Optomechanical Sensor for Species Concentration in Liquid Media

Abstract

A blood concentration sensor for at least one biological species comprising a support (2), at least one waveguide (4), an optomechanical resonator (6) suspended from the support (2), said optomechanical resonator (6) being optically coupled to the waveguide, said optomechanical resonator being configured to vibrate in volume mode and comprising at least one face extending in the plane of the sensor and configured to receive molecules of said given species, the optical resonator comprising a body (C) including an optically active zone (MO) and an optically insulating layer (9) deposited at least directly above the optically active zone (MO) so as to confine at least part of an electromagnetic wave within the body. Figure for the abstract: 1B

Description

Title of the invention: OPTOMECHANICAL SENSOR FOR THE CONCENTRATION OF SPECIES IN A LIQUID MEDIUM

[0001] TECHNICAL FIELD AND STATE OF THE PRIOR ART

[0002] The present invention relates to an optomechanical sensor for the concentration of species in a liquid medium, in particular biological species.

[0003] There are different techniques for detecting and quantifying biological species in a liquid. For example, the enzyme-linked immunosorbent assay (ELISA) is a laboratory test that allows the presence of an antibody or antigen in a sample to be detected.

[0004] This method uses an immunological test, in which the dosage is coupled with an enzyme-catalyzed reaction that releases a colored component followed by spectroscopy. This method is long and single-use.

[0005] There is also a method based on surface plasmon resonators. The binding of a molecule to the surface is monitored by surface plasmon resonance, which detects changes in optical index at the surface, and allows the concentration of molecules to be deduced. This method is easy to use and fast, but it is not very sensitive.

[0006] There are also devices implementing an optomechanical resonator, as described in document [1] comprising an optomechanical disk on which a bacterium is deposited. The bacterium has the effect of modifying the mechanical resonance frequency of the disk, which modifies the optical path in the disk, modifying the light intensity. From this variation in intensity, it is possible to determine the mass deposited on the disk.

[0007] The optical mode is generally located on a part of the disc, which can be defined as the optical active zone. This zone is generally located on the periphery of the disc.

[0008] However, the optical mode is not completely confined in the disk. As a result, when a mass to be detected is deposited on the optical active zone, it induces a mechanical response but it also disturbs the optical mode, producing a wavelength shift of the mode and losses which degrade its quality. It is then necessary to implement a closed loop to follow the wavelength of the optical mode, which is modified as mass is deposited on the disk in order to take this variation into account in determining the mass. deposited. In addition, the quality of the optical mode degrades with the added mass, limiting the lifespan of the sensor.

[0009] These drawbacks are all the more troublesome since the sensitive area on which the mass to be detected is deposited and the optical active area correspond at least in part to the same area of ​​the sensor surface. Statement of the invention

[0010] It is therefore an aim of the present invention to provide a sensor for the concentration of species in a liquid medium which does not have the drawbacks of the state of the art stated above.

[0011] The aim stated above is achieved by a concentration sensor of at least one species contained in a liquid comprising at least one optical resonator and at least one mechanical resonator coupled to each other, at least one waveguide optically coupled with the optical resonator. The sensor comprises an optical isolation layer formed on the surface of the optical resonator so as to at least cover the optical mode and to isolate the optical mode from the surface of the optical resonator and thus make the optical mode insensitive, or even insensitive to the surface state of the optical resonator. The optical mode is then sensitive only or almost only to the movement of the resonator.

[0012] Thus when a mass is deposited on the optical resonator, it does not disturb the optical mode. Or when the optical properties of the surface of the resonator are modified due to a treatment, for example the deposition of a bonding layer, the optical mode is little or not disturbed.

[0013] Preferably, the material of the optical isolation layer is chosen so as to have an optical index relative to that of the material of the optical resonator such that the optical mode remains confined in the resonator.

[0014] Preferably, the material of the optical insulation layer has mechanical properties such that the function of the sensor is not or only slightly degraded.

[0015] In the case of a disk-shaped optical resonator, the optical mode is generally located at the periphery of the disk, the optical insulation layer may be annular in shape covering the periphery of the disk.

[0016] In other words, the optical mode is isolated so as to make it insensitive or very insensitive to effects on the surface of the sensor.

[0017] Preferably, the mechanical resonator vibrates in volume mode in the plane of the sensor and at high frequency.

[0018] In a preferred embodiment, the optical resonator and the mechanical resonator are formed by the same object, forming an optomechanical resonator. Advantageously, the optomechanical resonator is at least partly opera- nationalized so as to be selective with respect to said at least one species.

[0019] The subject of the present application is then a structure for a sensor for the concentration of at least one given species in a liquid medium comprising a support, at least one waveguide, at least one optical resonator suspended from the support, said optical resonator being optically coupled to the waveguide, so that the waveguide injects an electromagnetic wave into the optical resonator and collects said electromagnetic wave leaving the waveguide, said optical resonator comprising an optical active zone for circulation of the electromagnetic wave, at least one mechanical resonator suspended from the support, said mechanical resonator and said optical resonator being coupled, said mechanical resonator being configured to vibrate in volume mode and comprising at least one face extending in the plane of the sensor and configured to receive molecules of said given species.The optical resonator comprises a body comprising the optical active zone, said body comprising a first face and a second face, the second face being opposite the support and the first face being oriented opposite the support, said optical resonator also comprising an optical insulation layer deposited at least on the first face at least directly above the optical active zone so as to confine at least partially the electromagnetic wave in the body.

[0020] The optical insulation layer is advantageously also deposited on the waveguide.

[0021] Preferably, the ratio between the optical refractive index of a material of the optical insulation layer and the optical refractive index of a material of the body is less than or equal to 0.75.

[0022] Also preferably, the ratio between the Young's modulus of a material of the optical isolation layer and the Young's modulus of a material of the body is less than or equal to 10.

