172 research outputs found
Cancer biomarkers detection in cell lysates by means of anisotropic fluorescence at the surface of 1D photonic crystal biochips
No full textNovel 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
La Nano-Biophotonique au USA
No full textRapport de la mission scientifique de l'Ambassade de France aux Etats-UnisH. Rigneault, A. Alexendrou, S. Brasselet, L. Cognet, C. Royer, D. Marguet et C. Boccara
La Nano-Biophotonique au USA
No full textRapport de la mission scientifique de l'Ambassade de France aux Etats-UnisH. Rigneault, A. Alexendrou, S. Brasselet, L. Cognet, C. Royer, D. Marguet et C. Boccara
La Nano-Biophotonique au USA
No full textRapport de la mission scientifique de l'Ambassade de France aux Etats-UnisH. Rigneault, A. Alexendrou, S. Brasselet, L. Cognet, C. Royer, D. Marguet et C. Boccara
La Nano-Biophotonique au USA
No full textRapport de la mission scientifique de l'Ambassade de France aux Etats-UnisH. Rigneault, A. Alexendrou, S. Brasselet, L. Cognet, C. Royer, D. Marguet et C. Boccara
On Grothendieck transformations in Fulton–MacPherson’s bivariant theory
No full textAbstractW. Fulton and R. MacPherson have introduced a notion unifying both covariant and contravariant theories, which they called a Bivariant Theory. A transformation between two bivariant theories is called a Grothendieck transformation. The Grothendieck transformation induces natural transformations for covariant theories and contravariant theories. In this paper we show some general uniqueness and existence theorems on Grothendieck transformations associated to given natural transformations of covariant theories. Our guiding or typical model is MacPherson’s Chern class transformation c∗:F→H∗. The existence of a corresponding bivariant Chern class γ:F→H was conjectured by W. Fulton and R. MacPherson, and was proved by J.-P. Brasselet under certain conditions
Multitoric surfaces, Euler obstruction and applications
No full textNeste trabalho estudamos superfícies com a propriedade que suas componentes irredutíveis são superfícies tóricas. Em particular, apresentamos uma fórmula para calcular a obstrução de Euler local destas superfícies. Como uma aplicação desta fórmula, calculamos a obstrução de Euler local para algumas famílias de superfícies determinantais. Além disso, definimos a característica de Euler evanescente de uma superfície tórica normal Xσ, damos uma fórmula para calcular tal invariante e relacionamos este número com a segunda multiplicidade polar de Xσ. Apresentamos também, uma fórmula para a obstrução de Euler de uma função f : Xσ → C e para o número de Brasselet de tal função. Como uma aplicação deste resultado, calculamos a obstrução de Euler de um tipo de polinômio definido em uma família de superfícies determinantais.In this work we study surfaces with the property that their irreducible components are toric surfaces. In particular, we present a formula to compute the local Euler obstruction of such surfaces. As an application of this formula we compute the local Euler obstruction for some families of determinantal surfaces. Furthermore, we define the vanishing Euler characteristic of a normal toric surface Xσ, we give a formula to compute it, and we relate this number with the second polar multiplicity of Xσ. We also present a formula for the Euler obstruction of a function f : Xσ → C and for the Brasselet number of it. As an application of this result we compute the Euler obstruction of a type of polynomial on a family of determinantal surfaces
L'obstruction d'Euler et ses généralisations
No full textSoit f, g : (X, 0)→ (C, 0) des germes des fonctions analytiques définies sur un espace analytique complexe X. Le nombre de Brasselet d’une fonction f décrit numériquement la topologie de la fibre de Milnor généralisée. Dans cette thèse, nous présentons des formules qui compare les nombres de Brasselet de f dans X et de f restreinte à X ∩ { g=0 } dans le cas où g a un ensemble critique stratifié de dimension un. Si, en plus, f a une singularité isolée à l’origine, nous déterminons le nombre de Brasselet de g dans X et nous le mettons en relation avec le nombre de Brasselet de f dans X. Par conséquence, nous obtenons des formules qui permet mesurer l’obstruction locale d’Euler de X e de X {g = 0} à l’origine, en comparant ces nombres avec des invariants locales associés à f et à g. Nous étudions aussi la topologie locale d’une déformation de g, {g} = g+f N, où N>>1. Nous donnons une relation des nombres de Brasselet de g et {g} dans X ∩ {f = 0}, dans le cas où f a une singularité isolée à l’origine. Nous présentons encore une nouvelle preuve pour la formule de Lê-Iomdine pour le nombre de Brasselet.Let f, g : (X, 0) → (C, 0) be germs of analytic functions defined over a complex analyticspace X. The Brasselet number of a function f describes numerically the topology of its generalized Milnor fibre. In this thesis, we present formulas to compare the Brasselet numbers of f in X and of the restriction of f to X ∩ { g = 0 }, in the case where g has a one-dimensional stratified critical set and f has an arbitrary critical set. If, additionally, f has isolated singularity at the origin, we compute the Brasselet number of g in X and compare it with the Brasselet number of f in X. As a consequence, we obtain formulas to compute the local Euler obstruction of X and of X { g = 0 } at the origin, comparing these numbers with local invariants associated to f and g. We also study the local topology of a deformation of g, { g } = g+f N, for a positive integer number N>>1. We provide a relation between the Brasselet number of g and {g} in X ∩ { f=0 }, in the case where f has isolated singularity at the origin. We also provide a new proof for the Lê-Iomdine formula for the Brasselet numbe
Obstrução de Euler e generalizações
No full textLet f,g : (X, 0) → (C, 0) be germs of analytic functions defined over a complex analytic space X. The Brasselet number of a function f describes numerically the topology of its generalized Milnor fibre. In this thesis, we present formulas to compare the Brasselet numbers of f in X and of the restriction of f to X ∩ {g = 0}, in the case where g has a one-dimensional stratified critical set and f has an arbitrary critical set. If, additionally, f has isolated singularity at the origin, we compute the Brasselet number of g in X and compare it with the Brasselet number of f in X. As a consequence, we obtain formulas to compute the local Euler obstruction of X and of X ∩ {g = 0} at the origin, comparing these numbers with local invariants associated to f and g. We also study the local topology of a deformation of g, g = g + fN, for a positive integer number N ≫ 1. We provide a relation between the Brasselet number of g and g in X ∩ { f = 0}, in the case where f has isolated singularity at the origin. We also provide a new proof for the Lê-Iomdine formula for the Brasselet number.Sejam f,g : (X, 0) → (C, 0) germes de função analítica definidos sobre um espaço analítico complexo X. O número de Brasselet de uma função f descreve numericamente a topologia de sua fibra de Milnor generalizada. Neste trabalho, apresentamos fórmulas que comparam os números de Brasselet de f em X e de f restrita a X ∩ {g = 0} no caso em que g possui conjunto crítico estratificado de dimensão um. Se, adicionalmente, f possui singularidade isolada na origem, calculamos o número de Brasselet de g em X e o comparamos com o número de Brasselet de f em X. Como consequência, obtemos fórmulas para calcular a obstrução local de Euler de X e de X ∩ {g = 0} na origem, comparando esses números com invariantes locais associados a f e a g. Estudamos ainda a topologia local de uma deformação de g, g = g + fN, para um número natural N ≫ 1. Apresentamos uma relação entre os números de Brasselet de g e g em X ∩ { f = 0}, no caso em que f possui singularidade isolada na origem. Apresentamos também uma nova demonstração para a fórmula de Lê-Iomdine para o número de Brasselet
The Telobox, a Myb-related telomeric DNA binding motif found in proteins from yeast, plants and human
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