Cristian Ramírez

A nanomolecular approach to decrease adhesion of biofouling-producing bacteria to graphene-coated material

AbstractBackground Biofouling, the colonization of artificial and natural surfaces by unwanted microorganisms, has an important economic impact on a wide range of industries. Low cost antifouling strategies are typically based on biocides which exhibit a negative environmental impact, affecting surrounding organisms related and not related to biofouling. Considering that the critical processes resulting in biofouling occur in the nanoscale/microscale dimensions, in this work we present a bionanotechnological approach to reduce adhesion of biofilm-producing bacteria Halomonas spp. CAM2 by introducing single layer graphene coatings. The use of this nanomaterial has been poorly explored for antifouling application.ResultsOur study revealed that graphene coatings modify material surface energy and electrostatic interaction between material and bacteria. Such nanoscale surface modification determine an important reduction over resulting bacterial adhesion and reduces the expression levels of genes related to adhesion when bacteria are in contact with graphene-coated material.ConclusionsOur results demonstrate that graphene coatings reduce considerably adhesion and expression levels of adhesion genes of biofilm-producing bacteria Halomonas spp. CAM2. Hydrophobic-hydrophilic interaction and repulsive electrostatic force dominate the interactions between Halomonas spp. CAM2 and material surface in saline media, impacting the final adhesion process. In addition no bactericide effect of graphene coatings was observed. The effect over biofilm formation is localized right at coated surface, in contrast to other antifouling techniques currently used, such as biocides.

The Many Faces of Graphene as Protection Barrier. Performance under Microbial Corrosion and Ni Allergy Conditions

In this work we present a study on the performance of CVD (chemical vapor deposition) graphene coatings grown and transferred on Ni as protection barriers under two scenarios that lead to unwanted metal ion release, microbial corrosion and allergy test conditions. These phenomena have a strong impact in different fields considering nickel (or its alloys) is one of the most widely used metals in industrial and consumer products. Microbial corrosion costs represent fractions of national gross product in different developed countries, whereas Ni allergy is one of the most prevalent allergic conditions in the western world, affecting around 10% of the population. We found that grown graphene coatings act as a protective membrane in biological environments that decreases microbial corrosion of Ni and reduces release of Ni2+ ions (source of Ni allergic contact hypersensitivity) when in contact with sweat. This performance seems not to be connected to the strong orbital hybridization that Ni and graphene interface present, indicating electron transfer might not be playing a main role in the robust response of this nanostructured system. The observed protection from biological environment can be understood in terms of graphene impermeability to transfer Ni2+ ions, which is enhanced for few layers of graphene grown on Ni. We expect our work will provide a new route for application of graphene as a protection coating for metals in biological environments, where current strategies have shown short-term efficiency and have raised health concerns.

Technical Feasibility of Glucose Oxidase as a Prefermentation Treatment for Lowering the Alcoholic Degree of Red Wine

In the present work, the use of the glucose oxidase/catalase enzymatic system was evaluated as an alternative to decrease glucose concentration and eventually produce a reduced-alcohol wine. The effects of glucose oxidase, catalase, and aeration on glucose concentration were evaluated after 24 and 48 hr of treatment of 27°Brix Carmenere must. The results showed that the effect of aeration and glucose oxidase was not significant compared with the effect produced by glucose oxidase itself. In addition, the use of catalase combined with glucose oxidase provided the best result, decreasing the glucose concentration by 51 and 78% after 24 and 48 hr, respectively, when 200 U/mL of both enzymes was used. The alcoholic degree obtained after three and five days under this treatment and subsequent fermentations were 15% (v/v) ± 0.8 and 14% (v/v) ± 0.8, respectively. A major drawback of this treatment was the color change of Carmenere must because H2O2 was produced during the glucose oxidase treatment, despite the presence of catalase. The technical feasibility of using this prefermentative process led to a divided conclusion; obtaining a lower alcoholic degree using the glucose oxidase/catalase system was possible, but if the goal is the industrial application of this technique, the color change should be investigated further. An evaluation of the glucose oxidase/catalase ratio was projected to show an improvement of the H2O2 elimination and, subsequently, decrease the effect on color change.