Flexible graphite sheets or graphite paper are conductive substrates produced in large scale for use in a wide range of applications, such as in telecommunications, lighting, computer and ...peripherals, power conversion, and heat generating semiconductors (low-cost material). In this paper we show, for the first time, that commercially available graphite sheets can be used in the as-received condition for the construction of disposable electrodes with excellent performance for electroanalysis (comparable to glassy carbon). Nine different graphite sheets were evaluated by different techniques, such as scanning electron microscopy (SEM), Raman spectroscopy, cyclic voltammetry, square wave voltammetry, and amperometry. The obtained results revealed the existence of large variations between different commercially available materials (not all the sheets work well as sensors in the as-received condition). Our studies have shown that there are commercial flexible graphite sheets with higher electrical conductivity and superior homogeneous composition, which are ideal for use as disposable unmodified or modified sensors. The quality of the results obtained with graphite sheets are dependent on the type of material selected as substrate. However, repetitive results are obtained if the same material is always used. The graphite sheets were coupled to low cost 3D-printed cells forming easy to use disposable devices. The performance of the disposable devices was evaluated using ferri-ferrocyanide and ferrocene probes, dopamine (LOD=0.7μmolL−1), catechol (LOD=0.8μmolL−1), ciprofloxacin (LOD=5.9μmolL−1), cadmium (LOD=0.013μmolL−1), and lead (LOD=0.07μmolL−1) as model analytes. According to our knowledge, the electroanalytical performance of graphite sheets demonstrated here surpasses previously reported results.
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•Robust and disposable conductive substrates for production of electrochemical devices.•Sensor performance is highly dependent on the type of industrial graphite paper selected as a carbon substrate.•Large-area graphite films for construction of modified disposable sensors•Graphite paper and 3D-printed cells: a robust and cost-effective assembly
In this work, three composites with different contents (5, 10, and 15% w/w) of kraft pulp fibre were produced as reinforcing elements for natural latex matrix and the mechanical properties were ...evaluated. In order to improve the interfacial adhesion between the matrix and the reinforcing element, chemical modifications were carried out on the surface of the fibres using octanoyl and benzoyl chlorides as modifying agents. The extension of chemical modification of the fibres was visualized by the presence of absorption bands in the spectroscopy analyzes of the modified fibre in relation to the crude fibre (ester carbonyl 1700–1740 cm
−1
); in addition, the hydroxyl band was preserved, which indicates a modification of surface character. The modified fibres became more hydrophobic due to the decrease in surface energy and the change in the dispersive and polar components. An increase in the storage modulus was observed for the composites with surface-modified fibres, which agrees with the improved dispersion between the surface-modified fibres and the matrix verified by means of scanning electron microscopy images. The incorporation of fibres did not cause changes in the thermal properties of the composites.
Flaxseed gum (FG)-based films were developed with the addition of glycerol as a plasticizer and glutaraldehyde as a crosslinking agent. HCl was added to improve crosslinking and decrease the ...hydrophilicity of the matrix. Different cellulose nanocrystal (CN) amounts were used as reinforcements in the optimum FG formulation. The crosslinking process at pH 3.5 led to a lower solubility of FG in water (from 100% to 53%) and an increase in thermal stability (from 160 ºC to 209 ºC). FTIR analysis confirmed a reduction in the -OH band due to crosslinking between the hydroxyl groups of FG. A diffuse diffraction pattern was observed for all FG films. The addition of 4% w/w of CN contributed to reduction of water solubility (from 53% to 20.8%) and absorption (from 21.9% to 6.8%). Finally, an improvement was observed in the tensile mechanical properties in the nanocomposites, showing satisfactory results for the proposed formulations, mainly with 8% w/w of CN added to the matrix. Overall, this study demonstrated that FG/CN nanocomposites are promising materials to be use as a sustainable biopolymer for application as bioplastics.
