Carlos Manuel Melo Pereira

Abstract A novel, straightforward, and environmentally friendly direct coupling procedure to immobilize carbohydrates on solid supports is presented. A characterization study showed that all amino groups on solid supports participated in the linkage with a carbohydrate unit, implicating that the surface load can be easily adjusted by tuning the amination coverage of the surface. Most importantly, the integrity of the cyclic conformation of the linked sugar unit was demonstrated, a feature that is critical for most of the possible applications of carbohydrate-functionalized surfaces. Furthermore, carbohydrate-immobilized submicron particles synthesized by the direct coupling method, on which lectin profiling experiments were conducted, validated the successfulness of our simplistic approach.

Abstract The objective of this work was the exploration of low calcination temperature ranges (< 350 degrees C) to obtain molecularly imprinted microspheres (MIM) with a high crystallinity as anatase, in cooperation of an acidic pretreatment aiming at the preservation of the hollow shape and also of the selective binding sites. It was confirmed the possibility of obtaining bilirubin-imprinted crystalline TiO2 microspheres (highly crystalline anatase, as confirmed by XRD) exhibiting higher photocatalytic efficiency associated especially with the hollow shape and calcination at lower temperatures (200 degrees C or 250 degrees C). It was with the calcination temperature of 250 degrees C that the highest photocatalytic efficiency was obtained, under UV irradiation, associated with the highest adsorption selectivity (alpha(K) = 19) and degradation selectivity (alpha(k) = 2.7) observed for the degradation of the template against a closely related analogue compound.

Abstract Artificial receptors that mimic their natural biological counterparts have several advantages, such as lower production costs and increased shelf-life stability/versatility, while overcoming the ethical issues related to raising antibodies in animals. In this work, the proposed tailor-made molecularly imprinted polymer (MIP)-allergen receptors aimed at substituting or even transcending the performance of biological antibodies. For this purpose, a MIP was proposed as an artificial antibody for the recognition of hazelnut Cor a 14-allergen. The target protein was grafted onto the conducting polypyrrole receptor film using gold screen-printed electrodes (Au-SPE). The electrochemical assessment presented a linear response for the dynamic range of 100 fg mL(-1)-1 mu g mL(-1) and a LOD of 24.5 fg mL(-1), as determined by square wave voltammetry from the calibration curves prepared with standards diluted in phosphate buffer. Surface plasmon resonance (SPR) was used as a secondary transducer to evaluate the performance of the Cor a 14-MIP sensor, enabling a linear dynamic range of 100 fg mL(-1) - 0.1 mu g mL(-1) and a LOD of 18.1 fg mL(-1). The selectivity of the tailored-made Cor a 14-MIP was tested against potentially cross-reactive plant/animal species based on the rebinding affinity (Freundlich isotherm-K-F) of homologues/similar proteins, being further compared with custom-made polyclonal anti-Cor a 14 IgG immunosensor. Results evidenced that the MIP mimics the biorecognition of biological antibodies, presenting higher selectivity (only minor cross-reactivity towards walnut and Brazil nut 2S albumins) than the Cor a 14/anti-Cor a 14 IgG immunosensor. The application of electrochemical Cor a 14-MIP sensor to model mixtures of hazelnut in pasta enabled quantifying hazelnut down to 1 mg kg(-1) (corresponding to 0.16 mg kg(-1) of hazelnut protein in the matrix). To the best of our knowledge, Cor a 14-MIP is the first sensor based on an artificial/synthetic biorecognition platform for the specific detection of hazelnut allergens, while presenting high-performance parameters with demonstrated application in food safety management.

Abstract Graphene and its derivatives are generally portrayed as electron transfer enhancers that effectively boost the electrochemical response of classic electrodes for applications in renewable energy, electronics, or analysis (amongst others). However, a number of fundamental studies have challenged this view. In certain reports, not only could no beneficial effect be demonstrated, but the opposite was concluded. If we want to advance towards a more rational design of high-performance electrode devices, these discrepancies need to be cleared and the fundamental aspects of electron transfer reactions through graphene-electrodes further understood. The present study contributes to this cause by exploring the relationships between the structure and morphological appearance of graphene films and their electrochemical performance in fundamental proof-of-concept experiments. The results unveil that important differences in the structure and morphology of the films (which are tightly related to the composition and load of graphene materials) govern the electrochemical response of the modified electrodes. Thereby, a possible explanation for the apparently contradictory conclusions reported in the literature is provided.

Abstract Optosensing chitosan-based membranes have been applied for the detection of heavy metals, especially in drinking water. The novelty of this study is based on the use of sulphated polysaccharides, in such optosensing membranes, aiming at an improved analytical performance. The sulphated polysaccharides, such as ulvan, fucoidan and chondroitin sulfate, were extracted from by-products and wastes of marine-related activities. The membranes were developed for the analysis of aluminum. The variation in the visible absorbance of the sensor membranes after the contact between the chromophore and the aluminum cation was studied. The membranes containing sulphated polysaccharides showed improved signals when compared to the chitosan-only membrane. As for the detection limits for the membranes containing ulvan, fucoidan and chondroitin sulfate, 0.17 mg L-1, 0.21 mg L-1 and 0.36 mg L-1 were obtained, respectively. The values were much lower than that obtained for the chitosan-only membrane, 0.52 mg L-1, which shows the improvement obtained from the sulphated polysaccharides. The results were obtained with the presence of CTAB in analysis solution, which forms a ternary complex with the aluminum cation and the chromophore. This resulted in an hyperchromic and batochromic shift in the absorption band. When in the presence of this surfactant, the membranes showed lower detection limits and higher selectivity.