Device for performing surface plasmon resonance spectroscopy

Abstract

The invention relates to a device for performing surface plasmon resonance spectroscopy comprising a transparent substrate (1) which carries a metal layer (2) on its surface, wherein an analyte (10) to be investigated can be deposited on the surface of the metal layer (2) facing away from the substrate (1), a light source (4) for generating a light beam (3) with which the metal layer (2) can be illuminated through the substrate (1), in particular with which the contact surface of the metal layer (2) contacting the substrate (1) can be illuminated at least in a partial region, a light detector (9) with which the light reflected from the metal layer (2), in particular from its contact surface, and passing through the substrate (1) can be detected, wherein the substrate (1) has a surface facing the illuminating light beam (3) on its side (A) facing away from the metal layer (2).which comprises a lattice structure (6a, 6b).

Description

[0001] The invention relates to a device for carrying out surface plasmon resonance spectroscopy comprising a transparent substrate which carries a metal layer on a surface, wherein an analyte to be investigated can be deposited on the surface of the metal layer facing away from the substrate, further comprising a light source for generating a light beam with which the metal layer can be illuminated through the substrate, in particular with which the contact surface of the metal layer contacting the substrate can be illuminated at least in a partial area, and further comprising a light detector with which the light reflected from the contact surface, in particular from the illuminated partial area of ​​the contact surface and passing through the substrate can be detected.

[0002] The principle of surface plasmon resonance spectroscopy is generally known to those skilled in the art and refers to a spectroscopic analysis method with which the refractive index of an analyte can be measured with very high resolution. It can be used for the quantitative determination of layer thicknesses in the nanometer range. Surface plasmon resonance spectroscopy is used particularly in materials science for measuring the adsorption of substances and in biochemistry.

[0003] An apparatus for performing surface plasmon resonance spectroscopy is configured to excite surface plasmons at the metal / analyte interface of a thin metal layer using polarized light, particularly TM-polarized light. This is achieved by irradiation, for example, via a prism, in total internal reflection on the side of the metal layer facing away from the analyte. If the refractive index of the analyte and the prism, as well as the wavelength of the light, are precisely matched, the intensity-angle spectrum of the totally reflected light exhibits a minimum at a specific angle. The refractive index of the materials used and the wavelength of the light sensitively influence the excitation conditions and thus the angle of the minimum.

[0004] The problem is that polarized light is needed to perform spectroscopy, so that light sources emitting directly polarized light must be used or polarizers must be employed, which increases the cost of the devices.

[0005] It is therefore an object of the invention to provide a device in which spectroscopy can be carried out in a more economical manner, in particular with non-polarized light sources.

[0006] This problem is solved by providing the substrate with a surface facing the illuminating light beam on the side opposite the contact surface of the metal layer, and this surface comprises a lattice structure. Specifically, this side is the one opposite the side of the substrate where the surface in contact with the metal layer is located.

[0007] In particular, the grating structure is oriented such that the strips or bars of the grating structure are arranged perpendicular to the plane of incidence of the light on the substrate. In this orientation, a TE-polarized component of the incident light, i.e., the component whose electric field is perpendicular to the plane of incidence, is parallel to the grating strips or bars, so that this component is reflected to a maximum extent. Accordingly, the TM-polarized component is transmitted through the grating and strikes the metal layer to excite surface plasmons. Spectroscopy can be carried out in a known manner with this polarized component of the incident light, even if the light source emits unpolarized light. The substrate of the device according to the invention can preferably effect the polarization. The device can thus be operated with a light source that emits a beam of unpolarized light.

[0008] The invention preferably provides that the grid structure is formed by a strip-shaped coating on a flat surface of the substrate facing the light beam, or by grid webs formed on the side of the surface of the substrate facing the light beam and separated by grid grooves, wherein at least the surfaces of the grid webs of the grid structure have a coating at least in certain areas, preferably at least on their uppermost plateau, preferably wherein the grid grooves lying between the grid webs are uncoated.

