Investigating the impact of internal standard heterogeneity on gold quantification with total reflection X-ray fluorescence: A simulation study

Total reflection X-ray Fluorescence (TXRF) is a powerful analytical tool with high detection sensitivity that has been applied to a variety of biological samples. While its ability to quantify gold nanoparticles (AuNPs) in cancer cells has been demonstrated, the extension to tissue slices would be of interest. To that end, the preservation of the underlying tissue microstructure requires samples to be measured as microtome slices. In this form, internal standard spiking is warranted. Thus, it is important to examine the impact of sample heterogeneity on the TXRF's quantification accuracy. To address these questions, a TXRF spectrometer along with 5 μm thin heterogeneous and homogeneous samples were modeled using TOPAS. The simulation model generated TXRF spectra which were then analyzed to obtain recovery rates of Au in both sample types. The results showed near 100% recovery regardless of the elemental spatial distribution in the samples. This provides insights into the quantification potential for AuNPs inside tumors that are histologically processed into thin tissue slices. In addition, this simulation toolkit provides the first practical means of modeling TXRF spectroscopy which will hopefully be of use to the TXRF community.