Progress in ligand design for monolayer-protected nanoparticles for nanobio interfaces

Understanding mono- and bi-metallic Au and Ni nanoparticle responses to fast heating

Nanoparticle assembly, alloying and fragmentation are fundamental processes with significant implications in various fields such as catalysis, materials science, and nanotechnology. Understanding these processes under fast heating conditions is crucial for tailoring nanoparticle properties and optimizing their applications. For this, we employ molecular dynamics simulations to obtain atomic-level insights into nanoparticle behavior. The performed simulations reveal intricate details of sintering, alloying and fragmentation mechanisms shedding light on the underlying physical phenomena governing these processes. The calculation results help to visualize nanoparticle evolution upon undercritical and supercritical heating elucidating not only the role of temperature, but also of nanoparticle sizes and composition. In particular, it is shown that surface tension and surface energy play important roles not only in nanoparticle melting but also in its fragmentation. When the added energy exceeds a critical threshold, the nanoparticle begins to experience alternating compression and expansion. If the tensile stress surpasses the material's strength limit, fragmentation becomes prominent. For very small particles (with radius smaller than ∼10 nm), this occurs more rapidly, whereas sub-nano-cavitation precedes the final fragmentation in larger particles, which behave more like droplets. Interestingly, this effect depends on composition in the case of AuNi alloy nanoparticles, as expected from the phase diagrams and excess energy. The heating level required to overcome the mixing barrier is also determined and is shown to play an important role in the evolution of AuNi nanoparticles, in addition to their size. Furthermore, our findings provide insights into controlling nanoparticle synthesis for various applications in numerous nanotechnological domains, such as catalysis, sensors, material analysis, as well as deseas diagnostics and treatment. This study bridges the gap between experimental observations and theoretical predictions paving the way for designing advanced nanomaterials with enhanced functionalities.

Thiolate end-group regulates ligand arrangement, hydration and affinity for small compounds in monolayer-protected gold nanoparticles

The ability to control the properties of monolayer protected gold nanoparticles (MPNPs) discloses unrevealed features stemming from collective properties of the ligands forming the monolayer and presents opportunities to design new materials. To date, the influence of ligand end-group size and capacity to form hydrogen bonds on structure and hydration of small MPNPs (<5 nm) has been poorly studied. Here, we show that both features determine ligands order, solvent accessibility, capacity to host hydrophobic compounds and interfacial properties of MPNPs. The polarity perceived by a radical probe and its binding constant with the monolayer investigated by electron spin resonance is rationalized by molecular dynamics simulations, which suggest that larger space-filling groups - trimethylammonium, zwitterionic and short polyethylene glycol - favor a radial organization of the thiolates, whereas smaller groups - as sulfonate - promote the formation of bundles. Zwitterionic ligands create a surface network of hydrogen bonds, which affects nanoparticle hydrophobicity and maximize the partition equilibrium constant of the probe. This study discloses the role of the chemistry of the end-group on monolayer features with effects that span from molecular- to nano-scale and opens the door to a shift in the conception of new MPNPs exploiting the end-group as a novel design motif.

Prominence of the Instability of a Stabilizing Agent in the Changes in Physical State of a Hybrid Nanomaterial

Shaping ability of hybrid nanomaterials is a key point for their further use in devices. It is therefore crucial to control it. To this end, it is necessary that the macroscopic properties of the material remain constant over time. Here, we evidence by multinuclear Magic-Angle Spinning Nuclear Magnetic Resonance spectroscopic study including ¹⁷ O isotope exchange that for a ZnO-alkylamine hybrid material, the partial carbonation of amine into ammonium carbamate molecules is behind the conversion from highly viscous liquid to a powdery solid when exposed to air. This carbonation induces modification and reorganization of the organic shell around the nanocrystals and affects significantly the macroscopic properties of the material such as it physical state, its solubility and colloidal stability. This study, straightforwardly extendable, highlights that the nature of the functional chemical group allowing connecting the stabilizing agent (SA) to the surface of the nanoparticles is of tremendous importance especially if the SA is reactive with molecules present in the environment.

Automation and low-cost proteomics for characterization of the protein corona: experimental methods for big data

Nanoparticles used in biological settings are exposed to proteins that adsorb on the surface forming a protein corona. These adsorbed proteins dictate the subsequent cellular response. A major challenge has been predicting what proteins will adsorb on a given nanoparticle surface. Instead, each new nanoparticle and nanoparticle modification must be tested experimentally to determine what proteins adsorb on the surface. We propose that any future predictive ability will depend on large datasets of protein-nanoparticle interactions. As a first step towards this goal, we have developed an automated workflow using a liquid handling robot to form and isolate protein coronas. As this workflow depends on magnetic separation steps, we test the ability to embed magnetic nanoparticles within a protein nanoparticle. These experiments demonstrate that magnetic separation could be used for any type of nanoparticle in which a magnetic core can be embedded. Higher-throughput corona characterization will also require lower-cost approaches to proteomics. We report a comparison of fast, low-cost, and standard, slower, higher-cost liquid chromatography coupled with mass spectrometry to identify the protein corona. These methods will provide a step forward in the acquisition of the large datasets necessary to predict nanoparticle-protein interactions.

Effect of the Ligand Binding Strength on the Morphology of Functionalized Gold Nanoparticles

Functionalized gold nanoparticles are investigated by density functional theory calculations in the context of cancer radiotherapy. Several typical experimental shapes, including nanostars, nanospheres, and nanorods, are modeled by optimizing Au clusters covered by organic monolayers composed of hydrated short-chain polyethylene glycol (PEG) ligands. The PEGylation stabilizes significantly the stellation of decahedral Au₅₄ by deforming significantly its geometry at the spikes. The higher stability of the PEG molecules adsorbed on this stellated nanocluster with respect to the more spherical icosahedral Au₅₅ and truncated octahedral Au₇₉ leads to a larger energy cost to desorb them and thus a weaker propensity for the starred nanoparticle to exchange ligands with the cell membrane, in agreement with experiments. These results open interesting possibilities for advancing our understanding of the cellular uptake of gold nanoparticles.