[0009] In particular, a first embodiment can be provided in which only the surface of the grid webs has a coating, a second embodiment in which the surface of the grid webs and the bottom of the grid grooves have a coating, a third embodiment in which the surface of the grid webs and the side walls of the grid webs have a coating, or a fourth embodiment in which the surface of the grid webs, the side walls of the grid webs, and the bottom of the grid grooves have a coating. The coatings of the different areas of the grid structure can be identical or different. The surface of the grid webs preferably refers to the uppermost surface of the grid webs, in particular an upper plateau area of ​​the grid webs. The side walls of the grid webs border this surface on both sides.

[0010] The aforementioned coating is preferably designed with at least one of the following properties, and can therefore also form a combination of several of the aforementioned properties: a. the coating is metallic, in particular made of the material gold, b. the coating is dielectric, c. the coating is anisotropic, in particular optically anisotropic, d. The coating is nanostructured, preferably a metallic nanostructured coating. A coating is considered nanostructured, in particular, if it has structures with a size smaller than 100 nm.

[0011] It is further preferred that the grid grooves in the strip-shaped coating or in the substrate material taper towards the bottom of the grid grooves. This opens up an advantageous manufacturing method in which the grid structure on the substrate is created by molding from a template. A template can, for example, be made of PDMS (polydimethylsiloxane), onto which a polyimide layer is applied, for example by spin coating, and which is then peeled off the template.

[0012] The aforementioned coating can be deposited, for example, as a gold layer onto the lattice structure formed in the polyimide substrate, e.g., using the "oblique angle deposition" technique. This ensures that only the surfaces of the lattice struts, particularly in their tip / plateau regions, are coated, but not the side walls of the lattice struts or the lattice grooves.

[0013] The metal layer intended for the deposition of an analyte, in particular a gold layer, can directly contact the substrate, but an alternative embodiment is also provided in which the metal layer intended for the deposition of an analyte is arranged indirectly on the substrate via an intermediate layer, preferably wherein the intermediate layer arranged between the metal layer (preferably gold layer) and the substrate is formed by the material titanium or chromium.

[0014] The invention preferably offers the advantage that the light source is configured to generate unpolarized light, preferably wherein the lattice structure of the substrate is the only polarization-influencing element of the device. Particularly advantageous light sources can thus be used in a device according to the invention. Such a light source can emit coherent or incoherent light.

[0015] A preferred embodiment further provides that the distance between the bottom surfaces of the grid grooves arranged between the grid bars and the metal layer for the deposition of analytes is 70 to 100 nanometers.

[0016] Furthermore, it is preferably provided that the coating of the grid structure has a height of 20 to 50 nanometers, preferably 30 nanometers.

[0017] Preferably, the height of the grid webs, particularly above the bottom surfaces of the grid grooves, is 80 nanometers to 230 nanometers, preferably 130 nanometers. Preferably, the thickness of the coating is also taken into account.

[0018] Preferably, the width of the grid struts in the plane of their coating on their surface / uppermost plateau is in the direction of the spacing of the grid struts in the range of 150 to 300 nanometers.

[0019] Preferably, the distance between adjacent grid bars lies in the plane of their coating on their surface / uppermost plateau or in the area of ​​the bottom surface of the grid grooves in the range of 150 to 250 nanometers, preferably from 150 to 200 nanometers.

[0020] Furthermore, it is considered preferred that the substrate is formed from a flexible polymer, in particular from polyimide.

[0021] The device preferably comprises a light coupling element, in particular a prism, with which the light beam can be coupled into the substrate, in particular wherein the surface of the substrate with the grid structure indirectly contacts the light coupling element via a means for refractive index matching, in particular a liquid, in particular wherein the means for refractive index matching is arranged above the coated surface of the grid webs and between them in the grid grooves.

[0022] The invention is described in more detail with reference to the following figures.

[0023] The Fig. Figure 1 shows an overview of a device according to the invention.

