EP1080365A1 - Surface plasmon resonance sensor for the simultaneous measurement of a plurality of samples in fluid form - Google Patents

Abstract

The invention relates to a surface plasmon resonance sensor for the simultaneous measurement of a plurality of samples present in fluid form. The aim of the invention is to provide such a sensor which can be arranged into a defined array and where the surface plasmon resonance sensors can be produced using technology which is simpler and more economical than those produced according to the prior art. To this end several strip-like optical wave guides (2) are arranged on a planar support (1) at a defined distance to each other in such a way that their front faces (21, 22) are flush with opposite sides (11, 12) of the planar support (1). Each strip-like optical wave guide (2) in a section which is to be brought into contact with the fluid samples has at least one thin metal layer (3) which permits the excitation of surface plasmons. Means (14) are provided for which separate the measurement zones of the individual thin metal layers (3) from each other in such a way that each of the optical wave guides (2) can be assigned to only one sample.

Description

SPR sensor for simultaneous detection of a large number of samples in fluid form

description

The invention relates to an SPR sensor for the simultaneous detection of a large number of samples in fluid form, which enables rapid sample recognition in the context of a variety of applications. In particular, the proposed sensor is used for the parallel or serial detection of samples which have been placed in microtite slats.

As automation in the area of drug discovery continues to advance, the issue of miniaturization and parallelization is of increasing interest. The miniaturization of sample vessels and synthesis apparatus and the parallelization of the processes taking place necessitate a large number of substances to be investigated with less and less volume. Therefore, when implementing new types of detection and sensor systems, it is necessary to design them in such a way that several measurements run in parallel at the same time or a large number of samples can be measured in succession within a very short time and the quantities of substances required for this are minimized. Increasing the degree of automation plays an important role in this. The background of the invention is the necessity to also provide the sensors used for the measurement in a parallel and miniaturized format, so that the measurements of a large number of samples can be carried out in a very short time and with a minimum sample volume and consumption, in order to increase the throughput characterizing substances to increase. A very sensitive method for characterizing interfaces is known in the literature as surface plasmon resonance spectroscopy, usually called SPR (surface plasmon resonance). The method is based on the optical excitation of surface plasmons in thin metal layers. This method is described in detail by Striebel, Ch .; Brecht, A .; Gauglitz, G. in Biosensors & Bioelectronics 9 (1994), 139-146. The resonance conditions for the excitation of the surface plasmons strongly depend on the optical properties of the dielectric surrounding the metal layer. The determination of refractive index and layer thickness of thin dielectric layers is fundamentally possible with a high degree of accuracy according to the known prior art.

SPR spectroscopy is increasingly used e.g. in biochemical analysis, because with mr the direct investigation of the interaction between biomolecules is possible (e.g. antibodies / antigen reactions). For this purpose, one reaction partner (ligand) is immobilized on the metal surface, the other reaction partner (analyte) is passed over the surface in solution. The interaction is directly detectable as an increase in layer thickness via the change in refractive index. Conventional SPR sensors (see product description from Biacore AB, Rapsgatan 7, S-75450 Uppsala, Sweden 1996) use a prism that carries a thin metal layer. The sample to be measured is brought into contact with the metal or the modified metal surface, and the SPR reflection spectrum of the sample is measured by coupling light and measuring the intensity of the reflected light as a function of the angle of incidence or the wavelength.

Newer methods and devices (WO 94/16312) use fiber optic elements to build an SPR sensor. Commercial optical fibers with diameters between 1 μm and 2000 μm are used. The fibers are exposed at their ends or other defined areas, that is, the existing sheathing, consisting of waveguide sheath and buffer layer, is removed mechanically, chemically or thermally. The fibers are then provided with a metal layer radially or partially radially, and in the case of a fiber-optic sensor based on end reflection, the end face of the fiber is additionally mirrored. The radial coating is subject to very high requirements with regard to the layer thickness homogeneity, which can only be achieved technologically with great effort. A further disadvantage when using optical fibers is in particular the limited possibility of parallelization, since individual optical fibers must always be arranged manually in an array.

It is an object of the present invention to provide an SPR sensor for the simultaneous detection of a large number of samples in fluid form, which can be arranged in a predeterminable array, the SPR sensors using a unified technology and more cost-effectively than those according to the known state of the art Technology should be producible.

The object is achieved by the characterizing features of the first claim. Advantageous refinements are the subject of the subordinate claims.

