Mechanical properties of chemically modified portuguese pinewood

To turn wood into a construction material with enhanced properties, many methods of chemical modification have been developed in the last few decades. In this work, mechanical properties of pine wood were chemically modified, compared and evaluated. Maritime pine wood (Pinus pinaster) was modified with four chemical processes: 1,3-dimethylol-4,5- dihydroxyethyleneurea, N-methylol melamine formaldehyde, tetra-alkoxysilane and wax. The following mechanical properties were assessed experimentally: Modulus of elasticity measured statically, stiffness stabilization efficiency in different climates (30 and 87% of relative humidity), modulus of rupture, work maximum load, impact bending strength, compression, tensile and shear strength at indoor conditions (65% of relative humidity). In both types of active principle of modification, cell wall or lumen fill, no significant changes on the bending stiffness (modulus of elasticity) were found. In the remaining properties analysed significant changes in the modified wood-material took place compared to unmodified wood control: - Cell wall modification was the most effective method to achieve high stiffness stabilization efficiency (up to 60%) and also increased compression strength (up to 230%). However, modulus of rupture, tensile, shear and the impact bending strength were reduced by both resins, but in a varying extent, where the N-methylol melamine formaldehyde endured less reduction than 1,3-dimethylol-4,5-dihydroxyethyleneurea resin. In the latter, reduction up to 60% can take place. - In the lumen fill modification: tetra-alkoxysilane has no effect in the mechanical properties. Although, a slight increase in shear strength parallel to the grain was found. Wax specimens have shown a slight increase in bending strength, compression, tensile and shear strength as well as in the absorption energy capacity.

Towards a reliable technology for antioxidant capacity and oxidative damage evaluation: Electrochemical (bio)sensors

To counteract and prevent the deleterious effect of free radicals the living organisms have developed complex endogenous and exogenous antioxidant systems. Several analytical methodologies have been proposed in order to quantify antioxidants in food, beverages and biological fluids. This paper revises the electroanalytical approaches developed for the assessment of the total or individual antioxidant capacity. Four electrochemical sensing approaches have been identified, based on the direct electrochemical detection of antioxidant at bare or chemically modified electrodes, and using enzymatic and DNA-based biosensors.

Removal of sulfamethoxazole from solution by raw and chemically treated walnut shells

Purpose: The sorption of sulfamethoxazole, a frequently detected pharmaceutical compound in the environment, onto walnut shells was evaluated. Methods: The sorption proprieties of the raw sorbent were chemically modified and two additional samples were obtained, respectively HCl and NaOH treated. Scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric (TG/DTG) techniques were applied to investigate the effect of the chemical treatments on the shell surface morphology and chemistry. Sorption experiments to investigate the pH effect on the process were carried out between pH 2 and 8. Results: The chemical treatment did not substantially alter the structure of the sorbent (physical and textural characteristics) but modified the surface chemistry of the sorbent (acid���base properties, point of zero charge���pHpzc). The solution pH influences both the sorbent���s surface charge and sulfamethoxazole speciation. The best removal efficiencies were obtained for lower pH values where the neutral and cationic sulfamethoxazole forms are present in the solution. Langmuir and Freundlich isotherms were applied to the experimental adsorption data for sulfamethoxazole sorption at pH 2, 4, and 7 onto raw walnut shell. No statistical difference was found between the two models except for the pH 2 experimental data to which the Freundlich model fitted better. Conclusion: Sorption of sulfamethoxazole was found to be highly pH dependent in the entire pH range studied and for both raw and treated sorbent.

Can power laws help us understand gene and proteome information?

Proteins are biochemical entities consisting of one or more blocks typically folded in a 3D pattern. Each block (a polypeptide) is a single linear sequence of amino acids that are biochemically bonded together. The amino acid sequence in a protein is defined by the sequence of a gene or several genes encoded in the DNA-based genetic code. This genetic code typically uses twenty amino acids, but in certain organisms the genetic code can also include two other amino acids. After linking the amino acids during protein synthesis, each amino acid becomes a residue in a protein, which is then chemically modified, ultimately changing and defining the protein function. In this study, the authors analyze the amino acid sequence using alignment-free methods, aiming to identify structural patterns in sets of proteins and in the proteome, without any other previous assumptions. The paper starts by analyzing amino acid sequence data by means of histograms using fixed length amino acid words (tuples). After creating the initial relative frequency histograms, they are transformed and processed in order to generate quantitative results for information extraction and graphical visualization. Selected samples from two reference datasets are used, and results reveal that the proposed method is able to generate relevant outputs in accordance with current scientific knowledge in domains like protein sequence/proteome analysis.

