System and method for measuring at least one property of a particle using a mechanically coupled mechanical resonator and gravimetric sensor.

Abstract

The invention relates to a system for measuring at least one property of a particle (P), comprising: A mechanical resonator (1) having at least a first fixed part (10) and a first suspended part (11) capable of vibrating relative to the first fixed part, and a fluidic circuit integrated in its suspended part, through which a fluid containing said particle (P) is circulated; Excitation means (4) configured to vibrate the first suspended part (11) at an excitation frequency (F_smr); A first gravimetric sensor (2) comprising at least a second fixed part (20) and a second suspended part (21) capable of vibrating relative to the second fixed part (20); The first suspended part (11) of the mechanical resonator (1) and the second suspended part (21) of the first gravimetric sensor (2) being mechanically coupled to each other via a mechanical linkage element (3). Figure to be published with the abbreviation: Figure 4A

Description

Title of the invention: System and method for measuring at least one property of a particle using a mechanical resonator and a mechanically coupled gravimetric sensor. Technical field of the invention

[0001] The present invention relates to a system and a method for measuring at least one property of a particle using a mechanical resonator with an integrated fluidic channel and a mechanically coupled gravimetric sensor. State of the art

[0002] To detect the presence of biomarkers of interest such as proteins, exosomes, circulating RNA, circulating DNA, viruses, or larger target species such as bacteria and cells, it is known to use biosensors.

[0003] Among biosensors, there is the category of gravimetric sensors. These are based on the use of a mechanical oscillator or resonator, equipped with a suspended part that vibrates at its resonant frequency. Any target that attaches to the surface of the suspended part of the resonator causes an increase in its mass, which decreases its resonant frequency by a shift proportional to the mass of the captured target.

[0004] By continuously measuring the resonance frequency fluctuations, it is then possible to trace back to the mass adsorbed on the resonator in real time and, for example, to follow adsorption kinetics with targets.

[0005] A solution proposed in the prior art consists of integrating and delimiting a fluidic channel within the suspended portion of the resonator itself, while the latter oscillates in a fluid-free cavity. The advantage lies in a quality factor that is minimally affected, even in the presence of fluid circulating in the oscillator, and thus an optimized detection limit. This type of resonator is commonly called an SMR ("Suspended MicroChannel Resonator") or an SNR ("Suspended Nanochannel Resonator"), depending on the dimensions of its fluidic channel. It should be noted that a resonator with a fluidic channel whose width or thickness is less than Ipm will be referred to as an SNR; otherwise, it will be an SMR.

[0006] By applying a pressure gradient between a fluidic inlet and outlet of the circuit, it is possible to control the fluid flow (its flow rate and direction), and therefore the passage of suspended particles through the SMR (or SNR). This type of sensor has been used for various applications, including the individual weighing of biological particles such as cells, bacteria, nanoparticles, or the detection of specific proteins through prior functionalization of the Internal walls of the SMR. This operating principle is now well known. Patent application US2021 / 046477A1 and patents US8899102B1, US8631685B2 and US8312763B2 describe this type of sensor.

[0007] Although the solution using an SNR-type resonator has an improved detection limit compared to that using an SMR-type resonator, it has certain limitations: - The dimensions of the suspended part of the SNR lead to limitations on the size of its fluidic channel and therefore on the size of the particles that can be injected and analyzed; - These dimensional constraints may require prior preparation of the sample to be analyzed, so that the particles can circulate freely in the fluidic channel of the SNR resonator without risk of it becoming clogged due to the presence of particles larger than its fluidic section; in other words, the resonator is not necessarily suitable for the analysis of complex samples (such as blood, for example, because it contains both cells and proteins, covering a size range from nanometers to several micrometers for cells typically 10 to 15 µm in diameter);

[0008] There is therefore a need for a solution that allows both the dimensional constraints of the fluidic circuit of an SNR type resonator to be released and a detection limit at least equivalent to that of an SNR type resonator. Description of the invention

[0009] This goal is achieved by a measurement system for at least one property of a particle, comprising: - A mechanical resonator comprising at least a first fixed part and a first suspended part capable of vibrating relative to the first fixed part, and a fluidic circuit integrated into its suspended part, in which a fluid containing said particle is made to circulate, - Excitation means configured to vibrate the first suspended part at an excitation frequency, - A first gravimetric sensor comprising at least a second fixed part and a second suspended part capable of vibrating relative to the second fixed part at a vibration frequency, - The first suspended part of the mechanical resonator and the second suspended part of the first gravimetric sensor are mechanically coupled to each other via a mechanical linkage element, - Means of measuring the variations in the vibration frequency of the second suspended part of the first gravimetric sensor.

[0010] Advantageously, the excitation frequency corresponds to the resonance frequency of the resonator or to that of a higher natural mode of this resonance frequency.

[0011] According to an advantageous embodiment, the mechanical linking element has a first end fixed to the first suspended part on a first point corresponding to an antinode of vibration of the first suspended part, when the latter is excited at its resonance frequency or at that of a higher natural mode.

[0012] According to an advantageous embodiment, the mechanical linking element has a second end attached to the second suspended part at a second point corresponding to a vibration antinode of the second suspended part, when the latter is excited at the vibration frequency.

[0013] According to a particular embodiment, the first suspended part is chosen from a beam embedded on a single fixed part, a beam embedded between two fixed parts, and a plate held between several fixed parts.

[0014] According to a particular embodiment, the second suspended part is chosen from a beam embedded on a single fixed part, a beam embedded between two fixed parts, and a plate held between several fixed parts.

