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

Magneto-optic measurements on uneven magnetic layers on cardboard

Measurements of magnetic hysteresis loops by magneto-optic Kerr effect (MOKE) are usually performed on even surfaces which reflect the impinging laser beam without any disturbance. Alternatively, such measurements can be done on regularly structured samples, resulting in the possibility to investigate different diffraction orders who deliver different information about the magnetism in the magnetic particles. Rough magnetic surfaces, however, occur when rough substrates are coated with a magnetic layer, or when large magnetic particles are placed on a base material due to practical reasons. The article depicts the possibility to measure magnetic hysteresis loops on surfaces with a roughness about one order of magnitude higher than the light wavelength. This enables applied measurements of magnetic parameters on biological samples, textiles, irregular magnetic nanofibers etc

Highly regular polyampholytic structures adsorbed directly from solution

This article concerns the adsorption of the diblock polyampholyte poly(methacrylic acid)-block-poly((dimethylamino)ethyl methary-late) (PMAA-b-PDMAEMA) from aqueous solution on silicon substrates. The investigated polyampholyte is characterized by a small molecular weight around 15,000 g/mol and a big positively charged PDMAEMA block. The adsorbed amount determined by ellipsom-etry was str ongly influenced by the pH of the adsorption solution. Using dynamic light scattering polyampholytic structures with diameters around 50 nm were found in aqueous solution. The hy-drodynamic diameter was hardly affected by changing the pH of the polymer solution. Analogous regular structures were also found by scanning force microscopy (SFM) and grazing incidence, small angle X-ray scattering (GISAXS) at the silicon surface after the adsorption process. While SFM provides a topographical image of a small part of the adsorbed polyampholytic layer; GISAXS was used to get a statistical description of the lateral surface structures. The adsorbed structures were highly regular and their sizes were nearly pH independent over a lar ge pH region. Only directly at the isoelectric point of the polyampholyte larger adsorbed structures were observed. Compared with earlier investigated PMAA-b-PDMAEMA systems we are now able to prepare highly regular polyampholytic structures at silicon surfaces. There are two kinds of interactions for the adsorbed micelles. First, the charged block of the chains is directly attracted to the substrate via electrostatic interactions, while the uncharged part of the chains is only hydrophobically attracted via the hydrophobic core of the adsorbed micelle.Program SUPERNE