[0023] The optical insulation layer advantageously has a thickness less than or equal to the distance between the first face of the body and the second face of the body.

[0024] According to an additional characteristic, the optical insulation layer comprises several materials having different optical indices.

[0025] For example, the optical resonator has the shape of a disk, a ring or a racetrack and the optical active area is located in the outer peripheral part of the body and the optical isolation layer has the shape of a ring.

[0026] In an advantageous example, the mechanical resonator comprises a functionalization layer specific to said given species. Preferably, the functionalization layer is present only on the optical isolation layer.

[0027] According to an additional characteristic, the optical resonator and the mechanical resonator are the same element suspended from the support, the first face forming the face configured to receive molecules, said element being an opto-mechanical resonator.

[0028] For example, the body is made of silicon and the optical insulation layer is chosen from SiO2, PAIN or A12O3.

[0029] Preferably, the dimension of the mechanical resonator and / or the optical resonator in the direction normal to the plane of the sensor is at least 10 times smaller than the dimensions of the mechanical resonator and / or the optical resonator in the plane of the sensor.

[0030] The functionalization layer is advantageously homogeneous and / or has a thickness less than or equal to 20 nm.

[0031] According to an additional feature, the mechanical resonator is configured to vibrate in a radial mode.

[0032] In an exemplary embodiment, the mechanical resonator and / or the optical resonator is or are suspended by a foot connecting a face of the resonator(s) opposite the support and the support.

[0033] The concentration sensor structure may comprise means for exciting the mechanical resonator so as to cause it to vibrate, preferably at its resonant frequency.

[0034] According to an additional characteristic, the concentration sensor structure comprises several sets of coupled optical and mechanical resonators or several optomechanical resonators, coupled to a single waveguide.

[0035] Another subject of the present application is a sensor for the concentration of at least one given species in a liquid medium comprising at least one sensor structure according to the invention, a light source connected to one end of the waveguide, and means for processing the light wave connected to the other end of the waveguide.

[0036] Another subject of the present application is a microfluidic system comprising at least one channel for circulating the liquid in which the concentration of at least one species is to be measured and at least one concentration sensor according to the invention, the optical resonator and the mechanical resonator being arranged in the channel. Brief description of the drawings

[0037] The present invention will be better understood on the basis of the following description and the attached drawings in which:

[0038] [Fig. 1A] is a perspective view of an example of a concentration sensor according to the invention.

[0039] [Fig. IB] is an enlarged view of the optomechanical resonator of [Fig. IA].

[0040] [Fig.2] is a side view of another example of an optomechanical resonator.

[0041] [Fig.3A] is a side view of another example of an optomechanical resonator.

[0042] [Fig.3B] is a top view of the resonator of [Fig.3A].

[0043] [Fig.4] is a side view of a variant of the optomechanical resonator of the [Fig.3A].

[0044] [Fig.5] is a side view of an example of an optomechanical resonator comprising a functionalization layer.

[0045] [Fig.6] is a side view of an example of an optomechanical resonator comprising a bonding layer and a functionalization layer.

[0046] [Fig.7] is a schematically represented top view of an example of a sensor concentration involving means of excitation.

[0047] [Fig.8] is a schematically represented top view of a sensor of concentration whose resonator has holes to increase its precision.

[0048] [Fig.9] is a perspective view of another example of a concentration sensor having a particular waveguide structure.

[0049] [Fig. 10] is a side view of an exemplary embodiment of a resonator which can be implemented in the concentration sensor according to the invention.

[0050] [Fig. 11] is a top view of an example of a sensor implementing the re sonator of [Fig. 10].

[0051] [Fig. 12] is a schematic representation of an example of a micro-system fluidics implementing at least one concentration sensor according to the invention.

[0052] [Fig. 13] is a schematic representation of another example of a micro-system fluidics implementing at least one concentration sensor according to the invention.

[0053] [Fig. 14] is a schematic representation of another example of a micro-system fluidics implementing at least one concentration sensor according to the invention.

[0054] [Fig. 15] is a schematic representation of an example of a sensor comprising a optical resonator and a separate optical resonator coupled to each other.

[0055] [Fig.l6A]

[0056] [Fig.l6B]

[0057] [Fig.l6C]

[0058] [Fig.l6D]

[0059] [Fig.l6E]

[0060] [Fig. 16F] are schematic representations of elements obtained during of steps of an example of a method of manufacturing a sensor according to the invention.

[0061] DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0062] An optical mode is generally defined as a particular solution for the propagation of an electromagnetic wave in a cavity defined in, for example, an optical resonator. In the present application, the term "optical mode" designates the area of ​​the resonator in which the propagation path of this wave is located.

[0063] In [Fig. 1A], we can see an example of a sensor Cl for the concentration of species in a liquid medium according to the invention.

[0064] In the present application, the term “species” means biological species, such as bacteria or viruses, chemical molecules, atoms and / or nanoparticles.

[0065] The species to be detected have dimensions ranging from a few tens of nm to a few pm. The species have maximum dimensions less than or equal to the dimensions of the resonator in the plane, which will be described below.

[0066] The liquid can be blood, plasma, humors, and more generally any bodily liquid, water from watercourses, such as rivers, streams, ocean water, water from city water supply networks, etc., and any other liquid that one wishes to analyze.

[0067] The sensor C1 comprises a support or substrate 2, at least one waveguide 4 supported by the substrate and an optomechanical resonator 6 suspended from the substrate 2, a light source S and means T for processing the light wave leaving the waveguide. The support 2, the waveguide 4, the optomechanical resonator 6 form a sensor structure. The light wave is designated L.

[0068] The waveguide 4 comprises an input end 4.1 of a light wave connected to a light source via a coupling network 5.1, and an output end 4.2 connected to means for processing the light wave leaving the waveguide via a coupling network 5.2.