Desenvolvimento de um nanosensor para monitorizar a ciprofloxacina em ��guas superficiais

No presente trabalho pretendeu-se estudar o comportamento da ciprofloxacina por t��cnicas voltam��tricas e desenvolver novos sensores para monitorizar a ciprofloxacina em ��guas residuais. A investiga����o realizada contemplou essencialmente, os seguintes aspectos: estudo da influ��ncia do pH no comportamento voltam��trico da ciprofloxacina e compara����o entre o el��ctrodo de carbono v��treo e alguns el��ctrodos modificados. O estudo foi efectuado em voltametria c��clica a diferentes velocidades de varrimento e tamb��m em voltametria de impulso diferencial. O estudo mostrou que o el��ctrodo modificado com nanotubos de carbono permitiu a quantifica����o de n��veis mais baixos de ciprofloxacina. O novo sensor desenvolvido foi utilizado em ��guas do rio Douro e rio Le��a com o objectivo de monitorizar a concentra����o de ciprofloxacina. Tra��aram-se curvas de calibra����o directa e por adi����o padr��o de quantidades crescentes de ciprofloxacina. Os estudos efectuados com as ��guas do rio Douro e rio Le��a foram recolhidos pr��ximos da foz do rio estas amostras deveriam ser recolhidas em v��rios pontos do rio para se poder fazer uma compara����o de resultados. Os estudos de recupera����o permitiram verificar que a percentagem de recupera����o para o rio Douro se situava nos 90% e as do rio Le��a nos 75%, pelo m��todo da calibra����o directa. Usando o m��todo da adi����o padr��o a recupera����es foram de 99% para o rio Douro e 90% para o rio Le��a. Os estudos em curso permitem concluir que este sensor poder�� ser aplicado na monitoriza����o da ciprofloxacina em amostras ambientais.

Desenvolvimento de m��todos r��pidos para dete����o de drogas no meio aqu��tico

A vasta aplica����o de antibi��ticos em sistemas de aquacultura tem conduzido ao aparecimento de esp��cies microbianas resistentes, devendo ser evitada ou, se poss��vel, minimizada. A minimiza����o implica um controlo muito rigoroso das doses aplicadas, algo que s�� pode ser realizado se todo o processo anal��tico for simples, barato e puder ser implementado no local. O presente trabalho descreve para este efeito um sistema sensor constitu��do por papel quimicamente modificado, cujo procedimento anal��tico foi semelhante �� monitoriza����o de pH atrav��s das conhecidas tiras indicadoras de pH universal. O papel foi modificado com base em reac����es de monocamadas e assumiu uma colora����o t��pica ap��s contacto com o antibi��tico. A intensidade da colora����o estava tamb��m relacionada com a concentra����o desse antibi��tico. Como prova deste conceito, o sensor proposto foi desenhado tendo em vista a monitoriza����o de oxitetraciclina, um dos antibi��ticos utilizados neste contexto com elevada frequ��ncia. A modifica����o do papel foi baseada na altera����o qu��mica das unidades de glucose na matriz s��lida por reac����o covalente com reagentes apropriados. Foram utilizadas duas estrat��gias diferentes para este efeito: uma foi baseada em reac����es de tipo sol-gel e a outra em reac����o de adi����o nucle��fila. Posteriormente, o papel foi modificado com esp��cies met��licas capazes de mudar de cor na presen��a da oxitetraciclina. Estas modifica����es qu��micas foram avaliadas e optimizadas relativamente a v��rios par��metros, no sentido de promover uma varia����o de cor intensa face �� concentra����o de antibi��tico. Procedeu-se ainda ao controlo desta modifica����o por t��cnicas de espectroscopia de infravermelho. A varia����o de cor foi avaliada por compara����o visual, mas registada por imagem digital. Os materiais sensores preparados foram ainda caracterizados do ponto de vista do seu desempenho anal��tico. Inclu��ram-se aqui a identifica����o de uma rela����o linear entre coordenadas de cor e concentra����o, a atribui����o de uma gama de concentra����es capaz de fornecer uma resposta previs��vel e resposta cruzada face a outros antibi��ticos. Procedeu-se ainda �� aplica����o dos sensores numa amostra de ��gua ambiental dopada com antibi��tico. De uma forma geral, foi poss��vel estabelecer um processo simples de modifica����o de papel capaz de aferir a presen��a e a quantidade de tetraciclinas, mais concretamente a oxitetraciclina. O processo aqui estabelecido �� promissor, antevendo a concretiza����o de uma metodologia simples, barata e local para a monitoriza����o de anitbi��ticos em ��guas.

