1,720,998 research outputs found
Spatially resolved electrochemiluminescence through a chemical lens
No full textElectrochemiluminescence (ECL) microscopy is an emerging technique with a wide range of imaging applications and unique properties in terms of high spatial resolution, surface confinement and favourable signal-to-noise ratio. Despite its successful analytical applications, tuning the depth of field (i.e., thickness of the ECL-emitting layer) is a crucial issue. Indeed, the control of the thickness of this ECL region, which can be considered as an “evanescent” reaction layer, limits the development of cell microscopy as well as bioassays. Here we report an original strategy based on chemical lens effects to tune the ECL-emitting layer in the model [Ru(bpy)3]2+/tri-n-propylamine (TPrA) system. It consists of microbeads decorated with [Ru(bpy)3]2+labels, classically used in bioassays, and TPrA as the sacrificial coreactant. In particular we exploit the buffer capacity of the solution to modify the rate of the reactions involved in the ECL generation. For the first time, a precise control of the ECL light distribution is demonstrated by mapping the luminescence reactivity at the level of single micrometric bead. The resulting ECL image is the luminescent signature of the concentration profiles of diffusing TPrA radicals, which define the ECL layer. Therefore, our findings provide insights into the ECL mechanism and open new avenues for ECL microscopy and bioassays. Indeed, the reported approach based on a chemical lens controls the spatial extension of the “evanescent” ECL-emitting layer and is conceptually similar to evanescent wave microscopy. Thus, it should allow the exploration and imaging of different heights in substrates or in cells
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Dynamic Mapping of Electrochemiluminescence Reactivity in Space: Application to Bead-Based Assays
Get PDFAs an electrochemical technique offering an optical readout, electrochemiluminescence (ECL) evolved recently into a powerful microscopy technique with the visualization of a wide range of microscopic entities. However, the dynamic imaging of transient ECL events did not receive intensive attention due to the limited number of electrogenerated photons. Here, the reaction kinetics of the model ECL bioassay system was revealed by dynamic imaging of single [Ru(bpy)(3)](2+)-functionalized beads in the presence of the efficient tripropylamine coreactant. The time profile behavior of ECL emission, the variations of the ECL layer thickness, and the position of maximum ECL intensity over time were investigated, which were not achieved by static imaging in previous studies. Moreover, the dynamics of the ECL emission were confronted with the simulation. The reported dynamic ECL imaging allows the investigation of the ECL kinetics and mechanisms operating in bioassays and cell microscopy
Methods and strategies for robust electrochemiluminescence signal quantification
Get PDFEver since the discovery of electrochemiluminescence (ECL), researchers have been devoted to exploring various approaches to improve the signal-to-noise ratio by testing different luminophores and introducing nanostructures, with the ultimate goal of enhancing analytical performance and expanding ECL's areas of application. In order to identify the most effective method and materials, the ECL quantum efficiency (ECL-QE) is the key parameter utilized for objective comparison among systems including different luminophores, etc. However, due to the strong dependence of ECL on experimental parameters, developing an instrumentindependent ECL-QE equation has proven challenging, resulting in significant variations in its value. Herein, we examine the most recent approaches for determining the ECLQE in solution-phase and heterogeneous systems
Differential photoluminescent and electrochemiluminescent detection of anions with a modified ruthenium(II)-bipyridyl complex
No full textA new guanidinium 3,3’-functionalized
bipyridylruthenium(II) complex
has been prepared for the differential
sensing of l-glutamate and dihydrogenphosphate
anions depending on
the luminescent detection scheme. The
effects of such anions on the photoluminescent
(PL) and electrochemiluminescent
(ECL) properties of the complex
have been investigated and compared.
The PL intensity increases up to
fourfold in the presence of l-glutamate.
The increase of intensity in the presence
of dihydrogenphosphate is weaker
and no change in PL intensity is observed
in presence of acetate, iodide,
or chloride anions. With n-tripropyl-amine, ECL emission of the RuII complex
is initiated at 1.45 V versus Ag/
AgCl/KCl and the ECL intensity increases
only in the presence of dihydrogenphosphate.
Indeed, l-glutamate
is already oxidized at the relatively
high potential required for ECL generation
and thus it does not affect the
ECL signal. The comparison of the
competitive ECL and PL assays in a
mixture of anions confirms the differential
detection of l-glutamate and of
dihydrogenphosphate. Thus, both sensing
channels (i.e., PL and ECL) show
different selectivities depending on the
nature and on the electroactivity of the
target anions. Multianion analysis is
demonstrated in competitive assays
using complementary detection methods
Microscopic imaging and tuning of electrogenerated chemiluminescence with boron-doped diamond nanoelectrode arrays
No full textNanoelectrode arrays (NEAs) are increasingly applied for a variety of electroanalytical applications; however, very few studies dealt with the use of NEAs as an electrochemical generator of electrogenerated chemiluminescence (ECL). In the present study, arrays of nanodisc and nanoband electrodes with different dimensions and inter-electrode distances were fabricated by e-beam lithography on a polycarbonate layer deposited on boron-doped diamond (BDD) substrates. In particular, NEAs with 16 different geometries were fabricated on the same BDD sample substrate obtaining a multiple nanoelectrode and ultramicroelectrode array platform (MNEAP). After electrochemical and morphological characterization, the MNEAP was used to capture simultaneously with a single image the characteristic behaviour of ECL emission from all the 16 arrays. Experiments were performed using Ru(bpy)32+ as the ECL luminophore and tri-n-propylamine (TPrA) as the co-reactant. With a relatively limited number of experiments, such an imaging procedure allowed to study the role that geometrical and mechanistic parameters play on ECL generation at NEAs. In particular, at high concentrations of TPrA, well-separated individual ECL spots or bands revealed an ECL signal which forms a pattern matching the nanofabricated structure. The analysis of the imaging data indicated that the thickness of the ECL-emitting zone at each nanoelectrode scales inversely with the co-reactant concentration, while significantly stronger ECL signals were detected for NEAs operating under overlap conditions
Variations on the Author
Get PDF“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
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