The invention makes use of the task of planar waveguides, which are each provided with at least one SPR sensor area. SPR sensors according to the invention can be arranged in parallel and can simultaneously be brought into contact with a large number of samples (greater than 100).

The planar waveguides used lead the excitation light to the sensor area, which uses the measuring principle of surface plasmon resonance to characterize a solution that has been brought into contact with the sensor. Exactly one sample is brought into contact with each sensor area, so that n-different samples can be characterized with an SPR waveguide array consisting of n waveguides.

An SPR waveguide array is to be manufactured using technologies from semiconductor production and integrated optics in order to provide a large number of sensors in parallel and to arrange them at a defined distance from one another.

The invention further enables the SPR waveguide arrays in sample holders, e.g. B. integrate microtiter plates. The SPR waveguide arrays should be adaptable to existing formats of microtiter plates (96, 386, 1536, etc.) as well as to different or newly developed formats. Planar waveguides are receiving increasing attention in research and development in the field of integrated optics. For the production, a light-guiding layer is applied to a surface of a carrier material. The refractive index of the carrier material or a layer to be provided thereon for this purpose must be smaller than that of the waveguiding layer in order to guarantee an almost loss-free guidance of the light in the waveguide. Such flat waveguides are manufactured using known semiconductor technology and integrated optics, such as CVD processes, sputtering, electron beam evaporation, spin coating or various replication techniques. Known microtechnical processes also make it possible to produce finely structured waveguides and splitters. Waveguides with thicknesses in the range of a few micrometers to a few 100 μm and widths up to a few 1000 μm can be produced using a wide variety of structuring processes. The coating of defined waveguide sections with an SPR-capable layer can also be carried out in parallel in a few steps using known technologies. An SPR sensor according to the present invention consists of several planar strip-shaped optical waveguides, each of which has at least one two-dimensional measurement area between two end faces. These measuring areas are provided with an SPR-capable planar metal layer which is in direct contact with both the wave-guiding material and the sample to be characterized. The excitation light reaches the optical waveguide via known coupling mechanisms. There the light spreads along the waveguide and is guided to the sensor area. In the sensor area, the excitation of surface plasmons influences the light guided in the optical waveguide. In the further course, the modified light is either decoupled from the optical waveguide directly after passing through the sensor region via the known coupling principles and passed on for further processing, or it is reflected in itself by a reflective coating on the end face in the optical waveguide and via the same coupling mechanism, through which the light enters the optical fiber reached, decoupled again and thus passed on for further processing.

In the case of the coupling and decoupling of the light on one and the same side of the optical waveguide and reflection of the radiation at the other end, these are planar SPR waveguides based on the final reflection. If the coupled light emerges on the second side of the waveguide, one speaks of a waveguide sensor based on inline transmission.

The invention will be explained in more detail below with the aid of schematic exemplary embodiments. Show it:

1 shows a first possible embodiment of an emdimensional SPR sensor that can be expanded into an array, FIG. 1 a shows a top view of the SPR sensor according to FIG

Plane X-X, FIG. 1b a section from FIG. 1,

FIG. 2 shows a second embodiment of an SPR sensor which is essentially analogous to FIG. 1, FIG. 3a shows a perspective view of an SPR sensor according to FIG. 1 or FIG. 2, FIG. 3b shows an arrangement of several SPR sensors 3a to