In this work, nine different types of edible coating based on pectin, cellulose nanocrystals, glycerol, and essential oil of lemongrass were prepared and used to coat strawberries with a film formed ...directly on the surface of the coated fruit. The effects of the different edible coatings
on refrigerated fruits in terms of weight loss, titratable acidity, total soluble solids, pH, and anthocyanin content was evaluated after 2 days, 4 days, 6 days, and 8 days of storage. Application of the edible coatings reduced the weight loss of the coated strawberries and the anthocyanin
content. The total soluble solids content of or uncoated fruit increase more markedly than that of coated fruit. In contrast, pH was maintained for both coated and uncoated strawberries. The edible coatings were effective in minimizing of the weight loss, without worsening the physical chemistry
attributes. The treatments T5 and T9 presented the best results.
As Leishmanioses constituem um grupo de doenças que refletem grave problema de saúde pública no Brasil. A fisiopatologia da leishmaniose visceral (LV) parece estar intimamente relacionada as ...diferentes espécies causadoras da doença e à estreita relação da resposta imune do indivíduo contra o parasita. Após a infecção inicial, alguns indivíduos podem evoluir com formas assintomáticas e cura espontânea, enquanto outros podem evoluir com forma graves. Indivíduos que desenvolvem alguma imunossupressão podem apresentar quadro de LV muito além do período habitual de incubação. Questiona-se a possibilidade da desregulação do sistema imunológico secundária a infecção grave por coronavírus (COVID 19) ter sido um fator facilitador para apresentação da LV clinicamente manifesta no caso descrito. O objetivo do estudo é descrever um caso de paciente jovem, pós COVID 19 grave, evoluindo com febre de origem indeterminada. Trata-se de paciente, 24 anos, com obesidade grau II (IMC:36), diagnosticado com COVID 19 através de teste rápido de antígeno de swab da nasofaringe. Em unidade de terapia intensiva (UTI) no 9º dia de sintomas, necessitou de intubação orotraqueal, protocolo de prona e uso de antibioticoterapia. Recebeu alta da UTI tolerando bem desmame de oxigenioterapia. No 26º dia iniciou com febre persistente, sem foco identificado apesar de propedêutica extensa. No 29º dia foi verificada pancitopenia, não presente em exames prévios com hemoculturas negativas. Evoluiu com hipotensão e novo choque séptico, uso de drogas vasoativas, intubação e injúria renal aguda com terapia de substituição renal. Propedêutica complementar evidenciou esplenomegalia leve, visualizada em tomografia computadorizada de abdome. Provas inflamatórias elevadas assim como desidrogenase láctica e hiperferritinemia importante (>400000) e provas de hemólise negativas e pancitopenia em piora. Realizado mielograma no 13° dia de febre mantida com resultado de PCR para Leishmania positivo. Iniciado tratamento com Anfotericina B lipossomal, durante 7 dias (dose total de 20 mg/kg). Recebeu alta com exames melhorados, assintomático. Os quadros de febre persistente em pacientes sob terapia intensiva são um desafio para a equipe assistencial. Apesar das infecções associadas a assistência serem a principal causa de febre nesse contexto, pacientes que apresentam sintomas típicos de outras doenças infecciosas, necessitam de investigação, considerando o contexto epidemiológico do nosso país.
•Graphite sheets (GS) are efficient substrates to electropolymerize toluidine blue.•Electropolymerization was successfully achieved on untreated (“as-received”) GS.•Improved sensitivity towards ...tryptamine after potential cycling in a KOH solution.•Quantification of tryptamine in cheese samples with minimal sample pretreatment.•Inexpensive, easy-to-produce, high-performance disposable electrochemical sensors.
Tryptamine (TRYP) is a biogenic amine present in several foods and beverages, and despite some beneficial effects on human health, high intakes of TRYP can be harmful. Therefore, accurate analytical methods for TRYP quantification in food samples are necessary. This study describes a cost-effective electrochemical sensor for TRYP determination in cheese samples based on a poly(toluidine blue) (PTB) film electropolymerized onto graphite sheets (GS). Electrode preparation involved two simple steps: (1) electropolymerization of toluidine blue by potential cycling in phosphate buffer solution, and (2) PTB overoxidation by potential cycling in a 0.1 mol L–1 KOH solution. The overoxidation of PTB led to a remarkable increase in sensitivity and detectability towards TRYP, due to the introduction of negatively charged groups that electrostatically preconcentrate TRYP at electrode surface. Using square wave voltammetry, a linear range for TRYP from 0.05 to 0.9 μmol L−1 (0.008 – 0.144 ppm) was achieved with a detection limit of 12 nmol L−1 (0.002 ppm). Also, the electrodes exhibited a remarkable antifouling ability leading to highly reproducible voltammetric responses for TRYP. In addition to being inexpensive (disposable), GS substrates enabled PTB electropolymerization with no need for cleaning or surface preparation procedures. Therefore, the approach described here proved to be promising for the simple, inexpensive, and accurate determination of TRYP in cheese samples.