[0015] According to one particular feature, the excitation means are configured to vibrate the second suspended part at a vibration frequency close to the resonance frequency of the first suspended part or to that of a higher natural mode, plus or minus 30% of said resonance frequency or that of the higher natural mode.

[0016] According to one particular feature, the excitation means comprise at least one piezoceramic element.

[0017] According to another feature, the measuring means comprise one or more piezoresistive gauges.

[0018] According to another feature, the fluidic circuit integrated into the first suspended part of the mechanical resonator includes a main fluidic channel and a hydrodynamic trap positioned in its channel and intended to trap said particle.

[0019] According to another particular embodiment, the system comprises: - A second gravimetric sensor, comprising at least a third fixed part and a third suspended part capable of vibrating relative to the third fixed part at a second vibration frequency, - The first suspended part of the mechanical resonator and the third suspended part of the second gravimetric sensor are mechanically coupled to each other via a second mechanical linkage element, - Second means of measuring the variations of the second vibration frequency of the third suspended part of the second gravimetric sensor.

[0020] According to one particular feature, the third suspended part is chosen from a beam embedded on a single fixed part, a beam embedded between two fixed parts, and a plate held between several fixed parts.

[0021] The invention also relates to a method for measuring at least one property of a particle, implemented using a measurement system as defined above, the method comprising the following steps: - Injection of a fluid containing said particle into the fluidic circuit of the mechanical resonator, - Excitation of the first suspended part of the mechanical resonator at its resonant frequency, - Excitation of the second suspended part of the first gravimetric sensor at the vibration frequency, - Measurement of the variations in the vibration frequency of the second suspended part of the first gravimetric sensor.

[0022] According to one particular feature, the process includes a calibration step of the system by injection into the fluidic circuit of a fluid containing one or more calibrated particles.

[0023] The principle of the invention is thus based globally on the mechanical coupling of an oscillating structure incorporating a fluidic channel (i.e. an SMR), with a solid oscillator (without a fluidic channel) which is much smaller (and which will be called NEMS for Nano Electro-Mechanical System or otherwise MEMS for Micro Electro-mechanical System depending on the dimensions), and which is used to measure frequency fluctuations resulting from the passage of particles or targets circulating in the fluidic channel.

[0024] Within the framework of the invention, the small dimensions of the gravimetric sensor (i.e., the NEMS or MEMS) can thus be exploited by minimizing its effective mass (proportional to its volume, the density of the material from which it is made, and which is also a function of the resonance mode). An optimized detection limit can be obtained compared to that of the mechanical resonator including the fluidic channel (i.e., the SMR).

[0025] At the same time, the micrometric dimensions of the fluidic channel integrated into an SMR type resonator allow the circulation of targets or particles of micrometric size (typically 10 to 15qm in diameter for cells, or even more), as well as more complex fluids than in the case of standard SNR type resonators, the latter being constrained in dimensions by the sub-micrometric width (i.e. less than Ipm) of their fluidic channel.

[0026] In general, the mechanical coupling of the SMR resonator with the NEMS sensor will be implemented in such a way as to maximize the oscillation driving of the suspended part of the NEMS sensor by the suspended part of the SMR resonator, and to minimize the damping of vibrations of both, thereby optimizing the quality factor. The goal is for the mechanical coupling to dampen the vibrations of the NEMS sensor as little as possible, and conversely those of the SMR resonator, and thus obtain the most efficient transduction possible between the two coupled oscillators. Brief description of the figures

[0027] Other features and advantages will become apparent in the detailed description that follows, given with reference to the accompanying drawings in which: Figures IA and IB represent, respectively seen in perspective and seen from above, a mechanical resonator of the SMR type; Figure [Fig. 2] shows examples of deformation curves of an SMR type mechanical resonator under different vibration modes; Figures 3A and 3B represent, respectively seen in perspective and seen from above, a NEMS type sensor; Figures 4A and 4B show a particular embodiment of the measurement system of the invention and illustrate its operating principle; Figures 5 to 11 show several variants of the embodiment of the measurement system of the invention; Figure 12 shows the steps of an example of a manufacturing process for the measuring system of the invention;

[0028] Detailed description of at least one embodiment

[0029] The invention relates to a system used for measuring at least one property (for example, mass, volume, density) of a particle. A particle is understood to mean, for example, a biological particle such as a cell, exosome, virus, bacterium, etc. It is also understood to mean an inorganic particle such as, for example, a particle of gold, polystyrene, etc.

[0030] The system of the invention is based on the use of at least two entities mechanically coupled together. Mechanical Resonator SMR or SNR

[0031] [Fig.1A] [Fig.1B] [Fig.2]

[0032] A first entity of the system consists of a mechanical resonator 1, better known as an SMR ("Suspended MicroChannel Resonator" - hereinafter referred to as (also known as an SMR resonator) or SNR ("Suspended Nanochannel Resonator"), its micro or nano nature depending in particular on the dimensions of its integrated fluidic channel. A resonator with a fluidic channel whose width or thickness is less than Ipm will be referenced as an SNR; otherwise, it will be an SMR.

[0033] Indeed, such a mechanical resonator 1 (SMR or SNR) comprises at least one fixed part 10, and a suspended part 11 connected to the fixed part 10 and capable of vibrating when excited. The suspended part 11 is conventionally in the form of a beam extending along a so-called longitudinal axis.

