Optical sample analysis system

Abstract

The invention relates to a method for the optical analysis of a sample in a droplet actuation device operating by electrowetting, said actuation device comprising: A chamber (1) formed by two substrates (100, 101) arranged opposite each other along a principal axis, A first light source (S1) capable of generating said first light beam (L1) directed towards a photoconductive layer (C30) of the lower substrate (101), The upper substrate (100) comprising a second electrode, An optical sample analysis device comprising a second excitation light source (S2) positioned above the upper substrate (100), capable of generating a second light beam (L2) at an excitation wavelength, and a unit for detecting the light emitted by said sample through said upper substrate (100) caused by its excitation. Figure to be published with the abbreviation: Figure 2A

Description

Title of the invention: Optical sample analysis system Technical field of the invention

[0001] The present invention relates to an optical analysis system for a sample, comprising in particular a drop actuation device operating by electrowetting. State of the art

[0002] It is known to want to analyze cells or molecules by isolating them in droplets. Some droplets then constitute microreactors, and it is thus possible to rapidly scan a set of droplets to detect and isolate those in which a reaction is taking place. In this way, cells that may be of interest, for example, for the bioproduction of therapeutic molecules can be easily isolated.

[0003] However, it is necessary to be able to sort the drops of interest from among a set of several drops.

[0004] To manipulate and move droplets, the principle of electrowetting-on-dielectric (EWOD) is known. It allows droplets to be moved by activating electrodes between two substrates. The forces used are electrostatic forces. French patent application FR2841063A1 describes this principle, which uses a catenary placed opposite several juxtaposed electrodes. The electrodes are activated individually to move the droplet along the catenary. French patent application WO2006 / 070162A1 also describes a droplet dispensing device using this electrowetting principle to move the droplets.

[0005] A variant of the embodiment of a sorting device operating by electrowetting consists of creating a matrix of virtual electrodes, according to the principle called "Opto-EWOD" and described in the referenced publication PY Chiou, H. Moon, H. Toshiyoshi, CJ Kim, and MC Wu, “Light actuation of liquid by optoelectrowetting, ”, Sensors Actuators, A Phys., vol. 104, no. 3, pp. 222-228, 2003.

[0006] In this embodiment, one of the two substrates used comprises a stack of layers, including an unstructured photoconductive layer. Light radiation makes the photoconductive layer locally conductive, defining a virtual electrode both temporally and locally. The light beam thus induces the electrowetting effect locally at the scale of a droplet without having to fabricate an electrode array on the surface of the substrate where the drops rest. This results in a matrix of virtual electrodes generated by light. The light source used must allow image formation, or at least provide localized illumination on short durations. The type of technology that can meet these requirements may be a laser source that scans the surface of the electrowetting in order to activate the drops on the surface, a screen-type solution whether emissive (OLED, LED, ...), transmissive (LCD) or projection (video projector).

[0007] This principle is described in patent application WO2023 / 281274A1. It is implemented in conjunction with an optical droplet analysis device. In other words, electrowetting according to the "opto-EWOD" principle is used to precisely fix a droplet between two substrates, and an optical analysis (for example, by fluorescence) is performed on the droplet using an excitation light source and a detector. This patent application focuses more specifically on the problem of perturbations caused by the excitation light source on the light source used for electrowetting, and vice versa. In other words, it is possible that the excitation light source may also excite the photoconductive layer, potentially causing perturbations in the fixation of the droplet between the two substrates.

[0008] Furthermore, the light source required to activate the opto-EWOD can generate additional light that interferes with the optical analysis of the droplet. All of this makes it potentially difficult to optically analyze a droplet and activate it using opto-EWOD simultaneously.

[0009] To remedy this, it is proposed in patent application WO2023 / 281274A1 to activate the excitation light source used for optical analysis only when the electrostatic field is deactivated, i.e. when the electrowetting system is inactive.

[0010] However, this prior solution does not allow for continuous analysis of the droplets trapped in the system. It also requires fine-tuning of the activation and deactivation periods of the electrostatic field. During a period of electrostatic field deactivation, it is also possible for the droplets to move between the two substrates, which can cause errors in the optical analysis.

