Thiol Functionalization, Redox Reactivity, and Biological Compatibility of Gold Nanoparticles - Project Summary/Abstract (Description) Gold nanoparticles (AuNPs) are widely explored as drug carriers and diagnostic platforms, yet their behavior in biological environments remains poorly understood as the underlying surface chemistry that governs their reactivity has never been explored. Nearly all AuNPs used in biomedical settings are functionalized with thiol ligands, but key processes, including hydrogen atom adsorption, proton-coupled electron transfer (PCET), thiol attachment, oxygen-dependent surface restructuring, and thiol-driven dissolution, lack mechanistic clarity. These knowledge gaps limit our ability to control nanoparticle stability, tune drug release, and anticipate how AuNPs transform in complex, oxygen-variable tumor microenvironments. This project establishes the first integrated framework connecting fundamental AuNP surface chemistry to biological performance. Aim 1 quantifies how thiol ligands reshape the thermodynamics of hydrogen adsorption by determining the bond dissociation free energy (BDFE) of the Au–H bond on bare and thiol-functionalized nanoparticles using PCET equilibria, UV–vis spectroscopy, and open-circuit potential measurements. Aim 2 defines how oxygen availability controls the mechanisms and rates of thiol attachment and thiolate-induced gold atom loss, integrating stopped-flow kinetics, controlled-atmosphere functionalization, UV–vis monitoring, ICP-MS, and quadrupole mass spectrometry to resolve aerobic versus anaerobic pathways. Aim 3 examines how these chemical rules translate into cellular outcomes by evaluating nanoparticle stability, dissolution, drug-release behavior, and cytotoxicity in cancer cells under normoxic and hypoxic conditions, using ICP-MS, cryo-EM, and viability assays. By bridging molecular-level surface chemistry with cellular responses, this work will reveal why AuNPs frequently behave unpredictably in biological systems and identify specific design principles such as ligand identity, oxygen sensitivity, and functionalization thresholds that control nanoparticle stability and therapeutic efficacy. The resulting mechanistic insights will directly guide the engineering of safer, more stable, and more effective AuNP-based therapeutics for cancer treatment.