[0034] It also includes a fluidic circuit integrated into its suspended part, this fluidic circuit comprising at least one fluidic channel 12 hollowed inside its suspended part 11, covered with sealed walls on all four sides (top, bottom, sideways) and intended to be used to inject a fluid in which one or more particles P to be characterized are placed.

[0035] Advantageously, the mechanical resonator 1 is of the SMR type (rather than an SNR), so as to be able to circulate larger P-sized particles through it, and to analyze complex samples (see below).

[0036] The system includes excitation means 4 configured to vibrate the suspended part 11 of the mechanical resonator 1 at an excitation frequency F_smr. This excitation frequency is advantageously the resonant frequency of the resonator or a frequency equivalent to a higher mode of this resonant frequency.

[0037] In this type of resonator, the vibration is generally produced out of plane (as indicated by the curved arrow in [Fig. 1A]), but alternatively it can be generated in plane, or even in torsion. In-plane or out-of-plane vibration occurs in a horizontal or vertical plane, respectively, when the longitudinal axis of the beam is positioned horizontally.

[0038] The suspended part 11 can be simply fixed, connected to a single fixed part and thus having a free cantilevered end. In this example, it will be referred to as a "cantilever".

[0039] The suspended part 11 can also be double-fixed, joining two fixed parts.

[0040] The suspended part 11 can also be made in the form of a plate supported by several anchor points.

[0041] Whatever its architecture, this suspended part is capable of being set into vibration to oscillate at the excitation frequency F_smr, this frequency being advantageously the resonance frequency at its fundamental natural mode or one of its higher natural modes, or even a combination of these modes.

[0042] As a reminder, such a mechanical resonator 1 can be excited according to several modes of vibration, designated for example M_1, M_2, M_3 in [Fig. 2]. In this example, it This is an out-of-plane bending vibration.

[0043] For each mode of vibration, the resonator has vibration nodes and anti-vibration nodes.

[0044] As a reminder, a vibration antinode corresponds to an area of ​​the suspended part where the vibration amplitude is maximum for the vibration mode used.

[0045] Fig. 2 indicates the presence of vibration antinodes A_1, A_2, A_3 for each of the three vibration modes.

[0046] By imposing a pressure gradient between the ports located upstream and downstream of the fluidic channel 12 integrated into the suspended part 11, it is possible to control the flow of the fluid (its flow rate and direction of flow) in the fluidic channel 12, and therefore the passage of particles P suspended in the fluidic channel of the mechanical resonator 1. When a particle P circulates in the fluidic channel of the resonator, it transiently alters the mass (of Am) of the suspended part 11 of the resonator 1, causing a shift in its frequency (of resonance) which is proportional to the floating mass of the particle.

[0047] The shift in the frequency AF_smr ([Fig. 1 A]) of the resonator depends in fact on the added mass Am, the total mass m of the resonator as well as on a correction coefficient a which depends specifically on the position of the added particle P, according to the following relationship:

[0048] &F smr _ km F_smr m

[0049] Thus, when a particle of given floating mass Am is injected into the fluidic channel 12 of the resonator, a maximum vibration amplitude is obtained when this particle P is located at the antinode of vibration (for vibration mode M_1, for example), and therefore a maximum frequency shift is obtained. Note that, depending on the density difference between the particle and the carrier fluid, the floating mass Am will be positive (in the case of a denser particle) or negative (in the case of a less dense particle). Gravimetric sensor

[0050] - [Fig.3A] [Fig.3B]

[0051] The second entity of the system consists of a gravimetric sensor 2 (hereinafter also referred to as the NEMS sensor). By way of example, this gravimetric sensor 2 is advantageously implemented in the form of a NEMS (Nano Electro-Mechanical System).

[0052] This type of gravimetric sensor also relies on a mechanical oscillator, set into vibration at a vibration frequency F_nems, and devoid of a fluidic channel.

[0053] It thus comprises a fixed part 20 and a suspended part 21 connected to its fixed part and capable of vibrating relative to the fixed part 20 when it is excited.

[0054] The suspended part 21 is also classically presented in the form of a beam extending along a so-called longitudinal axis.

[0055] Unlike the mechanical resonator 1, which circulates the particles P in its fluidic channel 12, the gravimetric sensor 2 does not have a fluidic circuit. It is used only as a means of measuring frequency fluctuations (see below).

[0056] The excitation means 4 of the system are configured to vibrate the suspended part 21 of the gravimetric sensor 2 at the vibration frequency F_nems. It will be seen that the vibration of the NEMS sensor can be achieved via the mechanical resonator 1 and the mechanical link between the two elements, without external excitation means.

[0057] In this type of sensor, vibration is generally carried out out of plane (as indicated by the solid arrow in [Fig. 3A]) or alternatively in plane (as indicated by the dashed arrow in [Fig. 3A]). A variant of vibration can be achieved in a torsional mode. Vibration in plane or out of plane occurs in a horizontal or vertical plane, respectively, when the longitudinal axis of the beam is positioned horizontally.

[0058] The vibration frequency F_nems is for example equal to a value that can range from -30% to +30% of the value of the excitation frequency F_smr of the mechanical resonator, advantageously its resonance frequency or that of its upper natural mode.

[0059] This vibration frequency F_nems is advantageously chosen close to the resonance frequency F_smr of the mechanical resonator 1 or that of its upper natural mode in order to harmonize the vibration of the two suspended entities. Mechanical coupling

[0060] - [Fig.2] [Fig.4A] [Fig.4B]

[0061] The principle of the invention is based on a mechanical coupling between a mechanical resonator 1 as described above with a gravimetric sensor 2 as described above.