[0069] The resonator 6 is arranged close to a flank of the waveguide 4 so as to be optically coupled to it. The waveguide is in the evanescent field of the resonator, so that the light wave coming from the source is injected into the optical resonator and the light wave having circulated in the resonator is collected by the waveguide.

[0070] The width of the space between the side of the waveguide and the lateral edge of the resonator is for example between 10 nm and 200 nm.

[0071] In the example shown, the optomechanical resonator 6 has the shape of a disk suspended from a foot 8 fixed to a face of the disk facing the substrate. The disk extends in a plane of the sensor. The resonator has two end faces substantially parallel to the plane of the sensor and a lateral face ([Fig.lB]).

[0072] In the present application, the term “sensor plane” means a plane parallel to the substrate.

[0073] Preferably the foot has a small diameter compared to the dimensions of the disc in the plane of the sensor, more particularly a small diameter compared to the diameter of the disc, preferably the foot has a diameter 10 times smaller than the diameter of the disc.

[0074] More generally, the diameter of the foot is ten times smaller than the smallest dimension of the resonator in the plane of the sensor, so the foot has little or no effect on the radial vibration of the resonator.

[0075] Alternatively, the resonator is suspended by in-plane springs or by radially extending nanometer-sized beams compressed and tensioned by the vibration of the disk. The springs or beams are then dimensioned to have a lower axial stiffness than that of the resonator.

[0076] Any other form of resonator may be suitable, for example, seen from above, the resonator may have the shape of a ring, an ellipse or a racetrack. Alternatively, the resonator is a photonic crystal.

[0077] As shown in [Fig.lB], the resonator comprises a body C, comprising an optical mode MO and an optical insulation layer 9 covering the body. The optical mode MO is shown schematically by dotted lines. In this example, the optical mode MO is located in the outer periphery of the body C.

[0078] The optical isolation layer 9 is such that it provides isolation of the optical mode from the outside in order to limit disturbances of the optical mode by the effects on the external surface of the resonator.

[0079] The material of the optical isolation layer is chosen such that it offers a good optical refractive index contrast with the material of the body C, so that the optical mode remains confined in the body.

[0080] "Good optical refractive index contrast" means a difference between the optical refractive index of the body C and that of the optical insulation layer 9, such that a total reflection of the electromagnetic wave towards the body is obtained. The difference in optical indices depends on the optical mode of interest, but the optical index of the layer 9 is preferably less than 0.75 times that of the body C. Total reflection means a reflection of 100% of the Fonde which is reflected?

[0081] For example, the body C is made of silicon with an optical index of 3.4 and the optical insulation layer 9 is made of SiO2 with an optical refractive index equal to 2.3 for a wavelength of 1.55 qm.

[0082] Alternatively, the optical insulation layer 9 is made of AIN with a refractive index of 2 or of A12O3, with a refractive index of 1.7 for a wavelength of 1.55 qm.

[0083] Alternatively, the body C is made of GaAs with a refractive index of 3.4 or Ge with a refractive index of 4.25 for a wavelength of 1.55 qm.

[0084] The body C combined with the optical insulation layer 9 forms a waveguide for the electromagnetic wave.

[0085] In a particularly advantageous example, the optical insulation layer 9 is also deposited on all or part of the waveguide, which makes it possible to reduce the degradation of the performance of the waveguide resulting from a deposition of particles on this one.

[0086] Preferably, the material of the optical isolation layer 9 has mechanical properties close to or equal to those of the material of the body so as not to degrade the mechanical response of the resonator. Preferably, the material of the optical isolation layer has a Young's modulus of the same order of magnitude as that of the material of the body; the ratio between the Young's modulus of the isolation layer 9 and the Young's modulus of the material of the body is less than or equal to 10.

[0087] Indeed the resonator vibrates in the plane preferably in a radial mode, it is therefore preferable that the optical insulation layer 9 does not modify or only slightly modifies the mechanical resonance mode of the resonator.

[0088] For example, the body C is made of Si with a Young's modulus of 160 GPa and the insulation layer is made of SiO2, AIN or Al2O3 with Young's moduli of 65 Gpa, 277 GPa and 350 GPa respectively.

[0089] In the case where the optical resonator and the mechanical resonator are distinct as will be described below, the mechanical properties of the material of the optical isolation layer have no influence on the detection.

[0090] The thickness of the optical isolation layer 9 depends on that of the body. Preferably, the optical isolation layer 9 has a thickness less than or equal to that of the body C, and preferably equal to the thickness of the body ensuring isolation of the optical mode. A thickness close to or equal to that of the body makes it possible to ensure good confinement of the optical mode while limiting the mechanical effect of the isolation layer on the resonator.

[0091] By way of example, the body C has a diameter of between 200 nm and 200 pm, a thickness of between 1 / 100 and 1 / 10 of its diameter and the optical insulation layer has a thickness of between 2 nm and 500 nm.

[0092] Alternatively, the optical isolation layer comprises several different materials with specific optical properties. In one embodiment, the refractive index of the layer in contact with the body is the lowest and the refractive indices increase with distance from the body, similar to graded-index optical fibers. This makes it possible to combine several layers with different mechanical properties. This makes it possible, for example, to first deposit a layer of SiO2 (n=2.3, density 2.2 kg / m2), which is relatively low-density, followed by a second thin layer of Al2O3 (n=1.7, density 4 kg / m2) which is much denser but more optically insulating, to effectively confine the optical mode with the least impact on the mechanical mode.

[0093] The resonator is intended to collect the species to be detected, the surface area of ​​the resonator is therefore preferably as large as possible to maximize the quantity of catchable species.

[0094] However, we preferably seek to minimize the lateral surface of the resonator to limit viscous losses by interaction with the solvent and promote shearing. We therefore seek to maximize the end surfaces of the resonator and reduce the lateral surface. We also seek to reduce the mass of the optomechanical resonator to have good mass sensitivity.

