Development of a SIMS compatible internal standard spiked resin for quantitative bio-imaging of biological samples by laser ablation ICP-MS: an application to uranium contaminated kidney samples

International audienceIn the last decade, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has evolved as an efficient analytical technique for in situ quantitative analysis of solid samples with micrometer-scale spatial resolution and low limits of detection. However, the progress in biological or medical science application is still determined by the availability of calibration standards and appropriate internal standards (IS) to compensate signal variation during laser beam-sample interaction, transportation of the aerosol and instrumental drifts during analysis [1]. In addition, it would be desirable that both samples and calibrations standards could be shared by different imaging techniques. Therefore, the aim of this work is to find a sample/standard preparation methodology compatible with laser ablation and Secondary-Ion Mass Spectrometry (SIMS) analyses for a complementary analysis of uranium distribution in kidney with both techniques. On the one hand, in-house solid standards were prepared from uranium spiked kidney homogenate and their homogeneity was assessed by isotope dilution ICPMS after acid digestion. On the other hand, a novel approach based on IS doped resin was carried out in order to incorporate a more feasible internal standard than 13C. Indeed, carbon feasibility for quantitative LA-ICPMS imaging has been queried recently [2-4]. Therefore, thulium spiked pure EPON resin was synthetized and employed to embed dehydrated samples and doped homogenates based on the chemical sample preparation protocol of biological samples for SIMS analysis [5, 6]. Nevertheless, the chemical dehydration protocol was adapted to the viscous and liquid state of the homogenates. In parallel, with the objective of determining the real need of producing organ homogenates (laborious task and requires the access to animal facilities), uranyl nitrate (powder) spiked resin was also tested in order to compare slopes after laser ablation with those obtained with organ homogenates. Then, serial thin and ultra-thin sections were cut with microtome and the homogeneity of internal standard was evaluated by randomly analysing small selected areas by LA-ICP-MS and SIMS. Laser ablation conditions were optimized to achieve complete sample consumption of the tissue whilst minimizing the penetration into the glass slide. The advantages of this new methodology are 1) the addition of a suitable internal standard to both matrix-matched standards and biological samples without altering their original uranium distribution, 2) an appropriate sample preparation compatible with several imaging techniques (SIMS, TEM, LA), 3) ease to prepare and 4) room temperature storage as a solid material which would facilitate its transport. We believe that this methodology will positively contribute to the collaboration among bio-imaging techniques users