2D label-free imaging of resonant grating biochips in ultraviolet

International audience2D images of label-free biochips exploiting resonant waveguide grating (RWG) are presented. They indicate sensitivities on the order of 1 pg/mm2 for proteins in air, and hence 10 pg/mm2 in water can be safely expected. A 320×256 pixels Aluminum-Gallium-Nitride-based sensor array is used, with an intrinsic narrow spectral window centered at 280 nm. The additional role of characteristic biological layer absorption at this wavelength is calculated, and regimes revealing its impact are discussed. Experimentally, the resonance of a chip coated with protein is revealed and the sensitivity evaluated through angular spectroscopy and imaging. In addition to a sensitivity similar to surface plasmon resonance (SPR), the RWGs resonance can be flexibly tailored to gain spatial, biochemical, or spectral sensitivity

Biopuces sans marquage : structuration pour la haute sensibilité pour l'imagerie dans l'ultraviolet

Biosensors enables to detect biological interactions, between probes localized at the chip surface, and targets of a solution. Biological applications of biosensing are wide. Here, we present a label-free optical transduction, enabling 2D imaging, and consequently parallel detection of several reactions. It is based on the absorption of biological molecules (at 260 nm for DNA and 280 nm for proteins). In this framework, recently developed AlGaN components can be used. Their emission/responsivity spectrum enables to select the spectral band of interest. Sensitivity is a major requirement of biosensing devices. Configurations leading to enhancement of the interaction between light and biological molecules are of interest. The first multilayer structures enable to locate the biological molecules at the antinode of the electric field. For a better sensitivity, resonant grating structures are then studied. They enable a much better confinement of the electric field close from the biological layer. The protein used in this study is the methionyl-tRNA synthetase. Its absorption is representative of protein absorption, and it can then serve as a model for biological macromolecules detection. The successive steps of chip modelling, fabrication, characterization, biological preparation and then imaging of the chips are described. Imaging of resonant grating is not largely studied, but it results in good sensitivity. In order to increase signal to noise ratio, a pre-dispersed illumination is proposed. It enables to take benefit of all the useful photons of the source by illuminating the chip in () resonant condition for each wavelength.L'utilisation de bio-puces est basée sur la détection d'interactions biologiques ayant lieu entre des espèces immobilisées à la surface d'une puce ( sondes), et des espèces à détecter (cibles). Ces dispositifs ouvrent de nombreuses applications biologiques. On développe ici une méthode optique sans marquage, avec imagerie bidimensionnelle, basée de façon originale sur l'absorption dans l'ultraviolet des molécules biologiques (à 260 nm pour l'ADN et 280 nm pour les protéines). Dans ce cadre, les nouveaux composants à base d'AlGaN sont particulièrement adaptés car ils permettent de sélectionner précisément la bande spectrale d'intérêt. La sensibilité des méthodes de détection est un critère déterminant. Pour l'améliorer, on étudie ici des configurations qui amplifient l'interaction lumière-élément biologique. Les premières structures multicouches permettent de placer un ventre du champ électrique au niveau de l'élément biologique. Ensuite, on s'attache à utiliser des propriétés des "réseaux résonants", qui concentrent bien davantage le champ électrique au niveau des éléments biologiques. La protéine modèle utilisée est la méthionyl-ARNt synthétase. Elle est représentative et garantit l'applicabilité à n'importe quelle autre molécule biologique. Les étapes de définition des structures, fabrication, caractérisation, dépôt biologique et enfin l'étape finale d'imagerie des biopuces sont décrites. L'imagerie de biopuces optiquement résonantes sur réseau est peu développée, mais on vérifie qu'elle atteint cependant de bonnes sensibilités. Afin d'augmenter le rapport signal sur bruit, il est suggéré d'intégrer le signal sur toute la résonance en pré-dispersant l'éclairage

Resonant waveguide sensing made robust by on-chip peak tracking through image correlation

International audienceWe demonstrate a solution to make resonant-waveguide-grating sensing both robust and simpler to optically assess, in the spirit of biochips. Instead of varying wavelength or angle to track the resonant condition, the grating itself has a step-wise variation with typically few tens of neighboring "micropads." An image capture with incoherent monochromatic light delivers spatial intensity sequences from these micropads. Sensitivity and robustness are discussed using correlation techniques on a realistic model (Fano shapes with noise and local distortion contributions). We confirm through fluid refractive index sensing experiments an improvement over the step-wise maximum position tracking by more than 2 orders of magnitude, demonstrating sensitivity down to 2 × 10−5 RIU, giving high potential development for bioarray imaging

