Direct immobilization of avidin protein on AFM tip functionalized by acrylic acid vapor at RF plasma.

The atomic force microscopy (AFM) has been used as a force sensor to measure unbinding forces of single bound complexes in the nanonewton and piconewton range. Force spectroscopy measurements can be applied to study both intermolecular and intramolecular interactions of complex biological and synthetic macromolecules. Although the AFM has been extensively used as a nano force sensor, the commercially available cantilever is limited to silicon and silicon nitride. Those materials reduce the adhesion sensitivity with specific surface and/or molecule. Here, we functionalized the AFM tip with carboxylic groups by applying acrylic acid (AA) vapor at radio frequency plasma treatment at 100 W for 5 min. This method provides a remarkable sensitivity enhancement on the functional group interaction specificity. The functionalized tip was characterized by scanning electron microscopy. The electron beam high resolution images have not shown significant tip sharpness modification. Silicon wafers (1 0 0)-no treated and functionalized by AA plasma treatment-were characterized by Auger electron spectroscopy to elucidate the silicon surface sputtering and demonstrate functionalization. The Fourier transform-infrared spectroscopy spectrum shows a high absorbance of avidin protein over the silicon surface functionalized by AA plasma treatment.We carried out force spectroscopy assay to measure the unbinding force between the well-established pair biotin-avidin. At pulling speed of 2 µm/s, we measured the unbinding force of 106 ± 23 pN, which is in good agreement with the literature, demonstrating the effectiveness of the tip functionalization by AA plasma treatment in biological studies.

Modulating the electronic properties along carbon nanotubes via tube-substrate interaction.

We study single wall carbon nanotubes (SWNTs) deposited on quartz. Their Raman spectrum depends on the tube-substrate morphology, and in some cases, it shows that the same SWNT-on-quartz system exhibits a mixture of semiconductor and metal behavior, depending on the orientation between the tube and the substrate. We also address the problem using electric force microscopy and ab initio calculations, both showing that the electronic properties along a single SWNT are being modulated via tube-substrate interaction.

Optimization of sugarcane bagasse pretreatment using alkaline hydrogen peroxide through ANN and ANFIS modelling.

The present study compares the optimization using Artificial Neural Networks (ANN) and Adaptive Network-based Fuzzy Inference System (ANFIS) in the sugarcane bagasse delignification process using Alkaline Hydrogen Peroxide (AHP). Two variables were assessed experimentally: temperature (25-45 °C) and hydrogen peroxide concentration (1.5-7.5%(w/v)). The Klason Method was used to measure the amount of insoluble lignin, the High Performance Liquid Chromatography (HPLC) was used to determine the glucose and xylose concentrations and the Fourier Transform Infrared Spectroscopy (FT-IR) was applied to identify oxidized lignin structure in the samples. The analytical results were used for training and testing of ANN and ANFIS models. The statistical quality of the models was significant due to the low values of the errors indices (RMSE) and determination coefficient R2 between experimental and calculated values.

Neural network modeling to support an experimental study of the delignification process of sugarcane bagasse after alkaline hydrogen peroxide pre-treatment.

The present study examines the use of Artificial Neural Networks (ANN) as prediction and fault detection tools for the delignification process of sugarcane bagasse via hydrogen peroxide (H2O2). Experimental conditions varied from 25 to 45°C for temperature and from 1.5% to 7.5% (v/v) for H2O2 concentrations. Analytical results for the delignification were obtained by Fourier Transform Infrared (FT-IR) analysis and used for the ANN training and testing steps, allowing for the development of ANN models. The condition experimentally identified as the most suitable for the delignification process was of 25°C with 4.5% (v/v) H2O2, oxidizing 54% of total lignin. An ANN topology was selected for each proposed model, whose performance was evaluated by the correlation coefficient (R2) and error indices (MSE and SSE). The values obtained for R2 and the error indices indicated good agreements of the theoretical and actual data, of close to 1 and close to 0, respectively.

Measuring the strength of interaction between the Ebola fusion peptide and lipid rafts: implications for membrane fusion and virus infection.

The Ebola fusion peptide (EBO16) is a hydrophobic domain that belongs to the GP2 membrane fusion protein of the Ebola virus. It adopts a helical structure in the presence of mimetic membranes that is stabilized by the presence of an aromatic-aromatic interaction established by Trp8 and Phe12. In spite of its infectious cycle becoming better understood recently, several steps still remain unclear, a lacuna that makes it difficult to develop strategies to block infection. In order to gain insight into the mechanism of membrane fusion, we probed the structure, function and energetics of EBO16 and its mutant W8A, in the absence or presence of different lipid membranes, including isolated domain-resistant membranes (DRM), a good experimental model for lipid rafts. The depletion of cholesterol from living mammalian cells reduced the ability of EBO16 to induce lipid mixing. On the other hand, EBO16 was structurally sensitive to interaction with lipid rafts (DRMs), but the same was not observed for W8A mutant. In agreement with these data, W8A showed a poor ability to promote membrane aggregation in comparison to EBO16. Single molecule AFM experiments showed a high affinity force pattern for the interaction of EBO16 and DRM, which seems to be a complex energetic event as observed by the calorimetric profile. Our study is the first to show a strong correlation between the initial step of Ebola virus infection and cholesterol, thus providing a rationale for Ebola virus proteins being co-localized with lipid-raft domains. In all, the results show how small fusion peptide sequences have evolved to adopt highly specific and strong interactions with membrane domains. Such features suggest these processes are excellent targets for therapeutic and vaccine approaches to viral diseases.