Dependence of preferential bovine serum albumin oligomer adsorption on the surface properties of monodisperse polystyrene latices

Correlative Effects on Nanoplastic Aggregation in Model Extracellular Biofilm Substances Investigated with Fluorescence Correlation Spectroscopy

Recent studies show that biofilm substances in contact with nanoplastics play an important role in the aggregation and sedimentation of nanoplastics. Consequences of these processes are changes in biofilm formation and stability and changes in the transport and fate of pollutants in the environment. Having a deeper understanding of the nanoplastics-biofilm interaction would help to evaluate the risks posed by uncontrolled nanoplastic pollution. These interactions are impacted by environmental changes due to climate change, such as, e.g., the acidification of surface waters. We apply fluorescence correlation spectroscopy (FCS) to investigate the pH-dependent aggregation tendency of non-functionalized polystyrene (PS) nanoparticles (NPs) due to intermolecular forces with model extracellular biofilm substances. Our biofilm model consists of bovine serum albumin (BSA), which serves as a representative for globular proteins, and the polysaccharide alginate, which is a main component in many biofilms, in solutions containing Na+ with an ionic strength being realistic for fresh-water conditions. Biomolecule concentrations ranging from 0.5 g/L up to at maximum 21 g/L are considered. We use non-functionalized PS NPs as representative for mostly negatively charged nanoplastics. BSA promotes NP aggregation through adsorption onto the NPs and BSA-mediated bridging. In BSA-alginate mixtures, the alginate hampers this interaction, most likely due to alginate-BSA complex formation. In most BSA-alginate mixtures as in alginate alone, NP aggregation is predominantly driven by weaker, pH-independent depletion forces. The stabilizing effect of alginate is only weakened at high BSA contents, when the electrostatic BSA-BSA attraction is not sufficiently screened by the alginate. This study clearly shows that it is crucial to consider correlative effects between multiple biofilm components to better understand the NP aggregation in the presence of complex biofilm substances. Single-component biofilm model systems based on comparing the total organic carbon (TOC) content of the extracellular biofilm substances, as usually considered, would have led to a misjudgment of the stability towards aggregation.

Probing protein aggregation at buried interfaces: distinguishing between adsorbed protein monomers, dimers, and a monomer-dimer mixture in situ

Protein adsorption on surfaces greatly impacts many applications such as biomedical materials, anti-biofouling coatings, bio-separation membranes, biosensors, antibody protein drugs etc. For example, protein drug adsorption on the widely used lubricant silicone oil surface may induce protein aggregation and thus affect the protein drug efficacy. It is therefore important to investigate the molecular behavior of proteins at the silicone oil/solution interface. Such an interfacial study is challenging because the targeted interface is buried. By using sum frequency generation vibrational spectroscopy (SFG) with Hamiltonian local mode approximation method analysis, we studied protein adsorption at the silicone oil/protein solution interface in situ in real time, using bovine serum albumin (BSA) as a model. The results showed that the interface was mainly covered by BSA dimers. The deduced BSA dimer orientation on the silicone oil surface from the SFG study can be explained by the surface distribution of certain amino acids. To confirm the BSA dimer adsorption, we treated adsorbed BSA dimer molecules with dithiothreitol (DTT) to dissociate these dimers. SFG studies on adsorbed BSA after the DTT treatment indicated that the silicone oil surface is covered by BSA dimers and BSA monomers in an approximate 6 : 4 ratio. That is to say, about 25% of the adsorbed BSA dimers were converted to monomers after the DTT treatment. Extensive research has been reported in the literature to determine adsorbed protein dimer formation using ex situ experiments, e.g., by washing off the adsorbed proteins from the surface then analyzing the washed-off proteins, which may induce substantial errors in the washing process. Dimerization is a crucial initial step for protein aggregation. This research developed a new methodology to investigate protein aggregation at a solid/liquid (or liquid/liquid) interface in situ in real time using BSA dimer as an example, which will greatly impact many research fields and applications involving interfacial biological molecules.

