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Protein-surface interactions: the role of heterogeneous surface chemistry on protein adsorption

Transient spatial spike of FITC-IgG adsorption from albumin-fibrinogen-IgG mixture as measured by spatially-resolved TIRF occurred at the region of intermediate hydrophobicity on a methyl-silica gradient surface. Hydrophobicity increases in vertical direction.  The method has the spatial resolution of 5 µm, and temporal resolution of 1 s, total time: 11 minutes of adsorption followed by 11 minutes of desorption.

LEFT: Time course fluorescence images of albumin adsorption to the OTS SAMs.  Lower left section of each image is processed (bas-relief) to enhance the details of the af488-HSA distribution.  Upper six panels: Non-annealed pattern – HSA initially adsorbs more quickly to the stamped bands and eventually produces greater coverage on the more hydrophobic stamped bands.  Heterogeneities in the stamped bands are evidenced by spatial irregularities in protein adsorption. Lower six panels: Annealed pattern – albumin quickly adsorbs to the stamped band edges and reaches near maximal coverage on the stamped bands within minutes. Adsorption proceeds more slowly on the more hydrophilic unstamped bands but adsorbed amount eventually overtakes that in the stamped bands and a reversal in the band brightness is seen starting at 15 min. Dark spots within the non-stamped bands are small OTS islands, which contain protein coverage comparable to the stamped bands. RIGHT: Density histogram dynamics and normal distribution deconvolution.  upper panel – Timecourse evolution of the AF488-HSA density distribution on the nonannealed OTS pattern.  Delineation in adsorbed amounts on stamped and nonstamped areas quickly developed in the first few minutes of adsorption.  As adsorption proceeded, the stamped and nonstamped peaks broadened and slightly converged toward a single density.  lower panel – Timecourse evolution of the AF488-HSA density distribution on the annealed OTS pattern.  Little difference was observed between stamped and nonstamped density peaks in the histograms until the adsorbed amount in the nonstamped areas exceeded that in the stamped bands.  The stamped and nonstamped peaks did not broaden over time and continued to diverge after 12 minutes of adsorption. G.N. Hodgkinson and V. Hlady, How surface heterogeneity affects protein adsorption: annealing of OTS patterns and albumin adsorption kinetics. Croatica Chemica Acta, 80(3-4) (2007) 405-20.

Adsorption-desorption kinetics of AlexaFluor488-labeled Fgn (A), HSA (B) and IgG (C) from the ternary mixtures onto the sulfonate end, the center, and on the sulfhydryl end of the gradient. Vertical arrows mark the start of the desorption cycles with flow of PBS. Yong-Xue Ding and Vladimir Hlady, Competitive adsorption of three human plasma proteins onto sulfhydryl-to-sulfonate gradient surfaces, Croat Chem Acta, 2011; 84(2):193-202.