Desenvolvimento de sensores colorim��tricos para despiste de antibi��ticos

introdu����o de drogas que assegurem o crescimento e a preserva����o das esp��cies, mas que eventualmente se espalham para o meio aqu��tico envolvente, promovendo altera����es da biodiversidade e entrar, directamente ou indirectamente, na cadeia alimentar. Quando estas drogas s��o agentes antimicrobianos de uso humano, tais como a amoxicilina, tetraciclina ou sulfonamidas, h�� um alto risco de aparecimento de esp��cies bacterianas resistentes, algo que constitui uma amea��a grave para a sa��de p��blica. Esta introdu����o de agentes antimicrobianos no ambiente aqu��tico atrav��s do sector das pescas pode ser reduzida atrav��s da monitoriza����o regular ou cont��nua dos n��veis de antibi��ticos no sistema de ��gua, durante a execu����o, bem como antes da descarga para o meio aqu��tico. Para isso, �� necess��rio m��todos anal��ticos que permitam uma frequ��ncia anal��tica elevada e continua, nos tanques de cultivos dos peixes. O presente trabalho descreve para este efeito, um sensor constitu��do por papel quimicamente modificado por rea����es em monocamadas, assumindo uma colora����o t��pica ap��s contacto com o antibi��tico . A intensidade da colora����o estava relacionada com a concentra����o desse antibi��tico. A modifica����o do papel foi baseada na altera����o qu��mica das unidades de glucose do papel por meio de uma rea����o covalente com reagentes apropriados. De seguida, criou-se uma camada de quitosano sobre o papel modificado onde se adsorveu a esp��cie met��lica capaz de mudar de cor na presen��a de sulfadiazina. As modifica����es resultantes foram avaliadas em rela����o a v��rios par��metros, com o intuito de provocar uma varia����o de cor intensa face �� concentra����o de antibi��tico. Os sensores preparados foram caracterizados do ponto de vista do seu desempenho anal��tico, efetuou-se a constru����o de uma gama de concentra����o que permitiu obter uma resposta previs��vel e transversal em rela����o a outros antibi��ticos, bem como a identifica����o de uma rela����o linear entre concentra����o e coordenadas de cor e a aplica����o de sensores em amostra de ��gua ambiental dopados com antibi��tico. Generalizando, foi poss��vel estabelecer um processo de modifica����o simples de papel capaz de medir a presen��a e quantidade de sulfadiazina

���Green Electrodes��� Modified with Au Nanoparticles Synthesized in Glycerol, as Electrochemical Nitrite Sensor

A new environmentally friendly Au nanoparticles (Au NPs) synthesis in glycerol by using ultraviolet irradiation and without extra-added stabilizers is described. The synthesis proposed in this work may impact on the non-polluting production of noble nanoparticles with simple chemicals normally found in standard laboratories. These Au NPs were used to modify a carbon paste electrode (CPE) without having to separate them from the reaction medium. This green electrode was used as an electrochemical sensor for the nitrite detection in water. At the optimum conditions the green sensor presented a linear response in the 2.0��10���7���1.5��10���5���M concentration range, a good detection sensitivity (0.268���A���L���mol���1), and a low detection limit of 2.0��10���7���M of nitrite. The proposed modified green CPE was used to determine nitrite in tap water samples.

