1,720,990 research outputs found
Ferrocene-substituted calix[4]pyrrole modified carbon paste electrodes for anion detection in water
No full textA neutral redox-active receptor (ferrocene functionalized calix[4]pyrrole) was used as an active component in carbon paste electrodes and ion-selective electrodes ISEs, for the detection of anions in aqueous solution. Measurements with the carbon paste electrodes were conducted using Osteryoung square-wave voltammetry. At the surface of the modified electrode the redox potential of ferrocene-substituted calix[4]pyrrole was found to be at ca. 400 mV. Amongst the anions studied, dihydrogen phosphate and fluoride caused the strongest decrease of peak current (approximately 25%), followed by bromide and chloride. This sensitivity sequence was compared with that obtained with ISEs containing the ferrocene-substituted calix[4]pyrrole. The influence of the interface between host molecule environment and aqueous solution containing target anion on the molecular recognition process and electrochemical signal generation has been investigated
Development and characterization of electrochemical genosensors for the detection of Avian Influenza H5N1 Virus
No full textPraca była realizowana w Instytucie Rozrodu Zwierząt i Badań Żywności Polskiej Akademii Nauk w Olsztynie i współfinansowana w ramach:
Programu Innowacyjna Gospodarka, nr WND-POIG.01.01.02-00-007/08,
Projektu 679 / N-BELGIA / 2010/0,
Projektu COST Action CM10005 "Supramolekularna Chemia w Wodzie"Przedmiotem niniejszej rozprawy było opracowanie czułych elektrochemicznych genoczujników i zastosowanie ich do selektywnego wykrywania specyficznych sekwencji DNA i/lub RNA wirusa ptasiej grypy typu H5N1. Opracowano trzy bioczujniki z zastosowaniem złotych elektrod roboczych. Każdy z nich różnił się sposobem przyłączenia sondy DNA do powierzchni elektrody. Do obserwacji procesów hybrydyzacji zastosowano techniki elektrochemiczne: woltamperometrię cykliczną, woltamperometrię fali prostokątnej oraz elektrochemiczną spektroskopię impendancyjną w trójelektrodowym układzie pomiarowym. Jako analitów użyto 20-merowych sekwencji DNA, ok. 180-pz sekwencji DNA, a także 280-merowych sekwencji RNA. Długie testowane anality posiadały 20-merowe sekwencje komplementarne znajdujące się w różnych położeniach (na końcu 3', na końcu 5' lub na środku). Podjęto również próbę miniaturyzacji jednego z zaproponowanych genoczujników z zastosowaniem elektrod sitodrukowanych z pracującą elektrodą złotą. Za jego pomocą wykrywano m.in. niewymagające odwrotnej transkrypcji sekwencje RNA, co może stanowić podstawę do aplikacji w warunkach poza laboratoryjnych. Biorąc pod uwagę czułość i selektywność trzech przedstawionych genoczujników, można stwierdzić, że każdy z nich z powodzeniem nadaję się do wykrywania materiału genetycznego wirusa ptasiej grypy typu H5N1. Opracowane genoczujniki umożliwiały nie tylko wykrywanie 20-merowych fragmentów komplementarnych do sondy ssDNA znajdujących się w długich łańcuchach DNA i/lub RNA, ale także rozróżnienie ich położenia w analizowanych długich oligonukleotydach.The subject of this dissertation was to develop sensitive electrochemical genosensors and their application for the selective detection of specific DNA and/or RNA sequences derived from the avian influenza virus subtype H5N1. Three DNA biosensors were developed using gold electrodes. The proposed sensors differed in the method of DNA probe attachment to the gold electrode surface. For observation of the hybridization processes electrochemical techniques was apllied: cyclic voltammetry, square wave voltametry and electrochemical impendance spectroscopy in a three-electrode configuration. 20-mer DNA sequence, ca. 180-bp DNA, and ca. 280-mer RNA sequences were used as analytes. The long testing analytes possessed 20-mer complementary sequences in the different positions (at the 3'-end, 5'-end or in the middle). One of the presented genosensor has been miniaturized screen printes electrodes. It was able to detect for example 280-mer RNA sequences, which do not require reverse transcription. It could provide a basis for the application in the field. Taking into account the sensitivity and selectivity, three genosensors demonstrated, were suitable to detect genetic material of avian influenza virus H5N1 subtype. A significant advantage of the genosensors proposed was ability to detect 20-mer fragments complementary to the probe ssDNA located in a 180-bp DNA or a 280-mer RNA. The developed genosensors also are able to distinguish the position of complementary sequences located in the long analysed oligonucleotides.Instytut Rozrodu Zwierząt i Badań Żywności Polskiej Akademii Nau
Deposition of Ni(II)Porphyrin monolayer on the gold electrode via azide-alkyne click - coupling and its electrochemical characterization
No full textIn this work, a Ni(II) porphyrin containing two azide groups ((N-3)(2)-Ni(II) porphyrin) was applied for gold electrode modification via azide-alkyne click reaction. The [CuBr(PPh3)(3)] catalyst was used for the cycloaddition of diazido Ni(II) porphyrin to alkyne functionalized thiols previously assembled onto the gold surface. The self-assembled monolayer (SAM) incorporating Ni(II) porphyrin was characterized in aqueous solutions by cyclic voltammetry (CV), Osteryoung square-wave voltammetry (OSWV) and differential pulse voltammetry (DPV). The attachment of a ssDNA probe via a strained bicyclononyne group to the developed redox active monolayer via copper-free alkyne-azide click ligation is presented
Silver or gold? A comparison of nanoparticle modified electrochemical genosensors based on cobalt porphyrin-DNA
No full textWe applied a cobalt-porphyrin modified DNA as electrochemical marker, which was attached to nanoparticles, to detect specific DNA sequences. We compare the performance of gold and silver NPs in oligonucleotide sensors to determine if a change in metal will lead to either higher sensitivity or different selectivity, based on the redox behaviour of silver vs. gold. Surprisingly, we find that using either gold or silver NPs yields very similar overall performance. The electrochemical measurements of both types of sensors show the same redox behaviour which is dominated by the cobalt porphyrin, indicating that the electron pathway does not include the NP, but there is direct electron transfer between the porphyrin and the electrode. Both sensors show a linear response in the range of 5 × 10–17 to 1 × 10–16 M; the limit of detection (LOD) is 3.8 × 10–18 M for the AuNP sensor, and 5.0 × 10–18 M for the AgNP sensor, respectively, which corresponds to the detection of about 20–50 DNA molecules in the analyte. Overall, the silver system results in a better DNA economy and using cheaper starting materials for the NPs, thus shows better cost-effectiveness and could be more suitable for the mass-production of highly sensitive DNA sensors
Approaching single DNA molecule detection with an ultrasensitive electrochemical genosensor based on gold nanoparticles and Cobalt-porphyrin DNA conjugates
No full textWe describe an ultrasensitive electrochemical genosensor based on gold nanoparticles and cobalt-porphyrin functionalised ssDNA probes. The sensitivity at the attomolar concentration level arises from an increased density of redox labels on the electrode surface compared to sensors without NP modification. The electrode detects as few as 23 DNA molecules, approaching single molecule detection
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
A highly sensitive electrochemical genosensor based on Co-porphyrin-labelled DNA
Full text linkWe report the use of Co-porphyrins as electrochemical tags for a highly sensitive and selective genosensor. An avian influenza virus-based DNA sequence characteristic of H5N1 was detected at femtomolar levels from competing non-complementary sequences through hybridisation with the labeled DNA
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