Structure and Stability of PEG‐ and Mixed PEG‐Layer‐Coated Nanoparticles at High Particle Concentrations Studied In Situ by Small‐Angle X‐Ray Scattering

Abstract

Ligand‐layer structure and stability of gold nanoparticles (AuNP) coated with α‐methoxypoly(ethylene glycol)‐ω‐(11‐mercaptoundecanoate) (PEGMUA) layers and mixed layers of PEGMUA and 11‐mercaptoundecanoic acid (MUA) at high AuNP concentrations are studied in situ by small‐angle X‐ray scattering (SAXS). The thickness of the ligand layer is modified by the molecular weight of the PEG‐ligands (2 and 5 kDa), and the PEG‐grafting density is decreased by coadsorption of MUA. The response of the conjugates to a pressure of up to 4 kbar is probed. The results indicate strongly hydrated PEG layers at high grafting densities. The stability of the mixed ligand‐layer conjugates is lower. This is most probably due to enhanced interparticle PEG–PEG interactions at lower grafting densities. The presented study demonstrates that a detailed structural characterization of polymer ligand layers in situ and in response to external stimuli is possible with SAXS.

Gold Nanorods for LSPR Biosensing: Synthesis, Coating by Silica, and Bioanalytical Applications

“…To precisely model nanorods, some authors had to use a combination of form-factors [ 117 ]. To take into account interactions between nanorods, a structure-factor can also be combined to the form-factor [ 118 ]. Unfortunately, very thin silica coating cannot be efficiently characterized through this technique, as its scattering contribution is not significant enough, but thicker layers should be quantifiable if modelled with the appropriate form factor, as well as more complicated structures (e.g., core/satellite superstructures in [ 119 ]).…”

Local orientational order in self-assembled nanoparticle films: the role of ligand composition and salt

“…a significant decrease of the degree of orientational order. In addition, MUA addition leads to different ligand layer conformations that affect the stability of the particles (Schulz et al, 2018). Obviously, this way the assembly of layers in the (sub-)micrometre range as studied in this work is affected as well.…”

Supercrystal Formation of Gold Nanorods by High Pressure Stimulation

“…As shown previously, SAXS measurements are dominantly sensitive to the Au core, as the ligand shell has a much weaker scattering contrast. 20,33,34 With increasing hydrostatic pressure up to p = 2000 bar (200 MPa), only slight changes of the SAXS profile are present. In particular, the form factor does not change, while the intensity of the structure factor peak drops and the peak position shifts slightly to larger scattering angles (q max ≈ 0.17 nm −1 ).…”

“…We note that PEG high grafting densities are critical to achieve concentrations of AuNR@PEG as used in this study and that the specific PEG-ligand used, PEGMUA2k, allows for such high grafting densities. 34,37 For the crystal state, the ligand shell thickness can be determined as t = a/2 − R mean , which yields t = 7.0 -7.5 nm, pointing to a still hydrated PEG-shell. It is thus likely that not only attractive van der Waals interactions between the AuNR cores, but also the interactions between PEG-shells determine the crystallization.…”

“…This collapse of the ligand shell is accompanied by an increase of the attractive interparticle interactions, 33,34 resulting in the supercrystal formation. Having investigated in detail the role of different salt types and concentrations and ligand lengths, ideal conditions for the supercrystal formation of spherical nanoparticles have been determined.…”