FR2817962A1 - Reflective characterization of variable-thickness layers on prisms e.g. for observation and analysis of biological reactions, employs light beam, prism and total internal reflection - Google Patents

Abstract

Reflective characterization of variable-thickness layers on prisms e.g. for observation and analysis of biological reactions, employing a light beam, prism and total internal reflection, is new. A collimated light beam projected into a prism undergoes total internal reflection at its base. It illuminates a fixed part of the interface forming a working region of the surface (4) to be characterized. A reflected beam leaves an exit surface. Beam angle is varied to scan the working region, finding an incidence at which reflectivity of part or all of the active zones is minimum. An optimum angle of incidence is determined at which the sensitivity of detection in the active zones is maximum. Incidence is controlled to this angle. Reflectivity is measured by an imaging and detection system with a sensitive area receiving the entire exit beam from the working region. An Independent claim is included for imaging apparatus carrying out the method. It employs a prism (3) of given angle and index of refraction. An afocal optical system (1, 2) illuminates it and the layer as described, varying beam angle over 10 deg or more. A second afocal system (5) is aligned to pass the exit beam. A detection system with a planar incident surface normal to the beam is employed for analysis. The second conjugation system includes an orifice passing all light from the illuminated surface to the detector surface. The prism angle and index of refraction ensure that when the incident beam is parallel to the axis of the first optical system, the intermediate image of the useful zone forming the object for the second detection system, is perpendicular to its optical axis. A fluid is brought into contact with the sensitive layer. This can contain an analyte bonding with ligands immobilized on the active zones. Variations in reflectivity of active zones is measured as a function of time. Results are used for quantitative characterization of interactions of at least one bonding ligand/analyte pair. The reagents are selected from primitive or transferred oligomers or proteins; from protein fragments, random-sequence oligopeptides, antibodies or their fragments, non-protein antigens, haptenes, agonists or antagonists of natural ligands, cells, biological receptors and oligosaccharides. As ligands, a primitive oligomer and a transferred oligomer are used, having point mutation e.g. in a given position. The analyte used is a fragment of DNA in which mutation is sought at the given position. Reflectivity curves are compared with pre-established curves for the primitive type and the 3 mutations possible at the position. Mutation present in the analyte is deduced in the case where a mutation is presented at the position.

Description

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The invention relates to a method for characterizing a surface.

This process also allows a qualitative and quantitative measurement of molecular interactions.

It allows in particular to follow in real time, and without markers, several hundred molecular interactions at a time.

The method according to the invention is used in particular for the analysis of DNA fragments.

Most existing methods use fluorescent markers to reveal molecular interactions, which requires working under specific conditions.

These specific conditions do not allow several types of interaction to be analyzed simultaneously.

The method according to the invention aims to solve this problem by not using markers attached to the molecules to be studied. The measurement is carried out under non-specific conditions, so that several types of interactions can be studied simultaneously qualitatively and quantitatively.

To this end, the invention describes a surface characterization method using a device for imaging a metal surface comprising a light source, a system for collimating the incident light beam, a detection cell comprising at least one prism, a system imaging and detection of the beam reflected by the base of the prism.

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 The method is characterized in that it comprises the following steps: - sweeping at an angle the surface of a glass slide covered with a layer of gold and a layer to be characterized; - determination of the angle of incidence for which the sensitivity of the imaging and detection system is maximum for the entire slide; - positioning the device at the angle determined in the previous step; - measurement of the reflectivity by the imaging and detection system as a function of time.

Another object of the invention is an application of said method and a device for imaging a metal surface implementing said method, the elements to be characterized being arranged on said metal surface.

Other objects and advantages of the invention will appear during the following description with reference to the accompanying drawings given by way of non-limiting example, in which: - Figure 1 shows a diagram of the device according to the invention; - Figure 2 shows a diagram of the detection cell according to the invention.

The device according to the invention comprises: - a non-coherent light source 1; - A collimation system 2 of the incident light beam emitted by the light source; - a detection cell 3 comprising at least one prism 4; - An imaging and detection system 5 of the beam reflected by the base of the prism.

