Ligands for Nanoparticles

Abstract

This chapter deals with ligands of colloidal nanoparticles. In the first section, it provides an understanding of the many different ways ligands act as a go between in nanoparticle (NP) science and technology, emphasizing their role in NP synthesis, colloid stability, and chemical functionalization of NPs. In the second section, special attention is paid to the experimental in situ study of NP ligands with nuclear magnetic resonance (NMR) spectroscopy. We show how a combination of regular one-dimensional (1D) proton NMR in solution with more advanced 2D techniques, such as diffusion NMR and nuclear Overhauser effect (NOE)-based NMR, leads to a clear identification of ligands bound to colloidal nanoparticles. The so-called tightly bound ligands feature broadened resonances in the 1D 1 H spectrum, have the diffusion coefficient that agrees with the hydrodynamic radius of the entire nanoparticle, and show strongly negative NOE cross-peaks. Next, we show that adsorption/desorption of ligands manifests itself in deviations from this tightly bound ligand behavior. If the exchange is slow on the NMR timescale, bound and free ligands are observed simultaneously, enabling the analysis of the thermodynamics of the adsorption/desorption process. If the exchange is fast on the NMR timescale, the kinetics of the adsorption/desorption process can be studied. In the chapter, these different situations are illustrated by experimental examples of various colloidal nanoparticle systems.