Mimicking Pseudo-Virion Interactions with Abiotic Surfaces: Deposition of Polymer Nanoparticles with Albumin Corona

Abstract

Adsorption of human serum albumin (HSA) molecules on negatively charged polystyrene microparticles was studied using the dynamic light scattering, the electrophoretic and the solution depletion methods involving atomic force microscopy. Initially, the physicochemical characteristics of the albumin comprising the hydrodynamic diameter, the zeta potential and the isoelectric point were determined as a function of pH. Analogous characteristics of the polymer particles were acquired, including their size and zeta potential. The formation of albumin corona on the particles was investigated in situ by electrophoretic mobility measurements. The size, stability and electrokinetic properties of the particles with the corona were also determined. The particle diameter was equal to 125 nm, which coincides with the size of the SARS-CoV-2 virion. The isoelectric point of the particles appeared at a pH of 5. The deposition kinetics of the particles was determined by atomic force microscopy (AFM) under diffusion and by quartz microbalance (QCM) under flow conditions. It was shown that the deposition rate at a gold sensor abruptly vanished with pH following the decrease in the zeta potential of the particles. It is postulated that the acquired results can be used as useful reference systems mimicking virus adsorption on abiotic surfaces.

Keywords: adsorption of albumin; albumin coronas of particles; deposition of polymer albumin conjugates; stability of albumin corona; virus deposition; zeta potential of albumin corona.

Figure 1

(a) Dependence of the hydrodynamic diameter of the HSA molecule on pH derived from the DLS measurements: (■) 1 mM NaCl, (●) 10 mM NaCl. The line shows the average value of the hydrodynamic diameter equal to 8.0. (b) Dependence of the zeta potential of the HSA molecules (left-hand axis) and the electrophoretic mobility (right-hand axis) on pH derived from the LDV measurements: 1. (●) 10 mM NaCl, 2. (■) 1 mM NaCl. The lines represent the guide for the eyes.

Figure 2

Dependence of the normalized surface concentration of HSA, N/c_b [μm⁻² mg⁻¹ L], on the square root of the adsorption time t^1/2 [min^1/2]. The points denote experimental results obtained by a direct atomic force microscopy (AFM) enumeration of adsorbed HSA molecules on mica: pH 3.5, 10 mM NaCl, (▲) c_b = 0.1 mg L⁻¹, (●) c_b = 0. 5 mg L⁻¹. The solid line shows the theoretical results calculated from Equation (2). The inset shows the AFM image of the HSA layer on mica.

Figure 3

(a) Dependence of the hydrodynamic diameter of the polystyrene particles on pH: (●) 10 mM NaCl. The dashed line shows the average value of the hydrodynamic diameter equal to 115 ± 5 nm. (b) Dependence of the zeta potential of the particles on pH (left-hand axis) and the electrophoretic mobility (right-hand axis): (●) 10 mM NaCl. The solid line shows the average value of the zeta potential equal to −55 ± 5 mV.

Figure 4

Kinetics of the polystyrene particle deposition on PLL functionalized mica under diffusion conditions shown as the dependence of surface concentration N [μm⁻²] on the square root of the deposition time t^1/2 [min^1/2]. The points denote experimental results obtained by a direct AFM enumeration for c_p = 100 mg L⁻¹, pH 3.5 and 10 mM NaCl. The solid lines show the theoretical results derived from Equation (3) for the particle diameter equal to the following: 1. 100 nm, 2. 110 nm, 3. 120 nm.

Figure 5

Dependence of the zeta potential of the polystyrene particles on the HSA concentration in the suspension before mixing: pH 3.5, 10 mM NaCl, particle concentration 500 mgL⁻¹, (●) experimental results derived from the LDV measurements. The solid red line shows the linear fit of experimental data, and the dashed horizontal line shows the zeta potential of the protein in the bulk.

Figure 6

(a) A schematic view of the SARS-CoV-2 virion [37] and (b) the polymer particle with the HSA corona.

Figure 7

Dependence of the hydrodynamic diameter of the particles with the HSA corona on pH: corona coverage 0.80 mg m⁻², (●) 10 mM NaCl, (■) 1 mM NaCl. The lines represent guides to the eyes.

Figure 8

Dependencies of the zeta potential on pH derived from the LDV measurements: (a) 1 mM NaCl, (b) 10 mM NaCl. The green lines show the bulk zeta potential of HSA molecules, the red lines show the bulk zeta potential of the bare polymer particles and (●,●) represents experimental data for the particles with the HSA corona (the coverage of 0.80 mg m⁻²).

Figure 9

Kinetics of the polymer particle with HSA corona deposition on bare mica under diffusion conditions shown as the dependence of the absolute coverage $\Theta$ (left-hand axis) or the mass coverage ${\Gamma }_p$ (right-hand axis) on the square root of the deposition time t^1/2 [min^1/2]: the corona coverage 0.80 mg m⁻², pH 4, 10 mM NaCl, particle bulk concentration 100 mg L⁻¹. The red points show experimental results obtained by AFM imaging of particles. The inset shows the AFM image of the particle with the HSA corona layer of mica. The blue points show the reference results obtained for the positively charged polymer particles. The solid red line shows the theoretical results derived from the random sequential adsorption (RSA) model.

Figure 10

(a) Kinetics of the polymer particle deposition on the gold sensor derived from quartz microbalance (QCM) measurements: the corona coverage 0.80 mg m⁻², pH 4, 10 mM NaCl, c_b = 50 mg L⁻¹, flow rate 2.5 × 10⁻³ mL s⁻¹. The solid lines show the experimental data derived from the Sauerbrey model for various overtones, the dashed lines show the results predicted using the RSA model and the point shows the dry particle coverage derived from AFM. (b) Reference kinetic results for the positively charged amidine particle deposition on the gold sensor derived from QCM measurements: pH 3.5, 10 mM NaCl, c_b = 50 mg L⁻¹, flow rate 2.5 × 10⁻³ mL s⁻¹. The solid lines show the experimental data derived from the Sauerbrey model for various overtones and the dashed lines show the results predicted using the RSA model.

Figure 11

Kinetics of the polymer particle with HSA corona deposition on the gold sensor under flow conditions: the corona coverage 0.80 mg m⁻², pH 4, 10 mM NaCl, c_b = 50 mg L⁻¹, flow rate 2.5 × 10⁻³ mL s⁻¹. The solid red line shows the corrected QCM result for the third (red line) and the seventh overtone (green line), and the black dashed shows the theoretical results calculated from the RSA model.

Figure 12

Kinetics of the polymer particle with HSA corona deposition on the gold sensor derived from QCM measurements for various pHs: the corona coverage 0.80 mg m⁻², 10 mM NaCl, cb = 50 mg L⁻¹, flow rate 2.5 × 10⁻³ mL s⁻¹. The solid lines show the experimental data derived from the Sauerbrey model for the third overtone: 1. pH 4.0, 2. pH = 4.5, 3. pH = 5.5, 4. pH = 7.4.