Ailton José Terezo

Biosensor based on atemoya peroxidase immobilised on modified nanoclay for glyphosate biomonitoring.

A biosensor based on atemoya peroxidase immobilised on modified nanoclay was developed for the determination of glyphosate by the enzyme inhibition method. The inhibitor effect of the biocide results in a decrease in the current response of the hydroquinone that was used as a phenolic substrate to obtain the base signal. The biosensor was constructed using graphite powder, multiwalled carbon nanotubes, peroxidase immobilised on nanoclay and mineral oil. Square-wave voltammetry was utilised for the optimisation and application of the biosensor, and several parameters were investigated to determine the optimum experimental conditions. The best performance was obtained using a 0.1 mol L(-1) phosphate buffer solution (pH 7.0), 1.9×10(-4) mol L(-1) hydrogen peroxide, a frequency of 30 Hz, a pulse amplitude of 50 mV and a scan increment of 4 mV. The glyphosate concentration response was linear between 0.10 and 4.55 mg L(-1) with a detection limit of 30 μg L(-1). The average recovery of glyphosate from spiked water samples ranged from 94.9 to 108.9%. The biosensor remained stable for a period of eight weeks.

Electrochemical biosensor for carbofuran pesticide based on esterases from Eupenicillium shearii FREI-39 endophytic fungus

In this work, a biosensor was constructed by physical adsorption of the isolated endophytic fungus Eupenicillium shearii FREI-39 esterase on halloysite, using graphite powder, multi-walled carbon nanotubes and mineral oil for the determination of carbofuran pesticide by inhibition of the esterase using square-wave voltammetry (SWV). Specific esterase activities were determined each 2 days over a period of 15 days of growth in four different inoculation media. The highest specific activity was found on 6th day, with 33.08 U on PDA broth. The best performance of the proposed biosensor was obtained using 0.5 U esterase activity. The carbofuran concentration response was linear in the range from 5.0 to 100.0 µg L(-1) (r=0.9986) with detection and quantification limits of 1.69 µg L(-1) and 5.13 µg L(-1), respectively. A recovery study of carbofuran in spiked water samples showed values ranging from 103.8±6.7% to 106.7±9.7%. The biosensor showed good repeatability and reproducibility and remained stable for a period of 20 weeks. The determination of carbofuran in spiked water samples using the proposed biosensor was satisfactory when compared to the chromatographic reference method. The results showed no significant difference at the 95% confidence level with t-test statistics. The application of enzymes from endophytic fungi in constructing biosensors broadens the biotechnological importance of these microorganisms.

Ag Nanoparticles-Based Zinc Hydroxide-Layered Hybrids as Novel and Efficient Catalysts for Reduction of 4-Nitrophenol to 4-Aminophenol

Silver nanoparticles and zinc hydroxide-layered hybrid materials (AgNPs/ZHL) have been successfully developed as efficient catalysts for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) with sodium borohydride. A facile and rapid visible-light assisted green route was used for the deposition of silver nanoparticles (AgNPs) on the external surface of ZHL material. The resulting AgNPs/ZHL hybrids contained AgNPs with spherical morphology and uniform size distribution. Moreover, the AgNPs/ZHL compounds exhibited excellent catalytic performance (the reduction reaction was finished within 4 min) and reusability (three cycles) toward the reduction of 4-NP to 4-AP in presence of sodium borohydride. The reduction reaction obeyed the pseudo-first-order kinetics. The rate constants increased with the increase of amount of the AgNPs deposited into the hybrid materials. These results suggest that the as-prepared catalysts (AgNPs/ZHL) have great potential for heterogeneous catalytic applications.

An experimental and theoretical study on the electronic and structural properties of CdSe@TiO2 nanotube arrays

In this work, the effects of the structural (crystallite size, stress) and electronic parameters (band gap, lifetime) on the photoelectrocatalysis and electron transport over CdSe electrodeposited inside TiO2-nanotubes (CdSe@TiO2NT) were investigated. Density functional theory (DFT) calculations of TiO2 were used to elucidate the electronic band structure and to correlate with experimental values. CdSe was grown by pulsed electrodeposition into previous and late thermal-treated TiO2NT (Sample-PTT and Sample-LTT, respectively) without blocking the nanotubes entrance. The Rietveld refinement method was used to obtain information from crystallographic data of each photoelectrode. The lattice strains calculated from the Rietveld analysis for Sample-PTT and Sample-LTT were 0.472 and 0.540, and the average volume of the TiO2-anatase unit cell increased from 133.235(0) Å3 to 136.950(6) Å3, respectively. Sample-PTT exhibited higher experimental electron lifetime, larger than 1.0 order of magnitude compared to Sample-LTT photoanodes. The band structures and DOS obtained by computational modelling showed theoretical band gap values of 2.54 eV and 2.75 eV, which were close to the experimental values. All studies evidenced a strong dependence of the electronic properties of the CdSe@TiO2 samples on their morphology, and, consequently, on their photoelectrochemical activity in water splitting.