pH- and Ionic Strength-Controlled Switching between Protein Monolayer and Multilayer Adsorption on Gold Nanoparticles

Area of Science:

• Nanoparticle-Surface Science
• Biomolecular Interactions
• Physical Chemistry

Background:

• Protein adsorption on nanoparticles forms a protein corona (PC), crucial for nanoparticle behavior in biological systems.
• Competing intermolecular forces, particularly electrostatic interactions, govern PC formation.
• pH and ionic strength are key tunable parameters influencing electrostatic interactions.

Purpose of the Study:

• To systematically investigate the impact of pH and ionic strength on protein adsorption onto gold nanoparticles (GNPs).
• To elucidate the role of electrostatic interactions in both multilayer and monolayer protein corona formation.
• To compare adsorption behavior on GNPs of varying sizes (15-60 nm).

Main Methods:

• In situ monitoring of protein adsorption using dynamic light scattering (DLS).
• Quantification of adsorption using Brunauer-Emmett-Teller (BET) analysis and modified Langmuir isotherms.
• Salt titration experiments to differentiate electrostatic and non-electrostatic forces.

Main Results:

• Multilayer adsorption observed at pH 5.2 (below pI), with distinct first and subsequent layer binding constants.
• Monolayer adsorption saturated at pH 7.4 and 10.2 (near and above pI).
• Increased ionic strength reduced multilayer formation, confirming electrostatic screening's role; smaller GNPs exhibited stronger interprotein electrostatic coupling.

Conclusions:

• Electrostatic interactions significantly influence protein corona formation, dictating multilayer versus monolayer adsorption.
• pH and ionic strength are critical for controlling protein adsorption and corona structure.
• Nanoparticle size modulates electrostatic coupling within the protein corona.