Fabrizio De Cesare

Use of sonication for measuring acid phosphatase activity in soil

Extracellular enzymes in soil often occur in immobilised forms, a state that may alter their interactions with substrates in comparison with enzymes in the solution phase. Sonication was evaluated for its usefulness in studying immobilised acid phosphatase by dispersing soil aggregates. Factors affecting soil dispersion during ultrasound application were soil extraction ratio, total applied energy and power output ml−1 of sonicated soil slurry. For the clay loam soil used, optimal values for these variables were, respectively, 1:6 (w/v) and, at least, 1800 J ml−1 and 15 W ml−1. At the optimal sonication conditions for soil dispersion a substantial increase in phosphatase activity (up to 156% greater than the non-sonicated control) was induced by sonication. This increase in activity with sonication, which coincided with a release of soil chromophores, might be related to the exposure or release from aggregates of the extracellular enzyme fraction immobilised on humic colloids. Analysis of multiple regression between the phosphatase activity (dependent variable) and chromophore solubilisation and ATP release (independent variables) suggested the increased activity was from complexed enzymes that were released and not due to cell lysis. Soil treatment with sonication appeared to have liberated a large dormant portion of acid phosphatase activity. Coefficients of variation of the activity decreased greatly (from 20% in control soil to 4% as an average after sonication).

Electrospinning-Based Nanobiosensors

Biological interactions in biosensors occur through different mechanisms, on the basis of the type of biological receptor elements employed therein that confer the biological specificity to the biosensors themselves (biocatalytic, biocomplexing or bioaffinity biosensors). The use of different transduction systems (amperometric, potentiometric, field-effect transistors, piezometric and conductometric) defines the mode of detection. The interest and relevance of nanomaterials in the fabrication of nanobiosensors lie in their extraordinary properties that make them ideally suited and very promising for sensing applications. The resulting nanobiosensors are capable of sensing analytes in traces with fast, precise and accurate biological identification through miniaturised and easy to use systems. These advanced sensors are also characterised by lower detection limits, higher sensitivity values and high stability, and can further offer multi-detection possibilities. These exceptional features make nanobiosensors as the favourite tools in quality control, food safety, and traceability for their capacity of revealing and warning people against the presence of pathogens, toxins and pollutants, as well as bioterrorism agents. Despite the outstanding properties of these nanobiosensors, however, the efficiency of the biorecognition agent and the number of biorecognition sites available for interacting with target analytes can limit the sensitivity of this kind of sensors. The number of available biorecognition sites is directly related to the surface area of the sensor. Electrospinning technology can significantly increase the sensitivity of biosensors by replacing the typical planar interactive surface of conventional biosensors with a mat of electrospun nonwoven nanofibres, thereby taking advantage of the ultrahigh surface area offered by electrospun nanofibres. Moreover, adjusting the electrospinning process to produce hollow nanofibres can further increase the surface area of electrospun nanofibres. The immobilisation of bioreceptors into or onto electrospun nanofibres remarkably increases the number of recognition sites for biosensing, i.e. available for capturing the analytes through specific binding mechanisms. Furthermore, electrospinning technology can provide the deposition onto transducers of 3D frameworks of electrospun nanofibrous mat, with a tunable interconnected porosity, predictable pore geometries and sizes, and large global pore volumes. Such feature can supply further properties to the resulting nanobiosensor suitable for the detection of analytes in particular environments, where an efficient transport of the analytes through the membrane toward the electrode surface is required. Due to such an extreme versatility, electrospinning is expected to have several strategic advantages over other nanotechnologies as concerns nanobiosensing.

Passive Sampling of Gaseous Elemental Mercury Based on a Composite TiO2NP/AuNP Layer

Passive sampling systems (PASs) are a low cost strategy to quantify Hg levels in air over both different environmental locations and time periods of few hours to weeks/months. For this reason, novel nanostructured materials have been designed and developed. They consist of an adsorbent layer made of titania nanoparticles (TiO2NPs, ≤25 nm diameter) finely decorated with gold nanoparticles. The TiO2NPs functionalization occurred for the photocatalytic properties of titania-anatase when UV-irradiated in an aqueous solution containing HAuCl4. The resulting nanostructured suspension was deposited by drop-casting on a thin quartz slices, dried and then incorporated into a common axial sampler to be investigated as a potential PAS device. The morphological characteristics of the sample were studied by High-Resolution Transmission Electron Microscopy, Atomic Force Microscopy, and Optical Microscopy. UV-Vis spectra showed a blue shift of the membrane when exposed to Hg0 vapors. The adsorbed mercury was thermally desorbed for a few minutes, and then quantified by a mercury vapor analyzer. Such a sampling system reported an efficiency of adsorption that was equal to ≈95%. Temperature and relative humidity only mildly affected the membrane performances. These structures seem to be promising candidates for mercury samplers, due to both the strong affinity of gold with Hg, and the wide adsorbing surface.

Thermally Driven Selective Nanocomposite PS-PHB/MGC Nanofibrous Conductive Sensor for Air Pollutant Detection

The potentials to use the working temperature to tune both the sensitivity and the selectivity of a chemical sensor based on a nanostructured and nanocomposite polymer layer have been investigated and described. Thus, in a single step, a peculiar chemical layer was grown up onto IDE (Interdigitated Electrode) microtransducers by electrospinning deposition and using a single-needle strategy. The 3-component nanofibers, obtained from a mixture of polystyrene and polyhydroxibutyrate (insulating thermoplastics) and a known concentration of mesoporous graphitized carbon nanopowder, appeared highly rough on the surface and decorated with jagged islands but homogeneous in shape and diameter, with the nanofillers aggregated into clusters more or less densely packed through the fibers. The resulting sensor was conductive at room temperature and could work between 40 and 80°C without any apparent degradation. As the fibrous sensing layer was heated, the current increased and the sensitivity to some classes of VOCs such as an oxidizing gas drastically changed depending on the working temperature. More in detail, the sensor resulted highly sensitive and selective to acetic acid at 40°C but the sensitivity fell down, decreasing by 96%, when the sensor operated at 80°C. On the other hand, although an increase in temperature caused a general decrease in sensitivity to the tested VOCs (with a maximum of 14, 81, and 78% for amine, acetone and toluene, respectively) and water vapors (with a maximum of 55%), higher temperature affected only slightly the amine permeation, thus modifying the partial selectivity of the sensor to these chemicals. Conversely, when the operating temperature increased, the sensitivity to the detected gas, NO2, increased too, reporting a ~2 ppb limit of detection (LOD), thus confirming that the temperature was able to drive the selectivity of nanocomposite polymeric sensors.