FI84940C - SENSOR SOM AER BASERAD PAO YTPLASMONRESONANSFENOMENET. - Google Patents

Description

84940

A sensor based on the surface plasmon resonance phenomenon

The invention relates to a sensor which exploits the phenomenon of surface plasmon resonance and which is intended for the analysis of various substances, such as gases and liquids, and the features of which are set out in the preamble of claim 1.

The sensors according to the invention can be used in particular for the analysis of the chemical composition of substances and in immunology and enzymology for the detection and monitoring of various reactions.

Surface plasmon resonance is an optical surface phenomenon that has been introduced in sensor technology in recent years. For a theory and physical description of this phenomenon, reference is made to H. Raether's article in Phys. Thin Films, 74, pp. 237-244 (1977). The surface plasmon is a surface charge density wave on a metallic surface. In the phenomenon, the p-polarized light beam that arrives at the interface between the insulator and the metal clearly loses its intensity at a certain rate. at the reflection angle due to the above-mentioned resonance phenomenon.

This angle is first determined by the insulating properties of the insulator adjacent to the metal surface 25 as well as the properties of the metal surface itself. In practice, the metal surface is formed by the surface of the thin metal film facing the light-transmitting insulating material. However, the resonance phenomenon is also affected by the conditions on the other side of this thin metal-30 dirt film, as a result of which the measurement technique based on this phenomenon has been widely used in various analyzes. GB patent application publication 2197065 and European patent application publication publication 35 326291.

In the devices described in the above-mentioned publications, the dependence of the resonance phenomenon on the angle of reflection of light entering the surface is generally measured. In this case, 2 84940 light sources are used, for example, a light emitting diode which emits light only at a certain wavelength. Alternatively, a gas laser with a well-defined wavelength of 5 may be used as the light source.

Em. the disadvantage of the devices is that they are strictly limited to the use of only one variable (angle of reflection) in the measurement. However, it has been found that the resonance phenomenon depends very strongly on the wavelength of the light coming to the surface. This has not been sufficiently taken into account in previous devices, and if it is desired to measure the phenomenon at a second wavelength, it has therefore been necessary to replace the light source 15 with a completely new light source. Again, if it is desired to measure the phenomenon at different wavelengths and with only one light source, the light source is then a "white light", i.e. a light source emitting light of all wavelengths, and this light is divided into different wavelengths by complex optical arrangements. Such devices have been described e.g. European Patent Application No. 257955 and Swalen et al., "Plasmon surf ace Polar ton dispersion by direct optical observation", Am. J. Phys. 48, ss ·; · 25 659-672, 1980. However, the light sources used in previous devices "·. Force the developer into certain predetermined solutions and do not allow the devices to be diversified and difficult to miniaturize.

30

The object of the invention is to eliminate the above drawbacks. To achieve this object, the sensor according to the invention is mainly characterized by the features set forth in the characterizing part of claim 1. The starting point of the sensor according to the invention is that the point from which the beam produced by the light source 3 84940 is directed towards the surface is fixed with respect to this surface, and the wavelength of the light emitted by the same light source can be varied.

5 With this arrangement, it is possible to detect the resonance point using a wavelength as a variable with a simple sensor that does not require complex lattice structures or other optical arrangements between the light source and the surface, and if desired, the resonance point can be measured using both the light wavelength and the wavelength.

The appended subclaims set out some preferred alternatives for implementing the sensor. A device for storing intensity values obtained at different wavelengths can be connected to the detector. In addition, a device that automatically traverses a specific wavelength range can be connected to the light source. This device is arranged synchronously with the recording device, whereby at different wavelengths the following are obtained: ·; : The values are saved automatically. Furthermore, according to a preferred embodiment, the light coming from the light source at each wavelength is arranged to be scattered at different incident angles with respect to the surface, the reflected light intensity detector correspondingly consisting of a series of detectors, each detector measuring the light reflected from the reflected surface at a certain reflection angle. On the one hand, this achieves the use of two different variables in the measurement as well as a simple structure without moving parts, which allows the sensor to be miniaturized.