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 The non-coherent light source 1 is for example a light-emitting diode of predetermined wavelength and of narrow spectral width.

It may for example be a light emitting diode with a wavelength of 660 nanometers and a spectral width of 30 nanometers.

The beam emitted by the light source 1 is collimated by a collimation system 2.

This collimation system 2 is for example a system of two microscope objectives making it possible to make the light beam parallel.

The light is then polarized parallel to the plane of incidence by a polarizer 6 in order to be able to excite the surface plasmon.

This polarized light illuminates the entry face of a glass prism 4 of the detection cell 3.

In one embodiment, the polarized light is reflected by an oscillating galvanometric mirror 7 towards the entry face of the prism 4 as shown in FIG. 1.

The oscillating mirror 7 is conjugated on the base of the prism using two lenses 8 and 9.

It is thus possible to vary the angle of incidence of the beam on the prism by the rotation of the oscillating mirror 7.

The oscillating mirror 7 undergoes a partial rotation, controlled for example by a low frequency generator.

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 The rotational movement of the oscillating mirror rotation device 7 must be able to be discretized using a continuous component in order to be able to fix the angle at which it is desired to carry out the experiments.

The diameter of the mirror 7 is such that it allows the entire incident beam to be reflected on the prism 4.

In the embodiment considered, this diameter must be at least 10 mm.

The total travel of the mirror 7 is then 160 for a frequency of 300 megahertz.

focale F'=50mm avec un diamètre de 25mm pour une excursion de 170. The lenses 8, 9 used to conjugate the mirror 7 with the prism 4 can be focal lenses F '= 75mm with a diameter of 35mm for an excursion of 19, or lenses of

focal length F '= 50mm with a diameter of 25mm for an excursion of 170.

During its rotation, the oscillating mirror 7 has a continuous stroke at a fixed frequency. The angle of incidence of the beam reflected by the mirror 7 on the prism 4 can be determined in two different ways.

In a first variant, the portion of the beam reflected by the entry face of the prism is collected by a strip of CCD charge coupled circuits 10 of sufficient length.

This CCD strip 10 makes it possible to detect the incidence of the beam.

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 The beam thus reflected by the entry face of the prism is focused on the CCD strip 10 using a lens 11 whose focal length is chosen so as to use the entire surface of the strip 10.

For a CCD strip 10 of length L = 12.7mm made up of 512 pixels, it is possible, for example, to use a lens 11 with focal length F '= 48mm and diameter 30mm.

In another variant, not shown, the rotation of the oscillating mirror 7 is ensured by a motor making it possible to determine the position of incidence for each position of the mirror. One can for example use a variable pitch motor.

The detection cell 3 comprises at least one glass prism 4 whose geometry and index are such that the intermediate image of the object plane in the prism 4 is almost parallel to the detection plane of the imaging and detection system 5 .

In a variant, the prism is made of glass with an index of 1.8 and has the characteristic of an apex angle of 40, a base of 10mm in width and 25mm in height. The distance between the two parallel faces of the prism is then 8mm.

A glass slide 12 of the same index as the prism 4 is fixed to the base of the prism by means of an index adaptation oil.

On this glass slide 12, a thin layer of chromium 13, a thin layer of gold 14 and a layer to be characterized 15 are successively deposited.

For an application to a qualitative and quantitative measurement of molecular interactions, the layer to be characterized is, for example, an organic layer 15.

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The organic layer 15 can include sensors.

The term “sensor” is intended to mean a geographical area of the organic layer 15 which may include several thousand probes which will be able to react with molecules.

The chromium layer 13 ensures the adhesion of the gold layer 14 on the glass slide 12 in the presence of an aqueous medium.

The thickness of the thin layer of chromium 13 is between 1.5 and 2 nanometers.

The thickness of the thin layer of gold 14 is between 40 and 50 nanometers and preferably of the order of 45 nanometers.

As part of the study of interactions between oligonucleotides and single-stranded DNA fragments to be studied, the organic layer 15 consists of the attachment of oligonucleotides to the gold layer 14 by means of a polymer. such as for example polypyrrol. The oligonucleotides being grafted onto the polypyrrol.

