A novel absolute quantitative imaging strategy of iron, copper and zinc in brain tissues by Isotope Dilution Laser Ablation ICP-MS.

Isotope Dilution Laser Ablation ICP-MS (ID-LA-ICP-MS), because of its impressive spatial resolution capacity and precise means for quantification, is one of the most promising tools for in-situ quantitative imaging of trace elements in biological samples. In the ID-LA-ICP-MS strategy for tissue section, the tissue must be maintained intact during the whole sample preparation process. Therefore, how to homogeneously distribute enriched isotope spike on tissue section and how to confirm isotope equilibration between sample and spike are two important challenges. In this study, we reported a novel quantitative imaging strategy for biological thin section based on ID-LA-ICP-MS. To distribute the enriched isotope spikes on tissue section homogeneously, a "border" was constructed to make spike droplet stay on the tissue for isotope exchange. Laser ablation and isotope exchange parameters were also investigated to obtain optimal ID-LA-ICP-MS conditions. The prepared homogeneous in-house standard was used to validate the ID-LA-ICP-MS approach and good agreement with the bulk analysis was achieved. On this basis, quantitative imaging of Fe, Cu and Zn in real mouse brain of Alzheimer's Disease (AD) were measured by the improved methodology. Assessment of the method for real sample was undertaken by comparison of the LA-ICP-MS data with that obtained by micro-XRF. Moreover, comparative analysis of elements distribution and immunohistochemical markers in AD mouse brain was also carried out. The similar distributional patterns demonstrated that the proposed methodology is potential to investigate the correlation of biomarker heterogeneity and elements distribution, and may be useful to understand such complex brain mechanisms in the future.