According to a preferred embodiment of the invention, between the light source and the surface there are means for dividing the light beam from the light source into a measuring beam and a reference beam directed at a surface measuring area and a reference area spaced apart on the surface, respectively. This makes it possible to improve the measurement accuracy and the signal-to-noise ratio by having an actual sample to be measured at the measuring range and a reference sample at the reference range, or otherwise having different characteristics of the measuring range and the reference range.

The invention can furthermore be implemented in the form of a measuring head inserted into the substance to be analyzed, the sensor having optical fibers for connecting the surface at the measuring head to the light source and the detector.

For carrying out the invention, the light source may be a fixed tunable laser 1., or a dimmable radiation source as disclosed, for example, in International Patent Application WO-88/10462.

20

The invention will now be described in more detail with reference to the accompanying drawings, in which Figure 1 is a principle of a sensor according to the invention, Figure 2 shows an embodiment of a sensor according to the invention with simultaneous reflection angles, Figures 3a and 3b show an embodiment of Figure 2. Fig. 4 shows an embodiment of the invention in which the measurement takes place with a certain predetermined reflection angle and a wide surface area, Fig. 5 shows an embodiment of the embodiment according to Fig. 4, in which surface is a special reference area 1. a reference area 10 for improving measurement accuracy, Figs. 6a and 6b show an embodiment according to Fig. 5, with which the measurement can be performed over a wider surface area according to Figs. 3a and 3b, and Fig. 7 shows a preferred method according to the invention. the sensor structure.

Figure 1 shows the basic principle of the invention, the various alternatives of which are described below. The sensor according to the invention has a variable wavelength light source 1 from which the outgoing light is directed to a body 3 of electrically insulating and light-transmitting material 25 partially coated with a thin metal film 4. The body in question is a prism one side of which is coated with a metal film. The light beam is passed through a suitable optics 2 through a prism to the interface of the metal foil 4 and the prism, whereby it 30 is reflected from the surface of the metal film at a certain angle and the reflected light beam is guided through the necessary optics 6 to a detector 7 which measures the reflected light. The polarization of the light from the light source 1 is also performed before the interface. In addition, both the light source 1 and the detector 7 are connected to a device 8, such as a microprocessor or a computer, which stores the intensity value and the values measured by the detector 7 for processing and analysis. In order to combine the values obtained at the different wavelengths emitted by the light source with the corresponding intensity values, a microprocessor or computer is additionally connected to the light source 1.

The device 8 may be arranged to give instructions to the light source by going through a certain wavelength range, and to store the different intensity values obtained in this wavelength range. This "scanning" can be performed in such a way that the light source 1 emits light, preferably in less than 10 seconds, light at different wavelengths in this range.

The metal film 4 arranged on the outer surface of the prism 3 may be any material previously used in this measurement technique 15, and may be coated with a selectively sensitive film 5 of electrically insulating material depending on the measurement purpose.

The light beam, which is p-polarized light, is reflected from the interface of the prism 3 and the metal layer and interacts with the surface plasmons of the metal film. Plasmon excitation can be detected with a certain:; : at the wavelength as a sharp pit or "drop" in a graph depicting the intensity of reflected light-25 t as a function of the angle of incidence. The shape and location of this well is very sensitive to the insulating properties of the medium immediately in the vicinity of the metal film. According to the invention, the analysis is performed by measuring the phenomenon at different wavelengths at a certain reflection angle-30a, whereby the point of the light source from which the light beam is directed along a fixed path towards the prism 3 and the film 4 is fixed, i.e. this point remains in place with respect to said interface. The term "fixed orbit" in this context means that after the ... 35 points in question, the beam is guided to the surface along a certain path determined by stationary refracting and / or reflecting optics without optical fibers, etc. The light beam emanating from the point can be arranged differently. focus on a certain point on the measuring surface, where different rays of the beam have different angles of incidence and reflection, assemble into a beam of parallel rays directed to a certain area, or a beam of light emanating from this point can be arranged into several beams of parallel rays, different input and reflection angles, as will be presented later. 10 In addition, the beam consisting of the above-mentioned parallel beams can be divided into different areas located on the measuring surface.

Although the invention is mainly focused on measuring at different wavelengths, which can be quickly changed by the same light source, it can also be combined with the observation of a phenomenon at different reflection angles. Thus, changes in resonance can be determined simultaneously as a function of both variables rapidly without the need for mechanical moving parts or readjustment.

