Molecule-assisted NMR Spectroscopy: Nanoparticle-Based Strategies for Enhanced Detection and Hyperpolarization

Modern chemistry increasingly demands analytical tools that not only characterize molecular structures, but also operate effectively within complex, heterogeneous environments. In this landscape, the ability to identify, quantify, and interpret molecular species in mixtures such as biological fluids, environmental samples, or synthetic reaction media represents a fundamental challenge. Traditional analytical approaches, typically relying on chromatographic separation, are often time-consuming and poorly suited for the analysis of unknown compounds. Nuclear magnetic resonance (NMR) spectroscopy stands out as a powerful, non-destructive technique capable of delivering detailed structural information with minimal sample preparation. Its strength lies in the intrinsic molecular specificity of its signals, allowing the analysis of even unknown compounds. However, its broader applicability to real world systems is frequently hampered by spectral crowding, due to the excess of information in complex matrices, and its inherently low sensitivity due to the small population difference between the Zeeman eigenstates. To address these challenges, this thesis explores the use of functionalized gold nanoparticles (AuNPs) as active molecular tools to assist and enhance NMR-based analysis. On one side, molecule-assisted NMR chemosensing leverages macromolecular recognition elements to selectively interact with target analytes and improve spectral resolution via Nuclear Overhauser Effect (NOE)-based sequences. On the other, hyperpolarization techniques aim to boost the NMR signal itself, overcoming fundamental sensitivity limitations by increasing the population imbalance between nuclear spin states. Here, AuNPs are investigated not only as receptors, but also as polarization mediators in hyperpolarized environments. The present thesis is structured around four conceptually interconnected research modules, all rooted in the use of engineered AuNPs to address different analytical challenges in NMR spectroscopy. The first focuses on chemosensing strategy, describing the development of custom AuNPs functionalized with sulfonates, peptides, and fluorinated ligands for the selective detection of 3-methoxytyramine (3-MT), a key metabolite in the diagnostic profiling of neuroblastoma. The second and third ones, explore the implementation of AuNPs in the context of hyperpolarization techniques: the second explores the use of AuNPs in Signal Amplification By Reversible Exchange (SABRE), integrating parahydrogen-based hyperpolarization with nanoparticle-assisted systems to selectively amplify target signals; the third investigates AuNPs in Overhauser Dynamic Nuclear Polarization (OE-DNP), where nanoparticles functionalized with paramagnetic thiols are tested to enhance signal intensity under microwave (MW) irradiation. The fourth is dedicated to the design and statistical optimization of the synthesis of mixed-monolayer AuNPs, using Design of Experiments (DOE) to rationally tune surface composition and improve binding performance, overcoming empirical trial-and-error strategies. While these four projects differ in their objectives and technical approaches, they are connected by a common strategy: the use of functional AuNPs as adaptable molecular tools, and NMR spectroscopy as the main analytical method, ranging from standard experiments to hyperpolarized techniques. This work brings together both molecular recognition and hyperpolarization applications within a unified framework, using AuNPs across different roles. The results presented here may support future developments in diagnostic analysis, metabolomics, and molecular sensing in complex environments.