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

International audienc

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

"Peak tracking chip" for label-free optical detection of bio-molecular interaction and bulk sensing

A novel imaging method for bulk refractive index sensing or label-free bio-molecular interaction sensing is presented. This method is based on specially designed "Peak tracking chip" (PTC) involving "tracks" of adjacent resonant waveguide gratings (RWG) "micropads" with slowly evolving resonance position. Using a simple camera the spatial information robustly retrieves the diffraction efficiency, which in turn transduces either the refractive index of the liquids on the tracks or the effective thickness of an immobilized biological layer. Our intrinsically multiplex chip combines tunability and versatility advantages of dielectric guided wave biochips without the need of costly hyperspectral instrumentation. The current success of surface plasmon imaging techniques suggests that our chip proposal could leverage an untapped potential to routinely extend such techniques in a convenient and sturdy optical configuration toward, for instance for large analytes detection. PTC design and fabrication are discussed with challenging process to control micropads properties by varying their period (step of 2 nm) or their duty cycle through the groove width (steps of 4 nm). Through monochromatic imaging of our PTC, we present experimental demonstration of bulk index sensing on the range [1.33-1.47] and of surface biomolecule detection of molecular weight 30 kDa in aqueous solution using different surface densities. A sensitivity of the order of 10(-5) RIU for bulk detection and a sensitivity of the order of similar to 10 pg mm(-2) for label-free surface detection are expected, therefore opening a large range of application of our chip based imaging technique. Exploiting and chip design, we expect as well our chip to open new direction for multispectral studies through imaging

High-throughput particle manipulation by hydrodynamic, electrokinetic, and dielectrophoretic effects in an integrated microfluidic chip

Integrating different steps on a chip for cell manipulations and sample preparation is of foremost importance to fully take advantage of microfluidic possibilities, and therefore make tests faster, cheaper and more accurate. We demonstrated particle manipulation in an integrated microfluidic device by applying hydrodynamic, electroosmotic (EO), electrophoretic (EP), and dielectrophoretic (DEP) forces. The process involves generation of fluid flow by pressure difference, particle trapping by DEP force, and particle redirect by EO and EP forces. Both DC and AC signals were applied, taking advantages of DC EP, EO and AC DEP for on-chip particle manipulation. Since different types of particles respond differently to these signals, variations of DC and AC signals are capable to handle complex and highly variable colloidal and biological samples. The proposed technique can operate in a highthroughput manner with thirteen independent channels in radial directions for enrichment and separation in microfluidic chip. We evaluated our approach by collecting Polystyrene particles, yeast cells, and E. coli bacteria, which respond differently to electric field gradient. Live and dead yeast cells were separated successfully, validating the capability of our device to separate highly similar cells. Our results showed that this technique could achieve fast pre-concentration of colloidal particles and cells and separation of cells depending on their vitality. Hydrodynamic, DC electrophoretic and DC electroosmotic forces were used together instead of syringe pump to achieve sufficient fluid flow and particle mobility for particle trapping and sorting. By eliminating bulky mechanical pumps, this new technique has wide applications for in situ detection and analysis

Embedded Effective-Index-Material in Oxide-Free Hybrid Silicon Photonics Characterized by Prism Deviation

International audienceHybrid silicon photonics offers novel opportunities to control light propagation with nanostructured media on the silicon side. In the specific case of oxide-free heteroepitaxial bonding of III-V layers on silicon, it is particularly crucial to assess the role of nanostructures in the post-bonding situation. We propose here a method of internal light source and integrated prism deviation to evaluate the effective index of small sub-wavelength periodic shallow holes that are completely embedded and do not lend themselves to alternative such as e.g. ellipsometry. We achieve a precision Δn <; 0.01, a good accuracy both for the understanding and optimization of optical components performances. Measured data are in good agreement with the theoretical expectation, as obtained using an improved homogenization strategy and further confirmed by 3D Bloch mode calculation

Real time hybridization studies by resonant waveguide gratings using nanopattern imaging for Single Nucleotide Polymorphism detection

2D imaging of biochips is particularly interesting for multiplex biosensing. Resonant properties allow label-free detection using the change of refractive index at the chip surface. We demonstrate a new principle of Scanning Of Resonance on Chip by Imaging (SORCI) based on spatial profiles of nanopatterns of resonant waveguide gratings (RWGs) and its embodiment in a fluidic chip for real-time biological studies. This scheme allows multiplexing of the resonance itself by providing nanopattern sensing areas in a bioarray format. Through several chip designs we discuss resonance spatial profiles, dispersion and electric field distribution for optimal light-matter interaction with biological species of different sizes. Fluidic integration is carried out with a black anodized aluminum chamber, advantageous in term of mechanical stability, multiple uses of the chip, temperature control and low optical background. Real-time hybridization experiments are illustrated by SNP (Single Nucleotide Polymorphism) detection in gyrase A of E. coli K12, observed in evolution studies of resistance to the antibiotic ciprofloxacin. We choose a 100 base pairs (bp) DNA target (similar to 30 kDa) including the codon of interest and demonstrate the high specificity of our technique for probes and targets with close affinity constants. This work validates the safe applicability of our unique combination of RWGs and simple instrumentation for real-time biosensing with sensitivity in buffer solution of similar to 10 pg/mm(2). Paralleling the success of RWGs sensing for cells sensing, our work opens new avenues for a large number of biological studies