Insights into nanoparticle surface bonding and coating architecture via multinuclear NMR

Area of Science:

• Nanotechnology
• Materials Science
• Biomedical Imaging

Background:

• Tantalum oxide nanoparticles (TaO_x NPs) offer superior contrast for computed tomography (CT) imaging compared to iodinated contrast media (ICM) at high X-ray voltages.
• TaO_x NPs have undergone extensive preclinical safety and efficacy testing, with engineered coatings promoting favorable pharmacokinetics and rapid renal clearance.
• Structural modifications, including core size and surface coatings, are crucial for optimizing TaO_x NP performance and safety.

Purpose of the Study:

• To thoroughly characterize the carboxybetaine zwitterionic siloxane polymer (CZ) coating on a lead candidate TaO_x NP using advanced NMR techniques.
• To elucidate the binding interactions between the CZ coating and the TaO_x NP surface.
• To compare the efficacy of diafiltration versus dialysis for purifying TaO_x NPs.

Main Methods:

• Multinuclear/multidimensional nuclear magnetic resonance (NMR) spectroscopy, including ¹H, ¹H/¹³C heteronuclear multiple bond correlation, and ²⁹Si NMR.
• Carr-Purcell-Meiboom-Gill (CPMG) NMR pulse sequence to probe surface interactions.
• Spectral analysis to identify structural features and impurities.

Main Results:

• NMR confirmed the structure of the CZ coating and described the siloxane architecture bound to the TaO_x NP surface.
• ²⁹Si NMR identified T-region bonding modes of the CZ coating.
• Diafiltration proved superior to dialysis for purification, effectively removing a cyclic siloxane impurity present in the dialysis-purified product.

Conclusions:

• NMR is a powerful tool for characterizing TaO_x NP coatings and their surface interactions.
• Diafiltration is the preferred method for purifying TaO_x NPs, ensuring higher purity and potentially improved performance.
• This detailed characterization advances the development of TaO_x NPs as effective CT contrast agents.