Elemental imaging at the nanoscale: NanoSIMS and complementary techniques for element localisation in plants

Abstract

The ability to locate and quantify elemental distributions in plants is crucial to understanding plant metabolisms, the mechanisms of uptake and transport of minerals and how plants cope with toxic elements or elemental deficiencies. High-resolution secondary ion mass spectrometry (SIMS) is emerging as an important technique for the analysis of biological material at the subcellular scale. This article reviews recent work using the CAMECA NanoSIMS to determine elemental distributions in plants. The NanoSIMS is able to map elemental distributions at high resolution, down to 50 nm, and can detect very low concentrations (milligrams per kilogram) for some elements. It is also capable of mapping almost all elements in the periodic table (from hydrogen to uranium) and can distinguish between stable isotopes, which allows the design of tracer experiments. In this review, particular focus is placed upon studying the same or similar specimens with both the NanoSIMS and a wide range of complementary techniques, showing how the advantages of each technique can be combined to provide a fuller data set to address complex scientific questions. Techniques covered include optical microscopy, synchrotron techniques, including X-ray fluorescence and X-ray absorption spectroscopy, transmission electron microscopy, electron probe microanalysis, particle-induced X-ray emission and inductively coupled plasma mass spectrometry. Some of the challenges associated with sample preparation of plant material for SIMS analysis, the artefacts and limitations of the technique and future trends are also discussed.

Multi-element bioimaging of Arabidopsis thaliana roots

“…With respect to spatial resolution, nano-SIMS outcompetes all other imaging techniques, reaching as low as a 50-nm spatial resolution (Moore et al, 2012), whereas x-ray-based techniques reach between 1 and 2 mm and LA-ICP-MS systems typically range from 5 to 200 mm (Becker et al, 2010b). New LA designs, however, like the near-field LA type, can go below 5 mm, and substitution of the LA unit with a laser microdissection unit has been used to improve resolution down to 1 mm (Becker et al, 2010a).…”

“…One of the main limitations with SIMS is the poor sensitivity for detection of certain elements, such as Zn, Mn, and cd. This is due to a low secondary ion yield of these particular elements (Moore et al, 2012). With detection limits observed in the sub-mg g 21 level for many elements, LA-ICP-MS is more sensitive than either SIMS or x-ray-based techniques (Becker et al, 2010b).…”

“…Also, absolutely planar sections need to be obtained, since LA-ICP-MS is sensitive to sample topography and matrix composition. Hence, with respect to sample preparation, LA-ICP-MS analyses face similar challenges as nano-SIMS (Moore et al, 2012. As was shown here and elsewhere, existing protocols for microscopy are not designed to maintain the ionic composition of plant samples.…”

“…After drying, both the biological structures and the elemental ion composition of the specimen need to be maintained in order for the analysis to be meaningful (Moore et al, 2012). Also, absolutely planar sections need to be obtained, since LA-ICP-MS is sensitive to sample topography and matrix composition.…”

Review of combined isotopic and optical nanoscopy

“…The NanoSIMS imaging technique has proved to be useful in a wide range of research fields, such as material science, 31 biological geochemistry and cosmochemistry, 30 plant research, 32 environmental microbiology, 33 cell biology, 34 and others. An outstanding spatial resolution has allowed it to be applied in biological studies, specifically, imaging cells and their compartments.…”