Development of polyaniline microarray electrodes for cadmium analysis

Disposable screen-printed electrodes (SPCE) were modified using a cosmetic product to partially block the electrode surface in order to obtain a microelectrode array. The microarrays formed were electropolymerized with aniline. Scanning electron microscopy was used to evaluate the modified and polymerized electrode surface. Electrochemical characteristics of the constructed sensor for cadmium analysis were evaluated by cyclic and square-wave voltammetry. Optimized stripping procedure in which the preconcentration of cadmium was achieved by depositing at ���1.20 V (vs. Ag/AgCl) resulted in a well defined anodic peak at approximately ���0.7 V at pH 4.6. The achieved limit of detection was 4 �� 10���9 mol dm���3. Spray modified and polymerized microarray electrodes were successfully applied to quantify cadmium in fish sample digests.

Biosensor based on multi-walled carbon nanotubes paste electrode modified with laccase for pirimicarb pesticide quantification

This study focused on the development of a sensitive enzymatic biosensor for the determination of pirimicarb pesticide based on the immobilization of laccase on composite carbon paste electrodes. Multi- walled carbon nanotubes(MWCNTs)paste electrode modified by dispersion of laccase(3%,w/w) within the optimum composite matrix(60:40%,w/w,MWCNTs and paraffin binder)showed the best performance, with excellent electron transfer kinetic and catalytic effects related to the redox process of the substrate4- aminophenol. No metal or anti-interference membrane was added. Based on the inhibition of laccase activity, pirimicarb can be determined in the range 9.90 ��10- 7 to 1.15 ��10- 5 molL 1 using 4- aminophenol as substrate at the optimum pH of 5.0, with acceptable repeatability and reproducibility (relative standard deviations lower than 5%).The limit of detection obtained was 1.8 �� 10-7 molL 1 (0.04 mgkg 1 on a fresh weight vegetable basis).The high activity and catalytic properties of the laccase- based biosensor are retained during ca. one month. The optimized electroanalytical protocol coupled to the QuEChERS methodology were applied to tomato and lettuce samples spiked at three levels; recoveries ranging from 91.0��0.1% to 101.0 �� 0.3% were attained. No significant effects in the pirimicarb electro- analysis were observed by the presence of pro-vitamin A, vitamins B1 and C,and glucose in the vegetable extracts. The proposed biosensor- based pesticide residue methodology fulfills all requisites to be used in implementation of food safety programs.

Analysis of the nano-surface of a modified glassy carbon electrode by pseudo phase plane method

This paper presents the Pseudo phase plane (PPP) method for detecting the existence of a nanofilm on the nitroazobenzene-modified glassy carbon electrode (NAB-GC) system. This modified electrode systems and nitroazobenze-nanofilm were prepared by the electrochemical reduction of diazonium salt of NAB at the glassy carbon electrodes (GCE) in nonaqueous media. The IR spectra of the bare glassy carbon electrodes (GCE), the NAB-GC electrode system and the organic NAB film were recorded. The IR data of the bare GC, NAB-GC and NAB film were categorized into five series consisting of FILM1, GC-NAB1, GC1; FILM2, GC-NAB2, GC2; FILM3, GC-NAB3, GC3 and FILM4, GC-NAB4, GC4 respectively. The PPP approach was applied to each group of the data of unmodified and modified electrode systems with nanofilm. The results provided by PPP method show the existence of the NAB film on the modified GC electrode.

New modified electrochemical conductive paper support for BSA detection

Chemical sensors and biosensors are widely used to detect various kinds of protein target biomolecules. Molecularly Imprinted Polymers (MIPs) have raised great interest in this area, because these act as antibody-like recognition materials, with high affinity to the template molecule. Compared to natural antibodies, these are also of lower cost and higher stability. There are different types of supports used to carry MIP materials, mostly of these made of gold, favourably assembled on a Screen Printed Electrode (SPE) strategy. For this work a new kind of support for the sensing layer was developed: conductive paper. This support was made by modifying first cellulose paper with paraffin wax (to make it waterproof), and casting a carbon-ink on it afterwards, to turn it conductive. The SPAM approach previously reported in1 was employed herein to assemble to MIP sensing material on the conductive paper. The selected charged monomers were (vinylbenzyl) trimethlammonium chloride (positive charge) or vinylbenzoic acid (negative charge), used to generate binding positions with single-type charge (positive or negative). The non-specific binding area of the MIP layer was assembled by chronoamperometry-assisted polymerization (at 1 V, for 60, 120 or 180 seconds) of vinylbenzoate, cross-linked with ethylene glycol vinyl ether. The BSA biomolecules lying within the polymeric matrix were removed by Proteinase K action. All preparation stages of the MIP assembly were followed by FTIR, Raman spectroscopy and, electrochemical analysis. In general, the best results were obtained for longer polymerization times and positively charged binding sites (which was consistent with a negatively-charged protein under physiological pH, as BSA). Linear responses against BSA concentration ranged from 0.005 to 100 mg/mL, in PBS buffer standard solutions. The sensor was further calibrated in standard solutions that were prepared in synthetic or real urine, and the analytical response became more sensitive and stable. Compared to the literature, the detection capability of the developed device is better than most of the reported electrodes. Overall, the simplicity, low cost and good analytical performance of the BSA SPE device, prepared with positively charged binding positions, seems a suitable approach for practical application in clinical context. Further studies with real samples are required, as well as gathering with electronic-supporting devices to allow on-site readings.