[0095] The shape of the disc is therefore particularly advantageous in terms of surface area ratio. A resonator with a large aspect ratio, a large dimension in the plane of the sensor / thickness of the resonator ratio, is preferably chosen.

[0096] In the case of a disc, the ratio Disc diameter / thickness is preferably between 10 and 100. The maximum diameter of the resonator is preferably a few hundred μm.

[0097] In an exemplary embodiment, the resonator comprises tapered edges advantageously improving the optical performance of the resonator.

[0098] The resonator is further preferably such that it vibrates in a volume mode in the plane, making it possible to achieve a high vibration frequency, for example at least equal to 100 MHz.

[0099] Preferably, the resonator vibrates in a radial mode or RBM (Radial Breathing Mode in English terminology), such a mode makes it possible to achieve very good coupling between the optical mode and the mechanical mode. Indeed, the radial vibration of the disk has a significant impact on the optical properties of the disk, in particular on the length of the optical path within the resonator and therefore on the light power recovered by the waveguide 2.

[0100] Alternatively, the resonator may vibrate in a tangential mode or a wine glass mode. However, it has reduced efficiency compared to the resonator in a radial mode.

[0101] In [Fig.2], we can see another example of the embodiment of the opto resonator mechanical in which the optical insulation layer 9' is formed only on the upper face Cl of the body in the representation of [Fig.2], i.e. the face which is not opposite the support.

[0102] In Figures 3A and 3B we can see another example of embodiment of the optomechanical resonator, in which the optical isolation layer 9” is formed only on the peripheral zone of the body C above the optical mode MO. The implementation of an optical isolation layer of reduced surface makes it possible to limit the influence of the optical isolation layer on the mechanical properties of the mechanical resonator. In addition, the outer peripheral zone is the zone which sees the most displacement in the radial vibration mode. Alternatively, the optical isolation layer covers also the lateral edge of the body and the outer peripheral area of ​​the underside of the body.

[0103] In another embodiment shown in [Fig.4], the optical mode MO is not located at the outer periphery of the body but inside on a diameter smaller than the outer diameter of the body and the optical insulation layer 9”' is located opposite the optical mode MO.

[0104] In the examples described, the optical insulation layer has a constant thickness taking into account the manufacturing method. Alternatively, the layer has different thicknesses depending on the covered area. Preferably, it has a greater thickness at the optical mode and a smaller thickness at the other areas of the body, which advantageously makes it possible to limit the influence of the optical insulation layer on the mechanical properties of the resonator.

[0105] In the examples described above, the sensor does not include a functionalization layer, the sensor is then not selective with respect to the species detected.

[0106] In Figures 5 and 6, we can see an advantageous example of embodiment in which the sensor is functionalized so as to be specific to one or more species to be detected.

[0107] The functionalization layer may be sensitive to biological species, individual atoms or nanoparticles. In the case of nanoparticles, the specificity may be directed against markers present on the surface of these nanoparticles or against the atomic element constituting the nanoparticle. Specificity towards the size of the nanoparticles may also be envisaged.

[0108] In [Fig.5], the functionalization layer 10 is formed directly on the optical isolation layer 9'.

[0109] In [Fig.6], a bonding layer 11 is deposited on the optical isolation layer 9' and the functionalization layer 10 is deposited on the bonding layer. In this example, the bonding layer 11 and the functionalization layer 10 completely cover the optical isolation layer 9'. The molecules E of species to be detected trapped by the functionalization layer 10 are shown diagrammatically.

[0110] Alternatively, the bonding layer and the functionalization layer or the functionalization layer only cover part of the optical insulation layer.

[0111] The implementation of an optical isolation layer is all the more advantageous in the case of a functionalized sensor since the bonding layer is generally produced prior to the functionalization or grafting layer, and since the latter has the effect of reducing the quality of the surface of the body. The production of a disk with precise optical properties at the level of the optical active zone is then made difficult. The optical isolation layer limits, or even prevents such degradation of the surface of the body.

[0112] For example, the functionalization layer comprises at least one macromolecule capable of specific recognition of a target, i.e. the given species to be detected.

[0113] The functionalization of the resonator to several species is obtained for example by functionalizing different parts of the resonator, each specific to a species, or by producing a functionalization layer which mixes different bioreceptors each specific to a species.

[0114] By way of example, the functionalization layer comprises antibodies specific to a protein or a small molecule, for example a toxin, aptamers specifically recognizing a protein or a small molecule, strands of DNA or RNA which will hybridize with a strand of DNA or RNA complementary to that grafted onto the surface of the resonator, molecular imprinting polymers (MIP in English terminology).

[0115] The functionalization of the surface of the resonator consists of modifying the molecules present on the surface of the sensor and / or grafting onto the surface of the sensor the new molecules allowing the specific recognition of the target sought.

[0116] The modification of the molecules present on the surface of the sensor may, for example, consist, in a non-limiting manner, of the oxidation of a function, the dehydration of an alcohol function, the nucleophilic substitution of one group by another or an esterification. All these transformations are well known to those skilled in the art who will know how to go from one chemical function to that of interest.

[0117] Functionalization by grafting may generally require an intermediate layer supporting the layer of new molecules providing the desired functionalization. There are several methods for functionalizing a silicon surface. A first method consists of grafting a layer of PEG (polyethylene glycol polymer chain) onto the silicon surface. One end of the PEG chain binds covalently to the silicon surface and the other end remains free, thus allowing the molecule of interest to be grafted for specific recognition of the sensor. This method is described in document [2]. Another method consists of using carbon chains, one end of which has a silane function and the other end is chosen so as to subsequently graft the molecule allowing specific recognition of the sensor.The other end can be an epoxy function, subsequently allowing DNA to be grafted, or an N-hydroxysuccimide ester function which will allow the grafting of a protein, for example immunoglobulin, by means of an amine radical within the structure of the latter. This method is described in documents [3] and [4]. Finally, another method consists of grafting onto the silicon surface an alkynene having an alkene function at one end and an alkyne function protected by a trimethylgermanyl group at the other end. After grafting onto . the silicon surface, the alkyne function is used to couple the molecule of interest by click chemistry. This method is illustrated in document [5].

