Exploring LA-ICP-MS as a quantitative imaging technique to study nanoparticle uptake in Daphnia magna and zebrafish (Danio rerio) embryos

The extent and the mechanisms by which engineered nanoparticles (ENPs) are incorporated into biological tissues are a matter of intensive research. Therefore, laser ablation coupled to inductively coupled plasma mass spectrometry (LA-ICP-MS) is presented for the detection and visualization of engineered nanoparticles (Al2O3, Ag, and Au) in ecotoxicological test organisms (Danio rerio and Daphnia magna). While ENPs are not taken up by the zebrafish embryo but attach to its chorion, incorporation into the gut of D. magna is clearly visible by a 50-μm spot ablation of 40-μm-thick organism sections. During laser ablation of the soft organic matrix, the hard ENPs are mobilized without a significant change in their size, leading to decreasing sensitivity with increasing size of ENPs. To compensate for these effects, a matrix-matched calibration with ENPs of the same size embedded in agarose gels is proposed. Based on such a calibration, the mass of ENPs within one organism section was calculated and used to estimate the total mass of ENPs per organism. Compared to the amount determined after acid digestion of the test organisms, recoveries of 20-100% (zebrafish embryo (ZFE)) and of 4-230% (D. magna) were obtained with LODs in the low ppm range. It is likely that these differences are primarily due to an inhomogeneous particle distribution in the organisms and to shifts in the particle size distribution from the initial ENPs to those present in the organism. It appears that quantitative imaging of ENPs with LA-ICP-MS requires knowledge of the particle sizes in the biological tissue under study.