[0062] The mechanical coupling is achieved by integrating a mechanical linking element 3 between the suspended part 11 of the mechanical resonator and the suspended part 21 of the gravimetric sensor. This mechanical linking element 3 is, for example, a simple beam connecting the two suspended parts. It may, in particular, be one or more nanobeams produced according to the manufacturing process used.

[0063] The mechanical resonator 1 is thus used to convey the circulating particles P in its fluidic channel 12. It is set into vibration at its excitation frequency F_smr (advantageously its resonant frequency or a higher eigenmode thereof). The gravimetric sensor 2 is also excited at the vibration frequency F_nems, advantageously close to the excitation frequency of the mechanical resonator, and is used to measure the frequency fluctuations at the level of the resonator 1 when it receives a particle in its fluidic channel 12.

[0064] The mechanical coupling of the mechanical resonator 1 (advantageously of the SMR type) with the gravimetric sensor 2 (advantageously of the NEMS type) and the reading of frequency fluctuations at the gravimetric sensor 2 makes it possible to: - Cover a wider range of particles P than when using a mechanical resonator alone (for example, an SNR), particularly in terms of the size of objects to be weighed; the fluidic channel 12 integrated into the SMR-type resonator is enlarged (for example, 20x20qm² for an SMR resonator versus 0.7x0.7qm² for an SNR-type resonator, i.e., a gain of approximately 816 in terms of surface area ratio). The corollary of this increase in the fluidic cross-section is the reduction of the fluidic resistance and therefore the increase in flow rate at the same pressure gradient. - To reduce the risks of clogging inherent in the nano-fluid channels of SNR-type resonators, - To offer a mass detection limit comparable to that of SNR type resonators (currently attogram-order detection limit) by reading frequency fluctuations at the NEMS gravimetric sensor mechanically coupled to the SMR type resonator.

[0065] The beam (or suspended part) 12 of the mechanical resonator 1 is capable of being excited according to several vibration modes (for example, M_1, M_2, M_3), each of these modes resulting in a deformation of the beam 12 exhibiting local nodes and antinodes of vibration (also called antinodes) at different locations predetermined by the laws of mechanics and structural dynamics. As a reminder, an antinode A_1, A_2, A_3 of vibration corresponds to a region where the vibration amplitude is maximum.

[0066] The mechanical coupling of the NEMS 2 sensor with the SMR resonator is advantageously designed to maximize the transmission of vibrational waves between the two oscillators, and to limit as much as possible the damping of the oscillations of one and the other, generated by this coupling.

[0067] It is important that any fluctuation AF_smr of the excitation frequency of the SMR 1 resonator results in a variation AF_nems of frequency at the NEMS 2 sensor ([Fig. 4B]). One example is to position the mechanical link at a vibration antinode of the SMR 1 resonator in the vibration mode for which the latter is actuated in order to maximize the transduction between it and the NEMS sensor. Means of arousal

[0068] - [Fig.4A]

[0069] It should be noted that several transduction / excitation modes are possible for: - Actuating the SMR resonator and the NEMS gravimetric sensor at the chosen frequency (for example, resonance frequency for the SMR and vibration frequency for the NEMS), and - To enable the measurement of frequency and its fluctuations at the level of the NEMS gravimetric sensor.

[0070] The vibration of the NEMS sensor can be achieved solely and directly via the mechanical linkage between the suspended part 11 of the mechanical resonator 1 and the suspended part 21 of the NEMS sensor. It can also be achieved by controlling the excitation means 4, configured to excite simultaneously (see below the advantageous combination) the suspended part 11 of the mechanical resonator 1 at the excitation frequency (for example, the fundamental resonance frequency or a higher natural mode thereof) and the suspended part 21 of the NEMS sensor at the desired vibration frequency.

[0071] Preferably, an advantageous combination is based on: - Piezoelectric actuation / excitation (for example, by bringing a piezoelectric ceramic into contact with the back of the component) to simultaneously actuate the SMR resonator and the NEMS sensor. The piezoelectric ceramic is bonded to a printed circuit board, which is designed to apply an electrical potential that deforms the piezoelectric material. The material is then set into vibration by applying, for example, an electrical signal at the resonant frequency of the SMR or NEMS sensor, or a signal containing the different frequency signals corresponding to the modes of the oscillators present on the chip. The advantage of this configuration lies in the fact that the applied signal can collectively actuate the different oscillators on the component (NEMS and SMR) and the different resonant modes desired for each of them. This is therefore a very suitable approach for an oscillator network. - A reading by piezoresistive effect by implanting, for example, the NEMS layer with dopants and an appropriate concentration, either locally to delimit a gauge at the NEMS sensor's mounting point or across the entire surface by exploiting the structuring of suspended strain nano-gauges connecting, for example, the NEMS sensor either to the SMR resonator or to fixed pads.

[0072] Actuation by capacitive coupling is also a possible solution. In this case, it is necessary to integrate an electrode as close as possible to the NEMS sensor 2 and the SMR 1 resonator if it also requires this actuation source. This transduction mode is well suited for lateral vibration modes but requires that the oscillating suspended part and the opposing actuation electrode be sufficiently conductive to provide transduction capacity.