[0024] This comprises a transparent substrate 1, e.g. made of polyimide. In one possible embodiment, the substrate 1 itself is in the Fig. 2 is shown, which is also referenced.

[0025] The substrate 1 carries a metal layer 2, e.g., made of gold, on side B. This side B is related to Fig. 1. The metal layer 2 is turned away from the incident light beam 3 of the light source 4. An analyte 10, for example, can be deposited on the metal layer 2, with which surface plasmon spectroscopy is performed. For this purpose, it can be arranged in a chamber 5 which covers the metal layer 2, which in Fig. 2 is not shown. Chamber 5 is in the Fig. 1 indicated.

[0026] On side A, from which the light ray 3 occurs, the substrate 1 has a lattice structure 6 formed by lattice bars 6a, which are separated by lattice grooves 6b. In this configuration, the lattice bars 6a and lattice grooves 6b are incorporated into the material of the substrate 1. The longitudinal extent of the lattice bars 6a and the lattice grooves 6b is perpendicular to the plane of the paper. Fig. 2 and thus also perpendicular to the plane of incidence of the light ray 3, which is parallel to the plane of the paper Fig. 1 is.

[0027] The grid bars 6a have a coating 7, e.g. also made of gold. This coating 7 is located at least on the surface / the uppermost plateau of the grid bars 7, possibly - as shown - also on the side walls of the grid bars 6a, but preferably not in the valleys or not on the bottom surfaces of the grid grooves 6b.

[0028] The surface or uppermost plateau of the grid webs 6a can be flat and parallel to the metal layer 2, or flat and aligned at an angle other than zero degrees to it.

[0029] In the device shown, the light source 4 generates a light beam 3 of unpolarized or randomly polarized light, which passes through a prism 8 onto the lattice structure 6. The TM-polarized or p-polarized component passes through the substrate 1 in transmission and strikes the surface of the metal layer 2, which makes contact with the substrate. This allows surface plasmons to be generated by the light, which interact with any adsorbed analyte 10.

[0030] The prism 8, with its surface facing the substrate 1, covers the grating structure 6. A liquid for refractive index matching can preferably be arranged between the grating structure 6 and the prism 8, so that in this case the substrate 1 contacts the prism 8 indirectly via the liquid. It is preferably provided that the arrangement of prism 8 and substrate 1 with analyte 10 is rotatable about an axis perpendicular to the plane of incidence of the light beam 3, e.g. by a motor.

[0031] In the device according to the invention, preferably only the grid structure 6 of the substrate 1 polarizes the unpolarized light beam 3 emitted by the light source 4. Therefore, simpler light sources that do not emit polarized light can also be used with the grid-structured substrate 1, and external polarizers can be avoided. The substrate 1 inherently possesses its own polarizing effect, which can be adapted to the specific application by the geometry of the grid structure 6.

[0032] The components shown here between the light source 4 and the prism 8 preferably act only in a wavelength-selective and / or intensity-attenuating manner, but not in a polarizing manner. These components may preferably comprise a bandpass filter 10a and / or a chopper 10b and / or a neutral density filter 10c and / or a diffuser optic 10d. These components may also be omitted entirely or partially.

[0033] To detect the light reflected from the metal layer 2, a light detector 9 is used, e.g. comprising a camera 9a and lens 9b, possibly further lenses 9c, essentially as is usual with the measuring principle.

[0034] The Fig. Figure 3 shows possible variants of the substrate when the lattice structure 6 is formed in the material of substrate 1. View A corresponds to the substrate as it appears in Fig. 2 is shown and described.

[0035] In view B, the surfaces / uppermost plateau areas of the grid bars 6a and the bottom surfaces of the grid grooves 6b have a coating, but not the side walls of the grid bars.

[0036] In view C, the surfaces / uppermost plateau areas and the side walls of the grid webs 6a have a coating on only one side, but not the bottom surfaces of the grid grooves 6b and the other side walls.

[0037] In view D, all surface areas of the grid structure 6 have a coating.

