Oxidative stress (OS) is increasingly implicated as an underlying pathogenic mechanism in a wide range of diseases, resulting from an imbalance between the production of reactive oxygen species (ROS) and the system's ability to detoxify the reactive intermediates or repair the resulting damage. ROS can be difficult to detect directly; however, they can be detected indirectly from the effects on oxidative stress biomarkers (OSB), such as glutathione (GSH), 3-nitrotyrosine, homocysteine, and cysteine. Moreover the reaction of transition metals with thiol-containing amino acids (for example GSH) oxidized by ROS can yield reactive products that accumulate with time and contribute to aging and diseases. The study of the interaction between OSB using functionalized nanoparticles (fNPs) has attracted interest because of potential applications in bio-sensors and biomedical diagnostics. A goal of the present work is to use fNPs to detect and ultimately quantitate OS in retinal pigment epithelial (RPE) cells subjected to external stressors, e.g. nonionizing (light) and ionizing (gamma) radiation. Specifically, we are investigating the assembly of gold fNPs mediated by the oxidation of GSH in irradiated RPE cells. The dynamic interparticle interactions had been characterized in previously reported work by monitoring the evolution of the surface plasmon resonance band using spectroscopic analysis (UV-VIS absorption). Here we are comparing the dynamic evolution of fNP assembly using photoacoustic spectroscopy (PAS). We expect that PAS will provide a more sensitive measure allowing these fNP sensors to measure OS in cell-based models without the artifacts limiting the use of current methods, such as fluorescent indicators.