[0011] The object of the invention is to propose an optical analysis system for a liquid sample, which uses the "opto-EWOD" type electrowetting principle and which is capable of overcoming the disadvantages of the prior art. Description of the invention

[0012] This objective is achieved by an optical analysis method for a sample in a droplet actuation device operating by electrowetting, said actuation device comprising: - A chamber formed by two substrates arranged opposite each other along a main axis, so as to form a so-called lower substrate and a so-called upper substrate superior, the two substrates being spaced apart to form a space for the sample, - The lower substrate is made up of a stack of layers in which a photoconductive layer is excitable by a first displacement control light beam via electrowetting to form a first electrode, - A first light source capable of generating said first light beam destined for the photoconductive layer of the lower substrate, - The upper substrate includes a second electrode, - A voltage source connected to the first electrode and the second electrode so as to form an electrostatic field across said receiving space, - An optical sample analysis device comprising a second excitation light source positioned above the upper substrate, capable of generating a second light beam at an excitation wavelength, and a unit for detecting the light emitted by said sample through said upper substrate caused by its excitation, - The process of: - Optically treat the second light beam to cut off wavelengths likely to excite the photoconductive layer of the lower substrate.

[0013] The invention also relates to an optical sample analysis system comprising a droplet actuation device operating by electrowetting and capable of implementing the process defined above, said droplet actuation device comprising: - A chamber formed by two substrates arranged opposite each other along a main axis, so as to form a so-called lower substrate and a so-called upper substrate, the two substrates being spaced apart to form a space for receiving said sample, - The lower substrate is made up of a stack of layers in which a photoconductive layer is excitable by a first displacement control light beam via electrowetting to form a first electrode, - A first light source capable of generating said first light beam destined for the photoconductive layer of the lower substrate, - The upper substrate includes a second electrode, - A voltage source connected to the first electrode and the second electrode so as to form an electrostatic field across said receiving space, - An optical sample analysis device comprising a second excitation light source positioned above the upper substrate, capable of generating a second light beam at an excitation wavelength, and a unit for detecting the light emitted by said sample through said upper substrate caused by its excitation, - The system comprises a first optical element positioned between the sample reception area and the photoconductive layer of the first substrate, - Said optical element being chosen to cut said excitation wavelength of the second light beam so that it does not excite the photoconductive layer.

[0014] According to a particular embodiment, the first optical element is positioned between an insulating layer of the lower substrate and the photoconductive layer.

[0015] According to another particular embodiment, the first optical element is positioned between an insulating layer of the lower substrate deposited on the photoconductive layer and the host space.

[0016] According to another particular embodiment, the first optical element is integrated into an insulating layer of the lower substrate deposited on the photoconductive layer.

[0017] According to another particular embodiment, the system includes a second optical element positioned between the first light source and the reception space, this second optical element being chosen to cut the wavelengths of the first light beam likely to overlap with the wavelengths of the light emitted by the sample caused by its excitation.

[0018] Advantageously, the first optical element and the second optical element are combined in a single deposit made on the photoconductive layer of the lower substrate, this deposit also playing the role of an electrical insulating layer.

[0019] According to one particular feature, said deposit is made in the form of a stack of alternating layers of TiO2 / Al2O3 or SiO2 / Al2O.

[0020] The invention also relates to an optical sample analysis system comprising a drop actuation device operating by electrowetting and capable of implementing the process defined above, said drop actuation device comprising: - A chamber formed by two substrates arranged opposite each other along a main axis, so as to form a so-called lower substrate and a so-called upper substrate, the two substrates being spaced apart to form a space for receiving said sample, - The lower substrate is made up of a stack of layers in which a photoconductive layer is excitable by a first light beam for displacement control by electrowetting to form a first electrode, - A first light source capable of generating said first light beam directed towards the conductive layer of the lower substrate, - The upper substrate includes a second electrode, - A voltage source connected to the first electrode and the second electrode so as to form an electrostatic field across said receiving space, - An optical sample analysis device comprising a second excitation light source positioned above the upper substrate, capable of generating a second light beam at an excitation wavelength, and a unit for detecting the light emitted by said sample through said upper substrate caused by its excitation, - The system comprising: - A first polarizer positioned between the second light source and the aforementioned reception space, this first polarizer having polarization lines oriented in a first direction, - A second optical polarizer positioned between the sample reception space and the photoconductive layer of the first substrate, this second polarizer having polarization lines oriented in a second direction orthogonal to the first direction.

