Francisco E. G. Guimarães

Mapping the lignin distribution in pretreated sugarcane bagasse by confocal and fluorescence lifetime imaging microscopy

BackgroundDelignification pretreatments of biomass and methods to assess their efficacy are crucial for biomass-to-biofuels research and technology. Here, we applied confocal and fluorescence lifetime imaging microscopy (FLIM) using one- and two-photon excitation to map the lignin distribution within bagasse fibers pretreated with acid and alkali. The evaluated spectra and decay times are correlated with previously calculated lignin fractions. We have also investigated the influence of the pretreatment on the lignin distribution in the cell wall by analyzing the changes in the fluorescence characteristics using two-photon excitation. Eucalyptus fibers were also analyzed for comparison.ResultsFluorescence spectra and variations of the decay time correlate well with the delignification yield and the lignin distribution. The decay dependences are considered two-exponential, one with a rapid (τ1) and the other with a slow (τ2) decay time. The fastest decay is associated to concentrated lignin in the bagasse and has a low sensitivity to the treatment. The fluorescence decay time became longer with the increase of the alkali concentration used in the treatment, which corresponds to lignin emission in a less concentrated environment. In addition, the two-photon fluorescence spectrum is very sensitive to lignin content and accumulation in the cell wall, broadening with the acid pretreatment and narrowing with the alkali one. Heterogeneity of the pretreated cell wall was observed.ConclusionsOur results reveal lignin domains with different concentration levels. The acid pretreatment caused a disorder in the arrangement of lignin and its accumulation in the external border of the cell wall. The alkali pretreatment efficiently removed lignin from the middle of the bagasse fibers, but was less effective in its removal from their surfaces. Our results evidenced a strong correlation between the decay times of the lignin fluorescence and its distribution within the cell wall. A new variety of lignin fluorescence states were accessed by two-photon excitation, which allowed an even broader, but complementary, optical characterization of lignocellulosic materials. These results suggest that the lignin arrangement in untreated bagasse fiber is based on a well-organized nanoenvironment that favors a very low level of interaction between the molecules.

Self-Assembled Films of Dendrimers and Metallophthalocyanines as FET-Based Glucose Biosensors

Separative extended gate field effect transistor (SEGFET) type devices have been used as an ion sensor or biosensor as an alternative to traditional ion sensitive field effect transistors (ISFETs) due to their robustness, ease of fabrication, low cost and possibility of FET isolation from the chemical environment. The layer-by-layer technique allows the combination of different materials with suitable properties for enzyme immobilization on simple platforms such as the extended gate of SEGFET devices enabling the fabrication of biosensors. Here, glucose biosensors based on dendrimers and metallophthalocyanines (MPcs) in the form of layer-by-layer (LbL) films, assembled on indium tin oxide (ITO) as separative extended gate material, has been produced. NH3+ groups in the dendrimer allow electrostatic interactions or covalent bonds with the enzyme (glucose oxidase). Relevant parameters such as optimum pH, buffer concentration and presence of serum bovine albumin (BSA) in the immobilization process were analyzed. The relationship between the output voltage and glucose concentration shows that upon detection of a specific analyte, the sub-products of the enzymatic reaction change the pH locally, affecting the output signal of the FET transducer. In addition, dendritic layers offer a nanoporous environment, which may be permeable to H+ ions, improving the sensibility as modified electrodes for glucose biosensing.

Active waveguide effects from porous anodic alumina: An optical sensor proposition

We present in this paper an active waveguide effect observed in porous anodic alumina (PA), which can be applied in optical sensors. The spectral position, shape, and polarization effect of the narrow waveguide modes is described. An analytical test with a commercial pesticide was performed.

Electrical Detection of Dengue Biomarker Using Egg Yolk Immunoglobulin as the Biological Recognition Element

Nonstructural protein 1 (NS1) is secreted by dengue virus in the first days of infection and acts as an excellent dengue biomarker. Here, the direct electrical detection of NS1 from dengue type 2 virus has been achieved by the measurement of variations in open circuit potential (OCP) between a reference electrode and a disposable Au electrode containing immobilized anti-NS1 antibodies acting as immunosensor. Egg yolk immunoglobulin (IgY) was utilized for the first time as the biological recognition element alternatively to conventional mammalian antibodies in the detection of dengue virus NS1 protein. NS1 protein was detected in standard samples in a 0.1 to 10 µg.mL−1 concentration range with (3.2 ± 0.3) mV/µg.mL−1 of sensitivity and 0.09 µg.mL−1 of detection limit. Therefore, the proposed system can be extended to detect NS1 in real samples and provide an early diagnosis of dengue.