Said organic layer 15 does not include markers.

This polymer has the advantage of being very stable, which makes it possible to reuse the organic layer 15 comprising the probes several times.

The production and deposition of such a layer of polypyrrol grafted onto a layer of gold are for example described in patents EP 0 691 978 and FR 2 789 401.

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 Once the glass slide 12 is fixed on the base of the prism 4, it is hermetically covered with a tank 16.

17. Une pompe péristaltique 18 à débit variable peut alors être utilisée pour faire circuler ces solutions. This tank 16 is for example made of Teflon and makes it possible to pass the organic solutions using one or more pipes.

17. A peristaltic pump 18 with variable flow can then be used to circulate these solutions.

In order to optimize the introduction of solutions, the peristaltic pump 18 meets the following criteria: - be remotely controllable; - be able to generate flow rates between a few micro liters per minute and a few hundred micro liters per minute (of the order of 300 to 400 micro liters / min); - allow input / output control of the rotation speed at the start and end of the injection.

The whole of the detection cell 3 (prism 4 and tank 16) can be enclosed in an adiabatic enclosure 19 shown in FIG. 2, in order to control and fix the temperature of the system and of the products injected.

The temperature will for example be maintained at 370 in order to allow the detection of any type of biological molecules.

The adiabatic enclosure 19 preferably comprises an opening (not shown) allowing easy access to the detection cell 3.

It may in particular include a heating base 20, such as for example a copper resistor, on which the tank will be fixed.

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 of Teflon reaction 16. This base 20 is covered with a cover 21 encompassing the whole of the detection cell 3. Lateral portholes 22, 23 are provided in the cover 21 in order to let the light beams pass through and through. other of the prism. They are for example made of glass or any other material allowing the beams to pass without disturbing them.

A winding (not shown) wound around the pipe 17 of the tank 16 keeps the products injected at the temperature of the cell.

An imaging and detection system 5 is arranged on the side of the outlet face of the prism 4 in order to recover the beam reflected by the base of the latter.

This system includes an afocal magnification system 24 and a CCD camera 25.

The afocal magnification system 24 makes it possible to enlarge the image of the useful area of the gold blade 14 on the entire CCD camera 25.

The useful area of the gold blade 14 is indeed of small dimension, of the order of approximately 25 mm 2.

In the embodiment shown, an enlargement G = 1.6 is carried out and a digital aperture system O. N. = 1.6 is used to conjugate the image on the plane of the CCD camera 25.

The afocal system 24 can for example comprise a lens 26 with a focal length F '= 50mm and a diameter of 35mm, then another lens 27 with a focal length F' = 80mm and a diameter of 40mm.

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 The CCD camera 25 (or simply a CCD matrix) can, for example, have a sensitive surface of 6.4 mm × 5.8 mm composed of 768 × 576 pixels.

All the elements of the device according to the invention are controlled automatically by means of a computer chain not shown.

The method of using said device comprises the following steps: - scanning at an angle of the surface of the glass slide 12 covered with the gold layer 14 and the layer to be characterized 15; - Determination of the angle of incidence for which the sensitivity of the imaging and detection system 5 is maximum for the entire blade 12; - positioning of the oscillating mirror 7 to obtain this angle of incidence; - measurement of the reflectivity by the imaging and detection system 5 as a function of time.

The device is then used to characterize the surface of the layer to be characterized 15.

The device can be applied to the study of molecular interactions.

The layer to be characterized is then, for example, an organic layer.

In order to measure the interactions between the organic layer 15 and molecules, the step of measuring the reflectivity is carried out simultaneously with the introduction into the detection cell 3 of

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 molecules free of markers whose interactions with the organic layer 15 are to be analyzed. The evolution of the interactions between the organic layer 15 and the molecules introduced is thus measured.

These measurements can be performed under non-selective conditions, so that all interactions can occur and be studied.

The imaging and detection system 5 makes it possible to measure the optical thickness, product of the geometric thickness and the refractive index of the medium, at any point of the gold layer 14.

It is thus possible to visualize topologically the zones of equal optical thickness and to characterize the surface.

