flea is the testbed for a non-destructive 3D imaging method that pinpoints metals in vivo.

Laszlo Vincze, from Ghent University, Belgium, and his colleagues in Belgium, Hungary and Germany have combined x-ray techniques to allow them to detect metal ions and their locations in biological samples - including living systems.

The study of trace metals within organisms - metallomics - is a rapidly expanding research area as metals play many vital roles in biological systems. Yet most of the techniques currently used to analyse metal content in biological samples are destructive and give no clues about metal distribution within the system.

Vincze had already used one such technique, mass spectrometry, to study metal uptake by water fleas and the relative contributions from different exposure routes, such as water or diet. But the total decomposition of the flea required to prepare the samples for this experiment meant that it was impossible to distinguish local metal accumulation in the different tissues. Instead, by combining synchrotron radiation x-ray fluorescence and laboratory x-ray absorption microtomography, Vincze's team was able to unravel the tissue-specific 2D and 3D metal distribution within the fleas without invasive sample preparation techniques.

Vincze explains the techniques' advantages: 'Thanks to the highly penetrating character of x-rays, a sample can be investigated in three dimensions in an essentially non-destructive manner, leaving most - if not all - other analytical techniques behind. Owing to recent advances in x-ray science, imaging of transition metal distributions with micrometre to nanometre spatial resolution and with parts per billion sensitivity is becoming possible.'

Vincze warns that although the techniques are not immediately destructive, there are other issues to consider. 'With biological imaging, the problem of radiation damage is one of the most challenging aspects of future scanning x-ray fluorescence measurements,' he says. Nevertheless, he adds that he can imagine the combined techniques being used in a wide variety of disciplines. 'We expect to see a rapid evolution towards in situ elemental imaging on the nanoscopic scale in various areas, including earth and environmental science, material science, archaeology and functional biology,' he says.

Edward Morgan