Competitive adsorption-desorption of IgM monomers-dimers on silica and modified silica surfaces

Understanding competitive adsorption-desorption of proteins onto surfaces is an important area of research in food processing and biomedical engineering. Here, we demonstrate, how electrospray-differential mobility analysis that has been traditionally used for characterizing bionanoparticles, can be used for quantifying complex competitive adsorption-desorption of oligomeric proteins or multiprotein systems using monomers and dimers of IgM as a model example onto silica and modified silica surfaces. Using ES-DMA, we show that IgM dimers show a preference to stay adsorbed to different surfaces although monomers adsorb more easily and desorption rates of monomers and dimers of IgM are surface-type-dependent and are not significantly affected by shear. We anticipate that this demonstration will make ES-DMA a popular "label-free" method for studying multicomponent multi-oligomeric protein adsorption to different surfaces in the future.

Characterizing the adsorption of proteins on glass capillary surfaces using electrospray-differential mobility analysis

We quantify the adsorption and desorption of a monoclonal immunoglobulin-G antibody, rituxamab (RmAb), on silica capillary surfaces using electrospray-differential mobility analysis (ES-DMA). We first develop a theory to calculate coverages and desorption rate constants from the ES-DMA data for proteins adsorbing on glass capillaries used to electrospray protein solutions. This model is then used to study the adsorption of RmAb on a bare silica capillary surface. A concentration-independent coverage of ≈4.0 mg/m(2) is found for RmAb concentrations ranging from 0.01 to 0.1 mg/mL. A study of RmAb adsorption to bare silica as a function of pH shows maximum adsorption at its isoelectric point (pI of pH 8.5) consistent with literature. The desorption rate constants are determined to be ≈10(-5) s(-1), consistent with previously reported values, thus suggesting that shear forces in the capillary may not have a considerable effect on desorption. We anticipate that this study will allow ES-DMA to be used as a "label-free" tool to study adsorption of oligomeric and multicomponent protein systems onto fused silica as well as other surface modifications.

Heteroenergetics of Bovine Serum Albumin Adsorption from Good Solvents Related to Crystallization Conditions

Total internal reflection fluorescence (TIRF) was applied to study adsorption of bovine serum albumin (BSA) from a thermodynamically good solvent commonly used as a buffer for BSA crystallization. BSA adsorption is shown to exhibit heteroenergetics, which is possibly a general property of protein interfacial behavior. For example, BSA adsorption on quartz, SnO2 , and alkyl-modified surfaces demonstrates broad continuous distributions of energies of adsorption activation and protein-surface binding. For heteroenergetic adsorption, the type of the isotherm and kinetics depends on the type of the energy distribution functions and the type of correlation between the energies. In the case of BSA adsorption on quartz and SnO2 surfaces, protein interfacial behavior is consistent with a model suggesting rectangular distributions both of activation energies of adsorption and energies of protein-surface binding. In the case of an alkyl-modified surface, BSA adsorption kinetics is interpreted in terms of a heteroenergetic model suggesting initial adsorption at selected adsorption sites with maximum rate constants. The model also suggests that lateral diffusion quickly redistributes the molecules from the initial adsorption sites to the sites with higher binding energies. The combination of TIRF spectroscopy with an electrochemical system was used to study the effect of surface charge on protein adsorption on a transparent SnO2 electrode. BSA behavior on the SnO2 electrode was found to correlate with surface hydrophobicity and indifferent to charges both of the surface and the protein. Hydrophobic interactions seem to be the principal driving force in determining the behavior of BSA at the solid-liquid interface and likely plays an important role in protein crystallogenesis.