[0021] According to a particular embodiment, the system also includes a third optical polarizer positioned in front of the first light source, having polarization lines oriented along said first direction.

[0022] Advantageously, the first light source is an OLED display. Brief description of the figures

[0023] Other features and advantages will become apparent in the detailed description that follows, given in relation to the accompanying drawings, in which: - Fig. 1 shows an optical analysis system for a liquid sample and illustrates its operating principle; - Fig. 2A shows the optical analysis system of the invention according to a first particular embodiment and Fig. 2B illustrates the principle of optical filtering used; - Fig. 3A shows the optical analysis system of the invention according to a second particular embodiment and Fig. 3B illustrates the principle of optical filtering used; - Figure [Fig. 4A] shows the optical analysis system of the invention according to a third particular realization and [Fig.4B] illustrates the principle of optical filtering used; - Fig. 4C shows an example of the realization of a multilayer assembly capable of providing electrical insulation and optical filtering; - Fig. 5 shows the optical analysis system of the invention according to a fourth particular embodiment;

[0024] Figures 2B, 3B and 4B show normalized optical transmission as a function of wavelength. When at the high plateau (=1), all wavelengths are transmitted, and when at the low plateau (=0), no wavelengths are transmitted.

[0025] Detailed description of at least one embodiment

[0026] In the following description, the terms "lower", "upper", "above", "below" are to be understood with regard to an axis drawn vertically in the plane of the sheet. Of course, these terms should not be considered restrictively.

[0027] According to the invention, the optical analysis system comprises: - A drop actuation device operating by electrowetting; - An optical analysis device;

[0028] The system is intended for the analysis of a liquid sample.

[0029] The liquid sample is advantageously in the form of one or more drops 40 presented successively for analysis. The drop actuation device is controlled to move each drop 40 and fix it for optical analysis within the system.

[0030] Optical analysis means, for example, fluorescence analysis or equivalent, based on an image of each droplet. For fluorescence analysis, fluorophores present in one or more drops 40 are excited using an excitation source (second light source S2) and an image of a population of drops is captured using a camera to determine the fluorescence emitted by the fluorophores after excitation.

[0031] This could of course be another type of optical analysis. The invention applies in the case where this optical analysis requires the use of a second light source S2, in addition to the light source S1 used for controlling the movement of the drops 40 by electrowetting.

[0032] In the following description, we will consider in a non-limiting manner that optical analysis is fluorescence analysis.

[0033] Electrowetting droplet actuation device

[0034] [Fig.1]

[0035] This device includes a component having a chamber 1 defining a space for each drop to be analyzed. 40.

[0036] The reception space is defined by the spacing present between two substrates 100, 101 arranged in parallel.

[0037] A first substrate, referred to as lower 101, is configured to form a first matrix of (virtual) electrodes - see below. It is optionally covered with a hydrophobic layer or incorporates this hydrophobic layer C50.

[0038] A second substrate, called upper 100, includes a counter electrode (layer C2).

[0039] The two opposing faces of chamber 1 are advantageously flat and parallel to each other. The lower face is designated the bottom of chamber 1 and acts as the electrode array, and the upper face incorporates the counter electrode.

[0040] A voltage source (V) connected to the first electrode and the second electrode allows the formation of electrostatic fields through the system and in particular in the insulating layer C40 and the photosensitive layer C30.

[0041] As in any electrowetting microfluidic system, the device operates by electrostatic effect and includes means for generating several independent and juxtaposed electrostatic fields between the two substrates 100, 101. The electrostatic fields are generated perpendicular to the two substrates.

[0042] According to a particular feature of the invention, at the lower substrate level, the device implements a virtual electrode array called "Opto-EWOD" as described in the referenced publication PY Chiou, H. Moon, H. Toshiyoshi, CJ Kim, and MC Wu, “Light actuation of liquid by optoelectrowetting, ”, Sensors Actuators, A Phys., vol. 104, no. 3, pp. 222-228, 2003.

[0043] According to this principle, the lower substrate 101 comprises a stack of layers, including a photoconductive layer C30. Light radiation L1 makes the photoconductive layer C30 locally conductive, defining a virtual electrode both temporally and locally. The light beam thus induces the electrowetting effect locally at the scale of a droplet without having to physically fabricate an electrode array. This results in a virtual electrode array.