Photoinduced photoluminescence intensity enhancement in poly(p-phenylene vinylene) films

We report measurements of photoluminescence (PL) intensity enhancement in poly(p-phenylene vinylene) (PPV) films induced by light irradiation in the presence of air. This effect is dependent on laser intensity and the ratio between film thickness and excitation penetration depth. The results suggest that an efficient spectral diffusion of excited carriers to nondegraded PPV segments by Forster energy transfer is an important consideration in the PL efficiency of conjugated polymers light-irradiated in air.

The role of quantum confinement and crystalline structure on excitonic lifetimes in silicon nanoclusters

The emission energy dependence of the photoluminescence (PL) decay rate at room temperature has been studied in Si nanoclusters (Si-ncl) embedded in Si oxide matrices obtained by thermal annealing of substoichiometric Si oxide layers SiyO1−y, y=(0.36,0.39,0.42), at various annealing temperatures (Ta) and gas atmospheres. Raman scattering measurements give evidence for the formation of amorphous Si-ncl at Ta=900 °C and of crystalline Si-ncl for Ta=1000 °C and 1100 °C. For Ta=1100 °C, the energy dispersion of the PL decay rate does not depend on sample fabrication conditions and follows previously reported behavior. For lower Ta, the rate becomes dependent on fabrication conditions and less energy dispersive. The effects are attributed to exciton localization and decoherence leading to the suppression of quantum confinement and the enhancement of nonradiative recombination in disordered and amorphous Si-ncl.

Production and characterization of natural rubber-Ca/P blends for biomedical purposes.

This study presents the development of natural rubber-Ca/P blends, as promising candidates for biomedical purposes. The specific objective was the incorporation of Ca/P into a natural rubber polymeric matrix. Ca/P crystalline phases were synthesized by the sol-gel method and the polymeric matrices were produced using natural rubber extracted from latex of the Hevea brasiliensis. The shape and size of natural rubber particles present in the NR membrane, as well as, the way the Ca/P powder grains aggregate in the polymeric matrix were investigated, giving information about the interactions between the Ca/P and the natural rubber particles. Confocal fluorescence scanning microscopy measurements allowed us to propose a structure where the Ca/P grains are surrounded by natural rubber particles. This structure may mediate Ca(2+) release for tissue regeneration. The system investigated may open new horizons for development of a bandage which provides the controlled-release of biomaterials.

Indium tin oxide synthesized by a low cost route as SEGFET pH sensor

2 atmosphere using a low-cost chemical vapor deposition (CVD) system. The films were evaluated as pH sensors in separative extended gate field-effect transistor (SEGFET) apparatus, exhibiting a sensitivity of 53 mV/pH, close to the expected Nernstian theoretical value for ion sensitive materials. The use of CVD process to synthesize ITO, as described here, may represent an alternative for fabrication of SEGFET pH sensors at low cost to be used in disposable biosensors since H + ions are the product of several oxireductase enzymes.

Influence of surface structure on segregation and alloy properties in (100)- and (311)-oriented InGaAsGaAs heterostructures

Abstract The influence of surface orientation and surface structure on indium segregation and alloy properties were systematically studied in InGaAs GaAs quantum well structures grown by molecular beam epitaxy. (100), (311)A and (311)B surface orientations and different approaches in the growth interruption at the interfaces were used in this investigation. The segregation process and alloy parameters were obtained by photoluminescence and RHEED measurements. We find significant differences in the optical properties and growth kinetic for the three orientations. Using growth interruption we were able to change the surface structure and reduce the segregation process for all orientations.

On the subtle tuneability of cellulose hydrogels: implications for binding of biomolecules demonstrated for CBM 1

Cellulose-based hydrogel materials prepared by regeneration from cellulose solutions in ionic liquids, or ionic liquid containing solvent mixtures (organic electrolyte solutions), are becoming widely used in a range of applications from tissue scaffolds to membrane ionic diodes. In all such applications knowledge of the nature of the hydrogel with regards to porosity (pore size and tortuosity) and material structure and surface properties (crystallinity and hydrophobicity) is critical. Here we report significant changes in hydrogel properties, based on the choice of cellulose raw material (α- or bacterial cellulose - with differing degree of polymerization) and regeneration solvent (methanol or water). Focus is on bioaffinity applications, but the findings have wide ramifications, including in biomedical applications and cellulose saccharification. Specifically, we report that the choice of cellulose and regeneration solvent influences the surface area accessible to a family 1 carbohydrate-binding module (CBM), CBM affinity for the cellulose material, and rate of migration through the hydrogel. By regenerating bacterial cellulose in water, a maximum accessible surface area of 33 m2 g-1 was achieved. However, the highest CBM migration rate, 1.76 μm2 min-1, was attained by regenerating α-cellulose in methanol, which also resulted in the maximum affinity of the biomolecule for the material. Thus, it is clear that if regenerated cellulose hydrogels are to be used as support materials in bioaffinity (or other) applications, a balance between accessible surface area and affinity, or migration rate, must be achieved.