Protein adsorption on preadsorbed polyampholytic monolayers

The adsorption behaviour of five different globular proteins on pure silicon substrates and on preadsorbed polyampholytic monolayers has been investigated as a function of protein concentration. The prelayers were prepared by adsorption of the ampholytic diblock copolymer poly(methacrylic acid)-block-poly ((dimethylamino)ethyl methacrylate) (PMAA-b-PDMAEMA). This polyampholyte adsorbs in densely packed micelles directly from aqueous solution. Ellipsometry was used to determine the amount of adsorbed polyampholyte and protein. While ATR-IR spectroscopy gives information about the adsorption and desorption behaviour of the preadsorbed polyampholytic layer, the lateral structures of the dried films were investigated by scanning force microscopy (SFM). The amount of protein adsorbed was found to be strongly influenced by the preadsorbed polyampholyte compared to the adsorption on the pure silicon substrates. No displacement of the polyampholyte by the proteins was detected. In most cases the protein adsorption was reduced by the preadsorbed polyampholytic layer. The observed trends are explained by the change in electrostatic and hydrophilic characteristics of the substrates. Furthermore, the entropy of adsorption has to be taken into account.Peer reviewe

"Life, Memory, Recognition and Aging" of Grey Tin

Abstract It was shown that tin has two types of memory: 1) "memory of the structure" about of the event when it was in the α configuration, and 2) "memory of recognition (discern)" whereby tin recognises that an object with which it in contact, was previously in contact with substances of a particular type ("infection"). Transformations of metallic white tin into the grey semiconductor occur with the help of either small pieces of grey tin or other substances isomorphous with grey tin . These pieces (when pressed into white tin) initiate phase transition (by "infection") from white tin into grey tin. Once the tin is transformed into its grey form, it retains a "memory" about this after it is transferred back into white tin. Thus, for second and subsequent phase transformations, there is no need for external initiators to be used. The tin has the "memory of recognition" too-when the tin can recognises that an object with which it is in contact, was previously in contact with the "infection". This phenomenon is concerned with the aging of tin: firstly, with the loss of "memory of the structure" of tin of the event when it was in the grey tin configuration, and, secondly, with the loss of "memory of recognition" of tin whereby the tin recognises that an object with which it is in contact, was previously in contact with substances of a particular type. Factors that effect the aging of tin has been studied in detail and an explanation of the mechanism of action of these factors has been suggested

Structure of self-assembled layers on silicon: Combined use of spectroscopic variable angle ellipsometry, neutron reflection and atomic force microscopy

Neutron reflection (NR), spectroscopic ellipsometry (SE), and atomic force microscopy (AFM) have been used to characterize the structure of self-assembled octadecyltrichlorosilane (OTS) layers on silicon. The first two of these techniques rely on modeling of the experimental data and may thus result in the unrealistic representation of the composition and structure at the interface. Ambiguities arise from model-dependent analysis complicated by the lack of sufficient external constraints to converge nonunique solutions to a unique one. We show in this work that AFM measurements provide extra constraints to allow us to obtain a physical description closer to the actual structure of the film. It was found that “the simpler the better” modeling strategy very often employed during the fitting of ellipsometric and neutron reflection data is, therefore, not necessarily the best way to obtain a reliable description of the interfacial structure. Our AFM findings necessitated the refit of both neutron and ellipsometric data that were previously described by a single-layer model. Interpretation of the structure of thin layers that is based only on indirect measurements such as SE, NR, and x-ray reflection techniques may be, therefore, misleading. A combined analysis of SE, NR, and AFM data suggests that the OTS film may comprise a rough layer, with pinholes down to bare silicon oxide surface, consisting at least of mono-, bi- and trilayers of OTS molecules