Biomedical subjects

Julio Raba

Publications and source records attributed to Julio Raba.

4 recordsLinked to original sources

PubMed2006

Sensitive determination of ciprofloxacin and norfloxacin in biological fluids using an enzymatic rotating biosensor.

The high sensitivity that can be attained using an enzymatic system and mediated by catechol has been verified by on-line interfacing of a rotating biosensor and continuous-flow/stopped-flow/continuous-flow processing. Horseradish peroxidase, HRP, [EC 1.11.1.7], immobilized on a rotating disk, in the presence of hydrogen peroxide catalyzed the oxidation of catechol, whose back electrochemical reduction was detected on glassy carbon electrode surface at -200mV. Thus, when ciprofloxacin (CF) or norfloxacin (NF) was added to the solution, these piperazine-containing compounds participate in Michael addition reactions with catechol to form the corresponding aminoquinone derivative, decreasing the peak current obtained in proportion with the increase of its concentration. CF was used as the model piperazine-containing compound for the study. The influence of indicator composition on the nature of the analytical response has been assessed through examining the electrochemical properties of three derivatives. Interference by electroactive species (ascorbate, urate, and tyrosine) and other physiological constituents (cysteine, glutathione) has also been assessed.

Biosensing Techniques↗

PubMed2005

Continuous-flow/stopped-flow system using an immunobiosensor for quantification of human serum IgG antibodies to Helicobacter pylori.

Conventional methods, such as gastric biopsy, enzyme-linked immunosorbent assay (ELISA), culture, require a long time for the determination of Helicobacter pylori infections. This study reports an amperometric immunoreactor for rapid and sensitive quantification of human serum immunoglobulin G (IgG) antibodies to H. pylori. Antibodies in the serum sample are allowed to react immunologically with the purified H. pylori antigens that are immobilized on a rotating disk. The bound antibodies are quantified by horseradish peroxidase (HRP) enzyme-labeled second antibodies specific to human IgG. HRP in the presence of hydrogen peroxide catalyzes the oxidation of hydroquinone to p-benzoquinone. The electrochemical reduction back to hydroquinone is detected on a glassy carbon electrode surface at -0.15 V. The electrochemical detection can be done within 1 min, and the analysis time does not exceed 30 min. The calculated detection limits for amperometric detection and the ELISA procedure are 0.6 and 1.9 U ml-1, respectively. The amperometric immunoreactors showed higher sensitivity and lower time consumed than did the standard spectrophotometric detection ELISA method. It can also be used for rapid analysis in conventional and field conditions in biological, physiological, and analytical practices.

Antibodies, Bacterial↗

PubMed2004

Continuous-flow/stopped-flow system for enzyme immunoassay using a rotating bioreactor: determination of Chagas disease.

The high sensitivity that can be attained using an immunoassays coupled to a rotating bioreactor with electrochemical detection mediated by [Os(bpy)2Cl(pyCOOH)]Cl, has been verified for the detection of Trypanozoma cruzi (T. cruzi), This protozoan parasite causes Chagas disease, affecting more than 18 million people in central and south America. Antibodies in the serum sample are allowed to react immunologically with whole homogenates of the parasite as antigen that are immobilized on a rotating disk. The bound antibodies are quantified by a horseradish peroxidase (HRP) enzyme labeled second antibodies specific to human IgG in presence of hydrogen peroxide using an osmium complex [Os(bpy)2Cl(pyCOOH)]Cl as enzymatic mediators. The amperometric measurement performed at 0.00 V versus Ag/AgCl can be done within 2 min and the analysis time does not exceed 23 min. The calculated detection limits was 0.01 mIU ml(-1). Reproducibility assays were made using repetitive serum of 0.182 mIU ml(-1) T. cruzi specific antibody (measured as the activity of the correspondent anti-serum's enzyme conjugated); the percentage standard error was less than 5%. The amperometric immunoreactors showed significantly higher sensitivity and lower time consumed than the standard spectrophotometric detection ELISA method.

Animals↗

PubMedDate not supplied

Immobilized artificial membrane chromatography: quantitative structure-retention relationships of structurally diverse drugs.

The chromatographic capacity factors (log k') for 32 structurally diverse drugs were determined by high performance liquid chromatography (HPLC) on a stationary phase composed of phospholipids, the so-called immobilized artificial membrane (IAM). In addition, quantitative structure-retention relationships (QSRR) were developed in order to explain the dependence of retention on the chemical structure of the neutral, acidic, and basic drugs considered in this study. The obtained retention data were modeled by means of multiple regression analysis (MLR) and partial least squares (PLS) techniques. The structures of the compounds under study were characterized by means of calculated physicochemical properties and several nonempirical descriptors. For the carboxylic compounds included in the analysis, the obtained results suggest that the IAM-retention is governed by hydrophobicity factors followed by electronic effects due to polarizability in second place. Further, from the analysis of the results obtained of two developed quantitative structure-permeability studies for 20 miscellaneous carboxylic compounds, it may be concluded that the balance between polarizability and hydrophobic effects is not the same toward IAM phases and biological membranes. These results suggest that the IAM phases could not be a suitable model in assessing the acid-membrane interactions. However, it is not possible to generalize this observation, and further work in this area needs to be done to obtain a full understanding of the partitioning of carboxylic compounds in biological membranes. For the non-carboxylic compounds included in the analysis, this work shows that the hydrophobic factors are of prime importance for the IAM-retention of these compounds, while the specific polar interactions, such as electron pair donor-acceptor interactions and electrostatic interactions, are also involved, but they are not dominant.

Algorithms↗