Thus, during the angled scanning of the surface of the glass plate 12 covered with the gold layer 14, the system 5 makes it possible to determine the geometric thickness of each point of the layer 14 and therefore to check the state of surface of it.

The contrast measured during scanning also serves as a reference level for real-time measurement.

During the measurement in real time, the imaging and detection system 5 measures the variation of the reflectivity relative to the reference level recorded during the angular scanning.

This measurement of the variation of the reflectivity is carried out at every point of the gold layer 14.

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 Since the reflectivity varies as a function of the molecules present on the surface, this measurement allows a qualitative analysis by determining the different interactions between the organic layer 15 / the gold layer 14 and the molecules introduced.

Thus, when one places oneself at the angle optimizing the sensitivity of the device, a positive variation in the reflectivity signifies the presence of molecules interacting with the organic layer 15, a zero variation signifying the absence of molecules.

A negative variation then represents on the contrary a loss of material, that is to say a degradation of the layer to be characterized, organic or not.

Measuring the amplitude of the variation in reflectivity in real time makes it possible to access the number of molecules per unit area and therefore the concentration at each point of the gold layer 14 of the molecules introduced.

The device according to the invention therefore also allows a quantitative analysis of the molecules having interacted with the organic layer 15.

Depending on the strength of the bond between the organic layer 15 and the gold layer 14 and the nature of the interactions studied, it will be possible at the end of the measurement to regenerate the organic layer 15 by eliminating all the molecules which have reacted with it.

It is then possible to reuse the organic layer 15 to study interactions with new molecules.

In order to optimize the sensitivity of the measurement, it is also possible to optimize the distribution of the sensors fixed on the organic layer 15. It is indeed necessary that the number of probes

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 per sensor is high enough to distinguish it from the background noise of the measured signal without the probes being too close to each other.

Indeed, a large number of probes results in a large steric hindrance and hinders the interaction of molecules with neighboring probes.

In the context of the study of interactions between oligonucleotides and single-stranded DNA fragments to study the method according to the invention has many advantages.

The interactions are studied under non-selective hybridization conditions, ie at a temperature of the order of 37 ° C., so that all of the interactions between molecules can be observed simultaneously.

The device makes it possible to follow several hundreds of molecular interactions at the same time and without markers. It is able to discriminate the presence of a point mutation within a DNA fragment.

The discrimination technique is based on the fact that the molecular association can either be total if the DNA sequence is strictly complementary to that of the oligonucleotide, or partial if the DNA sequence has a mutated base.

Thermodynamics applied to DNA stipulates that depending on the type of mutation, for a fixed location in the sequence, the optical thickness varies. It follows that the device can precisely determine the type of mutation.

Under non-selective conditions, if a normal sequence and the three sequences carrying the mutation of one of the bases of said

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 sequence, that is to say the four sequences of which one of the bases has been mutated, are deposited on the gold layer 14, the device can measure a different signal for each of the immobilized sequences.

Indeed, whatever the sequence of the fragment to be analyzed, the device measures a total interaction and three partial interactions.

Depending on the immobilized sequences, it suffices to refer to the existing tables giving the interaction strength between bases to go back to the exact nature of the DNA sequence.

Consequently, if the detection system is calibrated, for example with respect to the value of a completely complementary signal, it is no longer necessary to immobilize the normal sequence and the three mutated sequences: the immobilization of a single sequence is sufficient.

The capacity to address DNA sequences on a solid substrate is therefore multiplied by four.

The device according to the invention following the molecular interactions directly and in real time, it is not necessary to carry out the measurement at a temperature favoring a single interaction as in the case of the methods using fluorescent markers.

Indeed, these methods only reveal a single interaction visible at a given temperature. If these methods were used at room temperature, all the markers would fluoresce at the same time and therefore could not be distinguished.

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 Furthermore, in the case of studying oligonucleotides, these methods require the immobilization on a support of all the sequences relating to a gene and selective conditions.

It goes without saying that this method can be applied to the study of all types of interactions between molecules.

