Using alternating layers of charged polymers, we have constructed reactive thin films by incorporating enzymes, specifically alkaline phosphatase (AP) and glucose oxidase (GOD), into multilayers of a polycation, branched polyethylenimine (PEI), and a polyanion, poly(styrenesulfonate) (PSS), supported on a glass substrate. Experiments using a quartz crystal microbalance (QCM) demonstrated that the films grew sequentially on a solid support, while X-ray photoelectron spectroscopy (XPS) further confirmed the growth and deposition of successive enzyme layers. For both enzymes, the reactive films demonstrated increased activity with the successive number of deposited enzyme layers. In hybrid films, consisting of alternating layers of AP and GOD, both enzymes retained activities similar to those of their corresponding films of either enzyme alone. The effect of elevated temperature was also investigated for these reactive films. Increased thermal stability was found to be associated with the increase in the number of deposited enzyme layers.

No abstract

A water-soluble, blocked diisocyanate was proven to support stable growth of bilayers with branched poly(ethylenimine), bPEI, in a layer-by-layer (LBL) technique. A quartz crystal microbalance and ellipsometry were employed to measure bilayer formation and infrared spectroscopy of LBL deposited films of hexamethylene-1,6-di(aminocarboxysulfonate) and bPEI revealed in situ cross-linking between successive layers. Erratic film growth with poly(diallyldimethylammonium chloride) with which covalent linkage was not possible, and film stability in high salt and diethanolamine solutions also supported cross-linking. Silica beads coated with alkaline phosphatase (ALP)−bPEI bilayers were capped with the cross-linking agent, and loss of enzymatic activity and less dissolution of active ALP were observed, relative to uncapped or alternately caped assemblies. Consequently, such a cross-linking agent alone or diluted with other polyanions, like poly(sodium 4-styrenesulfonate), might prove useful in controlling network and dissolution properties of LBL films having a variety of biologic and other functions, such as for controlled release.

The utility of the atomic force microscope (AFM) for measuring forces is now well established. The AFM is capable of measuring forces from tens of piconewtons to tens of nanonewtons. Systems ranging from the adhesion of clean or functionalized tips interacting with different surface, to singlemolecule measurements of the force required to rupture protein-ligand interactions, to the forced unfolding of single protein molecules have been studied. The adhesion of a clean silicon nitride tip to a clean glass surface is one of the simplest systems to study and was the first system to demonstrate quantized adhesion. AFM cantilevers will adhere to glass surfaces in the presence of water and the force required to separate the surfaces is on the order of 1-6 nN at low pH. The adhesion mechanism is believed to be due to hydrogen bonds formed between the silanol groups present on both the glass and AFM tip. Deuterium oxide (D2O) has physical properties significantly different from that of H2O; the density, melting temperature and heat capacity are all greater than that of water. These and the differences between H2O and D2O can be attributed to the lower vibrational frequency of the OD bond and the fact that O-D…O bonds are about lkJ/mol stronger than O-H…O bonds.