XII Iberian Meeting of Electrochemistry XVI Meeting of the ...

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XII Iberian Meeting of Electrochemistry & XVI Meeting of the Portuguese Electrochemical Society O B 03 An electrochemical biosensor for toxic amides determination: Merits and Limitations Nelson A. F. Silva 1 , Manuel J. Matos 1 , Amin Karmali 1 , Maria Manuela Rocha 2 1 CIEQB-ISEL - Instituto Superior de Engenharia de Lisboa, Portugal 2 DQB Faculdade de Ciências da Universidade de Lisboa, Portugal nsilva@deq.isel.ipl.pt The present work reports some experimental results concerning an investigation that is presently being conducted in order to develop and implement an electrochemical biosensor for toxic amides determination [1]. The biological recognition element consists of whole cells of Pseudomonas aeruginosa containing intracellular amidase activity, which catalyses the hydrolysis of amides, such as acrylamide, producing ammonium ions and acrylic acid. The transduction process is provided by an ammonium ion selective electrode. Whole cells were firstly immobilized in several types of polymeric membranes, such as polyethersulfone, nitrocellulose, polycarbonate or nylon, which were attached to the surface of the transductor according to different procedures. The reaction time was 6 minutes. These biosensors, typically, exhibited a linear response in the range of 10 -4 -10 -1 mol.L -1 of acrylamide, a detection limit in the order of 10 -4 mol.L-1 of acrylamide, and a sensitivity of 48.0 mV/decade. Other figures of merit such as, selectivity, correlation coefficient, response time or half life time, concerning the ility, were also investigated. example, the time needed for complete removal of ammonium ions from the vicinity of the transducer, after the catalytic reaction, so that each assay could start with identical conditions, was about 45 minutes. This period of time is not compatible with continuous measurements or even environmental monitoring of acrylamide. In order to overcome this limitation, some investigation studies are being conducted regarding the development and optimization of other immobilization matrices for whole cells of Pseudomonas aeruginosa. Some main characteristics of these matrices, such as, high substrate and product diffusion rates, easy removal of ammonium ions after each assay; biochemical compatibility with the biological recognition element and mechanical stability, should be accomplished. Glutaraldehyde, bovine serum albumin (BSA), gelatin, nafion, agarose, zeolites, sol-gel technology, alginates beds, and other immobilization agents and procedures, have been used and combined, to prepare several different immobilization matrices. [refs!] The results that we will present, bearing in mind the characteristics mentioned above, range from poor to frankly good. In future we hope to be able to use this biosensor for acrylamide and other toxic amides determination in food and environmental samples. References [1] Silva, N.; Gil, D.; Karmali, A.; Matos, M.; Biocat Biotransf, 2009, 27, 143. September, 811, 2010. ISEL - Lisbon 36
XII Iberian Meeting of Electrochemistry & XVI Meeting of the Portuguese Electrochemical Society O B 04 Construction of a nitrite biosensor based on the direct electrochemistry of a multihemic nitrite reductase on carbon nanotube modified electrodes Célia M. Silveira 1 , Marta Pimpão 1 , Fernando Pereira 2 , José J.G. Moura 1 , M. Gabriela Almeida 1 1 REQUIMTE Departamento de Química, CQFB, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal 2 LCM Laboratório de Catálise e Materiais, DEQ - Faculdade de Engenharia da Universidade do Porto, R. Dr. Roberto Frias, 4200-465 Porto, Portugal celia.silveira@dq.fct.unl.pt In recent years, biosensors have been an intense research field, as they constitute advantageous alternatives to conventional analytical methods. The electrochemical enzyme based devices are of particular interest due to their operational simplicity, low cost fabrication, portability and real-time monitoring capability. The devices based on direct electron transfer between the electrode and the redox enzyme represent the most attractive and simple approach. However, several issues still challenge the direct electrochemistry of proteins. As so, the development of appropriate electrodes and protein immobilization methods to enhance the direct electron exchange while retaining biological activity is crucial. In this regard, the modification of electrode surfaces at a molecular scale using carbon nanotubes (CNTs) has become increasingly popular. CNT deposits on solid supports generate three dimensional porous structures that greatly enlarge electrode surfaces. As a result we can obtain higher loadings of proteins on electrodes and achieve optimal distances to their redox centers. The efficiency of heterogeneous electron transfer and bioelectrocatalysis is thus markedly improved [1-3]. This work reports the use carbon nanotubes to promote the direct electrochemistry of the multihemic nitrite reductase (ccNiR) from Desulfovibrio desulfuricans ATCC 27774. Multi-walled (MWCNT) CNTs were used to modify the surface of pyrolytic graphite electrodes (PGEs). A layer-by-layer deposition method was used, in which drops of CNTs dispersions are successively applied on the electrode, followed by the addition of enzyme. Dispersions were prepared in water, organic solvents and detergents. The catalytic response to nitrite was considerably improved in the presence of the carbon nanotubes when compared to plain electrodes modified with enzyme only. The electrocatalytic characteristics of the bioelectrodes responses were compared and evaluated in terms of the structural and chemical properties of the different CNTs. The analytical performance of the bioelectrodes will also be presented and discussed. Acknowledgments: C.M. Silveira thanks the financial support funded by Fundação para a Ciência e Tecnologia (SFRH/BD/28921/2006). References [1] J.J. Davis, K.S. Coleman, B.R. Azamian, C.B. Bagshaw, M.L. Green, Chem. Eur. J. 9 (2003) 3732. [2] J.J. Gooding, R. Wibowo, J. Liu, W. Yang, D. Losic, S. Orbons, F.J. Mearns, J.G. Shapter, D. B. Hibbert, J. Am. Chem. Soc. 125 (2003) 9006. [3] K. Gong, Y. Yan, M. Zhang, L. Su, S. Xiong, L. Mao, Anal. Sci. 21 (2005) 1383. September, 811, 2010. ISEL - Lisbon 37
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