Immersion tip and associated RAMAN probe

Abstract

Immersion tip and associated RAMAN probe Immersion tip (20) of a probe for Raman spectroscopy comprising a cylindrical body (30) provided with collimation optics (32) and / or a porthole (34) and intended to be immersed in a liquid to be analyzed (12), the cylindrical body consisting of two parts separated by a slit (62) intended to allow the liquid to be analyzed to pass through it, the first part (30A) being hollow and traversed by light emission and reception signals, the other end opposite the first being closed by the collimation optics and / or the porthole, the second part (30B) being configured to prohibit any reception of light other than that passing through the slit and comprising a part made of an absorbent material (64) arranged opposite the porthole. Figure for the abstract: Fig. 1.

Description

Title of the invention: Immersion tip and associated RAMAN probe Technical field

[0001] The present invention relates to the field of measurement by Raman spectrometer and it concerns more particularly an immersion tip of a probe for Raman spectroscopy. Prior art

[0002] Raman spectroscopy is increasingly used in certain cutting-edge fields, particularly in biotechnology. It can provide real-time information on the concentration of several nutrients such as glucose, lactate, glutamine. It is also possible to obtain information on the total concentration of antibodies produced by cells or on the glycosylation of antibodies.

[0003] However, cell culture processes are long (several weeks) and complex to control due to the use of living cells with highly variable behavior and requiring constant nutrient requirements (the consumption of the nutritional medium depends on the type of cells) to ensure good growth and sufficient cell production. In addition, these processes are difficult to repeat at an industrial level due to a batch effect and change of scale (transition from experimental reactor of 0.51 to several hundred liters in the production phase).

[0004] Raman spectroscopy uses the principle of inelastic scattering which is generated when illuminating a sample with intense monochromatic light. Current devices use a laser source with a fixed wavelength. This source is focused on a small diameter spot (typically 100 pm to 200 pm) in order to have sufficient density to generate the Raman effect. This is very weak compared to other interaction phenomena existing between light and matter and which are, in order of importance: elastic scattering (Rayleigh, Mie), light absorption, fluorescence and the Raman effect.

[0005] The Raman effect being the weakest of these light / matter interaction phenomena, the measuring device (laser spectrometer), to capture the slightest photon, must eliminate these other unwanted phenomena by a series of filters and by a choice of suitable wavelength. For example, since 532nm lasers often generate fluorescence in biological environments, Raman spectrometers rely instead on the use of lasers with a longer wavelength, in particular 785nm or 830nm.

[0006] Furthermore, when it is desired to carry out an in situ liquid measurement in such biological environments, due to the high sensitivity to humidity and heat of the optical elements, it is impossible to directly place the measuring device against or in this liquid and it is therefore necessary to transfer this measurement by means of optical fibers.

[0007] [Fig. 3] shows a current example of a biological reactor 10 containing a liquid 12 whose properties are to be analyzed. This reactor is equipped with a paddle stirrer 14 and can receive a Raman probe 16 and possibly another optical probe (for example an optical turbidimeter 18). The Raman probe has an immersion tip 20 immersed in the liquid to be analyzed 12 and it is connected by a first fiber 22 to a laser source 24 delivering a laser emission signal and by a second fiber 26 to a spectrometer 28 receiving a reception light signal to be analyzed (the measurement signal).The immersion tip 20 is generally made up of a cylindrical body 30 equipped with collimating optics (lens or microbead 32) and provided at its free end with a porthole 34 (the lens or the ball can also act as a porthole) held fixedly to the body 30 by seal, glue, solder, welding or any other means making it possible to constitute a perfectly sealed assembly with respect to the liquid to be analyzed 12.

[0008] The internal structure of the probe is detailed in Figures 4A and 4B which illustrate two standard variants. In Figure 4A, the emission fiber 22 and the reception fiber 26 are independent and therefore each comprise at the end of the fiber a collimator 40, 42 followed by a filter, filter 44 to clean the light signal leaving the emission fiber 22 connected to the laser 24 which emits the radiation or filter 46 to allow only the measurement signal resulting from the Raman effect from the analyzed medium (the sample) to pass. A prism 48 and a dichroic plate 50 complete this structure to separate the emitted light signal from the received measurement signal both circulating in the immersion tip 20. Sometimes the emission fiber 22 and the reception fiber 26 can be combined in a fiber bundle and collimated with a single optical element 52.In this case, the filters 44, 46 are most often placed directly on the fibers, or even mounted at the fiber output as illustrated in figure 4B.

