Method Development for Single Particle ICP-MS and Tissue Extraction for Metallic and Two-Dimensional Nanomaterials

Engineered nanomaterials (ENMs) are increasingly used in consumer, industrial, and biomedical applications, including diagnostics and therapeutics. To evaluate the functionality and potential toxicity of ENMs within biological tissues, extraction techniques must effectively liberate these target ENMs without altering their properties. Although various procedures have been developed for different tissues and ENM types, no standardized methods currently exist. Alkaline digestion using tetramethylammonium hydroxide (TMAH) is commonly employed to extract ENMs prior to single-particle inductively coupled plasma mass spectrometry (spICP-MS) analysis, but TMAH is not an ideal extractant as it poses risks to analysts. This dissertation investigates alternative extraction techniques, sample holding times, and size detection limits for two classes of nanomaterials: metallic ENMs (gold and silver) and two-dimensional manganese dioxide (MnO₂) nanosheets. The first part of the study evaluates tetrapropylammonium hydroxide (TPAH) and tetrabutylammonium hydroxide (TBAH) as less harmful alternatives to the widely used but risky TMAH for extracting 100 nm Au and Ag ENMs from biological tissues, followed by analysis via spICP-MS. TPAH (20%) demonstrated superior ENM recovery, with minimal transformations during extraction, making it a preferable option to TMAH. Notably, Au ENMs could be held for 48 hours in both TMAH and TPAH, while Ag ENMs showed stable recoveries in these extractants for up to 72 hours. This work represents a step towards establishing standardized alkaline extraction protocols for biological tissues. The second part of the study focuses on MnO₂ nanosheets, which hold potential in biomedical applications such as drug delivery and biosensing. spICP-MS was employed to assess the size detection limits of MnO₂ in different media, finding minimum detectable sizes of 34 nm (spherical) and 142 nm (planar) in alkaline solutions. However, extraction of MnO₂ from tissues using TMAH, TPAH, or TBAH was unsuccessful, likely due to the instability of MnO₂ in alkaline environments. This highlights the need for optimized extraction methods, such as modified digestion times or sequential extraction approaches, to maintain the integrity of MnO₂ nanosheets. Overall, this dissertation provides critical insights into optimizing ENM extraction and detection techniques, contributing to the development of safer and more effective methods for analyzing nanomaterials in biological and environmental matrices.