Modifications of mineral surfaces were performed in order to gain insight into what surface properties are decisive of the accumulation of dental plaque. A non-charged, hydrophilic surface was made by two consecutive plasma polymerizations, firstly with allyl alcohol, secondly with acrylic acid, followed by adsorption of a poly(ethylene glycol)-poly(ethylene imine) adduct. A strongly hydrophobic surface was obtained by plasma polymerization of hexamethyldisiloxane. Ellipsometry was used to monitor protein interaction with the surfaces. The hydrophilic surface gave very little adsorption of both a model protein, IgG, and of saliva proteins. The hydrophobic surface, on the other hand, adsorbed high amounts of both types of proteins. In vitro adhesion of an oral bacterium, S. mutans, as well as in uivo studies, gave the opposite result, the hydrophobic surface giving less adhesion and less plaque accumulation than the hydrophilic surface. A tentative explanation of this behaviour is that the saliva proteins that bind to the hydrophobic surface adsorb in an unnatural conformation which does not favour bacteria adherence.

Competetive adsorption from a ternary mixture of human serum albumin (HSA), human IgG, and human fibrinogen (FGN) at concentrations corresponding to blood plasma diluted 1/100 was investigated with the combination of Total Internal Reflection Fluorescence spectroscopy (TIRF) and ellipsometry. As substrates, three different plasma polymer surfaces, representing different surface charge and surface energy, were prepared from hexamethyldisiloxane (PP-HMDSO), acrylic acid (PP-AA), and 1,2-diaminocyclohexane (PP-DACH). In addition, adsorption from single and binary protein systems was investigated with ellipsometry. At the hydrophobic PP-HMDSO little or no displacement of any of the proteins was observed. The adsorbed layer was dominated by HSA and IgG, although Fgn was also present to a smaller extent. On PP-DACH and PP-AA, representing positively and negatively charged hydrophilic surfaces, respectively, Fgn completely dominated the adsorbed layer while HSA was almost absent and IgG was present only at a very low level.

Total internal reflection fluorescence (TIRF) and ellipsometry have been used to study competitive protein adsorption to a hydrophobic model surface prepared by radio frequency plasma deposition of hexamethyl disiloxane on silicon. Single, binary, and ternary protein solutions of human serum albumin (HSA), IgG, and fibrogen (Fgn) at concentrations corresponding to 1/100 of those in blood plasma were investigated. It is shown that by employing the combination of ellipsometry and TIRF, information on both the total adsorbed amount and the composition of the adsorbed protein layer can be obtained. It was found that adsorbed HSA is not displaced by IgG and/or Fgn to any large extent. IgG and HSA dominate the adsorption from the ternary protein mixture, although fibrinogen is also present in the adsorbed layer to a smaller extent.

The formation of protein layers during competitive adsorption was studied with ellipsometry. Single, binary, and ternary protein solutions of human serum albumin (HSA), IgG, and fibrinogen (Fgn) were investigated at concerntrations corresponding to blood plasma diluted 1/100. As a model surface, hydrophobic hexamethyldisiloxane (HMDSO) plasma polymer modified silica was used. By using multiambient media measurements of the bare substrate prior to protein adsorption the adsorbed amount as well as the thickness and refractive index of the adsorbed protein layer could be followed in situ and in real time. Under conditions used in these experiments neither IgG nor fibrinogen could fullydisplace serum albumin from the interface. The buildup of the protein layer occured via different mechanisms for the different protein systems. Fgn adsorbed in a rather flat orientation at low adsorbed amounts, while at higher surface coverage the protein reoriented to a more upright orientation in order to accommodate more molecules in the adsorbed layer. IgG adsorption proceeded mainly end on with little reorientation or conformational change on adsorption. Finally, for HSA an adsorbed layer thickness greater than the molecular dimensions was observed at high concentrations ( although not at low ), indicating that aggregates or multilayers formed on HMDSO plasma polymer surfaces. For all protein mixtures the adsorbed layer structure and buildup indicated that Fgn was the protein dominating the adsorbed layer, although HSA partially blocked the adsorption of this protein. At high surface concentration, HSA/Fgn mixtures show an abrupt change in both adsorbed layer thickness and refractive index suggesting, e.g., an interfacial phase transition of the mixed protein layer. A similar but less pronounced behavior was observed for HSA/IgG. For IgG/Fgn and HSA/Fgn a buildup of the adsorbed layer similar to that displayed by Fgn alone was observed.