Figure 2 shows the principle of focused beam. Here, the light beams-25 emanating from the point light source 1 and passing through the polarizer p are focused by the lens 2 on the interface of the prism 3 and the metal 4 at one point, whereby the rays entering the point at different angles of reflection are reflected at different reflection angles through the lens 6. adjacent individual detectors, each of which can be thought of as corresponding to a certain angle of reflection, or more specifically to a specific range or band of the angle of reflection. If the geometry of the beam is chosen correctly, it is possible to record the whole curve representing the intensity as a function of the reflection angle at one wavelength, and further, by changing the wavelength, a separate curve can be obtained for each wavelength. The device 8 connected to the light source 1, to which the detector array 7 is connected, can go through, i.e. "scan" a certain wavelength range and store the curves 5 thus obtained. The measurement can be made quickly, e.g. in a fraction of a second, and this method can be used e.g. to monitor the biochemical reaction on the selectively sensitive surface 5 on the metal film 4.

10

With the sensor according to Figures 3a and 3b, the point to be analyzed can be expanded, which in Figure 2 is limited to a very small area. Figures 3a and 3b show an arrangement at right angles to the 15 directions from each other. For example, this arrangement can be used to detect immunological reactions, in which the "focused beam" has been replaced by the so-called With a Köhler lighting system, in which light is first conducted from the actual point light source 1 to a bundle 9 of optical fibers 20, which is used to propagate light from the light source 1 over a wider area, e.g. a linear or planar area. The other end of the fiber bundle 9 then acts as a stationary point with respect to the interface ____ 25 of the prism 3 and the metal foil 4, forming a linear or planar light source from which the light beams are directed towards the interface by means of optics 2 (propagating lens 2a and collimating lens 2b). as parallel beams 30 to the interface at different incident angles and are reflected at different reflection angles therefrom, respectively. The polarizer p is placed between the lenses. At different reflection angles, the beams of parallel beams emanating from the prism are focused by a lens 6 on 7 different detectors of the detector array. The measurement can be performed in the same way at different wavelengths by “scanning” a 9 84940 wavelength period in a short time, as in the system of Figure 2, but with a wider surface area to monitor the phenomenon.

Fig. 4 shows a simplified version of the above, in which only one reflection angle is used, but the light rays emanating from the point light source 1 in different directions are assembled by means of optics 2 similar to Fig. 3 into parallel rays targeting a certain surface area 10. The angle of reflection is then always the same, and the reflected beam is reflected directly to a single detector 7. The angle of incidence and reflection is chosen to be close to the resonant state, taking into account the selective layer 15 5 and the substance to be measured by it. The measurement is thus performed solely by looking at the phenomenon as a function of wavelength. Because the space required by the optics in that arrangement is small, the sensor can be miniaturized to a very small size.

20

Figure 5 shows an arrangement that can improve the signal-to-noise ratio and improve the selectivity and sensitivity of the measurement in general. In this case, the biochemically sensitive layer 5 consists of ____ 25 two regions, an active region A and an inactive region B. The light beams scattered in different directions from the point light source 1 are first assembled into a beam of parallel rays by optics 2 according to Fig. 4, then scattered by a mirror system 2 into two parallel beam, i.e. a measuring radius for measuring area A and a reference beam for reference area B: ::. Mirror system may use any suitable system 35 e.g. similar to Figure 5, wherein the collimated ·. "Beam is guided through the track, which is the interface used to allow approximately half the intensity and reflects the other side of the mirror, which reflects a 10 84 940 of the beam member The beams are reflected from areas A and B directly to their own detectors, to the beam detector 5a of the beam reflected from the measuring range and to the detector 7b of the beam reflected from the reference area. , i.e. the difference between the intensities 10 obtained by the detectors 7a and 7b is used as measurement data, which avoids many sources of error.

This measurement system can be used in particular in immunology. In this case, layer 5 at region A comprises an active protein involved in the binding of antibody 15, and layer 5 at region B comprises a deactivated same protein which is not involved in the event in question. The measurement can be performed in a very short time, e.g. in less than a second, by quickly traversing a certain wavelength range 20 to obtain information about the state prevailing in this time interval.

