Nylon Nanofibrous Biosensors for Glucose Determination

Nanofibrous membranes have been produced by electrospinning to develop first generation glucose biosensors. The direct immobilization of glucose oxidase onto the polyamide nanofibrous surfaces by drop coating revealed a simple and efficient method for the development of sensitive, stable, and reproducible electrochemical biosensors. The biosensor showed a linear response over the range 1–9×10^?3 glucose (R²=0.9997) with a sensitivity of 1.11 μA/mM and a limit of detection of 2.5×10^?6 M (S/N=3). The uncertainty of repeatability was 2% (RSD%, n=30). After one month of storage, the signal decreased of 35%. The recovery of glucose, evaluated in real samples of honey, was 98% (RSD%=1%, n=3).     

Biocompatibility Studies of Functionalized Regioregular Poly(3‐hexylthiophene) Layers for Sensing Applications

There is a significant medical and biological need for cheap disposable analytical sensing devices, which can be used in clinical settings or medical research. Organic electronics based on polymeric materials, being suitable for large‐area, low‐cost, flexible, and maybe even disposable electronics, could satisfy this need in a very elegant way. Unfortunately, the ensurance of biocompatibility and biofunctionalization of conducting and semiconducting polymers is still often lacking. In the present study, we concentrate on one of the most promising polymeric materials, regioregular poly(3‐hexylthiophene) (P3HT), being both a reasonably conducting and optically active polymer. To overcome biocompatibility problems, protein‐based coatings and oxygen‐plasma treatments are performed to enable growth of adherent living cells on those modified surfaces. For our studies, the polymer material is spun or casted onto glass substrates under an inert nitrogen atmosphere. The toxic solvents are removed by thermal treatment with subsequent application of the coating or functionalizing materials. Cell‐growth studies and adhesion experiments on the modified P3HT thin‐film layers are carried out with mouse fibroblasts. This work demonstrates the biocompatibility and biofunctionalization of an active semiconducting organic polymer, hence opening new possibilities in the realization of biomedical test systems based on organic biosensors in life sciences.

     

Residue analysis of glucocorticoids in bovine milk by liquid chromatography–tandem mass spectrometry

A sensitive liquid chromatography–tandem mass spectrometry (LC-MS/MS) method for the simultaneous determination of 13 steroidal anti-inflammatory drugs in bovine milk is presented. Due to their weakly acid nature, analytes were separated by ion suppression reversed phase chromatography and detected in positive-ion mode by a high flow electrospray source. Dexamethasone-d4 was used as internal standard. The sample preparation was simple and reliable; it included acidic deproteinization of milk followed by sample enrichment and clean-up, utilizing a C18 solid phase extraction cartridge. Recoveries exceeded 70% with an intra-day precision not larger than 12%. The efficiency of the sample clean-up and internal standardization rendered negligible the matrix effect, estimated by comparing standard and matrix-matched calibration curves. A small-scale reconnaissance was carried out on several raw and whole fresh milk samples. A large number of analyzed samples showed a chromatographic peak, in the retention time window of cortisol, at levels included between its decision limit (CCα) and detection capability (CCβ). As a result of a heat-induced transformation, an isomeric product of triamcinolone was observed during the extract evaporation. Since this rearrangement might occur during the milk pasteurization process, LC-MS/MS and ¹H-NMR investigations were performed out to conclusively differentiate the two isomers. One- and two-dimensional proton NMR spectra were able to identify the transformation product as 9a-fluoro-11b,16a-trihydroxy-17b-hydroxymethyl-D-homoandrosta-1,4-diene-3,17a-dione.     

On silsesquioxanes’ accuracy as molecular models for silica-grafted complexes in heterogeneous catalysis

The achievement of a structure–activity relationship for heterogeneous catalysts is a desirable step for improving existing catalysts or for predicting new catalytic reactions. This article reviews the use of silsesquioxanes (POSS) organometallic complexes as molecular models for silica-grafted catalytic centers. It will show that POSS complexes, within some limits, have substantially contributed to gaining better molecular-level understanding of surface reactions and catalysts activity.     

Injection profiles in liquid chromatography. I. A fundamental investigation

This is a fundamental experimental and theoretical investigation on how the injection profile depends on important experimental parameters. The experiments revealed that the injection profile becomes more eroded with increased (i) flow rate, (ii) viscosity of the eluent, (iii) size of the solute, (iv) injection volume and (v) inner diameter of the injection loop capillary. These observations cannot be explained by a 1D-convection-diffusion equation, since it does not account for the effect of the parabolic flow and the radial diffusion on the elution profile. Therefore, the 1D model was expanded into a 2D-convection-diffusion equation with cylindrical coordinates, a model that showed a good agreement with the experimental injection profiles dependence on the experimental parameters. For a deeper understanding of the appearance of the injection profile the 2D model is excellent, but to account for injection profiles of various injection volumes and flow rates in preparative and process-chromatography using computer-optimizations, a more pragmatic approach must be developed. The result will give guidelines about how to reduce the extra-column variance caused by the injection profile. This is important both for preparative and analytical chromatography; in particular for modern analytical systems using short and narrow columns.     

