Interaction of colloidal particles with biologically relevant complex surfaces

Particle/wall electroviscous effects at the micron scale: comparison between experiments, analytical and numerical models

“…The general trend observed in figure 4 then suggest that the surface charge passivation is not as strong as expected or is not equally distributed or homogeneous all over the glass surface (the diffusion coefficients shown in the figures represents the average computed over different individual Brownian particles followed at different locations above the wall). As previously shown [41], characterization of the these surfaces using AFM confirms the heterogeneity of the functionalizations. In the following sections we shall explain the departure from classical hydrodynamic theory observed in all these cases as well as the reason why the other systems shown in figure 3 (particle/pLL and particle/glass with 10 mM of salt) obey, on the contrary, Brenner's formulas.…”

“…defining A = 3( ζ) 2 /μλ. Both, the experimental and theoretical ratios are plotted in figure 5 using the conductivity value of λ = 7.4 μS m −1 reported by the Barnstead purification system and a fitted value of ζ = −72 mV which is consistent with the ζ-potential magnitudes measured in particles covered with the same functionalizations as the ones used here [41]. We can therefore conclude, at this stage, that the simple electroviscous relations (1) and ( 11) are good enough to explain the experimental data given reasonable values of the conductivity and ζ-potentials.…”

“…The conductivity value of water reported by the Barnstead purification system was 7.4 μS m −1 . A full characterization of the particles including their effective size, polydispersity and surface potential are reported elsewhere [41].…”

“…The glass slides were first cleaned with a 2 : 1 sulfuric acid/hydrogen peroxide solution for 15 min, rinsed with DI water, dried at 35 • C and plasma cleaned for 1 min. The hyaluronic sodium salt (HA, 7.5 × 10 5 -1 × 10 6 Mw, Sigma-Aldrich) was bonded to glass via aminosilane groups ((3-aminopropyl)triethoxysilane, Sigma-Aldrich) using the EDC/NHS chemistry (see Hernández-Meza et al [41] for more details). To form the passivated polyelectrolyte layer we let the poly-L-lysine (pLL, Sigma-Aldrich) bind electrostatically to the −SiO − groups of the glass followed by charge screening with glutaraldehyde (if the last step is omitted, the glass wall is left with a positively charged layer of pLL).…”

“…We also studied a case where the particle interacts with an opposite (positive) charged wall (poly-L-lysine functionalization). The biological relevance of all these functionalizations as well as the characterization of the surface topologies (AFM measurements) are discussed in more detail elsewhere [41]. In this work we focus on the diffusion coefficient components of the particles diffusing above these surfaces and the results are discussed in the context of electroviscous theories and numerical models.…”