Dynamic nuclear polarization of spherical nanoparticles

Area of Science:

• Materials Science
• Nanotechnology
• Spectroscopy

Background:

• Silica nanoparticles (NPs) are versatile materials with applications in catalysis and imaging.
• Understanding their surface chemistry and the organization of surface-bound molecules is crucial for optimizing NP design.
• Dynamic Nuclear Polarization (DNP) offers a significant boost in Nuclear Magnetic Resonance (NMR) sensitivity.

Purpose of the Study:

• To investigate the surface chemistry and supramolecular organization of amino acids on silica NPs using DNP-enhanced NMR.
• To characterize the atomic-level structure of surface and core silicon nuclei in silica NPs.
• To explore the influence of NP size on DNP enhancement and polarization buildup for potential applications.

Main Methods:

• Modified Stoeber method for synthesizing spherical silica NPs (10-100 nm) using amino acids as catalysts.
• Dynamic Nuclear Polarization (DNP) enhanced Nuclear Magnetic Resonance (NMR) spectroscopy for ultra-sensitive detection.
• Atomic resolution characterization of surface and bulk silicon nuclei.

Main Results:

• Ultra-sensitive detection of trace amounts of surface-bound amino acids and their organization.
• Non-covalent binding of amino acids, indicating their incorporation into the NP structure.
• Observed dramatic changes in DNP enhancements with particle size, with smaller NPs (13 nm) showing higher efficiency.
• Determined DNP penetration depth (~4.2-5.7 nm) and faster polarization buildup in larger NPs.

Conclusions:

• DNP-enhanced NMR provides unique insights into silica NP surface chemistry and molecular organization.
• Amino acids act as both catalysts and integral components during NP formation.
• Smaller silica NPs exhibit superior hyperpolarization efficiency, making them promising for in vivo applications like MRI.