Biochip device
A biochip device comprising a substrate constituted by at least one plate of material forming a multimode planar waveguide and carrying chromophore elements suitable for emitting fluorescence in response to excitation by guided waves having an evanescent portion, the device being characterized in that it includes coupling means for coupling excitation light with the waveguide in the form of guided waves, the coupling means being substantially non-directional.
1. A biochip device for excitation by an excitation light having a wavelength, the biochip device comprising:
a multimode waveguide that is formed as a plate, with a thickness in a range supporting multiple light-propagating modes at the excitation wavelength, the multimode waveguide having a top face, and a side wall connecting the top face and the bottom face, the top face including a first portion and a second portion, the second portion carrying chromophore elements emitting fluorescence in response to the excitation light by guided waves having an evanescent portion, the chromophore elements being used to detect molecular attachments;
a light-diffusing element configured to diffuse the excitation light incoming from a direction out of the plane of the waveguide into the waveguide in a plurality of modes propagating inside the waveguide in the plane of the waveguide as guided waves and having a disordered spatial distribution of refractive index, the light-diffusing element diffusing the excitation light into the waveguide at one of: (i) the first portion of the and (ii) a portion of the bottom face opposite the first portion of the top face through the waveguide to the second portion carrying the chromophore elements, the light-diffusing element being a frosted portion formed as part of the one of: (i) the first portion of the top face, and (ii) the portion of the bottom face opposite the first portion of the top face at which the excitation light is diffused into the waveguide; and
a layer disposed on the top face or the bottom face of the waveguide, the layer having a refractive index smaller than the refractive index of the waveguide material such that some of the light-propagating modes are extracted from the waveguide and refracted inside the layer, the layer being separated from the light-diffusing element.
2. The device according to claim 1 , further comprising means for absorbing light, the layer interposed between the top face or the bottom face of the waveguide and the means for absorbing light, the layer and the means for absorbing light together eliminating the some of the light-propagating modes from the waveguide.
3. The device according to claim 2 , wherein the layer is located between the light-diffusing structure and the second portion carrying the chromophore elements.
4. The device according to claim 3 , wherein the means for absorbing is disposed on the index-matching layer.
5. The device according to claim 1 , further comprising a means for deflecting light placed on the layer.
6. The device according to claim 5 , wherein the means for deflecting comprises a prism.
7. The device according to claim 2 , wherein said waveguide has a thickness e and a guided mode having the greatest effective index reflecting inside the waveguide has a reflection angle θ, and
the layer and the means for absorbing extend over a distance that is longer than 2×e×tan θ.
8. The device according to claim 2 , wherein the layer extends upstream from the second portion carrying the chromophore elements and in part within the second portion.
9. The device according to claim 1 , further comprising a hybridizing chamber disposed on the top face of the waveguide and surrounding the second portion carrying the chromophore elements and a hybridizing fluid contained in the chamber,
wherein the refractive index of the layer is greater than or equal to the greatest refractive index of the hybridizing chamber and the hybridizing fluid.
10. The device according to claim 9 , wherein the value of the refractive index of the layer lies in the range n=1.30 to n=1.45.
11. The device according to claim 1 , wherein the layer is configured to extract guided modes for which the effective index is less than or equal to a predetermined threshold value from the plurality of modes from the waveguide.
12. The device according to claim 1 , further comprising a plurality of pads disposed at the second portion, the plurality of pads being configured to receive probe molecules deposited thereon, the chromophore elements being configured to hybridize with the probe molecules deposited on the pads.
13. The device according to claim 1 , wherein the frosted portion has a grain size in the range of 0.1 μm-50 μm in the plane of the waveguide and perpendicularly thereto.
14. The device according to claim 1 , wherein the value of the refractive index of the layer lies in the range n=1.30 to n=1.45.