Biomedical subjects

A M Oliveira Brett

Publications and source records attributed to A M Oliveira Brett.

6 recordsLinked to original sources

PubMed2005

Synthetic oligonucleotides: AFM characterisation and electroanalytical studies.

One of the most important steps in designing more sensitive and stable DNA based biosensors is the immobilisation procedure of the nucleic acid probes on the transducer surface, while maintaining their conformational flexibility. MAC Mode AFM images in air demonstrated that the oligonucleotide sequences adsorb spontaneously on the electrode surface, showing the existence of pores in the adsorbed layer that reveal big parts of the electrode surface, which enables non-specific adsorption of other molecules on the uncovered areas. The electrostatic immobilisation onto a glassy carbon electrode followed by hybridisation with a complementary sequence and control with a non-complementary sequence was studied using differential pulse voltammetry and electrochemical impedance spectroscopy. Changes in the oxidation currents of guanosine and adenosine were observed after hybridisation events as well as after control experiments. Modification of the double layer capacitance that took place after hybridisation or control experiments showed that non-specific adsorption of complementary or non-complementary sequences occur allowing the formation of a mixed multilayer.

Biosensing Techniques↗

PubMed2004

Editorial.

Explore the source record for details and available documents.

Biosensing Techniques↗

PubMed2004

AFM and electroanalytical studies of synthetic oligonucleotide hybridization.

The first and most important step in the development and manufacture of a sensitive DNA-biosensor for hybridization detection is the immobilization procedure of the nucleic acid probe on the transducer surface, maintaining its mobility and conformational flexibility. MAC Mode AFM images were used to demonstrate that oligonucleotide (ODN) molecules adsorb spontaneously at the electrode surface. After adsorption, the ODN layers were formed by molecules with restricted mobility, as well as by superposed molecules, which can lead to reduced hybridization efficiency. The images also showed the existence of pores in the adsorbed ODN film that revealed large parts of the electrode surface, and enabled non-specific adsorption of other ODNs on the uncovered areas. Electrostatic immobilization onto a clean glassy carbon electrode surface was followed by hybridization with complementary sequences and by control experiments with non-complementary sequences, studied using differential pulse voltammetry. The data obtained showed that non-specific adsorption strongly influenced the results, which depended on the sequence of the ODNs. In order to reduce the contribution of non-specific adsorbed ODNs during hybridization experiments, the carbon electrode surface was modified. After modification, the AFM images showed an electrode completely covered by the ODN probe film, which prevented the undesirable binding of target ODN molecules to the electrode surface. The changes of interfacial capacitance that took place after hybridization or control experiments showed the formation of a mixed multilayer that strongly depended on the local environment of the immobilized ODN.

Adsorption↗

PubMed2003

Electrochemical and spectroscopic studies of the oxidation mechanism of the herbicide propanil.

Electrochemical oxidation of propanil in deuterated solutions was studied by cyclic, differential pulse, and square wave voltammetry using a glassy carbon microelectrode. The oxidation of propanil in deuterated acid solutions occurs at the nitrogen atom of the amide at a potential of +1.15 V vs Ag/AgCl. It was also found that, under the experimental conditions used, protonation at the oxygen atom of propanil occurs, leading to the appearance of another species in solution which oxidizes at +0.60 V. The anodic peak found at +0.79 V vs Ag/AgCl in deuterated basic solutions is related to the presence of an anionic species in which a negative charge is on the nitrogen atom. The electrochemical data were confirmed by the identification of all the species formed in acidic and basic deuterated solutions by means of NMR spectroscopy. The results are supported by electrochemical and spectroscopic studies of acetanilide in deuterated solutions.

Deuterium↗

PubMed2002

Voltammetric behavior of benznidazole at a DNA-electrochemical biosensor.

Benznidazole is a drug used commonly as a therapeutic agent against Chagas' disease in Brazil. To clarify the cytotoxic action of benznidazole the electrochemical reduction of benznidazole has been investigated using a DNA-electrochemical biosensor, prepared by modification of a glassy carbon electrode with DNA, and the results compared with reduction at a bare glassy carbon electrode. The dependence of peak potential with pH follows slopes of 59 and 52 mV per pH unit in acid media, respectively, which corresponds to a mechanism involving the same number of electrons and protons. In neutral and alkaline solution no significant dependence of peak potential with pH was found. During the electrochemical reduction of benznidazole the formation of the hydroxylamine derivative occurs, involving a total of four electrons. The potentials for reduction were less negative when using the DNA-modified glassy carbon electrode than at the bare glassy carbon electrode although the mechanism was the same, and at pH 7.51 the peak current was four times higher than that obtained with the bare electrode. The DNA-biosensor enabled pre-concentration of the drug onto the electrode surface and the in situ damage caused to the DNA on the electrode surface by the product of benznidazole reduction could be detected electrochemically. The results are in agreement with the hypothesis that the hydroxylamine derivative is the reactive species responsible for the cytotoxic action of benznidazole.

Biosensing Techniques↗

PubMed2002

Detection of the damage caused to DNA by niclosamide using an electrochemical DNA-biosensor.

Niclosamide is the only commercially available molluscicide recommended by the WHO for large-scale use in schistosomiasis control programs. The electrochemical reduction and oxidation mechanism of niclosamide was studied using cyclic, differential and square wave voltammetry, at a glassy carbon electrode. An indirect procedure for in situ quantification of niclosamide using batch injection analysis with electrochemical detection, possible to be used for in situ determinations in river streams and effluents, was developed. It enabled a detection limit of 8 x 10(-7) M. The investigation of the niclosamide-DNA interaction using an electrochemical DNA-biosensor showed for the first time clear evidence of interaction with DNA and suggested that niclosamide toxicity can be caused by this interaction, after reductive activation.

Animals↗