Monosize microbeads based on polystyrene and their modified forms for some selected medical and biological applications

Polymeric particles are produced by different polymerization techniques. Phase inversion (dispersion) polymerization is one of the recent techniques to obtain monosize polymeric microbeads in the size range of 1-50 microns. The size and monodispersity of these microbeads can be adjusted by using several solvent systems (e.g., alcohol-water mixtures) with different polarities and by changing the type and amount of monomer, initiator and stabilizer. Surfaces of these microbeads can be further modified by different techniques including coating with different copolymers. Monosize polymeric microbeads are widely used in medical and biological applications as carriers, such as in immunoassays and cell separation, in site-specific drug delivery systems, in nuclear medicine for diagnostic imaging, in studying the phagocytic process, in affinity separation of biological entities, etc. Here, some important aspects of the production of monosize microbeads based on polystyrene and their modified forms are briefly discussed, and some selected medical and biological applications are summarized.

Adsorption/desorption of human serum albumin at the surface of poly(lactic acid) nanoparticles prepared by a solvent evaporation process

Biocompatible and biodegradable nanoparticles of poly(lactic acid) (100% L-lactic units = PLA) were prepared by an emulsion, microfluidization, and solvent evaporation method using human serum albumin (HSA) as a surface agent. A radiolabeling technique was employed to quantify the serum albumin bound to the nanoparticles and to measure its desorption kinetics in various media at 22 degrees C and 37 degrees C (phosphate buffer pH 7.4, serum albumin 40 g/L in phosphate buffer pH 7.4 and fetal calf serum). The amount of serum albumin bound to the nanoparticles was found to be a linear function of 1/D (where D is the nanoparticle mean diameter) and was related to the total developed area of the nanoparticles. The adsorption/desorption behavior of serum albumin at the surface of the nanoparticles suggested a multilayer adsorption model. Moreover, a part of the serum albumin molecules was irreversibly bound regardless of the incubation conditions. Consequently, the classical Langmuirian theories of equilibria could not be applied.

Adsorption of plasma proteins onto polymer latices

In this article we review the adsorption of plasma proteins onto polymer latices on the basis of our experimental data. First, the surface characteristics of the latices were examined. Hydrophilic polymer layers (water-soluble polymer layers) were found to exist on the surfaces of copolymer latices, e.g., a polyacrylamide (polyAAm) layer existed on the surface of the styrene/acrylamide copolymer [P(St/AAm)] latex. These diffuse layers strongly affected the protein adsorption, that is, the amount of plasma proteins adsorbed onto copolymer latices (viz. P(St/AAm) and styrene/2-hydroxyethyl methacrylate copolymer [P(St/HEMA)] latices), particularly in the alkaline pH region, was much smaller than that onto a hydrophobic polystyrene (PS) latex. The protein adsorption was also studied as a function of pH, ionic strength and electrolyte concentration. Further, the adsorbability of heat- and urea-denatured albumins was investigated. A higher affinity of denatured components for polymer latices was observed compared with that of the native components.

Identification of plasma proteins adsorbed to hemodialyzers during clinical use

An investigation has been made of the protein layers formed on hemodialysis membranes during clinical use. Dialyzers having membranes of polymethylmethacrylate (PMMA), Cuprophane, cellulose acetate (CA), and saponified cellulose ester (SCE) were examined. Immediately following dialysis the dialyzers were washed free of blood and the membranes eluted with 2% SDS. The eluates were examined by SDS-PAGE followed by protein immunoblotting. Antisera to 16 common plasma proteins were used to probe for the presence of these proteins in the eluates. Most of the proteins tested for were found in the different eluates, suggesting that the protein layers are extremely complex. The protein compositions were qualitatively different on the different membranes. Except for HMWK the contact phase clotting factors were present in very small amounts and were largely activated. The clear presence of HMWK and the relatively small amounts of fibrinogen provide support for the occurrence of the Vroman effect. Fibrinogen was found to be degraded and this may be related to the observation that plasminogen was activated to plasmin. Complement C3 was an abundant component of all eluates. It was degraded to small fragments in a way which could not be related to complement activation. Many of the other proteins, particularly those of high molecular weight, were extensively degraded. It is speculated that this heretofore unremarked phenomenon may be due to the action of enzymes released by cell damage.