Formation of an array, FIG. 4 shows a possibility of inserting a comb-like, sprinkled SPR sensor array consisting of planar SPR sensors according to FIGS. 1 or 2 into a microtitre plate in a sectional view, FIG. 5 shows a possible arrangement of SPR sensors, whereby the mutual spacing of which is formed by cuvette walls, FIG. 6a shows a possible arrangement of an SPR sensor, the individual sensor being additionally detected by cuvette walls, FIG. 6b shows a further embodiment of an SPR sensor array according to FIG. 6a, FIG. 6c shows a multiple arrangement a training according to Fig. 6a and Fig. 7 a further training possibility according to Fig. 6b. FIG. 1 shows a partial section of an SPR sensor in a first exemplary embodiment. In this case, a plurality of strip-shaped optical waveguides 2, which are arranged at a defined distance from one another, are provided on a planar carrier 1 in such a way that their end faces 21, 22 are flush with the sides 11, 12 of the planar carrier 1, each of the strip-shaped optical waveguides 2, in a section which is to be brought into contact with the fluid samples to be analyzed, which are not shown in FIG. 1, is provided with a thin metal layer 3 which enables the excitation of surface plasmons. In the example according to FIG. 1, a 4 "silicon wafer used in semiconductor technology has been assumed, in which the structures of a plurality of planar carriers 1 have first been transferred and structured. Long, narrow rectangular openings have been structured in the wafer 1. The canine-shaped recesses 14 shown in Fig. 1. The geometry of a mask used for this purpose in the example is to be designed in such a way that the carcinoma structures that arise after it has been separated can be immersed in 1536-format microtiter plates (32-48 cavities). It can be seen that only a section of this is shown in Fig. 1. In order to ensure the greatest possible stability of the individual carriers 1, a silicon wafer with a crystal orientation (110) is selected, which makes it possible to have rectangular free spaces structure vertical edges on at least two edges structured wafers, in the example using the PE-CVD process, coated with S> ₂ . This SiO ₂ layer serves as an optical buffer between the optical fibers 2 provided and the Si substrate. 1 consist of a silicon oxynitride layer which, for example, has a thickness of approximately 10 μm. The shaping of the optical waveguide 2 in the sense of the present invention is carried out by a customary dry etching process of the silicon oxynitride layer in such a way that parallel strips with widths between 10 μm to 2000 μm and distances between 10 μm and 5000 μm are formed. It is also possible within the scope of the invention to modify the aforementioned sequence of structure generation in such a way that all the coatings mentioned so far are initially on an unstructured Si wafer be carried out over the entire surface and then the known cam structure is produced in FIG. 1 by means of known selective structuring methods. In Figure la, the structures thus obtained are shown in plan view along a plane XX of FIG. 1. It is also within the scope of the invention to manufacture the optical waveguide 2 from a polymer that can be cured under the influence of UV light. For this purpose, a liquid polymer, for example PMMA, polycarbonate, UV-curing adhesives or silicon-containing polymers (Cyclotene or ORMOCERE), is spun onto or cast onto the wafer. The optical waveguides are structured by means of known photolithographic methods using an appropriately designed mask. The exposed areas are crosslinked and hardened by UV irradiation, the unexposed areas are detached again during development, so that the exposed areas remain as optical waveguides 2.

The cross section of the optical waveguide 2 is to be made largely square, with manufacturing-related deviations being possible, and in the example according to FIG. 2 it is approximately 190 μm • 190 μm, the width b of the fingers f is approximately 550-600 μm, with the optical waveguide 2 should be arranged centrally on the fingers f.

Such a dimensioning ensures the greatest possible adaptation to optical fibers, which will be discussed further below, with common diameters of 200 μm. The length h of the sections containing the fingers f is 5 mm in the example.

Provided that the optical refractive index of the material for the carrier 1 is lower than that of the polymer to be applied and that it is not absorbent, in the example according to FIG. 2 the additional previous application of an optical buffer layer 13, as shown in FIG . 1, to be dispensed with.

Likewise, other polymers can also be used, which are brought into the desired strip shape, for example by embossing or other replication techniques, the remaining material at the points where no light is to be guided in its thickness below the critical cut-off thickness must lie. After the structuring of the strip-shaped optical waveguides described above, the entire wafer is protected in both embodiments described so far by a cover except for the areas that are intended to carry the SPR-capable metal layer 3. Then these exposed areas are coated with the SPR-capable metal layer, for example with a thin gold layer by means of sputtering, and then the covered, remaining areas are freed from the protective layer.

The structures for the SPR sensors are advantageously produced on the wafer in such a way that the can structures oppose each other before mirroring. For a subsequent sawing process for separating the comb structures, it is necessary to passivate the optical waveguides 2 with the thin metal layers 3, which enable the excitation of surface plasmon, in order to prevent them from being damaged by splinters or the like. to preserve. For this, a thick protective coating is applied. Then there is a separation process, e.g. by sawing, as a result of which the desired comb structures are obtained and the end faces 21, 22, via which light can be coupled into and out of the optical waveguide, are produced.

Depending on the technology used to introduce the comb-like recesses into the carrier body 1, these recesses 14 can be produced before or after the application of the metal layer 3 mentioned. In the examples according to FIGS. 1 and 2, the application is then carried out at least to the areas of the optical waveguides 2 which are formed by the end face 22 in the area of the metal layer 3. The reflective coating 4 can be applied, for example, by a renewed coating process, for example sputtering an aluminum or silver layer. For this purpose, the entire surface of the wafer is provided with a protective layer prior to the separation process, which guarantees that the structures 2, 3 previously applied are not contaminated during the mirroring of the ends. After the mirror coating, this protective layer is removed. In the examples according to FIGS. 1 and 2, the individual SPR sensor areas formed by the metal layers 3 are separated from one another by the comb-shaped recesses 14, so that each of the optical waveguides 2 can only be assigned to one sample, for example by immersing them in a complementarily distributed receptacle of a microtiter plate is.