[0118] The functionalization layer 10 has a small thickness, or even comprises a single layer of functionalization molecules. Advantageously, the thickness of the functionalization layer is less than 20 nm, and preferably less than 10 nm. In addition, the layer has a constant thickness over the entire surface.

[0119] In the present application, the term “constant thickness” means a layer whose thickness varies by at most 25% of its thickness over its entire surface.

[0120] Furthermore, the functionalization layer is very advantageously homogeneous on the surface of the resonator, i.e. it comprises a relatively uniform number of molecules per unit of surface.

[0121] The homogeneity of the layer corresponds to the quantity of target recognition sites to be detected per unit area, which is a multiple of the number of bioreceptor molecules immobilized per unit area on the surface of the resonator. A unit area is defined as being at least 1 / 100th of the sensor surface. A layer is said to be homogeneous when the number of grafting / recognition sites available in each unit area varies by less than 5 / 100th around an average value. The number of recognition sites per unit area depends on the chosen functionalization protocol and the size of the bioreceptor molecule.

[0122] The implementation of a thin and advantageously homogeneous functionalization layer makes it possible to preserve the optical coupling and opto-mechanical coupling properties of the resonator after functionalization.

[0123] In addition, the implementation of a homogeneous layer makes it easier to trace the concentration of the species.

[0124] The functionalization layer can be localized, advantageously it can be deposited only on the end faces of the resonator, or even on only one of the end faces, and not on the lateral face of the resonator. In this case, the functionalization layer then does not intervene in the optical coupling between the waveguide and the resonator.

[0125] Even more advantageously, the sensor comprises a passivation layer blocking the absorption of the particles of interest, this layer is formed on the areas of the sensor where it is not desired that the target particles fix, i.e. on the areas other than those where the functionalization layer is formed. The passivation layer is for example formed at least on the substrate.

[0126] In the case where the functionalization layer covers a part of the upper end face of the resonator, preferably its peripheral zone, it then has for example a ring shape, the passivation layer also covers the central part of the upper end face of the resonator inside the functionalization layer.

[0127] Thanks to the implementation of a passivation layer, the attachment of the targets sought outside the sensitive zone of the sensor is limited. The effective detection of lower concentrations of species within the liquid medium is then improved.

[0128] In the case where the functionalization layer covers the entire sensitive surface of the sensor, the passivation layer is formed only on the substrate.

[0129] The passivation layer contains, for example, silanes of formula X3Si-(CH2 )nCH3. The X3Si- part allows attachment to the silicon and the saturated aliphatic chain -(CH2)nCH3 prevents the grafting of the molecules of interest.

[0130] For example, X can be a halogen (Cl, Br...) or a group R3O- (R= CH3-, CH3 CH2-...).

[0131] In another example, the passivation layer is a PLL-g-PEG (poly(L-lysine)-graft-poly(ethylene glycol)) polymer. The Lysine part allows grafting onto the substrate while the ethylene glycol chain prevents the molecules from grafting onto the substrate:

[0132] The operation of the sensor comprising a functionalization layer will now be described.

[0133] The wavelength of the light wave to be injected into the resonator is chosen close to the optical resonance of the resonator, i.e. on the edge of the optical resonance peak. The light wave resonating inside the optical resonator is then very sensitive to the mechanical deformation of the mechanical resonator, in particular when the optical and mechanical resonators are the same.

[0134] The light wave at the chosen wavelength is injected into the waveguide by a light source, by optical coupling. The light source is injected into the optomechanical resonator 6. L denotes the light wave circulating in the resonator. The modulation frequency of the power of the light wave is chosen so as to set the resonator vibrating in a volume mode, advantageously in a radial mode.

[0135] The sensor is immersed in a liquid for which the concentration of a given species is to be measured and for which the sensor has a suitable functionalization layer. The molecules of the given species are then captured by the functionalization layer and attach to the resonator, which modifies the mass of the resonator and therefore the vibration frequency of the resonator. Measuring the variation in the vibration frequency makes it possible to determine the quantity of the given species deposited on the resonator and to determine the concentration. The presence of the optical isolation layer prevents the optical mode from being modified directly by the mass deposited, it is modified mainly or only by the movement of the resonator.

[0136] Preferably, before the circulation of the sample containing the target to be detected, a biological buffer solution having a viscosity similar to that of the sample containing the target circulates around the sensor which allows the sensor to reach a stable resonance frequency. Then, the sample containing the target is injected and the sensor perceives the change in resonance frequency coming from the grafting of the target on the resonator This response of the sensor to the biological grafting has a dynamic in N*ex / t (k=Ae(Ea / RT)) and lasts of the order of 5 min to 40 min in practice.

[0137] In an advantageous example, several sensors are used.

[0138] In a two-sensor configuration, the first sensor is functionalized with a first biological molecule specifically recognizing the target. The second sensor is functionalized with a second biological molecule of a similar nature to the first molecule, but having a specific recognition capacity for a species other than the target sought.

[0139] The signal emitted by the first sensor contains information on the specific attachment of the target and information on the non-specific attachment, other elements than that sought, which is parasitic information. The signal emitted by the second sensor contains only the information on the non-specific attachment. By subtracting the signal from the second sensor from the signal of the first sensor, the information on the specific grafting is obtained, which makes it possible to detect the presence of the sought target.

[0140] After a measurement is made by the sensor, it can be cleaned.

[0141] According to an example of rinsing, a biological buffer solution is sent to the sensor via the fluid supply system. This solution causes the detachment of some of the targets immobilized on the sensor. Some targets may remain on the surface of the sensor, immobilized on their corresponding bioreceptors. These remaining elements cause a reduction in the quantity of sites available for subsequent analyses with the same sensors.

