Fibrinogen Adsorption on Mica Studied by AFM and in Situ Streaming Potential Measurements

Abstract

Adsorption of fibrinogen from aqueous solutions on mica was studied using AFM and in situ streaming potential measurements. In the first stage, bulk physicochemical properties of fibrinogen and the mica substrate were characterized for various ionic strength and pH. The zeta potential and number of uncompensated (electrokinetic) charges on the protein surfaces were determined from microelectrophoretic measurements. Analogously, using streaming potential measurements, the electrokinetic charge density of mica was determined for pH range 3-10 and the NaCl background electrolyte concentration of 10(-3) and 10(-2) M. Next, the kinetics of fibrinogen adsorption at pH 3.5 and 7.4 in the diffusion cell was studied using a direct AFM determination of the number of molecules per unit area of the mica substrate. Then, streaming potential measurements were performed to determine the apparent zeta potential of fibrinogen-covered mica for different pH and ionic strength in terms of its surface concentration. A quantitative interpretation of these streaming potential measurements was achieved in terms of the theoretical model postulating a side-on adsorption of fibrinogen molecules as discrete particles. On the basis of these results, the maximum coverage of fibrinogen Θ close to 0.29 was predicted, in accordance with previous theoretical predictions. It was also suggested that anomalous adsorption for pH 7.4, where fibrinogen and the mica substrate were both negatively charged, can be explained in terms of a heterogeneous charge distribution on fibrinogen molecules. It was estimated that the positive charge was 12 e (for NaCl concentration of 10(-2) M and pH 7.4) compared with the net charge of fibrinogen at this pH, equal to -21 e. Results obtained in this work proved that the coverage of fibrinogen can be quantitatively determined using the streaming potential method, especially for Θ < 0.2, where other experimental methods become less accurate.

Charged hydrophilic polymer brushes and their relevance for understanding marine biofouling

“…One reason for this is the amphoteric properties of the protein, with domains of different net charge, even though the whole fibrinogen molecule is net negatively charged at pH 7.4. (Wasilewska & Adamczyk 2011). Thus, the adsorption of fibrinogen on PDMAEMA, and to some extent also on PSPMA, can be associated with attractive electrostatic interactions (though this does not explain why adsorption is higher on the nominally neutral PHEMA-co-PEG10MA than on the zwitterionic PSBMA).…”

Revealing deposition mechanism of colloid particles on human serum albumin monolayers

“…Thus, for NaCl concentration of respectively (see Table 1). Knowing the mobility, one can calculate the electrokinetic charge per molecule Q c (expressed in Coulombs) from the Lorenz-Stokes relationship [11,34] 3…”

“…Knowing the zeta potential, one can calculate its electrokinetic (uncompensated) charge using the Gouy-Chapman relationship [11,34].…”

“…[21,34]. Knowing the streaming potential one can calculate the zeta potential of the interface using the Smoluchowski's equation and the electrokinetic charge density using the GouyChapman equation.…”

KfrA plasmid protein monolayers on latex particles-electrokinetic measurements

“…This is an interesting estimate because knowing N c one can predict the bulk electrophoretic mobility of KfrA molecules, which is impractical using conventional methods (micro-electrophoretic measurements). The mobility can be calculated form the formula using the Lorenz-Stokes relationship previously applied for fibrinogen [ 25 ] and HSA [ 27 ] …”