FIG. 3a shows a perspective view of an SPR sensor according to FIG. 1 or FIG. 2. In order to implement an array of sensors, several such strips are stacked one behind the other and, apart from the areas which are provided with the thin metal layer 3 which enables the excitation of surface plasmons, are grasped by a common holding means and are spaced apart from one another such that their spacing, e.g. corresponds to the recesses of an arbitrarily definable microtitre plate format. Arrays which can be adapted as desired, for example 8 ^• 12, as shown in FIG. 3b, can thus be produced by SPR sensors. Such an array is advantageously cast into a polymer after assembly in the area that does not carry the SPR-capable metal layer 3 in order to give the SPR waveguide array additional support, as is indicated schematically in FIG. 3 b by a polymer block encapsulation 6 . For measurements, this SPR waveguide array is brought into contact with a microtitre plate which carries the samples to be characterized. In order to achieve an optimal measurement, the SPR waveguide array is introduced into the microtitre plate 7 until the SPR-capable metal regions 3 are completely wetted by a sample 8, as is shown schematically in FIG. 4.

Another possible arrangement of the SPR sensors is indicated in FIG. 5. In this example, the individual SPR sensors are spaced apart by cuvette walls 71, each one

Include fingers f of said comb structure. In this example there is a

SPR array used according to the end reflection principle.

In the examples according to FIGS. 4 and 5 there is also an external one

Optical fiber 9 shown, which can be precisely positioned by means of an xy sliding table over the respective end faces of the optical waveguides 2. This optical fiber 9 couples light from a white light radiation source (not shown in more detail) into the respective optical waveguide 2, this light being guided to the excitation area of the surface plasmon and subsequently being reflected on the second, mirrored end face. After the guided light has passed the excitation area the second time after the reflection, the light is coupled out of the optical waveguide 2 via the end face and transferred into the common arm of a fiber splitter, not shown. From there it reaches, for example, a spectrometer (not shown) where it is spectrally evaluated. The spectrometer control and data acquisition is computer controlled via a PC.

Another way of determining the spectrum is to measure the SPR array in transmission. Instead of a fiber splitter, a simple optical fiber 9 is used to couple the light into the optical waveguide 2. A second optical fiber is positioned at the output of the optical waveguide 2. This leads the light to a grating spectrometer. With such a configuration, the mirroring of the end face of the optical waveguide 2 is dispensed with. However, the interaction length decreases, i.e. the effective sensor length by 50%. The signal is less pronounced by this factor. On the other hand, two coupling points have to be positioned, which increases the apperative and adjustment effort.

Depending on the measuring and computing technology used, however, it is also possible to assign an optical fiber 9 to each of the optical waveguides 2 provided, which enables a simultaneous evaluation of all the samples used.

In two further embodiments according to FIGS. 6a and 6b, it is provided that the means separating the detection areas of the individual thin metal layers 3 are formed by cuvette walls 15 connected to the planar carrier 1. Both of the above modes of operation are also possible here. An embodiment according to FIG. 6a is designed for an inline operating mode; one by Fig. 6b, by applying a mirror 4, for operation in reflection. FIG. 6c indicates how an SPR sensor array can be generated by a multiple arrangement, comparable to the stacking of individual cells of FIG. 6a carrying several SPR sensors, as described for FIG. 3b.

The invention is not restricted to the exemplary embodiments shown. It is essential in any case that planar carriers 1 are used, which are provided with essentially planar optical fibers, which each have at least one planar SPR-capable metal layer 3 in a sample detection area, each of which represents a sample detection area that is in contact with a sample is feasible. It is also within the scope of the invention to connect the created SPR-compatible areas with open bottoms of flow cells 16, FIG. 7, spaced apart from one another, which have a common inflow 17 and outflow 18. In such an embodiment in particular, one or more of the flow cells formed can be used as reference channels, for example for the compensation of temperature fluctuations. If the invention speaks of at least one two-dimensional measurement area, this means that the metal layer 3 provided as the sensor area can also be subdivided into several partial areas 31, 32, 33, as indicated in FIG. 1b. The SPR sensor according to the invention can also be used in such a way that a single sample is first immobilized on the sensor areas 3. This immobilization serves to provide a chemically modified measuring surface with which another sample, preferably in solution, can interact. In the case of the immobilized sample, one often speaks of ligands, the sample in solution often being referred to as a receptor or analyte. The interaction partners are thus, for example, ligand-receptor pairs. An SPR sensor according to the present invention then allows the simultaneous measurement of a large number of different samples (analytes). All of the features shown in the description, the subsequent claims and the drawing can be essential to the invention both individually and in a combination with one another. Reference list

