1,720,967 research outputs found
Preparation and characterization of screening methods for classification and quality control of olive oils
Full text linkIn questo lavoro di ricerca di Dottorato sono state sviluppate piattaforme sensoristiche, basate su elettrodi SPE modificati con nanomateriali, per permetterere una rapida, facile ed economica individuazione delle frodi legate alla produzione e al commercio dell'olio extravergine di oliva. Il risultato della ricerca è stata la creaziobne di due piattaforme in grado rispettivamente di catalogare oli extravergine di oliva a seconda della cultivar della pianta di origine e di quantificare il contenuto di antiossidanti polari in campioni incogniti di olii vegetali, permettendo di discriminare oli di oliva da oli di altri semi.In this PhD research work, sensor platforms have been developed, based on SPE electrodes modified with nanomaterials, to allow rapid, easy and economic identification of frauds linked to the production and trade of extra virgin olive oil. The result of the research was the creation of two platforms able respectively to catalog extra virgin olive oils according to the cultivar of the plant of origin and to quantify the content of polar antioxidants in unknown samples of vegetable oils, allowing to discriminate olive oils from oils of other seeds
Generation IV ionic liquids and nanomaterials to develop innovative electrochemical biosensing platforms
No full textDifferent types of modified electrodes have been prepared and tested to assembly and construct portable sensing devices, useful to analyze, in a simple, fast and economic way, many analytes.
Bare glassy carbon electrodes (GCE) of the screen-printed type (SPE), with silver electrode as reference, have been modified, via drop casting on the working electrode surface, with a mixture of generation IV room temperature ionic liquids (RTILs) and nanomaterials. The ionic liquids choline-amino acids, were synthetized in our laboratory following the methodology known in literature1. These RTILs differ from the previous generation ones because they are nontoxic and completely biodegradable2,3. Like those of the previous generations, the RTILs used in this work have interesting properties regarding low volatility, low flammability, high ionic conductivity, high chemical and electrochemical stability4. Furthermore, these compounds allow to significantly increase the work potential range (V), electroactive area (Aea) and electron transfer constant (k0), so that anode or cathode peaks can be detected even for extremely low concentration of analytes. The nanomaterials used in this work were Multi-Walled Carbon Nanotubes (MWCNT) and Titanium Dioxide nanoparticles (anatase form). These two nanomaterials have been used both alone and together in different proportions with the chosen RTIL [Ch] [Phe]. All the so developed electrodes have been studied by means of cyclic voltammetry measurements to calculate the electroactive area (Aea) of the working electrode, in order to find the best combination of nanomaterials/ionic liquid/water for the drop casting mixture. All the proposed combinations have also been studied for stability: cyclic voltammetry measurements have been carried out at various time intervals after the preparation to investigate variations of the Aea of the modified electrodes. The electrochemical platform so developed has been used, after functionalization with the proper enzyme, as a biosensor. In particular, it has been tested for measuring glucose in food matrices and antioxidants in olive oils using Glucose Oxidase5 and Lipase6 respectively.
References
1. S. De Santis, G. Masci, F. Casciotta, et al.; Phys. Chem., 2015, 17,20687.
2. J. Arning, S. Stolte, A. Böschen, F. Stock, W.R. Pitner et al.; Green Chem.,
2008, 10, 47-58.
3. A. Romero, A. Santos, J. Tojo, A. Rodriguez; J. Hazard Matter, 2008,151,268-273.
4. J.S. Xu, G.C. Zhao;Int. J. Electrochem. Sci., 2008, 4, 519-527.
5. M.L. Antonelli, F. Arduini et al.;Biosensors and Bioelectronics, 2009,24,1382-88.
6. Álvarez G.A., J.A. Rodríguez, J.C. Escamilla, C.A. Galán;J. Mex. Chem. Soc., 2015, 59, 19-23
Deep eutectic solvents (DES) as green extraction media for antioxidants electrochemical quantification in extra-virgin olive oils
No full textA new electroanalytical method has been developed for the determination of polar antioxidant compounds in
extra virgin olive oils. This method is based on the extraction of polar antioxidant compounds from extra-virgin
olive oils by means of a deep eutectic solvent and their determination by a modified screen-printed electrode
platform. The platform sensitivity was increased by modifying the working electrode with MWCNT and TiO2
nanoparticles as modifiers and Nafion as a binder. The platform showed very good sensitivity in detecting polar
antioxidant compounds in extra-virgin olive oils in a fairly wide range of concentrations. The measurements
were performed by using square wave voltammetry. The extraction was performed without using organic solvents,
making the method environmentally friendly. The proposed method has been compared with a common
spectrophotometric one, the results appeared in good agreement. The method is sufficiently easy and quick to be
used for screening analyses of polar antioxidant compounds in extra-virgin olive oils on the field
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Biologically friendly room temperature ionic liquids and nanomaterials for the development of innovative enzymatic biosensors
No full textMain purpose of the work is assembling, testing and optimizing new disposable amperometric biosensors to analyze substances in different application fields as agribusiness, clinical chemistry and environment protection.
Many kinds of modified electrodes have been prepared and tested to build portable devices to analyze quickly many analytes, in a simple and cost-effective manner.
Bare electrodes of the screen-printed type, with silver as reference, have been used for modification.
The glassy carbon electrodes with multi-walled carbon nanotubes or graphene or gold nanoparticles depositions were modified with generation IV ionic liquids. Choline as cation and amino acids, such as glycine, serine, phenylalanine and histidine, as anions have been employed for these ionic liquids.
The presence of nanostructured materials on the electrode brings an increased contact surface between analytes and receptor and, consequently, an amplification of the amperometric signal and a better sensibility. Moreover the use of new ionic liquids of generation IV, biologically friendly and water soluble, improves the electronic transfer, facilitating and strengthening the redox reaction nearby the electrode.
By immobilizing the proper enzymes onto the modified electrode surface, different compounds of analytical interest can be determined by means of sensitive, properly designed amperometric biosensors.
Analytes such as antioxidant components in extra-virgin olive oils, alcohols in beverages and glucose in food matrices have been tested, using a suitable enzyme: microbial lipase, alcohol dehydrogenase and glucose oxidase, respectively
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
The effect of ionic strength and phosphate ions on the construction of redox polyelectrolyte-enzyme self-assemblies
Full text linkLayer by layer assembly of polyelectrolytes with proteins is a convenient tool for the development of functional biomaterials. Most of the studies presented in the literature are based on the electrostatic interaction between components of opposite charges, limiting the assembly possibilities. However, this process can be tuned by modifying the environment where the main constituents are dissolved. In this work, the electron transfer behavior between an electroactive polyelectrolyte (polyallylamine derivatized with an osmium complex) and a redox enzyme (glucose oxidase) is studied by assembling them in the presence of phosphate ions at different ionic strengths. Our results show that the environment from which the assembly is constructed has a significant effect on the electrochemical response. Notably, the polyelectrolyte dissolved in the presence of phosphate at high ionic strength presents a globular structure which is preserved after adsorption with substantial effects on the buildup of the multilayer system, improving the electron transfer process through the film
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