[0142] Nevertheless, the sensor according to the invention has a high sensitivity and is therefore particularly suitable for detecting only a very small number of target molecules. Detection can often be done with the recognition of a number of target elements representing only a portion of the targets that can be grafted in full to the surface of the sensor. Thus, the sensors can, in particular in the application for detecting a small number of target molecules, carry out several successive analyses, because the analyzed samples do not contain enough target elements to saturate the surface of the sensor.

[0143] When one wishes to force the separation of the remaining target elements in order to release all the bioreceptors. Several techniques can be used to be adapted according to the target molecules.

[0144] In the case of hybridized DNA strands (target and bioreceptor), the temperature of the sensor can be increased to 80°C for a period of a few minutes, for example by means of an attached heating device, which causes the dehybridization of any DNA-DNA complex and releases the targeted elements from the surface of the disc. A rinsing solution such as a biological buffer can circulate simultaneously to collect the released elements.

[0145] For protein-protein or protein-other biological element recognition to be detected, such as toxins, bacteria or cells, weakly concentrated solutions of NaOH sodium hydroxide or guanadinium hydrochloride can be used which can cause the dissociation of the antigen-antibody bond and completely regenerate the sensor before new measurements. Regeneration can nevertheless degrade the receptor proteins, limiting the number of possible regenerations, for example depending on the functionalized surface, the number of regenerations can be between 10 and 40.

[0146] In the operating example described above, the resonator is set into vibration by the measuring light wave.

[0147] Alternatively, the resonator is not set into vibration by the light wave. Only the variation in resonance frequency is measured using the Brownian noise of the resonator; in fact, thermal agitation makes the resonator vibrate at its resonance frequency. In this alternative, the light wave is only used to detect the variation in vibration frequency.

[0148] In the other examples described above, the optomechanical resonator comprises a body provided with an optical insulation layer at least on its upper surface C1 at least in line with the optical mode.

[0149] In an advantageous variant, the sensor shown in [Fig.7] further comprises specific excitation means 14 for setting the resonator into vibration, at its resonance frequency, which allows great sensitivity in reading changes in mechanical frequency, and preferably at a significant amplitude to maximize the signal-to-noise ratio. Setting the resonator into vibration makes it possible to improve the resolution.

[0150] The grafting of biological targets increases the mass of the mechanical resonator, which modifies its resonance frequency, which is converted by the optical resonator forming a transducer.

[0151] Optical means for putting the optical resonator into optical resonance and means for putting the mechanical resonator into mechanical resonance can therefore coexist. The optical resonator forms a transducer, which then converts the mechanical resonance into light and then electrical information.

[0152] In another example, the excitation means 14 are of the electrostatic type, they comprise a first electrode 14.1 formed on the lateral edge of the resonator 4 for example by doping the silicon and a second electrode 14.2 formed on the support opposite the first electrode.

[0153] Alternatively, the excitation means are of the optical type by radiation pressure, for example using a so-called “pump-probe” mode using a light signal of a wavelength different from the light signal used for the measurement, and the amplitude of which is modulated at the resonance frequency of the disk. Alternatively, a single light signal is used which ensures both the measurement and the excitation; this is modulated by means of an electro-optical modulator.

[0154] In an advantageous variant, a phase lock loop is integrated, which makes it possible to control the phase of the vibration at resonance.

[0155] Advantageously, a reduced mass resonator is produced in order to increase the sensitivity of the sensor.

[0156] This can be achieved by making through holes 12 in the 6” resonator, as shown in [Fig.8]. The holes 12 offer the additional advantage of increasing the specific surface area covered by the functionalization layer. The holes are, for example, in the direction normal to the plane of the resonator. In addition, these holes can advantageously be used to facilitate the release of the resonator, when it is released by etching the sacrificial layer in a microelectronic process.

[0157] When the foot is made from the material of the sacrificial layer, for example in SiO2, its diameter before release is chosen so that at the end of the etching the “remaining” diameter is sufficient to support the resonator.

[0158] In [Fig.9], we can see an example of an advantageous sensor when the waveguide is supported by portions of the sacrificial layer.

[0159] When releasing the resonator, we do not want to completely release the waveguide 2, nor the coupling networks.

[0160] Furthermore, the width of the waveguides is determined to obtain particular optical properties (for example, to be optically single-mode). When this width is small compared to the distances to be etched under the resonator, wider waveguide portions 16 are advantageously provided at a distance from the coupling zones with the resonator and / or near the connections between the waveguide and the coupling networks 5.1, 5.2.

[0161] Thus the sacrificial layer under the portions 16 are not entirely etched and serve as support for the waveguide. The width of the portions 16 is chosen so as to be at least equal to the maximum distance to be etched in the plane + a width sufficient to support the waveguide.

[0162] In the example shown, the portions 16 are distributed regularly along the waveguide but this is not limiting.

[0163] In another advantageous embodiment shown in Figures 10 and 11, making it possible to overcome etching problems, the foot 8' of the resonator 6' and / or the supports of the waveguide 4' are made by vias 18, 20 made of a material insensitive to etching during release. For example, when the release is obtained by etching silicon oxide with HF, the vias are made of polysilicon or metal.

[0164] The waveguide is coupled to the light source and the analysis device, for example, by optical fibers positioned at an optimal angle using piezoelectric positioners above the coupling networks. Advantageously, a fiberizing technique can be used, consisting of "gluing" fibers directly onto the chip.

[0165] In [Fig. 12], we can see an example of a microfluidic system integrating the sensor.

[0166] The SF1 system comprises a microchannel 20, for example formed in a cover 22 which is attached to the substrate. The liquid to be analyzed is injected into the channel 20. The dimensions of the channel are such that the liquid is forced to circulate at the level of the resonator only. This maximizes the probability of capturing the species to be detected and reduces the analysis time. In addition, the volume of liquid required can be reduced. A typical microchannel can measure from 5 pm to 500 pm in height and from 10 pm to 700 pm in width.

