The adsorption of proteins to surfaces is a central concern for the rational design and application of materials. The rate and strengths of the initial physical interactions between proteins and surfaces dictate (to a large degree) the final conformation, stability, and activity of such proteins. This issue, that plays a major role in determining the biocompatibility of materials, can also dictate the analytical performance of almost every analytical device that uses a biorecognition element (antigen, antibody, enzyme, nucleic acids, or even whole cells). Here are described several of the project that we have recently published in this area.
Effect of Potential in the Adsorption of Proteins
This project investigated the effect of the applied potential on the adsorption of bovine serum albumin (BSA) to optically transparent carbon electrodes (OTCE). To decouple the effect of the applied potential from the high affinity of the protein for the bare surface, the surface of the OTCE was initially saturated with a layer of BSA. Experiments described in the article show that potential values higher than +500 mV induced a secondary adsorption process (not observed at open-circuit potential), yielding significant changes in the thickness (and adsorbed amount) of the BSA layer obtained. This mechanism could be responsible for the potential-dependent oversaturation of the surface and could bolster to the development of surfaces with enhanced catalytic activity and implants with improved biocompatibility.
Proteins Adsorbed to Nanoporous Substrates
A critical step for the development of biosensors is the immobilization of the biorecognition element to the surface of a substrate. Among other materials that can be used as substrates, block copolymers have the untapped potential to provide significant advantages for the immobilization of proteins. To explore such possibility, this manuscript describes the fabrication and characterization of thin-films of polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP). These films were then used to investigate the immobilization of glucose oxidase, a model enzyme for the development of biosensors. A maximum normalized activity of 3300 ± 700 U m-2 was achieved for the nanoporous film of PS-b-P2VP.
Biocompatibility of Surfaces in Microfluidic Devices
This project focused on the development of a simple and inexpensive procedure to produce thin-films of poly(dimethylsiloxane). Such films were characterized by a variety of techniques (ellipsometry, nuclear magnetic resonance, atomic force microscopy, and goniometry) and used to investigate the adsorption kinetics of three model proteins (fibrinogen, collagen type-I, and bovine serum albumin) under different conditions. The information collected from the protein adsorption studies was then used to investigate the adhesion of human dermal microvascular endothelial cells. The results of these studies suggest that these films can be used to model the surface properties of microdevices fabricated with commercial PDMS. Moreover, the paper provides guidelines to efficiently attach cells in BioMEMS devices.. This project is the result of a collaboration with Dr. Bizios (BME-UTSA).
Variable Angle Spectroscopic Ellipsometry
VASE is one of the most powerful techniques to investigate the adsorption process. In order to allow following this process in real time, we have described the hydrodynamic conditions in a flow cell designed to study adsorption processes by spectroscopic ellipsometry. The resulting cell enables combining the advantages of in situ spectroscopic ellipsometry with stagnation point flow conditions. An additional advantage is that the proposed cell features a fixed position of the “inlet tube” with respect to the substrate, thus facilitating the alignment of multiple substrates. Theoretical calculations were performed by computational fluid dynamics and compared with experimental data (adsorption kinetics) obtained for the adsorption of polyethylene glycol to silica under a variety of experimental conditions. Additionally, a simple methodology to correct experimental data for errors associated with the size of the measured spot and for variations of mass transfer in the vicinity of the stagnation point is herein introduced.