1,720,971 research outputs found
Dual monitoring of surface reactions in real time by combined surface-plasmon resonance and field-effect transistor interrogation
Full text linkBy combining surface plasmon resonance (SPR) and electrolyte gated field-effect transistor (EG-FET) methods in a single analytical device we introduce a novel tool for surface investigations, enabling simultaneous measurements of the surface mass and charge density changes in real time. This is realized using a gold sensor surface that simultaneously serves as a gate electrode of the EG-FET and as the SPR active interface. This novel platform has the potential to provide new insights into (bio)adsorption processes on planar solid surfaces by directly relating complementary measurement principles based on (i) detuning of SPR as a result of the modification of the interfacial refractive index profile by surface adsorption processes and (ii) change of output current as a result of the emanating effective gate voltage modulations. Furthermore, combination of the two complementary sensing concepts allows for the comparison and respective validation of both analytical techniques. A theoretical model is derived describing the mass uptake and evolution of surface charge density during polyelectrolyte multilayer formation. We demonstrate the potential of this combined platform through the observation of layer-bylayer assembly of PDADMAC and PSS. These simultaneous label-free and real-time measurements allow new insights into complex processes at the solid−liquid interface (like non-Fickian ion diffusion), which are beyond the scope of each individual tool.Fil: Aspermair, Patrik. Austrian Institute of Technology; Austria. CEST Competence Center for
Electrochemical Surface Technologies; Austria. Centre National de la Recherche Scientifique; Francia. Universite Valencienne; Francia. Universite Lille; FranciaFil: Ramach, Ulrich. CEST Competence Center for
Electrochemical Surface Technologies; AustriaFil: Reiner Rozman, Ciril. Austrian Institute of Technology; AustriaFil: Fossati, Stefan. Austrian Institute of Technology; AustriaFil: Lechner, Bernadette. Austrian Institute of Technology; AustriaFil: Moya, Sergio Enrique. Centro de Investigación Cooperativa en Biomateriales - CIC biomaGUNE; EspañaFil: Azzaroni, Omar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Dostalek, Jakub. Austrian Institute of Technology; AustriaFil: Szunerits, Sabine. Centre National de la Recherche Scientifique; Francia. Universite Valencienne; Francia. Universite Lille; FranciaFil: Knoll, Wolfgang. Austrian Institute of Technology; Austria. CEST Competence Center for
Electrochemical Surface Technologies; AustriaFil: Bintinger, Johannes. Austrian Institute Of Technology; Austri
Graphene-based field effect transistors for the biosensing of toxins
No full textA biosensor setup was designed for the detection of aflatoxin B1 based on field effect transistors (FET) using reduced Graphene-Oxide (rGO) as transducer. The dependence of the detection signal to the ion strength of the buffer solution was studied and results were superimposed with the Debye-length theory, demonstrating the applicable ion strengths for the shown type of biosensor. Furthermore characterization of pH responses and the binding of bovine serum album as a standard test for the biosensor have been tested.
As the next step, binding of aflatoxin B1 was characterized, measuring basic kinetic parameters according to the Langmuir binding theory for the description of the equilibrium surface coverage as a function of the bulk (analyte) concentration in aqueous solution. The obtained binding coefficient for aflatoxin B1 are found to be in the same magnitude as described in literature values. Furthermore the main aim of this project was the detection of aflatoxin B1 from real-life corn samples using anti-fouling layers for the protection of the rGO and the diminishment of unspecific surface potential and charge changes. Therefor a sensor array was used, implying a FET with the target aflatoxin B1-antibody and a FET with a non-targeted antibody (bovine serum albumin) for comparison of the response signals. For the realization, reduced graphene oxide (rGO) was synthesized using a wet-chemical method and then used for the fabrication of 50 µm channel-width field effect transistors. A passivation coating of 20 nm Ta2O5 was sputtered on the semiconductor (rGO) without pin-holes. Then, using a silane as linking molecule, the target antibodies (aflatoxin B1) were applied on the passivated surface just before measurement in liquid-gated configuration. The passivation prohibits binding of non-specific molecules from the food samples on the graphene surface, but still the surface potential is changed when flushing these food samples over the FET channel. Therefor a negative control FET is connected serially to the FET with the target antibodies and this negative control is performed using non-target antibodies (anti-bovine serum albumin).
The signals of both FETs are then compared and the difference in signal area is giving a read-out for the aflatoxin B1 binding on the target antibodies. A comparison of the integrated areas obtained by the response signals of the FETs during contaminated corn injections yields the final biosensor read-out. The limit of detection (LOD) in real-life samples was found to be around 10 nM, being two magnitudes higher than for measurements in buffer, but still below the maximum toxin concentration instructed by the EU food-stuffs regulatory. Calibration curves of the system were performed using a titration of 5 different contaminated corn food samples and one certified blank corn sample. The detection signals were then measured by the integration of the separate response signals and the difference of the target FET and the negative control.
