We describe a novel technology based on changes in the resonant frequency of an acoustically actuated surface and use it to measure temporal changes in the surface energy gamma (N m(-1)) of an elastomeric polymer membrane due to the adsorption of macromolecules from aqueous solution. The resonant elastomeric surface-tension (REST) sensor permits simultaneous determination of mass loading kinetics and gamma(t) for a given adsorption process, thereby providing a multivariable data set from which to build and test models of the kinetics of adsorption at solid-liquid interfaces. The technique is used to measure gamma(t) during the adsorption of either sodium dodecyl sulfate (SDS) or hen egg-white lysozyme (HEWL) onto an acrylic polymer membrane. The adsorption of SDS is reversible and is characterized by a decrease in gamma over a time period that coincides with that required for the mass loading of the membrane. For the adsorption of HEWL labeled with Alexa Fluor 532 dye, gamma continues to change long after the surface concentration of labeled HEWL, measured by using the elastomeric polymer membrane as an optical waveguide, reaches steady state. Gradual but significant changes in gamma(t) are observed as long as the concentration of protein in the bulk solution, c(b), remains nonzero. HEWL remains adsorbed to the membrane when c(b) = 0, but changes in gamma(t) are not observed under this condition, indicating that the interaction of bound protein molecules with those free in solution contribute to the prolonged change in the surface energy. This observation has been used to define a new model for the kinetics of globular protein adsorption to a solid-liquid interface that includes a mechanism by which the molecules in the bulk can facilitate the desorption of a sorbate molecule or change the energetic states of adsorbed molecules and, thus, the overall surface energy. The model is shown to capture the unique features of protein adsorption kinetics, including the relatively fast mass loading, the much more gradual change in surface energy that does not cease until the protein is removed from the bulk, the rapid desorption of an incubation-time-dependent fraction of bound protein when the protein is removed from the bulk, and the fixing of the residual surface concentration and surface energy at constant values once the removal of reversibly bound protein and free protein is complete.
The understanding individuals have about their epilepsy may influence the success with which that individual copes with his/her epilepsy. This paper presents the first evaluation of a video-assisted brief educational package for adults with mild learning disabilities and epilepsy ("Epilepsy and You"; Paul, 1996 21). Utilizing a deferred entry to treatment design to evaluate intervention effects eighteen subjects participated in the study. Their knowledge about epilepsy before and after training was assessed using a checklist of knowledge and the Epilepsy Knowledge Questionnaire-Revised for use with people with learning disabilities. Results demonstrated significant gains in knowledge which were durable over a short follow-up period (1 month). "Epilepsy and You" was found to be suitable for use with a wide range of individuals and subjects' opinions demonstrated they enjoyed taking part. This study is a preliminary investigation from which other research can develop. Therefore, criticisms and suggestions for further research have been made.
Proteins prefer interfaces, and in aqueous solutions they rapidly adsorb to available solid–liquid interfaces. The adsorption process often involves a change in protein conformation at the surface that can result in functional inactivation of the protein. These changes in protein conformation, which are thought to lead to the formation of an entangled gel-like layer of denatured protein, are responsible for a number of deliterious processes, including biofouling on contact lenses and medical implants. The adsorption process is generally irreversible; dilution of protein in the solution phase does not result in protein desorption from the solid. Presumably, this is due to the effects of the protein denaturation and entanglement process on the rate constant for desorption. Nonspecific protein adsorption to solid–liquid interfaces is, therefore, a kinetically controlled process. Hence, measuring and understanding the kinetics of protein adsorption to solid surfaces, including the kinetics of protein conformational changes, is of considerable interest. We have developed a sensor that responds to protein adsorption kinetics and also, we believe, is sensitive to protein conformational changes during adsorption. The device is operated by monitoring the change in resonant frequency of an elastomeric film (25 μm thick), as an aqueous protein solution is exposed to the surface. Since the mass of a monolayer of the protein or other adsorbent is an extremely small fraction of the mass of the film, the observed change in resonant frequency is due almost entirely to changes in the surface tension of the film. Upon exposing the elastomeric film to a protein solution, we observe a continuing change in resonant frequency for more than 24 h, which is well beyond the time it would take for the population of proteins on the surface to equilibrate under diffusion-limited kinetics. This prolonged response is likely due to the surface energy changes of the sensor as the adsorbed protein molecules change their conformation. We present a description of the basic operation of this sensor as well as some examples of its response to bulk protein and surfactant concentrations.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.