[0167] In the example shown, the system comprises a single sensor and the waveguide is transverse to the channel.

[0168] Alternatively, the system comprises several sensors arranged one after the other and functionalized differently and each coupled to its own waveguide. Thus, with a single system, it is possible to determine the concentrations of several species in the same liquid sample and almost simultaneously.

[0169] Alternatively, the waveguide is aligned with at least part of the channel and several resonators are coupled to it and by multiplexing it is possible to carry out the detection of several species, or even carry out positive controls, for example by using two sensors, a first sensor functionalized with a bioreceptor molecule and having a specificity towards the molecule sought and a second sensor functionalized with a bioreceptor molecule of the same type as the first sensor, but not having a specificity towards the molecule sought.

[0170] In [Fig. 13], we can see another example of a microfluidic circuit SF2 comprising a channel 24 in the form of a serpentine comprising straight portions 26 connected by curved portions 28 and a resonator RI, R2, R3 located in a straight portion 26 and waveguides Gl, G2, G3 coupled to each resonator, and transverse to the straight portions.

[0171] Alternatively, the resonators are coupled to the same waveguide and the detection is carried out by multiplexing.

[0172] In [Fig. 14], we can see yet another example of a SF3 microfluidic system which differs from the system of [Fig. 13] in that the straight portions 26 are not connected by curved portions and form independent microchannels which can be supplied with different liquids.

[0173] Advantageously, the functionalization can be carried out by circulating the functionalization liquid in the channel during manufacturing.

[0174] In the case of the SF2 system, it is advantageous to produce only the straight portions beforehand, which are functionalized with different liquids, so that each resonator has its own functionalization and then the curved portions are produced so as to form a single system with resonators having different functionalizations.

[0175] In [Fig. 15] we can see an example of a sensor in which the optical resonator and the mechanical resonator are distinct.

[0176] The sensor C2 comprises a sensor structure comprising a substrate 102, a waveguide 104, an optical resonator 106.1 optically coupled to the waveguide 104 and a mechanical resonator 106.2 arranged in the evanescent field of the optical resonator 106.1 and capable, due to its mass modification by particle capture, of modifying the optical properties of the optical resonator. The sensor C2 also comprises a light source S connected to one end of the waveguide 104 and processing means T connected to the other end of the waveguide 104.

[0177] The mechanical resonator 106.2 vibrates in volume mode preferably in radial mode.

[0178] In this example and preferably, only the optical resonator 106.1 comprises an optical insulation layer, this not being necessary on the mechanical resonator. Furthermore, the mechanical properties of the mechanical resonator are not modified. Nevertheless, such a layer can be produced on the mechanical resonator for simplicity of manufacturing process.

[0179] In this example, the mechanical resonator may have a discontinuous or irregular shape, for example a square shape since it is not intended to guide the light wave.

[0180] More generally, the diameter of the foot is ten times smaller than the smallest dimension of the mechanical resonator in the plane of the sensor, so the foot has little or no effect on the radial vibration of the resonator.

[0181] A mechanical resonator is preferably chosen having a high aspect ratio, a dimension ratio in the plane of the sensor / thickness of the resonator important.

[0182] The mechanical resonator can be excited by external electrical means or by thermal agitation, in the latter case the signal to noise ratio is less good.

[0183] An example of a method for producing the sensor C1 will now be described on the basis of FIGS. 16A to 16F.

[0184] For example, an SOI (Silicon on Insulator) substrate is used comprising a polysilicon substrate 200, a layer of SiO2 202, for example 2 pm thick, and a layer of monocrystalline silicon 204 for example 0.22 pm thick, shown in [Fig.16A].

[0185] In a first step, an optical insulation layer 206 is formed on the layer 204, for example by deposition. For example, a layer of SiO2 can be deposited by chemical vapor deposition (CVD).

[0186] For example, layer 206 is made of SiO2 and has a thickness of the order of 100 nm. The element thus formed is shown in [Fig.16B].

[0187] In a next step, the structure of the sensor, in particular the resonator and the waveguide, is defined by lithography and then etching. For example, the etching is a dry etching with a stop on layer 202.

[0188] The element thus obtained is shown in [Fig. 16C].

[0189] In a following step, an intermediate layer 208 is formed allowing the functionalization of the resonator. For example, a layer of Au with a thickness of approximately 10 nm is deposited by PVD. The layer 208 is then defined so as to be only directly above the optical mode, for example by transfer or lift-off.

[0190] The element thus obtained is shown in [Fig. 16D].

[0191] The element thus obtained is shown in [Fig. 16E].

[0192] The resonator is then released, for example, by isotropic wet etching, for example with HF, of the layer 202.

[0193] In a subsequent step, the functionalization layer is formed on the intermediate layer, for example a deposition of aptamers on the Au layer by chemical immersion techniques. The element thus obtained is shown in [Fig.16F]. An optomechanical resonator is obtained comprising the body C, the optical isolation layer 9' and the functionalization layer 10.

[0194] In the case of an electrostatically actuated sensor, a step is provided during which doping is carried out by localized implantation in order to produce conductive tracks.

[0195] Then a succession of deposits of layers of different metals is formed to form the electrical contacts. The stack of layers thus formed is for example Ti / TiN / Au. The stack of layers is formed for example by deposition then the contacts 206 are defined by lithography then etching.

[0196] In the case of the sensor of [Fig.10], additional steps for forming the metal suspension rods are required, for example steps for producing metal vias well known to those skilled in the art are carried out.

[0197] A functionalization of the sensor is then carried out. This may involve a functionalization of the entire structure, the functionalization layer being formed both on the resonator and on the waveguide, or else a localized functionalization, i.e. for example only on the end faces of the resonator. The functionalization layer may be carried out using one of the techniques described above.