[0044] When a virtual electrode is created under the drop 40 by means of the optical projection of a pattern, an electrowetting effect appears, which modifies the spreading of the drop 40 by electrostatic forces, and makes it possible to trap (static virtual electrode) or move (moving virtual electrode) the drop 40.

[0045] The first light source SI can be a laser source that scans the surface of the electrowetting to actuate the droplets on the surface, or it can be a screen-type technology, whether emissive (OLED, LED, etc.), transmissive (LCD), or projection (video projector). It is thus possible to use an OLED or equivalent display, placed nearby under the component, capable of generating light beams. The layers of the lower substrate 101 located under the C30 photoconductive layer are of course transparent to the radiation emitted by this first light source SI.

[0046] Fig. 1 gives an example of stacking layers forming the component, according to this "Opto-EWOD" principle.

[0047] The upper substrate consists of a layer of glass Cl, onto which a thin layer of ITO (indium tin oxide) C2, approximately 100 nm thick, or another transparent conductive material, is deposited, thus forming the counter electrode. Next, a very thin layer C3 of a material, for example, one chosen to be highly hydrophobic (e.g., PTFE for polytetrafluoroethylene, based on polysiloxane (as described in patent application FR2887891A1) or any other hydrophobic material known to those skilled in the art of electrowetting (Teflon - Registered Trademark)), is deposited. The substrate 100 is inverted to place the C3 layer downwards.

[0048] The lower substrate 101 comprises a layer of CIO glass, onto which an ITO layer C20 is deposited, forming the electrode. The photoconductive layer C30 is then deposited on the ITO layer C20. An insulating layer C40 is then deposited on the photoconductive layer, followed by a hydrophobic layer C50 (for example, PTFE). The two substrates 100 and 101 are placed opposite each other and joined externally to form the chamber 1 intended to hold the drops 40. The vertical distance between the two hydrophobic layers C3 and C50 is chosen to be sufficient to allow the placement of only a single drop, rather than a stack, thus enabling the detection of the drops of interest and the association of each drop with a single electrode of the matrix or with a group of several electrodes of the matrix.

[0049] The first light source SI is, for example, composed of a pixelated OLED display, used to generate each localized light beam through the lower substrate 101 and to enable the activation of virtual electrodes. The size of the light beam L1 that defines a virtual electrode should preferably be less than or equal to the size of the droplets.

[0050] Since the principle of the invention does not necessarily operate by the movement of drops on a surface (as in prior art documents) but by fixing the drops of interest, it is not necessarily required to use hydrophobic C3, C50 external layers. A PTFE (Teflon-Registered Trademark) layer or a chemical treatment, for example with a silane such as FDTS (for Perfluorodecyltrichlorosilane), may suffice.

[0051] The activation of a virtual electrode is, for example, carried out by a control and power supply unit 2. By activating one or more pixels of the display, it makes it possible to generate a virtual electrode and place it at an electrical potential distinct from the electrical potential of the counter electrode (the latter electrical potential being, for example, zero) and thus to create a potential difference between the activated electrode and the counter electrode. Optical analysis device

[0052] [Fig.1]

[0053] To perform an optical analysis of the drops 40 (for example by fluorescence), a second light source S2 of excitation must be added, conventionally placed above the component and the chamber 1 of the actuation device, to excite the sample (excitation of the fluorophores in the case of fluorescence).

[0054] This excitation light source S2 is associated with a detector D, also located above chamber 1, which is designed to capture the light signals FL1 reflected by the sample after excitation. Such a configuration is standard, used in all so-called epifluorescence microscopes. It can, in particular, be a fluorescence imaging system. The excitation light source S2 emits a light beam L2 intended to excite the fluorophores present in the sample, and the detector D, for example a camera, is responsible for capturing the fluorescence FL1 emitted by the sample after excitation.

[0055] The upper substrate 100 is chosen to be transparent to the light radiation L2 emitted by the excitation light source S2 and to the fluorescence radiation FL1 emitted by the sample following excitation.

