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Electrochemical characterization of self assembled monolayers on flexible electrodes
No full textSelf assembled assembled monolayers of amine- and carboxylic acid terminated thiols have been chemisorbed on gold electrodes deposited on flexible polyethylene terephthalate substrates. These devices, being flexible, low cost, and highly resistant could find application in several fields such as the design of implantable biomedical devices and disposable light-weight sensors.
Four different molecules have been investigated, namely cysteamine, 12-mercaptododecanoic acid, aminothiophenol, and 3-mercaptopropionic acid, each bearing either an amino or a carboxylic terminal group and different chain lengths. These molecules have been chosen since the SAM they can form could find application as such or constitute the basis for a further modification step. The modified surfaces have been characterized by electrochemical techniques and the surface pK(a) values of the terminal groups have been estimated by impedance titration
Organic Thin-film Transistors for pH Detection
No full textA novel, flexible and ductile organic field-effect transistor (OFET) able to detect pH changes in chemical solutions has been realized and successfully tested. With respect to other organic pH sensors, based on an ISFET-like structure, in our approach the organic transistor is completely separated from the sensing active area and its gate is left floating. The device is biased with a fourth electrode (control-gate) capacitively coupled to the floating-gate. The floating-gate is functionalized by deposition of a layer of thio-amines able to protonize proportionally to the pH value of the solution thus modulating the drain current. The structure does not need an Ag/AgCl counter-electrode since the control-gate is not in contact with the solution. Moreover, the sensing mechanism does not depend on the choice of the dielectric and semiconductor material since the working principle is based on charge separation in the metal induced by the electric field. This structure also simplifies the realization of the fluidics since all the contactable electrodes (drain, source and control-gate) are on the same side of the substrate. A differential measurement approach was adopted in order to get rid of device aging and process-related fluctuations. With the same structure, other chemical species may be detected provided that a proper functionalization procedure is adopted
An organic, charge-modulated field effect transistor for DNA detection
No full textA novel DNA sensor able to detect the DNA hybridization in liquids is presented. The device is a charge sensor, realized with an organic field effect transistor, sensitive to the negatively charged DNA phosphates groups. Compared to other examples of DNA sensors based on organic transistors, this device has two noticeable features: the probe area is completely separated from the transistor area and the sensing mechanism is not reliant on the choice of the device materials. Moreover, the device architecture has been designed in order to avoid any damaging treatment that may reduce the stability of the organic semiconductor. These features make this device especially suitable for the realization of portable and low cost sensors. Two devices (one used as reference and the other as sensor) are measured at the same time in order to get rid of current drifts which are due to organic semiconductor degradation or bias stress, and to enhance variations induced by the DNA sensing mechanism
Electrochemical characterization of self assembled monolayers on flexible electrodes
No full textSelf assembled monolayers of amine- and carboxylic acid terminated thiols have been chemisorbed on gold electrodes deposited on flexible polyethylene terephthalate substrates. These devices, being flexible, low cost, and highly resistant could find application in several fields such as the design of implantable biomedical devices and disposable light-weight sensors. Four different molecules have been investigated, namely cysteamine, 12-mercaptododecanoic acid, aminothiophenol, and 3-mercaptopropionic acid, each bearing either an amino or a carboxylic terminal group and different chain lengths. These molecules have been chosen since the SAM they can form could find application as such or constitute the basis for a further modification step. The modified surfaces have been characterized by electrochemical techniques and the surface pK a values of the terminal groups have been estimated by impedance titration
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
Charge sensing by organic charge-modulated field effect transistors: application to the detection of bio-related effects
No full textThe ability of field effect transistors (FETs) to detect charge variations on the gate may be exploited for realizing chemo- and bio-sensors. In this paper, we focus our attention on a particular kind of field effect device, named organic charge modulated FETs, whose features can be optimized for charge detection in liquid solutions. The results of the measurement of different bio-related effects are shown. In particular, DNA hybridization and pH detection in liquid media are proposed. Finally, preliminary considerations about the applicability of these devices to the detection of the electrical activity of cells are also provided. The device has considerable potential for being employed as a reliable, high sensitivity, low cost technology for sensing signals derived from living systems
Charge sensing by organic charge-modulated field effect transistors: application to the detection of bio-related effects
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