Design of specific biochips for contrast enhancement of UV biological absorption

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Biodetection of DNA and proteins using enhanced UV absorption by structuration of the chip surface

International audienceDNA and protein absorption at 260 and 280 nm can be used to reveal theses species on a biochip UV image. A first study including the design and fabrication of UV reflective multilayer biochips designed for UV contrast enhancement (factor of 4.0) together with spectrally selective AlGaN detectors demonstrated the control of chip biological coating, or Antigen/Antibody complexation with fairly good signals for typical probe density of 4x1012 molecules/cm2. Detection of fractional monolayer molecular binding requires a higher contrast enhancement which can be obtained with structured chips. Grating structures enable, at resonance, a confinement of light at the biochip surface, and thus a large interaction between the biological molecule and the lightwave field. The highest sensitivity obtained with grating-based biochip usually concerns a resonance shift, in wavelength or diffraction angle. Diffraction efficiency is also affected by UV absorption, due to enhanced light-matter interaction, and this mechanism is equally able to produce biochip images in parallel. By adjusting grating parameters, we will see how a biochip that is highly sensitive to UV absorption at its surface can be obtained. Based on the Ewald construction and diffraction diagram, instrumental resolution and smarter experimental configurations are considered. Notably, in conjunction with the 2D UV-sensitive detectors recently developed in-house, we discuss the obtainment of large contrast and good signals in a diffraction order emerging around the sample normal

Design of specific biochips for contrast enhancement of UV biological absorption

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UV imaging of biochips based on resonant grating

International audienceIn the frame of biological threat, security systems require label free biochips for rapid detection. Biosensors enable to detect biological interactions, between probes localized at the surface of a chip, and targets present in the sample solution. Here, we present an optical transduction, enabling 2D imaging, and consequently parallel detection of several reactions. It is based on the absorption of biological molecules in the UV domain. Thus, it is based on an intrinsic property of biological molecules and does not require any labelling of the biological molecules. DNA and proteins absorb UV light at 260 and 280 nm respectively. Sensitivity is a major requirement of biosensing devices. Configurations leading to enhancement of the interaction between light and biological molecules are of interest. For a better sensitivity, resonant grating structures are then studied. They enable to confine the electric field close to the biological layer. Imaging of resonant grating is not largely studied, even for visible wavelengths, but it results in good sensitivity. The protein used in this study is the methionyl-tRNA synthetase. Its absorption is representative of protein absorption, and it can then serve as a model for immunological detection. The best experimental contrast due to a monolayer of proteins is 40%. With data processing currently employed for biochip imaging: average on several acquisitions and on all the pixels imaging the biological spots, the device is able to detect a surface density of proteins in the 10 pg/mm range. © (2010) COPYRIGHT SPIE--The International Society for Optical Engineerin

Resonant spatial tracking using nanostructured Resonant Waveguide Grating for multispectral sensing by imaging (Orale)

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Resonant spatial tracking using nanostructured Resonant Waveguide Grating for multispectral sensing by imaging

International audienceResonant profile shift resulting from a change of resonant conditions is classically used for sensing, either liquid refractive index or immobilized biological layer effective thickness. Resonant waveguide gratings (RWG) allow sensing over a large spectral domain, depending on the materials and geometrical parameters of the grating. Profiles measurements usually involve scanning instrumentation. We recently demonstrated that direct imaging multi-assay RWGs sensing may be rendered more robust using spatial Fano profiles from "chirped" RWG chips. The scheme circumvents the classical but demanding scans: instead of varying angle or wavelength through fragile moving parts or special optics, a RWG structure parameter is varied. Our findings are illustrated with resonance profiles from nanostructured silicon nitride waveguide on glass. A sensitivity down to Δn=2x10-5 or biomolecules mass density of 10 pg/mm2 is demonstrated through theory and experiments. To assess different sensing wavelength, the period might also vary within the same chip support. We discuss guiding properties and sensing sensitivities of RWG sensing over the whole visible spectral range. Resonant profiles are analyzed using a correlation approach, correlating the sensed signal to a zero-shifted reference signal. This analysis was demonstrated to be more accurate than usual fitting, for analyzing signals including noise contribution. The current success of surface plasmon imaging suggests that our work could leverage an untapped potential to extend such techniques in a convenient and sturdy optical configuration. Moreover, extended spectral range sensing can be addressed by dielectric waveguide structures. This allows sensitive sensing of small volumes of analyte, which can be circulated close from the resonant waveguide. Together with the demonstration of highly accurate fits through correlation analysis, our scheme based on a "Peak-tracking chip" demonstrates a new technique for multispectral sensitive sensing through nanostructured chip imaging