Copper(II) complexes of salen analogues with two differently substituted (push-pull) salicylaldehyde moieties. A study on the modulation of electronic asymmetry and nonlinear optical properties

This paper presents some copper(II) complexes of salen analogues in which the two salicylaldehyde moieties carry different (electron donor, D, and acceptor, A) substituents in position 5, producing a push-pull charge asymmetry. The X-ray structures of some compounds show the presence of pairs of stacked molecules with head-to-tail intermolecular associations. The geometries of all complexes have been optimized through density functional theory (DFT) studies, which have shown that a major influence on the coordination bond lengths is given by the presence of the electron acceptor NO2 group. Such an influence operates mainly on the Cu-phenolato bonds: elongation of the Cu-O distance of the 5-nitrosalicylaldehyde moiety, with a concomitant decrease of the other Cu-O distance; the Cu-N bonds are less affected. The D groups have only a minor influence. The nonlinear optical responses, microgBetavec, of some molecules have been determined by EFISH measurements, and the Beta-vec values have been obtained using the DFT-calculated microg values because solubility problems hampered the experimental measurements of microg of some derivatives; the former, however, have been found to be in agreement with the experimental values that could be obtained. Deconvolution of the absorption bands in the near-UV region has allowed recognition of the charge-transfer (CT) transition, assigned to a ligand-to-metal CT (LMCT) by time-dependent DFT computations; we have then used the solvatochromism of this transition to obtain Beta0 and BetaCT values using the two-state model. These values were compared with those obtained by computational studies, which have also allowed evaluation of the influence of the substituents on the directions of microg and Betatot.     

Synergy between manipulative and digital artefacts: a teaching experiment on axial symmetry at primary school

This paper presents a study aimed at investigating the didactic potentiality of the combined use of two different kinds of artefacts for the purpose of constructing and conceptualizing mathematical meanings related to the notion of axial symmetry. In our view, the process of meanings construction can be fostered by the use of adequate artefacts, but it requires a teaching/learning model, which explicitly takes care of the evolution of meanings, from those personal, emerging through the activities, to the mathematical ones, aims of the teaching intervention. The main hypothesis of this study is that a potential synergy may occur between the use of different artefacts, synergy that can foster the integration of different and complementary meanings providing a rich support to the development of the expected mathematical meaning. The Theory of Semiotic Mediation offers the theoretical framework suitable to design the teaching sequence and to analyze the collected data. Specifically, the construct of semiotic potential provides the tool for describing the potentialities of the two artefacts, while that of didactic cycle offers a model for the organization of the different activities. The paper reports on a teaching sequence and its implementation in a teaching experiment, involving pupils at fourth grade level. We describe them, within the chosen theoretical framework, and provide the analysis of key episodes of the teaching sequence. We show evidence supporting our main hypothesis about the combined use of an artefact that can be manipulated (paper and pin), and a digital artefact (Dynamic Geometry Environment) in the development of the notion of axial symmetry and its properties: the combined, intentional and controlled use of the two artefacts may develop a synergy, so that each activity enhances the potential of the other.     

The divisible sandpile with heavy-tailed variables

This work deals with the divisible sandpile model when an initial configuration sampled from a heavy-tailed distribution. Extending results of Levine et al. (2015) and Cipriani et al. (2016) we determine sufficient conditions for stabilization and non-stabilization on infinite graphs. We determine furthermore that the scaling limit of the odometer on the torus is an $\alpha$-stable random distribution.     

A semiotic interpretation of the derivative concept in a textbook

Differential and integral calculus textbooks are widely used as the main resource for teaching. They appear in a variety of forms and adopt various approaches to present the content. In this paper, we turn our attention to one chapter of a calculus textbook and our focus is on the introduction of the derivative concept. With the purpose of examining the presentation of the derivative concept in the textbook, we give a view of Peirce’s semiotics, in particular of his classification of sign-vehicles. The analysis allows us to point out that the sign-vehicle in relation to the derivative concept may be iconic, indexical, or symbolic. These do not constitute mutually exclusive kinds of signs, but they are interrelated in such a way that we can identify iconicity in indexicality and indexicality in symbolicity. We conclude that the textbook has the potential to enable students to conceptualize the derivative. However, in some aspects, the book may constrain students’ conceptualization and it could be improved to meet the students’ needs to make meaning of the derivative concept.