Improvement of laccase biosensor characteristics using sulfur-doped TiO2 nanoparticles.

The search for new nanoscale materials with predictable properties to target the timely and fast detection of toxic components in wastewater is one of the most promising directions of modern biosensorics. We have shown that TiO2 nanoparticles modified with sulfur significantly improve the main operational parameters of laccase-based electrodes when compared with controls. The nanoparticle samples were labeled as TiO2S(0.75), TiO2S(1.5), and TiO2S(3.0), in which the numbers in parentheses refer to the quantity of H2SO4 (mL) used in the synthesis. The nanoparticles and enzyme were immobilized by means of Nafion film formed on a carbon rod electrode. It was shown that the modification of Nafion film by TiO2 or TiO2S(1.5) nanoparticles does not affect the size of the nanocavities and defect structure of the main polymer matrix as revealed by positron annihilation spectroscopy. It testifies that the structural-morphological difference between the film samples is rather small, and the improving of the sensor operational parameters for TiO2S(1.5)-based laccase electrodes is connected only with the impact of sulfur doping, but not the difference in membrane properties. The developed bioelectrodes were tested for phenol analysis in real communal wastewater samples spiked with these analytes, demonstrating the high accuracy of the assay.

Electron and hole capture processes in Cu-doped glass exhibiting radiophotoluminescence.

Radiophotoluminescence (RPL) is a radiation effect, and materials exhibiting RPL can be used in dosimeters. In this study, we observed remarkable RPL in Cu-doped aluminoborosilicate and silica glasses upon their exposure to60Coγ-rays. The RPL intensity increased proportionally with the irradiation dose up to several hundreds of grays and then saturated beyond a certain dose level. An equation was derived theoretically to express the relationship between the RPL intensity and irradiation dose based on the RPL mechanism, in which copper ions, Cu2+and Cu+, capture electrons and holes, generated by the irradiation, respectively, resulting in a change in the valence. The equation fitted well with the experimental results, providing two parameters for the equation. These parameters are associated with the saturation dose level and sensitivity, which are important for the application of materials to dosimeters. These parameters were discussed based on electron and hole capture processes in the RPL mechanism.

Structural defects and positronium formation in 40 keV B(+)-implanted polymethylmethacrylate.

Slow positron beam and optical absorption measurements are carried out to study structural defects and positronium formation in 40 keV B(+)-implanted polymethylmethacrylate (B:PMMA) with ion doses from 6.25 × 10(14) to 5.0 × 10(16) ions/cm(2). Detailed depth-selective information on defects in implanted samples was obtained by measuring of Doppler broadening of positron annihilation γ rays as a function of incident positron energy and these experimental results were compared with SRIM (stopping and range of ions in matter) simulation results. Two general processes, appearance of free radicals at lower ion doses (<10(16) ions/cm(2)) and carbonization at higher ion doses (>10(16) ions/cm(2)), are considered from the Doppler S-E and W-E dependences in the framework of the concept of defects formation during radiation damage of polymer structure. Probabilities of ortho-positronium (o-Ps) formation are analyzed using S-W plot and slow positron annihilation lifetime measurements. Dose dependence of o-Ps lifetime τ3 and intensity I3 at the incident positron energy of 2.15 keV correlates well with the dose dependence of S-parameter and seems to account for the existence of the expected two processes, i.e., scission of polymer chains and appearance of free radicals preceding the aggregation of the clusters resulting in the formation of network of conjugated bonds at lower ion doses and carbonization at higher ion doses. The increase of optical absorption observed with increasing ion implantation dose also suggests a formation of carbonaceous phase in the ion-irradiated PMMA.