The adsorption of some model proteins, human serum albumin (HSA), IgG and fibrinogen, at silica made hydrophobic by either methylation or plasma deposition of HMDSO (hexamethyldisiloxane) was investigated with in situ ellipsometry and TIRF. Ellipsometry experiments of the simultaneous adsorption of HSA and either IgG or fibrinogen revealed a preferential adsorption of the latter proteins. This is seen not only from the total adsorbed amount, but also from the adsorbed layer thickness, as well as from the build-up of the adsorbed layer. However, in sequential adsorption experiments, where HSA was first allowed to adsorb, followed by rinsing and addition of either IgG or fibrinogen, the additional adsorption is quite limited. Consequently, when HSA is allowed to adsorb on its own at hydrophobic surfaces, it is not removed by either IgG or fibrinogen to any larger extent. Furthermore, preadsorbed HSA was not exchanged by HSA added after adsorption and rinsing, implying that the mechanism behind this effect is an ”irreversible” adsorption of HSA at hydrophobic surfaces, possibly originating from a surface-induced conformational change of HSA at these surfaces. Analogous findings were obtained with both methylated and HMDSO-treated surfaces, using both ellipsometry and TIRF.

The interfacial exchange processes between human serum albumin (HSA) and fibrinogen at different surfaces was investigated with in situ ellipsometry and TIRF. With ellipsometry, it was found that the total adsorbed amount at silica on addition of fibrinogen after preadsorption of HSA was quite similar to that obtained without HSA preadsorption. From TIRF, it is concluded that the preadsorbed HSA is displaced, although not completely, on addition of fibrinogen. On the other hand, preadsorbed HSA effectively blocked further adsorption of fibrinogen and IgG at hydrophobic surfaces such as methylated silica. Furthermore, the competitive adsorption of HSA and fibrinogen at two phospholipid surfaces, i e, phosphatidylcholine (PC) and phosphatidic acid (PA), was investigated. It was found that at PA, fibrinogen adsorbs extensively even after preadsorption of HSA. This, however, is achieved with essentially no displacement of the preadsorbed HSA. For PC, finally, the fibrinogen adsorption is much lower than that of HSA, and fibrinogen is able neither to coadsorb with HSA nor to displace the preadsorbed protein.

The adsorption and immobilization of rabbit anti-human immunoglobulin (rabbit IgG), as well as the effects on the amount and reactivity of bound rabbit IgG of rinsing with buffer and addition of bovine serum albumin (BSA) or human IgG, were investigated with ellipsometry, TIRF and enzyme immuno assay (EIA). It was found that although rabbit IgG readily adsorbs at hydrophobic hexamethyldisiloxane (HMDSO) plasma polymer surfaces, a substantial fraction of the adsorbed protein molecules are desorbed on rinsing with buffer. BSA was found to adsorb readily at the surfaces obtained after rinsing, although also this protein desorbed to a large extent on further rinsing with buffer. The adsorption of BSA causes a further reduction in the amount of rabbit IgG adsorbed. Immobilization of rabbit IgG to acrylic acid (AA) plasma polymer surfaces, achieved by covalent coupling via a strongly adsorbed PEG-PEI copolymer, was found to overcome the problem of desorption of rabbit IgG on rinsing with buffer or addition of BSA. Furthermore, non-specific adsorption was virtually absent after immobilization. However, covalently bound rabbit IgG reacted strongly with human IgG, as observed by ellipsometry, TIRF and EIA. The immobilization of rabbit IgG to hydrophilized surfaces was found to facilitate the interpretation of EIA results.