[0073] Figure 4A shows the localization zone of a piezoresistor PZ_1 (via doping – for example, with boron) at the level of the suspended portion 11 of the SMR resonator 1 and the suspended portion 21 of the NEMS sensor. This zone terminates with the presence of a piezoresistive gauge PZ_2 extending from the connecting element 3 between the SMR resonator and the NEMS sensor. This solution makes it possible to determine the frequency variations at the NEMS sensor 2, since the current variations in the piezoresistor will be maximum at the resonant frequency of the NEMS sensor. System implementation variations

[0074] - Figures 4A to 11

[0075] Based on these principles, the mechanical connection between the beam of the SMR resonator and that of the NEMS sensor can be achieved in various configurations. It should also be noted that it is possible to mechanically couple a single SMR resonator to several NEMS sensors (for example, two NEMS sensors). The measurement means (for example, via piezoresistivity - PZ_1 + PZ_2) are not shown in Figures 5 to 11, but they should be assumed to be present.

[0076] It should be noted that in all configurations, the two suspended parts 11,21 extend, along their longitudinal axis, parallel to each other and the connecting element 3 extends, along its longitudinal axis, perpendicular to the two suspended parts and thus creates a junction between the two suspended parts.

[0077] Figures 4A to 11 illustrate several possible configurations. These are to be considered in a non-limiting manner. In each configuration, on the NEMS 2 sensor side, the mechanical linkage element 3 is fixed at a vibration antinode for one of its vibration modes. And on the SMR 1 resonator side, the mechanical linkage element 3 is fixed in an area of ​​its suspended portion that corresponds to an antinode for one or more vibration modes. It should be noted that the beam forming the mechanical linkage element can be made up of several nanobeams. - [Fig. 4A] - An SMR resonator + a NEMS sensor: A simply fixed beam 11 of the SMR resonator 1 is mechanically coupled to the beam 21 of a NEMS sensor by a lateral mechanical link. In this example, the mechanical linking element 3, formed by a coupling beam, is located at the first antinode of the beam 11 of the SMR resonator from its fixed position, for its second mode of vibration in out-of-flexural bending. plan. [Fig. 5] - An SMR resonator + a NEMS sensor: A simply fixed beam 11 of the SMR resonator 1 is mechanically coupled to the beam 21 of a NEMS sensor by a lateral mechanical link. In this example, the mechanical link element 3, formed by a coupling beam, is located at the free end of the beam 11, i.e., at an antinode for its first, second, and third out-of-plane bending vibration modes. [Fig. 6]: An SMR resonator + one or two NEMS sensors: A simple fixed beam of the SMR resonator is mechanically coupled to the beam of one or both NEMS sensors by a lateral mechanical link located at its free end, i.e., at an antinode, for its first, second, and third out-of-plane bending vibration modes. The same references are used for both NEMS sensors. [Fig. 7]: An SMR resonator + one or two NEMS sensors: A simple fixed beam of the SMR resonator is mechanically coupled to the beam of one or both NEMS sensors by a lateral mechanical link located at the first antinode of the SMR resonator beam from its fixed end for its second out-of-plane bending vibration mode. [Fig.8]: An SMR resonator + two NEMS sensors: A simple fixed beam of the SMR resonator is mechanically coupled to the beam of each of the two NEMS sensors, by a first lateral mechanical link located at its free end, and by a second mechanical link at its first antinode of the SMR beam from its fixed end for its second out-of-plane bending vibration mode. [Fig.9]: SMR resonator + a NEMS sensor: The beam of the SMR resonator is doubly fixed (between two fixed parts 10) and mechanically coupled to a NEMS sensor by a lateral mechanical link located on an antinode for its first mode of vibration in out-of-plane bending (or in-plane as well). [Fig. 10] - An SMR resonator + a NEMS sensor: A simply fixed beam 11 of the SMR resonator 1 is mechanically coupled to the beam 21 of a NEMS sensor by a lateral mechanical link. In this example, the mechanical linking element 3, formed by a single coupling beam, is located at the first antinode of the SMR resonator beam from its fixed position for its second out-of-plane bending vibration mode. Furthermore, the NEMS sensor is implemented as a bi-beam embedded (between two fixed parts 20). The connecting element 3 is connected on this beam to an antinode of the NEMS sensor for its first vibration mode in out-of-plane bending (or in-plane as well). - [Fig. 1 1] - An SMR resonator + a NEMS sensor: The fluidic circuit of the SMR resonator has one or more trapping zones, each dedicated to accommodating a particle. This allows for the trapping of one or more particles (for example, cells) within the fluidic circuit and the monitoring, with the precision of the coupled NEMS 2 sensor, of various parameters such as the particle's mass growth rate upon exposure to a drug (to assess its efficacy), the particle's growth in a medium, or the secretion of viral particles or exosomes. Instead of a cell, one (or more) functionalized beads (coated with antibodies or aptamers) can be trapped, and the grafting kinetics can be monitored with targets such as proteins.The hydrodynamic trap is made in the form of a bypass branch relative to the fluidic channel 12 of the SMR 1 resonator and includes a housing 120 dimensioned to accommodate the particle P and a restriction 121 extending said housing.

[0078] A combination of the characteristics of the different embodiments described above is also conceivable. Special project

[0079] By way of exception, the SMR resonator 1 and the NEMS sensor 2 are chosen to be cantilevered (a suspended part connected to a single fixed part). The length and thickness of the NEMS sensor 2 are chosen so that its fundamental frequency in the first vertical bending mode coincides with the resonance frequency for the second vertical bending mode of the SMR resonator.

