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- Development of paper-based color test-strip for drug detection in aquatic environment: Application to oxytetracyclinePublication . Gomes, HIAS; Sales, M. Goreti F.The wide use of antibiotics in aquaculture has led to the emergence of resistant microbial species. It should be avoided/minimized by controlling the amount of drug employed in fish farming. For this purpose, the present work proposes test-strip papers aiming at the detection/semi-quantitative determination of organic drugs by visual comparison of color changes, in a similar analytical procedure to that of pH monitoring by universal pH paper. This is done by establishing suitable chemical changes upon cellulose, attributing the paper the ability to react with the organic drug and to produce a color change. Quantitative data is also enabled by taking a picture and applying a suitable mathematical treatment to the color coordinates given by the HSL system used by windows. As proof of concept, this approach was applied to oxytetracycline (OXY), one of the antibiotics frequently used in aquaculture. A bottom-up modification of paper was established, starting by the reaction of the glucose moieties on the paper with 3-triethoxysilylpropylamine (APTES). The so-formed amine layer allowed binding to a metal ion by coordination chemistry, while the metal ion reacted after with the drug to produce a colored compound. The most suitable metals to carry out such modification were selected by bulk studies, and the several stages of the paper modification were optimized to produce an intense color change against the concentration of the drug. The paper strips were applied to the analysis of spiked environmental water, allowing a quantitative determination for OXY concentrations as low as 30 ng/mL. In general, this work provided a simple, method to screen and discriminate tetracycline drugs, in aquaculture, being a promising tool for local, quick and cheap monitoring of drugs.
- Reação dos mercados de CDS e de cotações bolsistas a anúncios de rating: o caso dos maiores bancos portuguesesPublication . Nobre, Nísia Raquel da Silva; Silva, ArmandoA presente dissertação tem como principal objetivo avaliar a capacidade que os mercados de Credit Default Swaps (CDS) e acionista apresentam de antecipar alterações nas notações das principais Agências de Rating mundiais. Para esse efeito serão analisadas as cotações diárias dos prémios de CDS e as cotações diárias de ações dos quatro principais bancos portugueses entre 2004 e 2012, bem como os eventos de rating associados a esses bancos. A literatura existente, apresenta, resultados que tendem a evidenciar que os CDS reagem, regra geral, de forma mais rápida a anúncios das Agências de Rating e que esta mesma reação é maior para eventos negativos (downgrade das notações de rating) do que para eventos positivos (upgrade das notações). O presente estudo detecta, para dois daqueles bancos alguma capacidade dos prémios dos CDS anteciparem eventos negativos de rating.