[0009] Despite numerous optimization works, the implementation of Raman spectroscopy remains complex. Indeed, most biological reactors are transparent (made of glass or disposable plastic) so that operators can see how the culture is progressing. This results in a high sensitivity to ambient light (reference 60 in [Fig.3]) or coming from other sensors used in the reactor and which can then interfere with the measurement (for example due to reflections on the agitator blades or other metal surfaces). In order to eliminate this phenomenon, manufacturers are obliged to cover their reactor with a black cloth or aluminum foil, an acceptable practice in the experimental or development phase but unthinkable in the production. Similarly, the measurement suffers from a significant lack of sensitivity often due to very low nutrient concentrations in the medium, resulting from very high dilution, and to the turbidity of this medium which increases with cell growth and causes a loss of Raman intensity (less intense and more diffuse spot). Statement of the invention

[0010] The main aim of the present invention is therefore to overcome the aforementioned drawbacks by limiting the parasitic effect of ambient light or other optical sensors present in the reactor and by improving the level of the Raman signal collected. Another aim is to increase cell densities to improve the profitability of the process.

[0011] These aims are achieved by an immersion tip for Raman spectroscopy comprising a cylindrical body provided with collimation optics and / or a porthole and intended to be immersed in a liquid to be analyzed, characterized in that the cylindrical body is made up of two parts separated by a slit intended to allow the liquid to be analyzed to pass through it, the first part being hollow and traversed by light emission and reception signals, the other end opposite the first being closed by the collimation optics and / or the porthole, the second part being configured to prohibit any reception of light other than that passing through the slit and comprising a part made of an absorbent material arranged opposite the porthole.

[0012] Thus, with this slit and the integration of an absorbent material, the effects of parasitic light are limited and the performance of the Raman probe is greatly improved.

[0013] According to an advantageous embodiment, the absorbent material constitutes the central part of a reflective material of concave spherical shape making it possible to redirect the collected Raman signal towards a single focusing point corresponding to the focusing point of the collimation optics.

[0014] Preferably, the slot has a width L of between 0.5 and 10 mm and typically of the order of 3 mm and a thickness E substantially equal to a width of the porthole.

[0015] Advantageously, the light-absorbing material is a black polymer or black-treated stainless steel.

[0016] Preferably, the cylindrical body is made of metal, in the case of reusable tips, or of plastic, in the case of single-use tips.

[0017] Advantageously, the cylindrical body is welded to a liquid collection bag in the case of single-use tips.

[0018] According to the embodiments envisaged, the first hollow part may be intended to receive at one end a single transmit / receive optical fiber, or a bundle of circular optical fibers with the transmit fiber arranged in the center and the receive fibers around this central fiber, or even a bundle of circular optical fibers cular with transmitting fibers arranged on the periphery of a receiving fiber. Brief description of the drawings

[0019] Other characteristics and advantages of the present invention will emerge from the description given below, with reference to the appended drawings which illustrate an exemplary embodiment thereof without any limiting character and in which:

[0020] [Fig-1] [Fig. 1] illustrates a first example of embodiment of an immersion tip according to the invention,

[0021] [Fig.2] [Fig.2] illustrates a second example of the embodiment of an immersion tip in accordance with the invention,

[0022] [Fig.3] [Fig.3] shows a reactor equipped for Raman spectroscopy, and

[0023] [Fig.4A-4B] Figures 4A and 4B show two examples of internal structure of a Raman probe suitable for the immersion tips of figures 1 and 2. Description of the embodiments

[0024] The principle of the invention is based on an immersion tip whose particular innovative structure associated with a traditional measuring chain makes it possible to respond to numerous industrial problems for the control of chemical formulation processes.

[0025] Typically, compounds will emit spectral bands or lines at specific wavelengths in the Near Infrared (NIR) allowing the compound to be identified and quantified. This quantification is conventionally done either directly by a linear regression made on these bands, or by a multivariate modeling approach (chemometrics and machine learning). In the latter case, different algorithms known to those skilled in the art and which it is therefore unnecessary to detail, can be used, such as PLS (Partial Least Square), PCA (Principal Component Analysis) or SVM (Support Vector Machine) for non-linear methods.

