The applications of gold nanoparticles (AuNPs) in biomedicine span the imaging, diagnosis and therapy domains. Current methods of nanoparticle quantification are based on inductively coupled plasmas (ICP) methods, which are heavily influenced by sample preparation. This becomes challenging when quantifying trace-level amount of AuNPs in the presence of organic
matrix. In this thesis, total reflection X-ray fluorescence (TXRF) spectrometry is proposed for quantifying cellular uptake of AuNPs in MDA-MB-231 breast cancer cell line suspensions. The most suitable internal standard and fitting approach that yield 90-110% recovery rate along with different sample preparation methods were investigated. Reference material AuNPs were used to validate the quantification capabilities of the newly developed method. Direct comparison of TXRF and ICP-AES showed ability of TXRF to accurately quantify nanoparticle uptake while further demonstrating the importance of sample preparation for ICP-AES. These results suggest that TXRF has potential for quantifying nanoparticle uptake and their kinetics.