[0080] The table below gives an example of dimensioning: Length and width (m) Width and depth (m) Integrated channel Width of inner wall and outer walls Total thickness (m) F0 / F2nd mode (Out of plane) SMR 200 / 33 8 / 3 5 / 6 3.4232 116.12kHz 727.7656kHz NEMS 19.5 / 0.5 0.2 725.67kHz / 4.548 MHz

[0081]

[0082]

[0083]

[0084]

[0085]

[0086]

[0087]

[0088]

[0089]

[0090]

[0091] As an example, the SMR 1 resonator has a simple embedded beam 11, a channel 3ft deep, 8ft wide, a central wall 5ft wide, and external walls 6ft wide, for a total width of 33ft. Beam 11 of the SMR resonator has a length of 200 pm, and the thickness of the lower and upper membranes covering the buried channel is 200 nm. Taking into account the bonding interface oxide layer for sealing the upper cover, the total thickness of the SMR resonator is estimated to be 3.4232 pm. This set of dimensional parameters leads to a theoretical resonance frequency estimated around 116.12 kHz for its fundamental out-of-plane bending mode, and 727.766 kHz for its second bending mode. Assuming an Allan variance on the order of ppm (10⁶), a mass detection limit of 14.4 fg is estimated. Considering a beam 21 of a NEMS 2 sensor which is mechanically coupled to the SMR resonator, the coupling is carried out for example by means of one or more suspended nano-beams 3 located perpendicular to the longitudinal axis of the beam of the SMR resonator, at the level of the first antinode of the second bending mode of the SMR resonator from its fixed position ([Fig.4A]). For example, we assume that the NEMS sensor and its nanobeams have a thickness equivalent to that of the upper cover over the fluidic channel of the SMR resonator. We dimension the width and length of beam 21 of the NEMS 2 sensor so that its resonant frequency according to its fundamental out-of-plane natural mode has a value similar to, if not close to, the frequency of the second bending mode of the SMR resonator. For the sizing of the NEMS 2 sensor, in relation to the operating frequency of the SMR, we rely on the following analytical formula derived from the application of the Euler-Bernoulli theorem: £ [ËT J n 2æ y pS Where E denotes Young's modulus, S corresponds to the cross-section of the NEMS beam in oscillation, and I its moment of inertia along the direction of the vibrations. Xn is an eigenvalue determined as a function of the order of the mode, its type (bending, torsion, etc.), and the boundary conditions of the beam, obtained by solving the differential equation of motion of the beam recalled below, in the absence of damping and external forces acting upon it: xf) ædxrj EI-^+pS-^^O 3 xdt In the case where we consider bending along an out-of-plane direction: f -tâ [He J n 4;~ y 3p With :

[0092] / =

[0093] and w and t which respectively designate the width and thickness of the NEMS sensor beam.

[0094] The following table lists the values ​​of Xn for beams with simple and double fixed ends: A! A2 A3 a4 Single recess 1.875 4.694 7.854 10.995 Double recess 4.73 7.853 10.995 14.14

[0095] Given the equation, the expression for the fundamental resonance mode of a fixed-end NEMS beam can be deduced from the following formula:

[0096] fz 4,732 HT '1 L2

[0097] Therefore:

[0098] L = 4.73^~j~

[0099] And for a simply fixed beam, we obtain:

[0100] L=1 875 / ZÇ-JÇ"

[0101] For a beam 21 of the NEMS 2 sensor with a thickness of 200 nm, if we consider, for example, a length of 19.5 μm and a width of 0.5 μm, we estimate a fundamental natural frequency of 725.67 kHz, representing an error of 0.2% compared to the estimated value of the second out-of-plane bending resonance mode of the SMR resonator. If the beam length of the NEMS sensor is now 19.48 μm, we then estimate a fundamental natural frequency of 727.161 kHz, representing an error reduced to 0.08% compared to the estimated value of the second mode of the SMR 1 resonator. On the other hand, controlling the length of the beam 21 of the NEMS 2 sensor with a dimensional resolution on the order of 1 μm appears incompatible at present with the precision of nanofabrication processes combining lithography and nano-etching. We assume an Allan variance of the order of ppm (106) for the NEMS sensor.

[0102] For its fundamental out-of-plane bending mode, the NEMS sensor mass detection limit is estimated to be 2.14 ag, i.e., a gain of 6728 compared to the detection limit of the SMR resonator.

[0103] As expected, the reduction in size of the NEMS 2 sensor is therefore favorable to the improvement (here of three orders of magnitude) of the mass detection limit compared to the SMR 1 resonator alone. Applications