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•Graphite sheets modified with electropolymerized film of poly(methylene blue) (PMB).•PMB-modified graphite sheets tested for voltammetric detection of nitrofurantoin.•PMB increased ...sensitivity for nitrofurantoin and provided antifouling properties.•Successfully applied to quantify nitrofurantoin in tap water and urine samples.
Electroanalytical methods are suitable to quantify pharmaceutical compounds. The typically high cost for preparing many electrochemical sensors, however, has been a drawback to their widespread use. We have used inexpensive graphite sheets (GS) as conductive substrates, and modified them by electropolymerizing a film of poly(methylene blue) (PMB) by a simple, fast, and reproducible procedure based on potential cycling. The PMB film increased the sensitivity for nitrofurantoin (NFT) and provided an antifouling property to the electrode. Under optimized conditions, GS/PMB exhibited a current increase proportional to the concentration of NFT in the range of 5–100 μmol L–1, with sensitivity and detection limit of 0.297 μA/μmol L–1 and 55 nmol L–1, respectively. The proposed sensor could successfully quantify NFT in tap water and urine samples. Considering the flexibility, lightweight, conductivity and surface properties of graphite sheets, and the vast number of monomers that can be electropolymerized at electrode surfaces, this approach may lead to the fabrication of several flexible, disposable, and portable devices with applications in electrochemical sensing and biosensing.
This work was conducted with the objective of improving the physicochemical properties of flaxseed gum with added agar. Three formulations of flaxseed gum/agar (FG/AG) blends (75/25, 50/50 and 25/75) ...were studied in the presence of glutaraldehyde as crosslinking agent and a glycerol plasticizing agent. Cellulose nanocrystals (CNCs) were used as reinforcing agents at different levels (2%, 4% and 8% w/w) to prepare nanocomposite films by casting polymeric blends of flax seed and agar with both additives. The interaction with water (vapor permeability and solubility), scanning electron microscopy and tensile tests were performed for films, blends and nanocomposites. The flaxseed gum, agar and additives showed good homogeneity, as demonstrated by scanning electron microscopy. All the formulations presented tenacity increase between 585 and 811%, and lower values of solubility relative to the control film (FG
control
). The best formulation of nanocomposites was 50/50–4% CNCs, that presented higher modulus of elasticity and increase in tenacity of 130% relative to the 50/50 blend and 1588% relative to the control film. The results showed that AG and CNC can modulate the properties of FG, opening numerous opportunities for investigation. Due to the significant improvement in the mechanical properties, FG/AG blends and nanocomposites have excellent potential in applications as sustainable packaging.
CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Devido a busca e necessidade da aplicação de produtos sustentáveis, as
blendas e os nanocompósitos a partir de biopolímeros surgem ...como uma proposta de
uso em diversos campos tais como: embalagens, biomedicina e agricultura. Nesse
sentido foram desenvolvidos blendas de goma de linhaça/ágar reticulados com
glutaraldeído utilizando nanocristais de celulose como reforço, obtidos através do
método “casting”. Testes preliminares foram realizados inicialmente variando a
proporção de agente reticulante e plastificante além da variação de pH do meio, com
o objetivo de promover ligações cruzadas na estrutura e consequente diminuição da
hidrofilicidade do material. Seguiu-se o desenvolvimento das blendas em meio ácido
fixando as proporções mássicas de aditivos (30% m/m de glicerol e 15% m/m de
glutaraldeído em relação a massa final para cada filme), além de variar as proporções
dos polímeros (75/25, 50/50 e 25/75 GL/AG). Os nanocompósitos foram obtidos a
partir de cada formulação (blendas e amostras controles) com a adição de 2, 4 e 8%
m/m de nanocristal de celulose (NC). Os filmes e blendas foram caracterizados pelas
técnicas: Calorimetria Exploratória Diferencial, Análise Termogravimétrica, Difração
de Raios-X e Infravermelho com Transformada de Fourier a fim de avaliar possíveis
interações e organização do sistema. O estudo da reticulação das matrizes
poliméricas, de suas blendas e dos nanocompósitos foram avaliados através da
interação com a água pelo teste de solubilidade, absorção de vapor de água, ângulo
de contato e permeabilidade ao vapor de água. A morfologia das amostras foi
estudada por Microscopia Eletrônica de Varredura e por fim, o ensaio sob tração foi
realizado para avaliação do desempenho mecânico das amostras. Os eventos
endotérmicos observados nas curvas de DSC podem estar associados a novas
interações estabelecidas no sistema. As curvas termogravimétricas apresentaram
aumento da estabilidade térmica para os filmes controles e as blendas reticuladas em
meio ácido. Os difratogramas de DRX apresentaram um padrão difuso de material
tipicamente amorfo. Os espectros de FTIR não apresentaram bandas específicas de
reticulação, apenas as existentes na estrutura original dos polissacarídeos. As
imagens de MEV mostraram boa agregação e dispersão para as blendas e
nanocompósitos. Os testes realizados de interação dos filmes com água mostraram
que a reticulação em meio ácido levou a menor solubilidade para a formulação de
goma de linhaça. A inserção de ágar bem como de NC contribuiu para uma menor
absorção de água e melhora nas propriedades mecânicas. As formulações 50/502% NC
e 50/504% NC apresentaram aumento da tensão na ruptura, elongamento e módulo de
Young demonstrando assim resultados que justificam tanto a obtenção destas blendas
quanto dos nanocompósitos. Além disso, com as diferentes morfologias obtidas nesse
estudo é possível estender a faixa de aplicação para as formulações propostas.
Nowadays, due to the incentive and the requirement for the use of sustainable
products, the blends and nanocomposites from biopolymers appear as a proposal for
application in several fields, such as: packaging, biomedicine and agriculture. In this
sense, flaxseed gum/agar blends were developed using glutaraldehyde as a
crosslinker and cellulose nanocrystals as reinforcement, produced by casting method.
Preliminary tests were fulfilled varying the amount of crosslinker agent and plasticizer,
changing the pH of the medium in order to insert crosslinks in the polymer structure
and consequently decrease the hydrophilicity of the samples. The development of the
blends in acid medium by setting the mass proportions of additives (30 wt.% glycerol
and 15 wt.% glutaraldehyde relative to the final mass for each film) and varying the
polymers proportions (75/25, 50/50 and 25/75 GL/AG). The nanocomposites were
obtained from each formulation (blends and control samples) with the addition of 2, 4
and 8% w/w of cellulose nanocrystals (NC). Films and blends were characterized by
Differential Scanning Calorimeter, Thermal Gravimetric Analysis, X-ray Diffraction and
Attenuated Total Reflectance with Fourier Transforms Infrared Spectroscopy
techniques in order to assess possible interactions and organization of the system.
The effect of the crosslinking in the polymer matrices, their blends and the
nanocomposites were evaluated through the interaction with water by the solubility
test, water vapor absorption, contact angle and water vapor permeability. The
morphology of the samples was studied by the Scanning electron microscopy and,
finally, the tensile test was performed to evaluate the mechanical performance of the
samples. The endothermic events observed in the DSC curves may be associated with
new interactions established in the polymeric systems. The thermogravimetric curves
showed increased thermal stability for the control films and crosslinked blends in acid
media. The X-ray diffractograms presented a diffuse pattern of the amorphous
material. The infrared spectra did not present specific bands of crosslinking, only those
being in the original structure of the polysaccharides. MEV images showed good
aggregation and dispersion for blends and nanocomposites. Tests performed on the
interaction of the films with water show that crosslinking in acid media led to a lower
solubility for the flax gum formulation. The insertion of agar, as well as, the insertion of
NC contributed to a lower water absorption and improvement in the mechanical tensile
properties. The 50/502%NC and 50/504%NC formulations showed increased tensile
rupture, Young's Modulus and elongation thus demonstrating results that justify both
blends and nanocomposites originated from these. Moreover, with the different
morphologies obtained in this study it is possible to extend the application range for
the proposed formulations.
Dissertação (Mestrado)
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