[0056] According to the invention, the coexistence of the first light source SI dedicated to electrowetting (an OLED display, for example) and the second light source S2, used to excite the sample in the context of optical analysis, is not obvious for the following two reasons: - The second light source S2 used during the optical analysis of the drops 40 must not trigger the electrowetting actuation system and cause an untimely movement or trapping of the drops 40 in the chamber 1; - Detector D must only be able to detect the light emitted by each excited drop 40 and not be disturbed by the light beams emitted by the first light source SI located below and used to create the virtual electrode of the electrowetting actuation device;

[0057] These two technical problems can be solved by separate means or by a single solution, capable of handling the two situations listed above.

[0058] In the first situation: - It is necessary to carry out optical filtering of the light emitted by the second light source S2 so that it does not excite the photoconductive layer C30 of the lower substrate 101 and cause disturbances in the control of the movement of the drops 40 by electrowetting;

[0059] In the second situation: - It is possible to use a suitable light source (SI), emitting over a range of wavelengths distinct from that which must be detected (for example that of fluorescence); - It is possible to implement optical filtering of the light emitted by the first light source SI in order not to interfere with the optical analysis; this emitted light must not overlap with the light emitted by the sample after excitation;

[0060] At a minimum, the solution of the invention must allow the first situation to be managed, since the second situation can be managed by simply adapting the type of source used for the first light source used in the actuation device.

[0061] In the case where the first light source SI is not suitable to handle the second situation (for example, the use of a simple video projector, or a white source with a very wide emission spectrum), it is also necessary to filter the light emitted by the first light source S1 so that it does not emit in the same wavelengths as those of the light emitted by the sample, after excitation. Optical filtering - first situation

[0062] [Fig.2A]

[0063] [Fig.2B]

[0064] In the case of the first situation, the invention consists of adding an optical filter Fl between the photoconductive layer C30 and the chamber 1 which accommodates the sample.

[0065] As indicated above, this optical filter Fl has the function of cutting off the wavelengths (denoted / ._L2) of the light beam L2 emitted by the second light source S2 that could excite the photoconductive layer C30. Thus, only the light emitted at wavelengths X_L1 by the first light source SI (that of the OLED display) should contribute to the excitation of the photoconductive layer C30 and be able to cause the fluorescence of a droplet 40 within the actuation device.

[0066] As indicated above, the lower substrate 101 is composed of a stack of layers, including in particular the photoconductive layer C30 surmounted by an insulating (hydrophobic) layer.

[0067] The optical filter can thus take three different positions: - A first position, between the insulating layer C40 and the photoconductive layer C30 (as in [Fig.2A]); - A second position between the insulating layer C40 and chamber 1 occupied by the sample; - A third position, integrated into the C40 insulating layer;

[0068] As illustrated by [Fig.2B], the Fl filter is advantageously a high-pass filter, blocking the excitation wavelengths / ._L2 of the fluorescence, emitted by the second light source S2, upstream of the photoconductive layer C30. It can also be a band-stop filter, allowing all wavelengths to pass, except for the wavelength / ._L2 of the source for the excitation of the fluorescence.

[0069] It can also be noted that the light emitted by the sample by fluorescence is a priori too weak to excite the photoconductive layer C30 and trigger activation of the electrowetting mechanism. If this is not the case, the filter must also block the wavelengths emitted by the sample by fluorescence. Optical filtering – second situation

[0070] [Fig.3A]

[0071] [Fig.3B]

[0072] To manage the second situation described above, a second optical filter F2 can be added.

[0073] In the second situation, it is indeed necessary to prevent the first light source SI, used for the control of the movement of the drops 40, from emitting at the emission wavelengths of the sample, after excitation, so as not to disturb the optical analysis (for example by fluorescence) of the drops 40 at the detector D.

[0074] For this purpose, the second optical filter F2 is added between the first light source SI and the chamber 1. In [Fig.3A], this second filter F2 is positioned between the first light source SI and the lower substrate 101.

[0075] In the simplest way, in connection with [Fig.3B], it is a matter of using a band-stop filter which allows all wavelengths (X_A allowing the activation of a virtual electrode) of the first light source SI to pass through, with the exception of the wavelengths (denoted X_P1) which would overlap with the wavelengths (denoted X_FL1) of the fluorescence emission of the sample and disrupt the optical analysis.

[0076] Classically, it should be noted that a fluorescence filter is already used in front of detector D, in order to collect only the fluorescence radiation emitted by the sample.

