Toward Diffusion Measurements of Colloidal Nanoparticles in Biological Environments by Nuclear Magnetic Resonance

Abstract

Protein corona formation on the surface of nanoparticles (NPs) is observed in situ by measuring diffusion coefficients of the NPs under the presence of proteins with a 19F nuclear magnetic resonance (NMR) based methodology. Formation of a protein corona reduces the diffusion coefficient of the NPs, based on an increase in their effective hydrodynamic radii. With this methodology it is demonstrated that the apparent dissociation constant of protein–NP complexes may vary over at least nine orders of magnitude for different types of proteins, in line with the Vroman effect. Using this methodology, the interaction between one type of protein and one type of nanoparticle can be studied quantitatively. Due to the NMR‐based detection, this methodology has no interference by absorption/scattering effects, by which optical detection schemes are affected. By using the potential of the NMR chemical shift, the detection of multiple 19F signals simultaneously opens the possibility to study the diffusion of several NPs at the same time. The 19F labeling of the NPs has negligible effect on their acute toxicity and moderate effect on NPs uptake by cells.

Fluorine Labeling of Nanoparticles and In Vivo 19F Magnetic Resonance Imaging

“…For comparison purposes, similar fluorinated NPs already reported by us ( NP-F and NP-PhF ) were prepared by the direct synthesis method (Figure A) and shown in Figure A. − The so-obtained NPs were very similar in core size ( r c = 1.47 ± 0.43 nm ( NP-F ) and 1.60 ± 0.45 nm ( NP-PhF )) to those obtained by the conjugation method and slightly smaller in hydrodynamic size because of the shorter length of the employed ligands ( r h = 8.99 ± 0.07 nm ( NP-F ) and 9.82 ± 0.10 nm ( NP-PhF )). The ligand density for both NPs was also around 5 ligands per nm 2 of gold core surface, as obtained by ICP-MS analysis.…”

“…Diffusion ordered spectroscopy (DOSY) measurements were performed to calculate the diffusion coefficient of NPs in water before and after conjugation. From the diffusion coefficient and through the Einstein–Stokes relation, it was possible to calculate the hydrodynamic size of each NP (Figure C, E). ,, It was observed that the conjugation of F and PhF produced a size increase of 2 nm in the hydrodynamic radius ( r h ) as compared to the size of NP-COOH ( r h = 13.53 nm), and the conjugation of branched more bulky F/OH and F/N 3 afforded an extra size increase of 3.54 and 2.65 nm, respectively (Figure C and Table S3). The data obtained from DOSY agreed with those obtained from dynamic light scattering (DLS) (Figure S7).…”

“…As we did not have any previous reference work for the in vivo use of such NPs and being SNR (signal-to-noise ratio) one of the significant limitations of 19 F-based MR detection, we chose the most favorable scenario, that is, the use of a fully fluorinated gold NP that maximized the fluorine atoms per NP ( NP-F with 1260 F atoms/NP) and a high concentration of those NPs (18 μM in NPs, approximately 23 mM in fluorine). NP-F was prepared as described previously by us, − with a gold core radius r c of 1.47 ± 0.43 nm as obtained by TEM (Figure G), and a hydrodynamic radius r h of 8.99 ± 0.07 nm as measured by DOSY. The UV–vis spectrum showed the typical surface plasmon band at 511 nm, which is expected for this size of NP, and displayed colloidal stability.…”

“…Thus, examples of fluorinated NPs composed of a metal core and fluorinated ligands that are water soluble are scarce in the literature. − In this context and in the last years, we and others have overcome the fluorine hydrophobicity challenge and prepared fluorinated inorganic nanoparticles that are totally or partially dispersible in water by different strategies. Such fluorinated NPs have been utilized in other nanomedicine related fields, such as to study protein corona in complex environments, , as potential contrast agents in 19 F MRI, ,, or as vehicles for enzyme transport, and delivery through fluorine-based interactions − (Figure C D). The strategies we used so far to introduce fluorinated moieties on the surface of inorganic NPs were either via the direct synthesis of gold NPs from chloroauric acid in the presence of custom-designed fluorinated-thiolated ligands and sodium borohydride (Figure A), − or by ligand exchange on presynthesized quantum dots with fluorinated-thiolated ligands to prepare fluorinated quantum dots (Figure B). − These methods, although useful, are limited to thiol-binding nanomaterials, and for the case of ligand exchange, a significant excess of ligand is needed and full exchange is hardly ever achieved.…”

Luminescent Quantum Dots Stabilized by N-Heterocyclic Carbene Polymer Ligands

“…Further proof of the NHC-polymer coordination on the QD surfaces has relied on DOSY NMR spectroscopy, where changes in the diffusion coefficient of the ligand protons are probed after coordination on the nanocrystals . This technique has gained much interest for use to characterize the surface coating of various nanocolloids. − It has also been shown to provide reliable data on the diffusion coefficient of nanometer size solutes (e.g., nanocrystals), where the ubiquitous dynamic light scattering (DLS) technique tends to fail because of very weak scattering laser signals . DOSY NMR relies on the application of two RF pulses carefully intercalated between two identical magnetic field gradient pulses, G z , applied along the z -axis.…”