[0104] Some examples of possible applications of the system of the invention are listed below, taking advantage of the versatility offered by the increased section of the fluidic channel 12 of the SMR resonator 1 compared to its nanometric version (SNR), combined with the mass measurement sensitivity of the NEMS sensor 2. - Weighing polydisperse samples, containing particles (whether inorganic, biological, synthetic or a mixture of these different objects) with size scales ranging from a few nanometers to a few micrometers (given the cross-section of the fluidic channel of the SMR resonator which is approximately 20x20qm2). - Weighing complex, heterogeneous biological samples, such as blood or other biofluids, in which coexist, for example, cells (red blood cells, lymphocytes, circulating tumor cells), circulating DNA, circulating RNA, proteins, cellular debris, extracellular vesicles (EVs), exosomes, potentially viruses, or even bacteria. This collection exhibits size ranges from nanometers to several millimeters, and floating masses ranging from 0.1 attograms to several picograms. - Isolate a biological cell in the fluidic channel of the SMR resonator by trapping it in a hydrodynamic trap (see variant of [Fig. 1 1]). Given the mass resolution of the NEMS 2 sensor, it would be possible to measure, with attogram-level precision, the rate of increase or loss of cell mass resulting from its growth or death, or from its broader reaction to exposure to a molecule (drugs). Another characteristic of this "in-situ" trapping, combined with the mass resolution of the NEMS sensor, concerns the dynamic monitoring of cell transfection by targets such as viral nanoparticles (adenoviruses, for example), or conversely, the production and secretion of viral nanoparticles or extracellular vesicles (EVs), objects characterized by a floating mass ranging from a few attograms to a few hundred attograms.This real-time secretion tracking capability can also be implemented by trapping the cell upstream of the fluidic channel integrated into the SMR resonator, which allows for clear tracking of the production kinetics of secretions flowing into the fluidic channel of the SMR resonator, without any possible bias with the intrinsic mass increase rate of the cell. - Another example concerns the detection of target biomarkers by weighing, either by grafting onto the previously functionalized surface of the fluidic channel integrated into the SMR resonator, or by grafting onto a or Several beads are trapped in the SMR resonator by means of hydrodynamic traps. Again, the advantage of this invention compared to SNR technology lies in the fact that the trapped bead can be much larger, several micrometers in diameter, its developed surface area allowing it to accommodate a much larger number of probes than would be possible with a sub-micrometer bead trapped in an SNR. Functioning

[0105] Consider a system according to the particular embodiment described above and which comprises: - A mechanical resonator 1 of type SMR; - A NEMS type 2 gravimetric sensor; - A linking element 3 mechanically coupling the suspended part of the SMR resonator to the NEMS gravimetric sensor;

[0106] To calibrate the mass sensitivity of the NEMS 2 sensor with respect to mass variations resulting from the passage of a particle through the SMR resonator, a monodisperse population of reference nanoparticles (i.e., of known density and size), such as gold nanoparticles, is circulated through the fluidic channel of the SMR resonator. The passage of each nanoparticle through the fluidic channel 12 of the SMR 1 resonator results in a transient change in its effective mass meff, and therefore a frequency shift that is propagated in the suspended portion 21 of the NEMS 2 sensor, to which it is mechanically coupled. The frequency shift AF_nems measured by the NEMS 2 sensor should, a priori, be maximal when the particle is positioned at a point in the fluidic channel of the SMR resonator where the mechanical coupling between the SMR resonator and the NEMS sensor is optimal.

[0107] In the invention, as indicated above, this is a position in which the nanoparticle is located on a maximum of vibration (anti-node) of the SMR resonator 1.

[0108] By measuring the frequency shift AF_nems measured using the NEMS 2 sensor, a sensitivity expressed in grams per Hertz is deduced. Once this sensitivity is calibrated, it is then possible to inject a sample into the SMR 1 resonator and deduce the mass of the particles circulating within it, without prior knowledge of their density.

[0109] The advantage of this invention lies in the fact that the dynamic range of particle and target sizes circulating in the fluidic channel 12 of the SMR resonator 1 is extended (compared to SNR-type technologies alone).

[0110] The mechanical coupling of the NEMS 2 sensor with the SMR 1 resonator is advantageously designed so that the mechanical linkage occurs at a vibration antinode (also called an antinode) of the SMR 1 resonator in the vibration mode for which the latter is activated in order to maximize the transduction between it and the NEMS sensor.

[0111] The particles P of interest are transported into the fluidic channel 12 of the SMR type mechanical resonator 1. Their circulation in the SMR resonator 1 causes a transient AF_smr shift in the resonance frequency of the SMR resonator 1 as is the case for conventional SMR resonators (taken alone, i.e. without mechanical coupling).

[0112] In contrast, according to the invention, this frequency variation is read via the frequency tracking of the NEMS 2 sensor, which is mechanically coupled to the SMR resonator. Since the NEMS sensor has a suspended part 21 with an effective mass (a fraction of the total mass of the NEMS, which depends on the vibration mode applied) reduced compared to the effective mass of the suspended part 11 of the SMR resonator, its detection limit is theoretically much lower, even with frequency stability on the order of ppm. It is therefore easier to read the frequency variation AF_nems at the level of the NEMS 2 sensor. Manufacturing

[0113] - [Fig.12]

[0114] The system of the invention can be manufactured using techniques already used for the manufacture of SMR and SNR solutions.

[0115] This involves, for example, using two SOI ("Silicon On Insulator") substrates bonded to each other (front face to front face) by molecular sealing, according to the following arrangement: - A lower SOI substrate (noted SOI_inf on [Fig.12]) whose active silicon layer (typically around 20qm thick for an SMR) is partially etched to delimit the shape of the fluidic channel which is integrated into the SMR resonator, - A top SOI substrate (noted SOI_sup on [Fig. 12]) whose active silicon layer is sealed by direct molecular sealing to the top face of the bottom SOI substrate.

[0116] The main manufacturing steps are, for example, the following:

[0117] El: Etching of the fluidic channel 12 in the lower SOI substrate as is customary for SMR or SNR technology;

[0118] Lithography and dry etching to etch the active silicon layer of the lower SOI substrate over its entire thickness. This step defines one or more holes / cavities adjacent to the fluidic channel footprint in the SMR resonator. Chemical etching of the buried oxide layer (called BOX = buried oxide) exposed through these holes. This chemical etching leads, in particular, to the suspension of what will constitute the suspended part 11 of the SMR 1 resonator or a fraction of its surface. It should be noted that at least one or more holes are positioned directly above the future suspended part of the NEMS 2 sensor and its nanobeams for connection with the SMR resonator, which will be etched later.

