Mass spectrometric imaging of elements in biological tissues by new BrainMet technique—laser microdissectioninductively coupled plasma mass spectrometry (LMD-ICP-MS)

Abstract

Bioimaging of elements in biological tissues is a fast growing technology in the life sciences since it provides direct information on the metal distribution which is involved in metabolism in all kinds of organisms. In the present study, we proposed a novel mass spectrometric imaging technique, laser microdissection inductively coupled plasma mass spectrometry (LMD-ICP-MS), which is intended to investigate elemental distribution in small areas of biological tissue with high spatial resolution down to the low-micrometre range and below. The LMD-ICP-MS technique combines a laser microdissection apparatus (LMD) with sensitive quadrupole-based inductively coupled plasma mass spectrometry (ICP-QMS) to utilize the tightly focused laser beam in LMD for the ablation of sample materials which then are analyzed by ICP-QMS. The laser beam with a 1 μm spot diameter was used to ablate the material from a Cu-spiked brain tissue slice, and corresponding ion intensities of elements of interest (for instance, ¹³C⁺ and ⁶³Cu⁺) were observed by ICP-QMS along the scan. First images of metals and selected non-metals were obtained using the new LMD-ICP-MS imaging technique on small regions of the brain standard slice. Inhomogeneous distribution of the materials (via the image of ¹³C⁺) and elements (via the images of ²³Na⁺, ²⁴Mg⁺, ³¹P⁺, ⁵⁶Fe⁺, ⁶³Cu⁺, ⁶⁴Zn⁺) in the scanned regions was revealed by LMD-ICP-MS imaging with a spatial resolution of 30 μm, 15 μm, and 8 μm, respectively. Additionally, images of P, Mg, K and Fe with a lateral resolution of 4 μm in a region of a mouse brain slice were obtained by imaging LMD-ICP-MS. Quantification in LMD-ICP-MS was possible via calibration curves generated by a set of synthetic brain standards similar to the procedure in laser ablation ICP-MS. Further studies with respect to the performance of LMD-ICP-MS and the optimization of experimental parameters when using laser beams with smaller spot sizes in LMD will be carried out in developing the LMD-ICP-MS imaging technique.