RESUMO
In this investigation, a hydrogen peroxide (H2O2) electrochemical sensor was evaluated. Prussian blue (PB) was electrodeposited at a glassy carbon (GC) electrode modified with titanium dioxide- and zirconia-doped functionalized carbon nanotubes (TiO2.ZrO2-fCNTs), obtaining the PB/TiO2.ZrO2-fCNTs/GC-modified electrode. The morphology and structure of the nanostructured material TiO2.ZrO2-fCNTs was characterized by transmission electron microscopy, the specific surface area was determined via Brunauer-Emmett-Teller, X-ray diffraction, thermogravimetric analysis, and Fourier transform infrared spectroscopy. The electrochemical properties were studied by cyclic voltammetry and chronoamperometry. Titania-zirconia nanoparticles (5.0 ± 2.0 nm) with an amorphous structure were directly synthesized on the fCNT walls, aged during periods of 20 days, obtaining a well-dispersed distribution with a high surface area. The results indicated that the TiO2.ZrO2-fCNT-nanostructured material exhibits good electrochemical properties and could be tunable by enhancing the modification conditions and method of synthesis. Covering of the nanotubes with TiO2-ZrO2 nanoparticles is one of the main factors that affected immobilization and sensitivity of the electrochemical biosensor. The electrode modified with TiO2-ZrO2 nanoparticles with the 20-day aging time was superior regarding its reversibility, electric communication, and high sensitivity and improves the immobilization of the PB at the electrode. The fabricated sensor was used in the detection of H2O2 in whey milk samples, presenting a linear relationship from 100 to 1,000 µmol L-1 between H2O2 concentration and the peak current, with a quantification limit (LQ) of 59.78 µmol L-1 and a detection limit (LD) of 17.93 µmol L-1.
RESUMO
A hydrogen peroxide (H2O2) sensor and biosensor based on modified multi-walled carbon nanotubes (CNTs) with titanium dioxide (TiO2) nanostructures was designed and evaluated. The construction of the sensor was performed using a glassy carbon (GC) modified electrode with a TiO2-CNT film and Prussian blue (PB) as an electrocalatyzer. The same sensor was also employed as the basis for H2O2 biosensor construction through further modification with horseradish peroxidase (HRP) immobilized at the TiO2-fCNT film. Functionalized CNTs (fCNTs) and modified TiO2-fCNTs were characterized by Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), and X-Ray DifFraction (XRD), confirming the presence of anatase over the fCNTs. Depending on the surface charge, a solvent which optimizes the CNT dispersion was selected: dimethyl formamide (DMF) for fCNTs and sodium dodecylsulfate (SDS) for TiO2-fCNTs. Calculated values for the electron transfer rate constant (ks) were 0.027 s-1 at the PB-fCNT/GC modified electrode and 4.7 × 10-4 s-1 at the PB-TiO2/fCNT/GC electrode, suggesting that, at the PB-TiO2/fCNT/GC modified electrode, the electronic transfer was improved. According to these results, the PB-fCNT/GC electrode exhibited better Detection Limit (LD) and Quantification Limit (LQ) than the PB-TiO2/fCNT/GC electrode for H2O2. However, the PB film was very unstable at the potentials used. Therefore, the PB-TiO2/fCNT/GC modified electrode was considered the best for H2O2 detection in terms of operability. Cyclic Voltammetry (CV) behaviors of the HRP-TiO2/fCNT/GC modified electrodes before and after the chronoamperometric test for H2O2, suggest the high stability of the enzymatic electrode. In comparison with other HRP/fCNT-based electrochemical biosensors previously described in the literature, the HRP-fCNTs/GC modified electrode did not show an electroanalytical response toward H2O2.
RESUMO
En el estado de Zacatecas se dispone de pocos datos epidemiológicos y epizootiológicos del ántrax y se desconoce la magnitud real de la enfermedad. Entre 1981 y 1983 se presentaron tres pequeños brotes epidémicos que afectaron a 34 personas en dos municipios. Todos los casos de ántrax en humanos se relacionaron con defunciones recientes de bovinos infectados que se habían destazado para ingerir su carne. La enfermedad fue más frecuente entre los hombres (55,8%) que entre las mujeres (44,1%) y el grupo de edad más afectado fue el de 35 a 54 años. La sintomatología fue semejante en todos los casos y se caracterizó por lesiones con pústula negra. La mayoría de los enfermos habían recibido tratamiento médico o se medicaban con remedios caseros cuando se detectaron. Algunos pacientes manifestaron dolor, malestar y fiebre, lo que puede atribuirse a complicaciones causadas por un tratamiento inadecuado ya que en algunos casos se prescribieron antiinflamatorios, pomadas exfoliantes e, incluso, compresas calientes. Aproximadamente la mitad de los enfermos se habían quemado las heridas por diversos procedimientos que son de uso común en la región como medida terapéutica. Los Servicios Coordinados de Salud Pública en el estado de Zacatecas proporcionaron tratamiento médico con penicilina procaína a razón de 800 000 U cada 12 horas hasta que desaparecieron las lesiones. No hubo ningún caso mortal en humanos. Por su parte, la Dirección de Ganadería de la Secretaría de Agricultura y Recursos Hidráulicos emprendió la vacunación de los animales susceptibles de contraer la enfermedad y orientó a las comunidades sobre la incineración y el enterramiento de los animales muertos. Sin embargo, las disposiciones sobre el control de los animales resultan poco eficaces debido a que las coberturas de vacunación son bajas y no se aplican medidas adecuadas con respecto a los pastizales contaminados donde pasta el ganado