[0119] E2: Once the holes or cavities have been made, molecular sealing is then carried out on the front face of this stack with the upper SOI substrate whose thickness of the active layer corresponds to the thickness of the future NEMS 2 sensor and its nanobeams (=linking element 3).

[0120] Thinning of the upper SOI substrate. The residual active layer of the upper SOI substrate serves to seal the fluidic channel integrated into the future SMR resonator, and also serves as a structural material in which the shape of the NEMS 2 sensor, as well as its mechanical connection elements to the SMR resonator and possible nano-strain gauges for a piezoresistive measurement, will be subsequently delimited.

[0121] E3: Engraving of the outline of the suspended part 11 of the SMR resonator 1, of the suspended part 21 of the NEMS sensor, its mechanical coupling element(s) with the SMR, and all other motifs necessary for the implementation of the component.

[0122] Other steps are then implemented to finalize the manufacture of the system, including sealing a glass fluidic cover, structuring to delimit cavities necessary for operation.

[0123] Other manufacturing techniques could of course be employed.

[0124] The invention thus offers numerous advantages, including: - It exploits the small dimensions of the NEMS type gravimetric sensor and takes advantage of its low effective mass, and therefore its improved detection limit compared to that of the SMR type mechanical resonator. - By coupling the NEMS gravimetric sensor to the SMR type mechanical resonator, we use the advantage that the latter has to inject more complex samples than if they were injected into an SNR resonator (taken alone) with much smaller channel dimensions.

Claims

Claims

1. System for measuring at least one property of a particle (P), comprising: - A mechanical resonator (1) comprising at least a first fixed part (10) and a first suspended part (11) capable of vibrating relative to the first fixed part, and a fluidic circuit integrated in its suspended part, in which a fluid containing said particle (P) is caused to circulate, - Excitation means (4) configured to vibrate the first suspended part (11) at an excitation frequency (F_smr), - Characterized in that it comprises: - A first gravimetric sensor (2) comprising at least a second fixed part (20) and a second suspended part (21) capable of vibrating relative to the second fixed part (20) at a vibration frequency (F_nems),- The first suspended part (11) of the mechanical resonator (1) and the second suspended part (21) of the first gravimetric sensor (2) being mechanically coupled to each other via a mechanical connecting element (3), - Means for measuring variations in the vibration frequency of the second suspended part (21) of the first gravimetric sensor.,

2. System according to claim 1, characterized in that the excitation frequency corresponds to the resonant frequency of the resonator or that of a higher natural mode of this resonant frequency.

3. System according to claim 2, characterized in that the mechanical connection element (3) comprises a first end secured to the first suspended part (11) at a first point corresponding to a vibration antinode of the first suspended part, when the latter is excited at its resonance frequency (F_smr) or at that of a higher natural mode.

4. System according to claim 3, characterized in that the mechanical connecting element (3) comprises a second end secured to the second part suspended on a second point corresponding to a anti-vibration node of the second suspended part (21), when the latter is excited at the vibration frequency (F_nems).

5. System according to one of claims 1 to 4, characterized in that the first suspended part (11) is chosen from a beam embedded on a single fixed part (20), a beam embedded between two fixed parts (20), and a plate held between several fixed parts.

6. System according to one of claims 1 to 5, characterized in that the second suspended part (21) is chosen from a beam embedded on a single fixed part, a beam embedded between two fixed parts, and a plate held between several fixed parts.

7. System according to one of claims 1 to 6, characterized in that said excitation means (4) are configured to vibrate the second suspended part (21) at a vibration frequency close to the resonance frequency of the first suspended part (11) or that of a higher natural mode, at plus or minus 30% of said resonance frequency or that of the higher natural mode.

8. System according to one of claims 1 to 7, characterized in that the excitation means (4) comprise at least one piezoceramic element.

9. System according to one of claims 1 to 8, characterized in that the measuring means comprise one or more piezoresistive gauges (PZ_2).

10. System according to one of claims 1 to 9, characterized in that the fluidic circuit integrated into the first suspended part of the mechanical resonator comprises a main fluidic channel (12) and a hydrodynamic trap positioned in its channel and intended to trap said particle.

11. System according to one of claims 1 to 10, characterized in that it comprises: - A second gravimetric sensor (2), comprising at least a third fixed part and a third suspended part capable of vibrating relative to the third fixed part at a second vibration frequency, - The first suspended part (11) of the mechanical resonator (1) and the third suspended part of the second gravimetric sensor (2) being mechanically coupled to each other via a second mechanical connecting element (3), - Second means for measuring variations in the second vibration frequency of the third suspended part of the second gravimetric sensor.

12. System according to claim 11, characterized in that the third suspended part is chosen from a beam embedded on a single fixed part, a beam embedded between two fixed parts, and a plate held between several fixed parts.

13. Method for measuring at least one property of a particle, implemented using a measuring system as defined in one of claims 1 to 12, characterized in that it comprises the following steps - Injection of a fluid containing said particle (P) into the fluid circuit of the mechanical resonator (1), - Excitation of the first suspended part (11) of the mechanical resonator (1) at its resonance frequency, - Excitation of the second suspended part (21) of the first gravimetric sensor (2) at the vibration frequency, - Measurement of the variations in the vibration frequency of the second suspended part (21) of the first gravimetric sensor.

14. Measuring method according to claim 13, characterized in that it comprises a step of calibrating the system by injecting into the fluid circuit a fluid containing one or more calibrated particles.

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