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| Author(s): |
Thiago Regis Longo Cesar da Paixão
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Conjunto das Químicas (IQ e FCF) (CQ/DBDCQ) |
| Defense date: | 2007-10-25 |
| Examining board members: |
Mauro Bertotti;
Lúcio Angnes;
Lauro Tatsuo Kubota;
Nelson Ramos Stradiotto;
Susana Inés Córdoba de Torresi
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| Advisor: | Mauro Bertotti |
| Abstract | |
Results on the development of microelectrodes fabricated by electrochemical etching using fibers of different materials (platinum, gold and carbon fiber) and dimensions (starting from 100 µm) for the application in micronenvironments are presented. In almost all cases this procedure was carried out using AC transformer. Array of microelectrodes were also fabricated by using litographic techniques. The applicability of Pt microelectrodes fabricated by electrochemical etching was evaluated in the in-situ monitoring of the ascorbic acid concentration in different fruits. The sensor allowed spatial distribution of ascorbic acid concentration in oranges to be found and concentration maps were constructed. A correlation between the ripening stage and the ascorbic acid concentration was also observed from electrochemical measurements, the ascorbic acid content being higher in mature fruits. Studies on the detection of species involved in the oxidative stress process, such as DNA and ascorbic acid, were also performed. Ruthenium oxide hexacyanoferrate (RuOHCF) modified electrode surfaces were used as amperometric detectors for 2\'-deoxyguanosine (dG) and ascorbic acid determinations in FIA apparatus. The method exhibited a linear response range to 2\'-deoxyguanosine from 3.8 to 252 µmol L-1 dG with detection limit of 94 nmol L-1. Applications in DNA samples were examined, and the results for determination of 2\'-deoxyguanosine were in good agreement with those obtained by HPLC analysis. The dG electrocatalytic oxidation at a RuOHCF glassy carbon (GC) modified electrode was investigated in acid medium by using rotating disc electrode (RDE) voltammetry. On this modified surface, the electrocatalytic process allowed the determination of ascorbic acid to be performed at 0.0 V and pH = 6.9 with a limit of detection of 2.2 µmol L-1 in a flow injection configuration. The usefulness of the method was demonstrated by an addition-recovery experiment with urine samples and the recovered values were in the 96 to 104 % range. Investigations on the mechanism of the electrocatalytic oxidation of ascorbic acid was also investigated at pH = 6.9 by using RDE voltammetry. The RuOHCF carbon fiber modified microelectrode was used to monitor the ascorbate uptake by control SH-SY5Y cells, and cells transfected with wild-type Cu,Zn-Superoxide Dismutase (SOD) or with a mutant SOD (SOD G93A) typical of familial Amyotrophic Lateral Sclerosis (ALS). Data on the rate of ascorbate uptake by these cells were in agreement with the level of oxidative stress induced by the mutant SOD. Attemps to use the microelectrodes inside single cells were also performed (AU) | |