[0077] Optical filtering - first situation and second situation

[0078] [Fig.4A]

[0079] [Fig.4B]

[0080] [Fig.4C]

[0081] To manage the two situations described above, it is possible to add the first filter Fl and the second filter F2 according to the arrangements proposed in both [Fig.2A] and [Fig.3A] and with the characteristics defined above.

[0082] Furthermore, it is noted that the management of the two situations can be carried out by positioning a single filter between the photoconductive layer C30 and the chamber 1 intended to be occupied by the sample.

[0083] It is therefore possible to place a single F3 filter having the following functions: - The function of blocking all wavelengths / ._L2 coming from the second light source S2, which could excite the photoconductive layer C30, and - The function of cutting the wavelengths / .PI coming from the first light source SI, which may overlap with the wavelengths / .FL I of fluorescence emitted by the sample after excitation.

[0084] This can be a high-pass filter in both directions, with a cutoff above the fluorescence wavelength / .FL I or a wider band-stop filter ( [Fig.4B]).

[0085] According to an advantageous embodiment, a single deposit is made on the photoconductive layer, this one playing both the role of filter F3 and that of the insulation layer (C40).

[0086] By way of example, as illustrated by [Fig.4C], this deposit can be a stack of alternating layers of TiO2 / Al2O3 or SiO2 / Al2O3. Optical polarization

[0087] To manage the first situation described above, it is also possible to employ the principle of optical polarization of the light beam L2 emitted by the second light source S2.

[0088] An optical polarizer typically has several polarization lines oriented in parallel. It is a component that will only allow the component of the optical signal having a polarization direction parallel to the axis of the polarizer to pass through.

[0089] The next step involves adding a first polarizer PI to linearly polarize, along a first direction, the light beam L2 generated by the second light source S2 (for excitation), and placing a second polarizer P2 between the photoconductive layer C30 and chamber 1, with a direction orthogonal to the first direction. That is, the polarization axis of the second polarizer is orthogonal to the axis of the first polarizer, and consequently, the light that has passed through the first polarizer will be blocked by the second polarizer. Thus, in this configuration, the light from the second light source S2 does not reach the photoconductive layer C30 and is therefore not absorbed by it.

[0090] In conjunction with [Fig. 5], to manage the two situations described above, a third polarizer P3 is added in front of the polarizers PI, P2 already present. first light source SI, the axis of polarizer P3 being oriented along the first direction (the same as the first polarizer PI). In this configuration, the light from the second light source S2 does not reach the photoconductive layer C30 and is therefore not absorbed by it, and the light from the first light source SI for actuation does not reach the sample, and consequently is not detected on the fluorescence detection channel. Layer structuring

[0091] In another embodiment, in order to manage the two situations described above, it would also be possible to provide for a structuring of the surface of the insulating layer located above the photoconductive layer.

[0092] This structure, having controlled diffraction or refraction properties, will allow the direction of the radiation to be changed. Thus, the light emitted by the second light source S2 will be deflected and will not be able to reach the photoconductive layer C30, and the light emitted by the first light source S1 will not be able to reach the detector D.

[0093] This structuring could, for example, create networks or metasurfaces.

[0094] The invention thus offers numerous advantages, including: - It allows for the simple resolution of conflicts between light sources in such an optical analysis system; - The various solutions proposed are easy to implement in an existing system and do not require any specific programming, as in the state of the art; - The proposed solutions use readily available and inexpensive means;

Claims

Demands

1. A method for the optical analysis of a sample in a droplet actuation device operating by electrowetting, said actuation device comprising: - A chamber (1) formed by two substrates (100, 101) arranged opposite each other along a principal axis, so as to form a so-called lower substrate (101) and a so-called upper substrate (100), the two substrates being spaced apart to form a space for receiving said sample, - The lower substrate being made by a stack of layers in which a photoconductive layer (C30) is excitable by a first electrowetting displacement control light beam (L1) to form a first electrode, - A first light source (SI) capable of generating said first light beam (L1) for the photoconductive layer (C30) of the lower substrate (101), - The upper substrate (100) comprising a second electrode,- A voltage source (V) connected to the first and second electrodes so as to form an electrostatic field across said receiving space, - An optical sample analysis device comprising a second excitation light source (S2) positioned above the upper substrate (100), capable of generating a second light beam (L2) at an excitation wavelength, and a unit for detecting the light emitted by said sample through said upper substrate (100) caused by its excitation, - Characterized in that the method consists of: - Optically processing the second light beam (L2) to cut off the wavelengths (X_L2) capable of exciting the photoconductive layer (C30) of the lower substrate.