[0198] In the case of manufacturing a microfluidic system, the method further comprises manufacturing a cover provided with at least one channel and a sealed assembly of the cover and the sensor. Functionalization can then take place by circulating a fluid ensuring the functionalization of the resonator. List of cited documents

[0199] [1] E. Gil-Santos et al., “Optomechanical detection of vibration modes of a single bacterium », Nature Nanotechnology, 15 (469-474), 2020,

[0200] [2] Zhang, M., Desai, T. & Ferrari, M. Proteins and cells on PEG immobilized Silicon surfaces. Biomaterialsl9, 953-960 (1998).

[0201] [3] Demes, T. et al. DNA grafting on Silicon nanonets using eco-friendly functions lization process based on epoxy silane. Materials Today: Proceedings6, 333-339 (2019).

[0202] [4] Wang, Z.-H. & Jin, G. Silicon surface modification with a mixed silanes layer to immobilize proteins for biosensor with imaging ellipsometry. Colloids and Surfaces B: Biointerfaces34, 173-177 (2004).

[0203] [5] Li, Y., Wang, J. & Cai, C. Rapid grafting of Azido-Labeled Oligo(ethylene glycol)s onto an Alkynyl-Terminated Monolayer on Nonoxidized Silicon via Micro wave-As sisted “Click” Reaction, Langmuir21, 2437-2445 (2011).

Claims

Claims

1. Structure for a sensor for the concentration of at least one given species in a liquid medium comprising a support (2), at least one waveguide (4), at least one optical resonator suspended from the support, said optical resonator being optically coupled to the waveguide, such that the waveguide (4) injects an electromagnetic wave into the optical resonator and collects said electromagnetic wave leaving the waveguide (4), said optical resonator comprising an optical active zone for circulation of the electromagnetic wave, at least one mechanical resonator suspended from the support (2), said mechanical resonator and said optical resonator being coupled, said mechanical resonator being configured to vibrate in volume mode and comprising at least one face extending in the plane of the sensor and configured to receive molecules of said given species, in which the optical resonator comprises a body (C) comprising the optical active zone (MO),said body (C) comprising a first face (Cl) and a second face, the second face being opposite the support (2) and the first face (Cl) being oriented opposite the support (2), said optical resonator also comprising an optical insulation layer (9) deposited at least on the first face (Cl) at least in line with the optical active zone (MO) so as to confine at least in part the electromagnetic wave in the body, the concentration sensor structure, intended to be immersed in a liquid medium, further comprising a functionalization layer (10) and covering the optical insulation layer (9), the functionalization layer (10) and the optical insulation layer (9) being either directly in contact or separated by means of a bonding layer (11).,

2. A concentration sensor structure according to claim 1, wherein the optical isolation layer is also deposited on the waveguide.

3. A concentration sensor structure according to claim 1 or 2, wherein the ratio of the optical refractive index of a material of the optical insulation layer (9) to the optical refractive index of a material of the body (C) is less than or equal to 0.

75.

4. A concentration sensor structure according to claim 1, 2 or 3, wherein the ratio of Young's modulus of a material of the optical insulation layer (9) and the Young's modulus of a body material (C) is less than or equal to 10.

5. Concentration sensor structure according to one of the preceding claims, in which the optical isolation layer (9) has a thickness less than or equal to the distance between the first face of the body (C) and the second face of the body (C).

6. A concentration sensor structure according to one of the preceding claims, wherein the optical isolation layer comprises several materials having different optical indices.

7. A concentration sensor structure according to one of the preceding claims, wherein the optical resonator (6) has the shape of a disc, a ring or a racetrack and wherein the optical active area is located in the outer peripheral portion of the body and the optical insulation layer has the shape of a ring.

8. Concentration sensor structure according to one of the preceding claims, in which the optical resonator and the mechanical resonator are the same element suspended from the support, the first face forming the face configured to receive molecules, said element being an optomechanical resonator (6).

9. Concentration sensor structure according to one of the preceding claims, in which the body is made of silicon and the optical isolation layer is chosen from SiO2, AlN or Al2O3.

10. Concentration sensor structure according to one of the preceding claims, wherein the dimension of the mechanical resonator and / or the optical resonator in the direction normal to the plane of the sensor is at least 10 times smaller than the dimensions of the mechanical resonator and / or the optical resonator in the plane of the sensor.

11. Concentration sensor structure according to one of the preceding claims, in which the mechanical resonator comprises a functionalization layer (10) specific to said given species.

12. A concentration sensor structure according to claims 11, wherein the functionalization layer is present only on the optical isolation layer.

13. A concentration sensor structure according to claim 11 or 12, wherein the functionalization layer (10) is homogeneous.

14. Concentration sensor structure according to one of claims 11 to 13, wherein the functionalization layer (10) has a thickness less than or equal to 20 nm.

15. A concentration sensor structure according to one of the preceding claims, wherein the mechanical resonator is configured to vibrate in a radial mode.

16. Concentration sensor structure according to one of the preceding claims, in which the mechanical resonator and / or the optical resonator is or are suspended by a foot connecting a face of the resonator(s) opposite the support and the support.

17. Concentration sensor structure according to one of the preceding claims, comprising means for exciting the mechanical resonator so as to set it into vibration, preferably at its resonance frequency.

18. A concentration sensor structure according to one of the preceding claims, comprising several sets of coupled optical and mechanical resonators or several optomechanical resonators, coupled to a single waveguide.

19. Sensor for the concentration of at least one given species in a liquid medium comprising at least one sensor structure according to one of the preceding claims, a light source connected to one end of the waveguide, and means for processing the light wave connected to the other end of the waveguide.

20. Microfluidic system comprising at least one channel for circulating the liquid in which the concentration of at least one species is to be measured and at least one concentration sensor according to claim 19, the optical resonator and the mechanical resonator being arranged in the channel.

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