Characterizing, Controlling, and Using Silver Nanoparticle Surface Chemistry

Surface chemistry is important at all length scales, but it is particularly important at the nanoscale, where the surface area per unit mass is much higher than that of bulk materials. However, surprisingly, little is known about how to characterize and control the surface chemistry of nanoparticles. A key first step in both understanding and leveraging nanoparticle surface chemistry is developing and implementing analytical methods to describe the chemical architectures present at the nanoparticle surface (e.g. ligand identity, quantity, and arrangement). We have developed an analytical method to quantify the molecules (also called ligands) adsorbed to nanoparticle surfaces using a combination of nuclear magnetic resonance spectroscopy, inductively coupled plasma mass spectrometry, and transmission electron microscopy. This method enables us to measure ligand quantities on a variety of metal nanoparticles and determine trends in these values as a function of initial ligand identity. Using these well-characterized nanoparticles, we then correlate ligand quantity to dissolution behavior for widely-used silver nanoparticles. We find unexpected trends, where some of the ligands tested do not exhibit ligand quantity-dependent dissolution in some conditions, which will be particularly important for understanding and leveraging their antimicrobial activity. Further, we determine the effect of the released silver ions on bacteria growth in specific, complex chemical environments and show that a combination of the silver nanoparticles and their released ions have a larger antimicrobial effect than the released ions alone. Taken together, these experiments highlight the importance of robust nanoparticle characterization overall, and specifically the importance of surface chemistry characterization. We have shown that characterizing and controlling metal nanoparticle surface chemistry provides insight into their performance in applications such as antimicrobials. We expect that these results will contribute to the evaluation of metal nanoparticles in a variety of antimicrobial and industrial applications