Human Serum Albumin Monolayers on Mica: Electrokinetic Characteristics

Abstract

Adsorption of human serum albumin (HSA) on mica from 0.15 M NaCl solutions and various pH values was studied using in situ streaming potential measurements, AFM imaging, and XPS. The results obtained by the streaming potential were consistent with AFM measurements and theoretical predictions based on the random sequential adsorption model. This allowed one to determine both the kinetics of adsorption and the maximum coverage of HSA as a function of pH. At pH 3.5, the maximum coverage of HSA was 0.45 (which corresponds to 1.4 mg m(-2) neglecting hydration). This decreased monotonically with the increase in pH, attaining 0.30 (pH 5.1) and 0.25 (pH 7.4). At pH >10.5, the adsorption of HSA on mica was negligible. Further experimental studies performed for HSA monolayers of well-controlled coverage revealed their stability against pH cycling. It was found in these experiments that at pH <4 and >8 the electrokinetic properties of HSA monolayers approached the reference data pertinent to the bulk. However, for an intermediate pH range, deviations from the bulk reference data were observed, suggesting a dipolar (heterogeneous) charge distribution over adsorbed HSA molecules. This caused a slight shift in the isoelectric point of the monolayer determined to be 4.7 compared to the bulk value of 5.1. However, for the HSA coverage below 0.2, the effect of the substrate was significant, making the zeta potential more negative and shifting the apparent isoelectric point to more acidic values. It was suggested that these results obtained for planar and smooth interfaces could be used as reference data for interpreting albumin adsorption on colloid carrier particles.

The Role of the Electrokinetic Charge of Neurotrophis-based Nanocarriers: Protein Distribution, Toxicity and Oxidative Stress in in Vitro Setting

“…It has been shown by various theoretical calculations performed using the chemical composition of proteins that the surface charge of the molecule is heterogeneously distributed in the form of positive and negative patches, existing over a wide range of pH. This hypothesis is supported by analogous results reported in the literature on proteins: HSA 43 , IgG 44 , brinogen 45 , NT-4 34 and lysozyme 46 .…”

“…We carried out BDNF adsorption at PAMAM dendrimers in high ionic strength (0.15M) solution, because the reduction of the repulsive interactions between the protein and polymers has been previously reported for different proteins, including polyclonal rabbit immunoglobulin (IgG) 47 , brinogen 45 , albumin 43 and NT-4 34 . By applying this approach, we obtained higher adsorbed amount of BDNF which makes our nanocarriers more biocompatible.…”

A multiscale investigation on controlling bovine serum albumin adsorption onto polyurethane films

“…Major assumption in our calculations was that particles were irreversibly adsorbed on the static lattice surface with a very high force as our experimental observations imply (adsorption isotherms in Figure ), as well as many studies suggest such a behavior . Adsorbed particles were assumed to form a monolayer over the lattice surface, as was observed for human SA adsorption on hydrophilic mica surfaces, and not to diffuse laterally among adjacent binding sites. The total amount of BSA particles, including both adsorbed and diffusing in the simulation box, was kept fixed during the simulations to mimic experimental conditions.…”

Revealing deposition mechanism of colloid particles on human serum albumin monolayers

“…Zeta potential of bare and HSA covered mica was determined via streaming potential measurements using a parallel-plate cell described in previous works [13,14].…”

“…Basic physicochemical characteristics of HSA such as the diffusion coefficient, hydrodynamic diameter, electrophoretic mobility as a function of pH and ionic strength have been determined in previous works [11][12][13][14]. It was shown that at pH 5.2 the electrophoretic mobility of the protein vanishes independently of ionic strength, therefore, this pH is defined as the isoelectric point.…”