2. An optical sample analysis system comprising a droplet actuation device operating by electrowetting and capable of to implement the method defined in claim 1, said drop actuation device comprising: - A chamber (1) formed by two substrates (100, 101) arranged opposite each other along a principal axis, so as to form a so-called lower substrate (101) and a so-called upper substrate (100), the two substrates being spaced apart to form a space for receiving said sample, - The lower substrate (101) is made up of a stack of layers in which a photoconductive layer (C30) is excitable by a first light beam (L1) for displacement control by electrowetting to form a first electrode, - A first light source (SI) capable of generating said first light beam (Ll) for the photoconductive layer (C30) of the lower substrate, - The upper substrate (100) comprising a second electrode, - A voltage source (V) connected to the first and second electrodes so as to form an electrostatic field across said receiving space, - An optical sample analysis device comprising a second excitation light source (S2) positioned above the upper substrate (100), capable of generating a second light beam (L2) at an excitation wavelength (X_L2), and a unit for detecting the light emitted by said sample through said upper substrate (100) caused by its excitation, - Characterized by the fact that: - The system comprises a first optical element (Fl) positioned between the sample reception area and the photoconductive layer (C30) of the first substrate, - Said optical element being chosen to cut said excitation wavelength (X_L2) of the second light beam (L2) so that it does not excite the photoconductive layer (C30).

3. System according to claim 2, characterized in that the first optical element is positioned between an insulating layer (C40) of the lower substrate (101) and the photoconductive layer (C30).

4. System according to claim 2, characterized in that the first optical element is positioned between an insulating layer (C40) of the lower substrate (101) deposited on the photoconductive layer (C30) and the receiving space.

5. System according to claim 2, characterized in that the first optical element is integrated into an insulating layer (C40) of the lower substrate (101) deposited on the photoconductive layer (C30).

6. System according to claim 2, characterized in that it comprises a second optical element (F2) positioned between the first light source (SI) and the reception space, this second optical element being chosen to cut the wavelengths (X_P1) of the first light beam (L1) likely to overlap with the wavelengths ( / .FL 1 ) of the light emitted by the sample caused by its excitation.

7. System according to claim 6, characterized in that the first optical element (F1) and the second optical element (F2) are joined in the same deposit made on the photoconductive layer (C30) of the lower substrate (101), this deposit also playing the role of an electrical insulating layer (C40).

8. System according to claim 7, characterized in that said deposit is carried out in the form of a stack of alternating layers of TiO2 / Al2O3 or SiO2 / Al2O.

9. An optical sample analysis system comprising a droplet actuation device operating by electrowetting and capable of implementing the method defined in claim 1, said droplet actuation device comprising: - A chamber (1) formed by two substrates (100, 101) arranged opposite each other along a principal axis, so as to form a so-called lower substrate (101) and a so-called upper substrate (100), the two substrates being spaced apart to form a space for receiving said sample, - The lower substrate (101) being made by a stack of layers in which a photoconductive layer (C30) is excitable by a first electrowetting control light beam (L1) to form a first electrode, - A first light source (SI) capable of generating said first light beam (L1) for the conductive layer of the lower substrate, - The upper substrate (100) comprising a second electrode, - A voltage source (V) connected to the first and second electrodes so as to form an electrostatic field through said receiving space, - An optical sample analysis device comprising a second excitation light source (S2) positioned above the upper substrate, capable of generating a second light beam (L2) at an excitation wavelength, and a unit for detecting the light emitted by said sample through said upper substrate caused by its excitation, - Characterized in that the system comprises: - A first polarizer (PI) positioned between the second light source (S2) and said receiving space,This first polarizer has polarization lines oriented in a first direction; - A second optical polarizer (P2) is positioned between the sample space and the photoconductive layer (C30) of the first substrate, this second polarizer having polarization lines oriented in a second direction orthogonal to the first direction.

10. System according to claim 9, characterized in that it comprises a third optical polarizer (P3) positioned in front of the first light source (SI), having polarization lines oriented along said first direction.

11. System according to any one of claims 2 to 10, characterized in that the first light source (SI) is an OLED type display.

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