Figures 6a and 6b, which show a measuring arrangement at right angles to each other, show a combination of the arrangements shown in Figures 3 and 5, i.e. it is possible to measure intensity at different reflection angles simultaneously at different wavelengths in both measuring area A and reference area B. Köhler lighting system, in which the light generated by the light source 1 is spread by means of an optical fiber bundle 9 into a linear or planar light surface, which is arranged by means of the optics 2 according to Fig. 3 into beam beams directed at the interface from different directions. Before the prism 3, however, these beams are divided into two different groups of beams by means of a specially designed mirror system 2c, similar to Fig. 5, each consisting of beams formed by parallel beams directed from the same direction to the same area at the interface 11,84940. The second group of beams directed to the reference area B is separated by means of the system 2c 5 directly adjacent to the group of beams directed to the measuring area A, preferably so as to be parallel to it, i. the levels at which the angles of entry of both groups vary are parallel. The group targeted to the measuring area A and the group directed to the reference area 10 are each reflected from the interface to its own detector array, the measuring area detector array 7a and the reference area detector array 7b, which are also parallel and parallel when the beam groups are parallel and parallel. The detector array 7a measures the light reflected from the measurement area A at different reflection angles, and the detector array 7b measures the light reflected from the reference area B at different reflection angles. The measurement can normally be performed by going through a certain wavelength range fast-20 ti, e.g. in less than a second, giving two curves describing intensity as a function of the reflection angle at each wavelength, one from measurement area A and the other from reference area B. In this case a very large measurement data can be obtained. utilize, e.g., in the immunoassays described above with reference to Figure 5.

Figure 7 shows a practical application in which the invention can also be exploited. Here, the light-transmitting body 1. the prism 3 forms a measuring head which is inserted into the substance to be analyzed. The first side 3a of the prism is coated with a metal foil 4 on which a layer 5 of selective material 35 is placed. The measuring head 3 is at the end of a special rod-shaped probe 10, and two optical fibers 11 are passed through this probe, one arranged to conduct light to the prism 3 and to the interface 12 84940 of the metal foil 4 and the other is arranged to dissipate the light reflected from the interface. The variable wavelength light source 1 is outside the probe 10, preferably in the same unit as the device 8, and the light is directed to the probe 5 via an optical fiber 11 running along the connecting cable 9 and extending through the probe body 10 to the probe body 3. Between the fiber 11 and the measuring head 3 there is a suitable collimating lens at the interface of the probe and the measuring head, e.g. a Selfoc-10 lens 12. This lens consists of a cylindrical body coaxial with the fiber 11, the refractive index of which changes longitudinally, collimating the fiber , from one point to beam parallel beams scattering in different directions and preferably spreads the beam over a wider cross-section of the fiber. The outer end of the lens may also have a polarizer to polarize the light before the interface. The outer end of the lens 12 forms a stationary point with respect to the interface of the film 4 and the prism 20, from which the light beam is always directed at the same incident angle through the prism to the interface, from where it is always reflected at the same reflection angle to the other side 3b of the prism 3. The second side 3b of the prism 3 is at an angle 25 to the reflection angle such that it reflects light rays inside the prism due to total reflection to the second optical fiber 11, which also has a Selfoc type lens 12 at its end. The fiber 11 passes through the body of the probe 10 and outside the probe , which also comprises a light source. The light beam going to the interface and the light beam reflected therefrom can thus be arranged to pass by means of an optical fiber pair between said unit and the probe 10 along the same connecting cable 9. The unit having a light source 35 1 also has a reflected light intensity detector 7, and the unit also comprises a device 8, such as an i3 84940 microprocessor or computer, for instructing the light source 1 and processing the measurement results as mentioned above.

5 The measurement is performed in the same way as above by going through a certain wavelength range quickly, e.g. in less than a second, by means of a device 8 in the unit.

The prism 3 forming the measuring head can be disposable, in which case it can be detached from the end of the probe 10 and exchanged for a new prism 3 with a metal foil 4 and a selective layer 5, respectively. In addition to the same probe body 10 with the measuring head ends of the fibers 11 are fixed, different permanent or disposable measuring heads can be exchanged to analyze 3 different substances. The connection point of the measuring head to the body of the probe 10 always remains the same, and the constant part in the measuring head is illustrated in Fig. 7 by the area to the right of the dots-20 hard line. The measuring head can be made of e.g. glass or light-transmitting plastic, in which case its optical density is chosen so that the total reflection ____ 25 back to the second fiber 11 always takes place on one side 3b of the prism. The measuring heads can always be made different for each reflection angle, and this possibility is illustrated by broken lines illustrating the interface between the metal film 4 and the prism 3, i.e. the direction of the side of the prism at the alternating measuring heads. The second side of the prism, from which the light reflected from the interface is reflected to the second fiber 11, is then arranged in a position suitable for the interface. Of course, the selective layer 5 at the measuring head can also be selected according to the substance to be measured.