1 - planar carrier

11, 12 - opposite sides of the carrier 1

13 - coating (buffer layer)

14 - recesses

15 - cell walls

16 - Flow cells

17 - inflow

18 - drain

2 - optical fiber

21, 22 - line surfaces of the optical waveguide 2

3 - SPR-capable metal layer

31, 32, 33 - partial areas of the metal layer 3

4 - highly reflective coating

6 - potting b - width of fingers f f - fingers h - length of fingers f

X-X - plane

Claims

claims 1. SPR sensor for the simultaneous detection of a plurality of samples in fluid form, characterized in that on a planar support (1) a plurality of strip-shaped optical waveguides (2) which are arranged at a defined distance from one another are provided such that they with their end faces (21, 22) flush with opposite sides (11, 12) of the planar carrier (1), each of the strip-shaped optical waveguides (2) in a section which is to be brought into contact with the fluid samples with at least a thin metal layer (3) which enables the excitation of surface plasmons is provided, means (14; 15) being provided which separate the detection areas of the individual thin metal layers (3) from one another such that each of the Optical waveguide (2) can only be assigned to one sample. 2. SPR sensor according to claim 1, characterized in that the strip-shaped optical waveguides (2) is essentially a square cross section. 3. SPR sensor according to claim 2, characterized in that the areal extension of the cross section of the stiffened optical waveguide (2) of the areal extension of the cross section of light-guiding cores of conventional optical fibers (9) is adapted. 4. SPR sensor according to claim 1 and / or 2, characterized in that an end face (22) of the strip-shaped optical waveguide (2) provided in the region of the samples is provided with a light-reflecting coating (4). 5. SPR sensor according to claim 1, characterized in that the detection areas of the individual thin metal layers (3) separating from each other by means of comb-shaped recesses (14) are introduced into the planar carrier (1). 6. SPR sensor according to claim 1, characterized in that the detection areas of the individual thin metal layers (3) separating means are formed by the planar support (1) connected to the cuvette walls (15). 7. SPR sensor according to claim 1, characterized in that the planar carrier (1) is made of silicon and at least below the strip-shaped optical waveguide (2) is provided with a coating (13), for example SiO 2, the optical refractive index of which is smaller than the optical refractive index of the material, e.g. Silicon oxynitride, which is used for the strip-shaped optical waveguide (2). 8. SPR sensor according to claim 1 or 7, characterized in that a silicon wafer with a for the planar carrier (1) (110) crystal orientation is selected. 9. SPR sensor according to claim 1, characterized in that the planar carrier (1) is made of a material whose optical refractive index is smaller than the optical refractive index of Material, for example a polymer, which is used for the stiffened optical waveguide (2). 10. SPR sensor according to claim 6, characterized in that the detection areas of the individual thin metal layers (3) separating cuvette walls (16) are interconnected via a common inflow (17) and outflow (18). 11. SPR sensor according to one of the preceding claims, characterized in that the fingers (f) of the planar carrier (1), the strip-shaped optical waveguide (2) carried by these with their thin metal layers (3) which enable the excitation of surface plasmon each of Recesses (8) of a microtitre plate (7) can be picked up. 12. SPR sensor according to claim 11, characterized in that the strip-shaped optical waveguide (2) provided with their excitation of surface plasmon thin metal layers (3) and optionally with a reflective front coating (4) provided optical waveguide (2) each with an intermediate arrangement Layer with a lower optical refractive index than that of the optical waveguide on a wall of a recess of a microtitre plate (7) are attached. 13. SPR sensor according to one or more of claims 1 to 11, characterized in that a plurality of the strip-shaped optical waveguide (2) and the other assemblies (3 and optionally 13, 4) carrying planar carriers (1) away from the areas, which are provided with the thin metal layer (3) which enables the excitation of surface plasmons, are gripped by a common holding means and are spaced apart from one another in such a way that their spacing corresponds to the spacing of the recesses of a microtitre plate format which can be predetermined in a manner which can be predetermined. 14. SPR sensor according to 13, characterized in that the common holding means is formed by a potting (6), which leaves the optical waveguiding properties of the strip-shaped optical waveguide (2) and the first end face (21) optically unaffected.