A Mechanistic Approach to Modeling Single Protein Adsorption at Solid-Water Interfaces

Characterization of electroosmotic flow through nanoporous self-assembled arrays

Characterization of EOF mobility for Tris and TBE buffer solutions is performed in nanoporous arrays using the fluorescent marker method to examine the magnitude of EOFs through nanopores with mean diameters close to electric double layer thickness (Debye length). Structures made from solid silica nanospheres with effective pore sizes from 104 nm down to 8 nm are produced within the microchannel using an evaporation self-assembly method. EOF results in nanoporous matrices show higher EOF mobilities for stronger electrolyte solutions, which are drastically different compared to microchannel EOF. The effects of scaling are also examined by comparing the EOF mobility for varying ratios of pore diameters to the Debye length, which shows a surprising consistency across all particle sizes examined. This work demonstrates various factors which must be considered when designing nanofluidic devices, and discusses the causes of these small scale effects.

Competitive adsorption of bacteriophage T4 lysozyme stability variants at hydrophilic glass surfaces

The competitive adsorption behavior exhibited by the wild-type T4 lysozyme and two of its structural stability variants was studied by 125I radioisotope labeling. The mutant lysozymes were produced by substitution of the isoleucine residue at position 3 in the wild type with a tryptophan residue, resulting in a protein with lower structural stability, or with a cysteine residue, resulting in a protein with higher structural stability. Adsorption kinetics were recorded for binary protein mixtures in contact with a clean glass surface, in which one variant had been radiolabeled and the other had not. All pair permutations were tested. The kinetic data show that in instances in which exchange reactions between adsorbed protein and dissolved protein occur, they occur such that more stable variants are removed from the surface by less stable variants. The less stable proteins thus exhibited an advantage in competitive adsorption over the more stable proteins, in these tests.

Concentration Effects on Adsorption of Bacteriophage T4 Lysozyme Stability Variants to Silica

The adsorption kinetics and dodeceyltrimethylammonium bromide-mediated elution of the wild type and two structural stability mutants of bacteriophage T4 lysozyme were recorded in situ, at silica surfaces. Experiments were performed at different solution concentrations, ranging from 0.01 to 1.0 mg/ml. Plateau values of adsorbed mass generally increased with increasing solution concentration, with the adsorbed layer being only partially eluted by buffer. Treatment with surfactant removed more of the adsorbed protein in each case, with the remaining adsorbed mass varying little with concentration. Comparison of the data to an adsorption mechanism allowing for three adsorbed states, distinguished by binding strength, showed that the fraction of adsorbed molecules present in the most tightly bound state (state 3) decreased as adsorption occurred from solutions of increasing concentration. However, the absolute amounts of state 3 molecules present in each case were less dependent on solution concentration. Adsorption of T4 lysozyme into state 3 is suggested to occur early in the adsorption process and continue until some critical surface concentration is reached. Beyond this critical value of adsorbed mass, adsorption is suggested to progress with adoption of more loosely bound states.

Effect of Electrostatic Interaction on the Adsorption of Globular Proteins on Octacalcium Phosphate Crystal Film

The electrostatic effect on the adsorption of globular proteins, such as bovine serum albumin (BSA), hen egg white lysozyme (LZM), and beta-lactoglobulin (beta-Lg), on octacalcium phosphate (OCP)-like crystal thin films was investigated. A poorly crystalline thin film was synthesized on a tissue culture polystyrene (TCP) surface and used as a model surface in this study. The solution pH clearly affected the electrostatic properties of both proteins and surface. The adsorbed amounts obtained at quasi-steady state were readily related to the solution pH for each protein. The adsorption rate is fast during the initial period and levels off gradually. The maximum adsorbed mass occurred at pH 7 for BSA and at pH 9 for LZM. beta-Lg adsorbed similar amounts at pHs lower than 9, but the adsorbed mass decreased at pHs higher than 9 where electrostatic repulsion exists. The pH values where the maximum adsorbed mass occurred may be considered as the conditions where electrostatic attraction is most favorable. The adsorbed mass of beta-Lg was the greatest among the proteins of interest while BSA adsorbed the least despite its greater molecular mass. LZM falls into the intermediate region. According to these observations, BSA has undergone conformational changes that prevent further adsorption to a greater extent than the others. A simple relationship between the adsorption rate and the electrostatic properties was not established. However, the order of magnitude of the adsorption rate at the initial period tends to be the same as that of maximum adsorbed mass for each protein.

Adsorption of thermomonospora fusca E(5) cellulase on silanized silica

The adsorption kinetics and dodeceyltrimethylammonium-bromide-mediated elution of Thermomonospora fusca E(5) cellulase were recorded in situ, at hydrophobic, silanized silica. Experiments were performed at different solution concentrations, ranging from 0.001 to 0.70 mg/mL. Plateau values of adsorbed mass generally increased with increasing solution concentration, with the adsorbed layer being only partially eluted by buffer. Treatment with surfactant removed more of the adsorbed enzyme in each case, with the remaining adsorbed mass varying little among experiments. Adsorption of E(5) into this nonremovable state was suggested to occur early in the adsorption process and continue until some critical surface concentration was reached. Beyond this critical value of adsorbed mass, adsorption progressed with the protein adopting more loosely bound states. Adsorption kinetic data were interpreted with reference to an adsorption mechanism allowing for irreversible adsorption into two dissimilar states. These states were distinguished by differences in occupied interfacial area, and binding strength, presumably a result of differences in structure. Comparison of the data to the kinetic model based on this mechanism showed that the fraction of adsorbed molecules present in the more tightly bound state decreased as adsorption occurred from solutions of increasing concentration. However, the absolute values of more tightly bound molecules were less dependent on adsorption conditions.