Claims (19)

 1. Method for characterizing a surface using a device for imaging a metal surface comprising a light source (1), a collimation system (2) of the incident light beam, a detection cell (3) comprising at least a prism (4), an imaging and detection system (5) of the beam reflected by the base of the prism, characterized in that it comprises the following steps: - angled scanning of the surface of a glass slide (12) covered with a layer of gold (14) and an organic layer (15); - Determination of the angle of incidence for which the sensitivity of the imaging and detection system (5) is maximum for the entire blade (12); - positioning the device at the angle determined in the previous step; - measurement of the reflectivity by the imaging and detection system (5) as a function of time. 2. Application of the method according to claim 1 to the qualitative and quantitative measurement of molecular interactions. 3. A characterization method used for the application according to claim 2 in which the layer to be characterized (15) is an organic layer carrying probes. 4. The method of claim 3 wherein the introduction into the detection cell (3) of molecules free of markers whose interactions with the probes of the organic layer (15) are to be analyzed is simultaneous to the measurement of the reflectivity by the imaging and detection system (5) as a function of time. <Desc / Clms Page number 16>  5. Method according to one of claims 1, 3 or 4, or used for the application according to claim 2, in which the measurements as a function of time are carried out under non-selective conditions. 6. Method according to one of claims 3 or 4, or according to claim 5 when it depends on claims 3 or 4, wherein at the end of the measurement, the organic layer probes (15) are regenerated by eliminating all the molecules that interacted. 7. Method according to one of claims 3,4 or 6, or according to claim 5 when it depends on claims 3 or 4, in which the number of probes fixed on the organic layer (15) is chosen so as to optimize signal detection sensitivity while limiting steric hindrance. 8. Device for imaging a metal surface implementing) the method according to claims 1 and 3 to 7, said device comprising a light source (1), a collimation system (2) of the incident light beam, a cell detection (3) comprising at least one prism (4), an imaging and detection system (5) of the beam reflected by the base of the prism, characterized in that the light source (1) is a non-coherent source and in that the prism (4) is a glass prism whose geometry and index are such that the intermediate image of the object plane in the prism (4) is almost parallel to the detection plane of the imaging system and of detection (5). 9. Device according to claim 8, characterized in that it comprises a galvanometric mirror (7) oscillating reflecting the beam emitted by the light source (1) on the input face of the prism (4) and capable of varying l angle of incidence of said beam. <Desc / Clms Page number 17> 10. Device according to claim 9 characterized in that a variable pitch motor makes it possible to determine the position of incidence of the oscillating mirror (7). 11. Device according to claim 9 characterized in that the incidence position of the oscillating mirror (7) is determined by means of a CCD camera (10) on which is collected the part of the beam which is reflected by the face of entry of the prism (4).  12. Device according to one of claims 8 to 11, characterized in that the detection cell (5) comprises at least the glass prism (4) on the base of which a glass slide (12) of the same index is fixed , this blade (12) being covered with a thin layer (14) of gold, and with a layer (15) of organic molecules whose interactions are to be analyzed.  13. Device according to one of claims 8 to 12, characterized in that the light source is a light emitting diode emitting at a given wavelength. 14. Device according to one of claims 8 to 13, characterized in that the prism (4) is made of glass of index 1.8 and has an apex angle of 40, a base of 10 mm and a height of 25 mm. 15. Device according to one of claims 8 to 14, characterized in that the detection cell (5) comprises a Teflon tank (16) hermetically covering the thin layer of gold (14) covered with the layer of molecules ( 15). 16. Device according to claim 15, characterized in that it comprises a peristaltic pump (18) and one or more pipes (17) connecting the pump to the tank (16) for circulating liquids in the tank (16) . <Desc / Clms Page number 18>  17. Device according to one of claims 8 to 16 characterized in that the imaging and detection system (5) comprises an afocal magnification system (24) and a CCD camera (25 -) - 18. Device according to claim 17, characterized in that the afocal system (24) of magnification comprises two focal lenses (26), (27) for enlarging the image of the area to be analyzed. 19. Device according to one of claims 8 to 18, characterized in that it comprises a computer system for controlling the various elements.