Dynamic Surface Properties of Solutions of Bovine Serum Albumin Complexes with Silica Nanoparticles
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mic Surface Properties of Solutions of Bovine Serum Albumin Complexes with Silica Nanoparticles O. Yu. Milyaeva* Chair of Colloid Chemistry, St. Petersburg State University, St. Petersburg, 198504 Russia *e-mail: [email protected] Received April 24, 2020; revised May 5, 2020; accepted May 8, 2020
Abstract—Surface properties of aqueous dispersions of bovine serum albumin complexes with silica nanoparticles have been studied using a set of methods that are sensitive to changes in the structure and composition of surface layers. In spite of the similar charges of the components, their interaction leads to changes in the surface properties of the dispersions; namely, the rates of variations in the dynamic surface elasticity and dynamic surface tension decrease due to the high electrostatic barrier of adsorption. The addition of an electrolyte decreases the electrostatic barrier. In this case, the adsorption of the complexes leads to a growth in the dynamic surface elasticity from the values characteristic of pure bovine serum albumin solutions (~80 mN/m) to 170 mN/m, which corresponds to the formation of macroscopically homogeneous adsorption film of nanoparticle–protein complexes. DOI: 10.1134/S1061933X20050117
INTRODUCTION Owing to their small sizes, solid nanoparticles can participate in cellular processes and penetrate into the regions of organism, which are inaccessible for larger particles, e.g., into brain [1–3]. When a nanoparticle gets into an organism, it is immediately coated with a shell consisting of proteins and other biomolecules [3–6]. In particular, bovine serum albumin (BSA) and fibrinogen form a stable shell on particle surfaces [7– 10]. When a shell (crown) is formed on a particle surface, the tertiary and secondary structures of a protein may change, and the changes further affect the interaction of the protein–nanoparticle complex with a cell [11–13]. The study of the adsorption of such complexes at a liquid–gas interface provides information about protein conformation in the complex [14]. In this work, dynamic surface rheology, as well as ellipsometry and dynamic light scattering were employed to study the adsorption of BSA–silica nanoparticle complexes. Note that the formation of such complexes in a bulk aqueous phase was studied by many authors [15–17]. The adsorption of BSA and silica particles at liquid–gas interfaces separately was also extensively studied [18–20]. Hydrophilic silica nanoparticles possess no surface activity. If their surface is modified, e.g., as a result of interaction with surfactants, the dynamic surface elasticity of aqueous dispersions of such complexes may reach high values (~150 mN/m) [20]. A BSA globule is heart-shaped, with the sizes of main axes being 1.7 nm × 4.2 nm, and carries a nega-
tive charge at neutral pH values [21]. When BSA is adsorbed at a liquid–gas interface, it forms a dense monolayer having a surface elasticity of nearly 80 mN/m [22, 23]. Kinetic dependences of the dynamic surface elasticity and surface pressure are monotonic, thus indicating the
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