Surface localization plays a key but ill defined role in activation of the Serum Complement System with or without related "opsonic" proteins. The adsorption of key complement components C3 and C1q and various opsonins, e. g., IgG, were therefore studied on different surfaces using in situ ellipsometry. The affinities of C3 and C1q for silica, methylated silica, and various phospholipid surfaces were shown to be largely reciprocal. While C3 adsorbed more extensively at (hydrophilic and negatively charged) silica than at (hydrophobic) methylated silica (3.1 versus 0.4 mg/m2, respectively) the opposite trend was observed for C1q (1.9 versus 2.6 mg/m2). C3 and C1q adsorbed in 10 to 15 nm thick layers on both silica and methylated silica. Each protein appeared to adsorb with consistent conformation and orientation on either surface. Adsorbed layer formation involves increased protein packing density, and molecular extension normal to the surface. Phospholipid head group properties strongly affect the adsorption of C3 and C1q at phospholipid coated surfaces. The saturation adsorption of C3 at phosphatidic acid was almost as significant as at silica, whereas the amount adsorbed at phosphatidylcholine was three times lower. C3 adsorption at phosphatidylinositol and various poly(ethylene glycol) modified surfaces was virtually absent, as was the adsorption of various opsonins. C1q adsorption was relatively low at all phospholipid and poly(ethylene glycol) coated surfaces investigated, more in the manner of IgG than C3. Preadsorption of IgG increased C1q deposition at phospholipid surfaces strongly. C3 and human serum albumin, but not C1q, showed appreciable hydrophobic affinity for a poly(ethylene glycol)-fatty acid ester of oleic acid. These results are discussed in relation to complement interaction with various surfaces and colloidal drug carriers.

The adsorption of C3 at poly(methyl methacrylate) (PMMA) and poly(styrene) (PS) surfaces was investigated with in situ ellipsometry and compared to that at (hydrophilic and negatively charged) silica and (hydrophobic) methylated silica. The adsorption of C3 at PMMA was higher than that at PS, while the adsorbed layer thickness was the same for the two surfaces. For both PMMA and PS the adsorbed layer thickness (10±2 nm) corresponds rather closely to that of end-on oriented C3 molecules. The adsorption of C3 at PMMA and PS was found to be intermediate between that at silica and methylated silica, although the adsorbed layer thickness was similar for all surfaces. The competitive adsorption between C3, human serum albumin (HSA), and factor B was investigated with ellipsometry and total internal reflection fluorescence spectroscopy (TIRF). Addition of HSA after C3 preadsorption resulted in fractional C3 desorption for both PMMA and PS. Factor B deposition at PS after preadsorption of C3 and blocking with HSA was found to be largely due to specific binding to C3/C3b, while in the case of PMMA, factor B was largely accumulated through passive (displacement) adsorption.

The sequential adsorption of human serum albumin (HSA), immunoglobulin G (IgG), and fibrinogen (Fgn) at hexamethyldisiloxane (HMDSO) plasma polymer surfaces was investigated with ellipsometry and total internal reflectance fluorescence spectroscopy (TIRF) as a function of adsorption time, pH, and excess electrolyte concentration. HSA was found to self-exchange very slowly (≈hours) at pH 7.2, irrespective of adsorption time in the range 90 seconds to 90 minutes. Preadsorbed HSA was exchanged by Fgn and IgG only to a limited extent irrespectively of pH (5≤pH≤8) and excess electrolyte concentration (5 mM≤Cs≤150 mM). At an excess electrolyte concentration of 150 mM, the sequential adsorption of Fgn and IgG was dramatically reduced by HSA preadsorption, irrespective of pH. At an excess electrolyte concentration of 5 mM, on the other hand, there were indications of second layer adsorption of Fgn and IgG.

Porous carbon materials are common materials used for sensor and absorbent applications. A novel approach for functionalizing porous carbons through the impregnation of porous carbon black with benzoxazine monomers, followed by thermal polymerization is introduced herein. The method not only establishes a new avenue for the functionalization of porous carbons but also endows the resulting material with both copper ion-binding and sensing properties. We showcase the versatility of the technique by illustrating that the polymerization of phenols with benzoxazine monomers serves as an extra tool to customize absorption- and sensing properties. Experimental validation involved testing the method on carbon black as a porous substrate, which was impregnated with both bisphenol-a benzoxazine and a combination of bisphenol-a benzoxazine and alizarin. The resulting materials were assessed for their dual functionality as both an absorbent and a sensor for copper ions by varied copper ion concentrations and exposure times. The dye absorption test demonstrated a notable capacity to accumulate copper ions from dilute solutions. Electrochemical characterization further confirmed the effectiveness of the modified carbons, as electrodes produced from inks were successful in detecting copper ions accumulated from 50 μM Cu2+ solutions. With this work, we aspire to set the steppingstone towards a facile functionalization of porous carbon materials towards water purification applications. © 2024 The Authors