1,721,198 research outputs found
Cancer biomarkers detection in cell lysates by means of anisotropic fluorescence at the surface of 1D photonic crystal biochips
Full text linkNovel disposable optical biochips based on one-dimensional photonic crystals (1DPC) sustaining Bloch surface waves (BSW) are an attractive tool for the detection of several disease-related biomarkers. In response to growing global burden of cancer, one of the most significant public health challenges of the 21st century is the prevention and early diagnosis of this disease. By diagnosing in advance such disease permits to increase the survival probability of patients and to improve their life perspectives. Consequently, cancer biomarkers have gained considerable attention. Within this framework, the herein proposed optical biochips can quantify low concentrations (sub ng/mL) of the ERBB2 breast cancer biomarker in biological complex matrices, such as cell lysate samples. The choice of focusing on this specific breast-cancer-related biomarker lies in the global issue represented by this type of cancer. According to the data provided by the World Cancer Research Fund, its incidence rate increases year per year establishing itself as the most commonly occurring cancer in women worldwide contributing 25% of the total number of new cases diagnosed in 2018 and as the second most common cancer overall after lung cancer. However, the versatility of the system opens up new possibilities for designing different assays, depending on the specific biomarker sought.
To discriminate ERBB2 levels in several different cell lysate samples, we made use of 1DPC biochips and on a reading instrument that can work in both a label-free and a fluorescence detection mode. Such combined configuration provides the advantage of complementary information and lower limit of detection (LoD) in the fluorescence mode. In the label-free mode, the BSW excitation is achieved by a prism coupling system (Kretschmann-Raether configuration), like in the surface plasmon resonance (SPR) technique, resulting in a dip in the angular reflectance spectrum. According to the interactions that take place at the surface, the angular position of such a dip shifts as a function of refractive index change at the interface.
Moreover, the fluorescence operation, in which fluorescence angular spectra are acquired, is obtained by making use of fluorophores or dye labelled antibodies bound at the 1DPC surface. Furthermore, coupling between the dye labels and the BSW results in strongly directional and enhanced fluorescence emission. The advantages brought by the 1DPC, when compared to metal structures, are the smaller energy losses and the narrower resonances.
Despite the great sensitivity offered by the fluorescence detection mode, the measurements are affected by a phenomenon that cannot be neglected when quantitative and accurate information is needed, as occurs in biosensing assays, i.e. photobleaching. Presently, there is no study about photobleaching in experiments with BSW sustained by 1DPC, despite its evident effects. Photobleaching denotes the irreversible loss of fluorescence emitted energy of a dye that dramatically changes its absorption and emission properties. The rate of such a fluorescence bleaching is affected by several factors such as the power of the illumination beam, the exposure time, and the photonic crystal structure itself. In addition, it is also influenced by the molecule’s transition dipole moment. In particular, fluorophores having a transition dipole moment oriented parallel to excitation polarized light will be excited preferentially, and in turn will be strongly photobleached. As a consequence, the fluorescence emission will be polarized and no more isotropic. This effect is more or less significant depending on the binding strength of the fluorophores to the surface.
In this dissertation, we report for the first time on cancer detection assays, carried out with our setup, in which the trustworthiness is guaranteed by a correct approach to data analysis, which accounts in a correct way for photobleaching, which could not only affect the overall emission intensity but also its polarization distribution via the TE and TM BSW modes provided by the 1DPC.
To get to such a result, the experimental data is interpreted by means of a theoretical model for the orientational distribution of dye labels over time, taking into account the density of the optical states of the 1DPC, photobleaching and rotational diffusion of surface bound emitters. The approach permits to model anisotropic fluorescence emission and to manage photobleaching effects in biosensing assays, leading to a correct data interpretation.
The theoretical description permits not only to manage photobleaching but also to exploit it as a new tool for probing rotational diffusion of any protein labelled with fluorescent emitters at the surface of 1DPC endowed with different chemistries. Such a possibility is related to the polarization dependent spectroscopic role played by the 1DPC, which permits to analyse simultaneously two polarizations, TE and TM, within a relatively simple optical layout and thus accessing either the orientation or the depolarization kinetics under non-stationary conditions of the resonant fluorescence signal. Such a type of measurement is not possible with conventional fluorescence anisotropy techniques or using other types of surface electromagnetic waves, such as surface plasmon polaritons, for example, that are only TM polarized
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
Strutture dielettriche a band-gap elettromagnetico (EBG): geometrie frattali e caratterizzazione dei difetti
No full textAppropriate 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
Study and Frabrication of Metamaterials for Electronics and Telecommunication Applications
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Studio e relaizzazione di metamateriali per applicazioni all'elettronica ed alle telecomunicazioni
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