Novel biosensing device for point-of-care applications with plastic antibodies grown on Au-Screen Printed Electrodes

A gold screen printed electrode (Au-SPE) was modified by merging Molecular Imprinting and Self-Assembly Monolayer techniques for fast screening cardiac biomarkers in point-of-care (POC). For this purpose, Myoglobin (Myo) was selected as target analyte and its plastic antibody imprinted over a glutaraldehyde (Glu)/cysteamine (Cys) layer on the gold-surface. The imprinting effect was produced by growing a reticulated polymer of acrylamide (AAM) and N,N���-methylenebisacrylamide (NNMBA) around the Myo template, covalently attached to the biosensing surface. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) studies were carried out in all chemical modification steps to confirm the surface changes in the Au-SPE. The analytical features of the resulting biosensor were studied by different electrochemical techniques, including EIS, square wave voltammetry (SWV) and potentiometry. The limits of detection ranged from 0.13 to 8 ��g/mL. Only potentiometry assays showed limits of detection including the cut-off Myo levels. Quantitative information was also produced for Myo concentrations ���0.2 ��g/mL. The linear response of the biosensing device showed an anionic slope of ~70 mV per decade molar concentration up to 0.3 ��g/mL. The interference of coexisting species was tested and good selectivity was observed. The biosensor was successfully applied to biological fluids.

Smart Plastic Antibody Material (SPAM) tailored on disposable screen printed electrodes for protein recognition: application to Myoglobin detection

This work introduces two major changes to the conventional protocol for designing plastic antibodies: (i) the imprinted sites were created with charged monomers while the surrounding environment was tailored using neutral material; and (ii) the protein was removed from its imprinted site by means of a protease, aiming at preserving the polymeric network of the plastic antibody. To our knowledge, these approaches were never presented before and the resulting material was named here as smart plastic antibody material (SPAM). As proof of concept, SPAM was tailored on top of disposable gold-screen printed electrodes (Au-SPE), following a bottom-up approach, for targeting myoglobin (Myo) in a point-of-care context. The existence of imprinted sites was checked by comparing a SPAM modified surface to a negative control, consisting of similar material where the template was omitted from the procedure and called non-imprinted materials (NIMs). All stages of the creation of the SPAM and NIM on the Au layer were followed by both electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). AFM imaging was also performed to characterize the topography of the surface. There are two major reasons supporting the fact that plastic antibodies were effectively designed by the above approach: (i) they were visualized for the first time by AFM, being present only in the SPAM network; and (ii) only the SPAM material was able to rebind to the target protein and produce a linear electrical response against EIS and square wave voltammetry (SWV) assays, with NIMs showing a similar-to-random behavior. The SPAM/Au-SPE devices displayed linear responses to Myo in EIS and SWV assays down to 3.5 ��g/mL and 0.58 ��g/mL, respectively, with detection limits of 1.5 and 0.28 ��g/mL. SPAM materials also showed negligible interference from troponin T (TnT), bovine serum albumin (BSA) and urea under SWV assays, showing promising results for point-of-care applications when applied to spiked biological fluids.

Numerical experiments with a modified regularization scheme for mathematical programs with complementarity constraints

On this paper we present a modified regularization scheme for Mathematical Programs with Complementarity Constraints. In the regularized formulations the complementarity condition is replaced by a constraint involving a positive parameter that can be decreased to zero. In our approach both the complementarity condition and the nonnegativity constraints are relaxed. An iterative algorithm is implemented in MATLAB language and a set of AMPL problems from MacMPEC database were tested.