1,721,010 research outputs found
ALP-Based Biosensors Employing Electrodes Modified with Carbon Nanomaterials for Pesticides Detection
Full text linkDue to the growing presence of pesticides in the environment and in food, the concern of their impact on human health is increasing. Therefore, the development of fast and reliable detection methods is needed. Enzymatic inhibition-based biosensors represent a good alternative for replacing the more complicated and time-consuming traditional methods (chromatography, spectrophotometry, etc.). This paper describes the development of an electrochemical biosensor exploiting alkaline phosphatase as the biological recognition element and a chemically modified glassy carbon electrode as the transducer. The biosensor was prepared modifying the GCE surface by a mixture of Multi-Walled-Carbon-Nanotubes (MWCNTs) and Electrochemically-Reduced-Graphene-Oxide (ERGO) followed by the immobilization of the enzyme by cross-linking with bovine serum albumin and glutaraldehyde. The inhibition of the biosensor response caused by pesticides was established using 2-phospho-L-ascorbic acid as the enzymatic substrate, whose dephosphorylation reaction produces ascorbic acid (AA). The MWCNTs/ERGO mixture shows a synergic effect in terms of increased sensitivity and decreased overpotential for AA oxidation. The response of the biosensor to the herbicide 2,4-dichloro-phenoxy-acetic-acid was evaluated and resulted in the concentration range 0.04-24 nM, with a limit of the detection of 16 pM. The determination of other pesticides was also achieved. The re-usability of the electrode was demonstrated by performing a washing procedure
Transient-doped organic electrochemical transistors working in current-enhancing mode as sensing devices for low concentration of oxygen dissolved in solution
Full text linkDissolved oxygen in cell culture media represents an interesting parameter worth monitoring, especially at very low concentrations. Indeed, cells grow faster and live longer in hypoxic conditions, and recent studies relate stronger tumor malignancy, recurrence, and progression with reduced oxygen levels. Standard techniques for dissolved oxygen evaluation rely either on optical investigations or on electrochemical methods. The former requires complex protocols and expensive instrumentations, while for the latter, the presence of a silver/silver chloride electrode hinders the device miniaturization and induces cytotoxic effects. In this work, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (Pedot:Pss)-based Organic Electrochemical Transistors (OECTs) are presented as dissolved oxygen sensors. The catalytic activity of the Pedot chains is exploited for the transduction since oxygen reduction reactions, occurring at the polymer/electrolyte interface, induce Pedot:Pss to switch from the less conductive neutral state (off) to the more conductive oxidized one (on). This transient-doping effect enhances OECT current output, which presents a high signal to noise ratio (i.e., >102-103). The transistor architecture allows for high output/input signal power amplification (i.e., >15 dB-22 dB) and excellent sensitivities [328 ± 11 mV/dec and -0.38 ± 0.02 mA/dec for transfer and Ids(t), respectively], together with a low detection limit (0.9 μM, which represents the 0.07% of oxygen partial pressure). Finally, the here reported OECT sensors are demonstrated to work also in a real-life complex biological environment. This work paves the way for reliable, real-time oxygen monitoring in in vitro cell cultures for various relevant applications, such as investigating the influence of hypoxia conditions on cell lines or tumors
Synthesis and characterization of layered double hydroxides as materials for electrocatalytic applications
Full text linkLayered double hydroxides (LDHs) are anionic clays which have found applications in a wide range of fields, including electrochemistry. In such a case, to display good performances they should possess electrical conductivity which can be ensured by the presence of metals able to give reversible redox reactions in a proper potential window. The metal centers can act as redox mediators to catalyze reactions for which the required overpotential is too high, and this is a key aspect for the development of processes and devices where the control of charge transfer reactions plays an important role. In order to act as redox mediator, a material can be present in solution or supported on a conductive support. The most commonly used methods to synthesize LDHs, referring both to bulk synthesis and in situ growth methods, which allow for the direct modification of conductive supports, are here summarized. In addition, the most widely used techniques to characterize the LDHs structure and morphology are also reported, since their electrochemical performance is strictly related to these features. Finally, some electrocatalytic applications of LDHs, when synthesized as nanomaterials, are discussed considering those related to sensing, oxygen evolution reaction, and other energy issues
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
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
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
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