The presented approach shows promising results for the development of a novel biosensor due to the low assay time (around 2 minutes), small device size, possible real-time read-out and it’s cost-efficiency. The work on aflatoxin B1 detection was performed in the framework of an industrial project in cooperation with Romer Labs®, Tulln, Austria.
Additionally to the sought experimental data on toxin detection in this phd-thesis from real-life samples a liquid-velocity sensor was accomplished and described, the use of impedance spectroscopy for FETs demonstrated and a novel characterization technique using surface electrochemical microscopy (SECM) for the assessment of the applicability of graphene surfaces for biosensors was developed.VI, 125, XXXIII Seite
Graphene-based field effect transistors for the biosensing of toxins
No full textA biosensor setup was designed for the detection of aflatoxin B1 based on field effect transistors (FET) using reduced Graphene-Oxide (rGO) as transducer. The dependence of the detection signal to the ion strength of the buffer solution was studied and results were superimposed with the Debye-length theory, demonstrating the applicable ion strengths for the shown type of biosensor. Furthermore characterization of pH responses and the binding of bovine serum album as a standard test for the biosensor have been tested.
As the next step, binding of aflatoxin B1 was characterized, measuring basic kinetic parameters according to the Langmuir binding theory for the description of the equilibrium surface coverage as a function of the bulk (analyte) concentration in aqueous solution. The obtained binding coefficient for aflatoxin B1 are found to be in the same magnitude as described in literature values. Furthermore the main aim of this project was the detection of aflatoxin B1 from real-life corn samples using anti-fouling layers for the protection of the rGO and the diminishment of unspecific surface potential and charge changes. Therefor a sensor array was used, implying a FET with the target aflatoxin B1-antibody and a FET with a non-targeted antibody (bovine serum albumin) for comparison of the response signals. For the realization, reduced graphene oxide (rGO) was synthesized using a wet-chemical method and then used for the fabrication of 50 µm channel-width field effect transistors. A passivation coating of 20 nm Ta2O5 was sputtered on the semiconductor (rGO) without pin-holes. Then, using a silane as linking molecule, the target antibodies (aflatoxin B1) were applied on the passivated surface just before measurement in liquid-gated configuration. The passivation prohibits binding of non-specific molecules from the food samples on the graphene surface, but still the surface potential is changed when flushing these food samples over the FET channel. Therefor a negative control FET is connected serially to the FET with the target antibodies and this negative control is performed using non-target antibodies (anti-bovine serum albumin).
The signals of both FETs are then compared and the difference in signal area is giving a read-out for the aflatoxin B1 binding on the target antibodies. A comparison of the integrated areas obtained by the response signals of the FETs during contaminated corn injections yields the final biosensor read-out. The limit of detection (LOD) in real-life samples was found to be around 10 nM, being two magnitudes higher than for measurements in buffer, but still below the maximum toxin concentration instructed by the EU food-stuffs regulatory. Calibration curves of the system were performed using a titration of 5 different contaminated corn food samples and one certified blank corn sample. The detection signals were then measured by the integration of the separate response signals and the difference of the target FET and the negative control.
The presented approach shows promising results for the development of a novel biosensor due to the low assay time (around 2 minutes), small device size, possible real-time read-out and it’s cost-efficiency. The work on aflatoxin B1 detection was performed in the framework of an industrial project in cooperation with Romer Labs®, Tulln, Austria.
Additionally to the sought experimental data on toxin detection in this phd-thesis from real-life samples a liquid-velocity sensor was accomplished and described, the use of impedance spectroscopy for FETs demonstrated and a novel characterization technique using surface electrochemical microscopy (SECM) for the assessment of the applicability of graphene surfaces for biosensors was developed
Enzyme-polyelectrolyte multilayer assemblies on reduced graphene oxide field-effect transistors for biosensing applications
Full text linkAbstractWe present the construction of layer-by-layer (LbL) assemblies of polyethylenimine and urease onto reduced-graphene-oxide based field-effect transistors (rGO FETs) for the detection of urea. This versatile biosensor platform simultaneously exploits the pH dependency of liquid-gated graphene-based transistors and the change in the local pH produced by the catalyzed hydrolysis of urea. The use of an interdigitated microchannel resulted in transistors displaying low noise, high pH sensitivity (20.3µA/pH) and transconductance values up to 800 µS. The modification of rGO FETs with a weak polyelectrolyte improved the pH response because of its transducing properties by electrostatic gating effects. In the presence of urea, the urease-modified rGO FETs showed a shift in the Dirac point due to the change in the local pH close to the graphene surface. Markedly, these devices operated at very low voltages (less than 500mV) and were able to monitor urea in the range of 1–1000µm, with a limit of detection (LOD) down to 1µm, fast response and good long-term stability. The urea-response of the transistors was enhanced by increasing the number of bilayers due to the increment of the enzyme surface coverage onto the channel. Moreover, quantification of the heavy metal Cu2+(with a LOD down to 10nM) was performed in aqueous solution by taking advantage of the urease specific inhibition
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
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