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Formation of Nanocones on Highly Oriented Pyrolytic Graphite by Oxygen Plasma.

ABSTRACT: Improvement in hemocompatibility of highly oriented pyrolytic graphite (HOPG) by formation of nanostructured surface by oxygen plasma treatment is reported. We have showed that by appropriate fine tuning of plasma and discharge parameters we are able to create nanostructured surface which is densely covered with nanocones. The size of the nanocones strongly depended on treatment time. The optimal results in terms of material hemocompatibility were obtained after treatment with oxygen plasma for 15 s, when both the nanotopography and wettability were the most favorable, since marked reduction in adhesion and activation of platelets was observed on this surface. At prolonged treatment times, the rich surface topography was lost and thus also its antithrombogenic properties. Chemical composition of the surface was always more or less the same, regardless of its morphology and height of the nanocones. Namely, on all plasma treated samples, only a few atomic percent of oxygen was found, meaning that plasma caused mostly etching, leading to changes in the surface morphology. This indicates that the main preventing mechanism against platelets adhesion was the right surface morphology.

SUBMITTER: Vesel A

PROVIDER: S-EPMC5453248 | biostudies-other | 2014 Mar

REPOSITORIES: biostudies-other

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Project description:BACKGROUND: The interest in introducing ecologically-clean, and efficient enzymes into modern industry has been growing steadily. However, difficulties associated with controlling their orientation, and maintaining their selectivity and reactivity is still a significant obstacle. We have developed precise immobilization of biomolecules, while retaining their native functionality, and report a new, fast, easy, and reliable procedure of protein immobilization, with the use of Adenylate kinase as a model system. METHODS: Self-assembled monolayers of hexane-1,6-dithiol were formed on gold surfaces. The monolayers were characterized by contact-angle measurements, Elman-reagent reaction, QCM, and XPS. A specifically designed, mutated Adenylate kinase, where cysteine was inserted at the 75 residue, and the cysteine at residue 77 was replaced by serine, was used for attachment to the SAM surface via spontaneously formed disulfide (S-S) bonds. QCM, and XPS were used for characterization of the immobilized protein layer. Curve fitting in XPS measurements used a Gaussian-Lorentzian function. RESULTS AND DISCUSSION: Water contact angle (65-70°), as well as all characterization techniques used, confirmed the formation of self-assembled monolayer with surface SH groups. X-ray photoelectron spectroscopy showed clearly the two types of sulfur atom, one attached to the gold (triolate) and the other (SH/S-S) at the ?-position for the hexane-1,6-dithiol SAMs. The formation of a protein monolayer was confirmed using XPS, and QCM, where the QCM-determined amount of protein on the surface was in agreement with a model that considered the surface area of a single protein molecule. Enzymatic activity tests of the immobilized protein confirmed that there is no change in enzymatic functionality, and reveal activity ~100 times that expected for the same amount of protein in solution. CONCLUSIONS: To the best of our knowledge, immobilization of a protein by the method presented here, with the resulting high enzymatic activity, has never been reported. There are many potential applications for selective localization of active proteins at patterned surfaces, for example, bioMEMS (MEMS--Micro-Electro-Mechanical Systems. Due to the success of the method, presented here, it was decided to continue a research project of a biosensor by transferring it to a high aspect ratio platform--nanotubes.

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Formation of Nanocones on Highly Oriented Pyrolytic Graphite by Oxygen Plasma.

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