Comparison of total reflection X-ray fluorescence spectroscopy and inductively coupled plasma atomic emission spectroscopy for thequantification of gold nanoparticle uptake

Studies involving nanoparticle uptake in cells and tissues are contingent upon adequate methods of quantification. For gold nanoparticles (AuNPs), the quantification of uptake typically relies on inductively coupled plasma (ICP) based techniques which require sample pre-treatment and large sample volume (5-10 ml). To address these shortcomings, a total reflection X-Ray fluorescence (TXRF) spectroscopy-based method was developed to measure uptake of AuNPs in breast (MDA-MB-231) and prostate (PC3) cancer cells without any sample pre-treatment. In order to directly compare the quantification of TXRF and ICP Atomic Emission Spectroscopy (ICP-AES), samples were pre-treated with the most commonly used ICP-AES wet digestion protocol adopted from literature. The accuracy of both spectrometers was assessed by calculating the recovery rate of 10 nm reference material AuNPs in MDA-MB-231 and PC3 cells. TXRF showed analytically acceptable recovery rates of 96.1% and 98.7% for unfiltered MDA-MB-231 and PC3 cells, respectively, while ICP-AES showed low recovery rate of 23.3% and 27.8% for filtered samples. The nearly 80% underestimation by ICP-AES highlights the importance of proper sample pre-treatment for ICP-based measurements. Furthermore, it also has important implications in the clinical translation of AuNPs as knowledge of uptake is required for determining the nanoparticle injected dose. This work demonstrates TXRF's ability to accurately quantify AuNP without ICP-required wet digestion protocols using only 5 mu l of sample per reflector, making the technique a suitable alternative to ICP-AES.