14 84940

The invention is not limited only to the alternatives presented above, but can be modified within the scope of the inventive idea. One practical application of the invention is also conceivable for glass plates coated with a metal film 4 which can be exchanged on the same prism 3, which can be provided with a selective layer and which can be attached to the prism, e.g. by means of immersion oil.

The polarization required by the invention can in principle be performed at any point between the surface of the light source 1 and the layer 4, but when using optical fibers, it is most preferably performed after the fibers. However, there are also optical fibers that retain polarization, whereby polarization can be performed before the fibers.

The applications of the various embodiments of the invention are very broad. By appropriately selecting a biochemically sensitive material, the properties of a large number of chemical and biochemical substances in the gas phase and in solution can be studied at different wavelengths in a short time.

Claims (9)

A sensor based on the surface plasmon resonance phenomenon comprising a light transmissible member (3) against which is a surface of a material layer (4), the surface being allowed to resonate with dMrp on incident electromagnetic radiation, wherein the layer at its opposite side may be contacted with the material to be examined, the sensor 10 comprising a further light source (1) directed by Mr towards the material layer (4) through the light transmissible portion (3), and a detector (7) provided by Mr measuring the intensity of the light reflected from the surface of the layer (4) through the portion (3), characterized in that the light emitted by the same source (1) is variable, the point of the light source from which the light beam Mr directed is solid web against the layer (4) Mr. fixed in relation to the surface of the layer (4). 20 2. Sensor according to Patent Claim 1, characterized in that a device (8) is connected to the detector (7) for recording the intensity values of the light reflected from the surface at different angles. 25 Sensor according to claim 2, characterized in that a device for automatic scanning (scanning) of a fixed high speed w / w range, preferably for 30 seconds, is connected to the light source (1). synchronously cooperating with the recording device (8). 4. Sensor according to any of the preceding claims, characterized in that at each path length the light coming from the light source (1) is arranged to spread to different angles of incidence relative to the surface of the layer (4) and that the detector (7) 1984940 corresponds to a corresponding method of a detector series for measuring the intensity of the light reflected at different reflection angles from the surface of the layer (4). Sensor according to any of the preceding claims, characterized in that between the light source (1) and the surface of the layer (4), means (2c) are provided for dividing the light beam coming from the light source (1) into a measuring beam and a reference beam. which are directed respectively to a measuring region (A) and a reference region (B) on the surface of the layer (4), the sensor comprising an additional detector (7a and 7b) for each region thereof. Sensor according to claims 4 and 5, characterized in that between the light source (1) and the surface there are means (2c) for dividing the light beams coming from the light source (1) into measuring beams and reference beams, both of which are arranged to spread to different incidence angles in relation to the respective measurement region (A) and the reference region (B) on the surface of the layer (4), the sensor comprising two further detector series (7a and 7b), one of which is arranged to measure it from the measurement region (A) at different reflection angles reflect the light and the other is arranged to measure from the reference area (B) at different reflection angles the light. Sensor according to any of the preceding claims 1, 2 or 3, characterized in that the layer (4) is located in a measuring tip (3) which can be inserted in the analyte blank, the sensor comprising an optical fiber (11) between the light source (1). and the measuring tip (3) for conducting the light on the surface of the layer (4) through the measuring tip, and an optical fiber (11) between the measuring tip and the detector (7) for conducting the light reflected from the surface of the measuring tip (4) 3) existing detector (7). 2 ° 84940 Sensor according to claim 7, characterized in that the measuring tip consists of a piece (3), such as a prism having the layer (4) on one of its outer sides. 5 Sensor according to claim 8, characterized in that the piece (3) forming the measuring tip is detachable from the body (10) of the sensor and can be replaced with a new one.