[0026] According to the invention, and as shown in the exemplary embodiment of [Fig.l], to limit the effect of stray light, the immersion tip which advantageously has a cylindrical body 30, comprises a slot 62 of width L separating the body into two parts 30A, 30B and allowing the liquid medium 12 to pass through it for the measurement (the slot of course has a thickness E less than the diameter of the body 30). The first part 30A, one end of which (not shown in this figure) is intended to receive the emission / reception fiber or the emission and reception fibers, is hollow in order to allow the collimated laser signal from the emission fiber(s) to pass through as well as the Raman measurement signal emitted in return by the sample, the other end opposite the first being closed by the lens 32 and / or the porthole 34. The second part 30B is advantageously solid (but a simple cover or cap is also possible) and therefore prohibits any reception of light that could enter from below in state-of-the-art devices, this ambient or artificial light being able to penetrate the immersion tip only on the side through the slit 64, over a maximum width defined by the width L of the slit (advantageously between 0.5 and 10 mm and typically of the order of 3 mm). This second part also comprises a part 64 arranged opposite the porthole 34 and formed of a light-absorbing material (for example a black polymer or black-treated stainless steel). This absorbent material makes it possible to eliminate any external light that would have managed to pass through the slit. Furthermore, it limits the Rayleigh laser reflections and scatterings that appear in particular on turbid matrices. This configuration is particularly advantageous when the laser emission is carried out by a single fiber which also ensures the reception of the Raman measurement signal..

[0027] The immersion tip can be made of metal, in the case of reusable tips, or of plastic in the case of single-use systems (use of the tip for a single batch, the immersion tip being delivered welded to the liquid sampling bag).

[0028] [Fig.2] shows another embodiment which allows additional amplification of the collected Raman signal by combining the absorbing material 64 with a reflecting material 66 and redirecting the Raman signal to a single focal point corresponding to the focal point of the collimating optics. This redirection to a single focal point prevents only classical Rayleigh scattering from being amplified. The reflecting material is formed in a concave spherical part whose external radius is equal to that of the porthole 34 which faces it and therefore with a radius substantially equal to the thickness E of the slit, to reflect a focal point in front of the porthole (the measurement window). At its center, this spherical part comprises the absorbing material 64.

[0029] In another embodiment not shown, depending on the type of optical fibers used, the absorbing 64 and reflecting 66 materials can be interchanged. The reflecting material is arranged in the center and the absorbing material at its periphery. More precisely, in the case where the laser illumination is carried out by a bundle of circular optical fibers with the emission fiber arranged in the center and the reception fibers around this central fiber, it is appropriate to place the absorbing material in the center and the reflecting material at the periphery. On the other hand, in the case where this illumination is carried out by a multimode single-core emission / reception fiber, the reflecting material will be placed in the center and the absorbing material on the edges.

Claims

Claims

1. Immersion tip (20) for a probe for Raman spectroscopy comprising a cylindrical body (30) provided with collimation optics (32) and / or a porthole (34) and intended to be immersed in a liquid to be analyzed (12), characterized in that the cylindrical body consists of two parts (30A, 30B) separated by a slot (62) intended to allow the liquid to be analyzed to pass through it, the first part (30A) being hollow and traversed from a first end by light emission and reception signals, the other end opposite the first being closed by the collimation optics and / or the porthole, the second part (30B) being configured to prevent any reception of stray light other than that passing through the slot and comprising a part made of a light-absorbing material (64) arranged opposite the porthole.

2. The immersion tip of claim 1, wherein the light absorbing material constitutes the central portion of a concave spherical reflective material (66) for redirecting the collected Raman signal to a single focal point corresponding to the focal point of the collimating optics.

3. Immersion tip according to claim 1 or claim 2, in which the slot has a width L of between 0.5 and 10 mm and typically of the order of 3 mm and a thickness E substantially equal to a width of the porthole.

4. An immersion tip according to claim 1 or claim 2, wherein the light absorbing material is a black polymer or black treated stainless steel.

5. An immersion tip according to claim 1 or claim 2, wherein the cylindrical body is made of metal, in the case of reusable tips, or of plastic, in the case of single-use tips.

6. An immersion tip according to claim 5, wherein the cylindrical body is welded to a liquid collection bag in the case of single-use tips.

7. The immersion tip of claim 1, wherein the first hollow portion is configured to receive at the first end a single transmit / receive optical fiber.

8. An immersion tip according to claim 2, wherein the first hollow portion is configured to receive at the first end a bundle of circular optical fibers with the transmitting fiber arranged in the center and the receiving fibers around this central fiber.

9. Immersion tip according to claim 2, in which the first hollow part is configured to receive at the first end a bundle of circular optical fibers with transmitting fibers arranged at the periphery of a receiving fiber.

10. A Raman probe comprising an immersion tip according to any one of claims 1 to 9.

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