Counterion distribution surrounding spherical nucleic acid-Au nanoparticle conjugates probed by small-angle x-ray...

Area of Science:

• Nanotechnology
• Biophysics
• Materials Science

Background:

• Spherical nucleic acid-Au nanoparticle conjugates (SNA-AuNPs) are advanced nanomaterials with unique electronic and structural properties.
• Understanding the ionic environment around SNA-AuNPs is crucial for controlling their assembly, stability, and function in biological and chemical applications.

Purpose of the Study:

• To determine the radial distribution of monovalent cations (Na+, K+, Rb+, Cs+) surrounding SNA-AuNPs.
• To compare experimental results with classical density functional theory (DFT) predictions.
• To validate the heavy ion replacement small-angle X-ray scattering (HIRSAXS) technique for probing cation distributions around nanoparticles.

Main Methods:

• In situ small-angle X-ray scattering (SAXS) was employed to measure diffraction patterns.
• The heavy ion replacement SAXS (HIRSAXS) approach was utilized to isolate cation-specific scattering contributions.
• Classical density functional theory (DFT) calculations were performed to model cation distributions and DNA conformations.

Main Results:

• Small but distinct differences in SAXS profiles were observed with varying monovalent cations.
• HIRSAXS successfully extracted cation-distribution-dependent scattering, showing good agreement with DFT predictions.
• The cation concentration in the SNA shell was found to be enhanced, up to 15-fold, depending on bulk ionic concentration.
• DNA conformation within the SNA shell was also elucidated through experiment-theory comparison.

Conclusions:

• The study successfully demonstrated the feasibility of HIRSAXS for characterizing monovalent cation distributions around nanoparticles with electron-dense cores.
• The findings provide quantitative insights into the ionic atmosphere and DNA structure within SNA-AuNP shells.
• This technique offers a powerful tool for designing and optimizing nanomaterials for various applications.