[0038] The Fig. Figure 4 shows another embodiment of a substrate 1 with a metal layer 2, in which the lattice structure 6, in particular its lattice webs 6a, is formed by a partially applied coating 7, e.g. of the metal gold, on the flat surface of the substrate 1, onto which the light beam (not shown here) is incident. The lattice grooves 6b are formed by uncoated areas, but can also be formed by coated areas whose layer thickness is less than that of the lattice webs 6a.

[0039] Here it is further shown that the metal layer 2 is indirectly arranged on the substrate 1 via an intermediate layer 11, e.g. made of chromium or titanium. However, such an intermediate layer 11 can also be omitted.

[0040] All in the Fig. 3 and Fig. The substrates 1 shown in the diagram with metal layer 2 can be used in the device according to the diagram. Fig. 1 can be used as an alternative to the substrate 1 shown there.

Claims

[1] Device for performing surface plasmon resonance spectroscopy comprising a. a transparent substrate (1) which carries a metal layer (2) on a surface, wherein an analyte (10) to be investigated can be deposited on the surface of the metal layer (2) facing away from the substrate (1), b. a light source (4) for generating a light beam (3) with which the metal layer (2) can be illuminated through the substrate (1), in particular with which the contact surface of the metal layer (2) contacting the substrate (1) can be illuminated at least in a partial area, c. a light detector (9) with which the light reflected from the metal layer (2), in particular from its contact surface, in particular from the illuminated part of the contact surface and passing through the substrate (1) can be detected, characterized by , that d. the substrate (1) has on its side (A) facing away from the metal layer (2) a surface facing the illuminating light beam (3) which comprises a lattice structure (6a, 6b). [2] Device according to claim 1, characterized by , that the lattice structure (6a, 6b) is formed by a. a strip-shaped coating (7) on a flat surface of the substrate (1) facing the light beam (3), or b. on the side (A) of the surface of the substrate (1) facing the light beam, lattice webs (6a) formed in its material separated by lattice grooves (6b), wherein at least the surfaces of the lattice webs (6a) of the lattice structure (6a, 6b) have at least a coating (7) in certain areas, preferably wherein the lattice grooves (6b) lying between the lattice webs (6a) are uncoated. [3] Device according to claim 2, characterized by, that the coating (7) is formed with at least one of the following properties: a. the coating (7) is metallic, in particular made of the material gold, b. the coating (7) is dielectric, c. the coating (7) is anisotropic, in particular optically anisotropic d. the coating (7) is nanostructured, preferably a metallic nanostructured coating. [4] Device according to any one of the preceding claims, characterized by , that the grid furrows (6b) in the strip-shaped coating (7) or in the material of the substrate (1) are tapered towards the bottom of the grid furrows (6b). [5] Device according to any one of the preceding claims, characterized by, that the metal layer (2) provided for the deposition of an analyte (10), in particular a gold layer, is arranged indirectly on the substrate via an intermediate layer, preferably wherein the intermediate layer (11) arranged between the metal layer and the substrate is formed by the material titanium or chromium. [6] Device according to any one of the preceding claims, characterized by , that the light source (4) is configured to generate an unpolarized light beam (3), preferably wherein the lattice structure (6a, 6b) of the substrate (1) is the only polarization-influencing element of the device. [7] Device according to any one of the preceding claims, characterized by , that the distance (A) between the bottom surfaces of the grid grooves (6b) arranged between the grid bars (6a) and the metal layer (2) for the deposition of analytes is 70 to 100 nanometers. [8] Device according to any one of the preceding claims, characterized by, that the coating (7) of the grid structure (6a, 6b) has a height of 20 to 50 nanometers, preferably 30 nanometers. [9] Device according to any one of the preceding claims, characterized by , that the height (y) of the grid webs (6a) above the bottom surfaces of the grid grooves (6b) is 80 nanometers to 230 nanometers, preferably 130 nanometers, particularly taking into account the height of the coating (7). [10] Device according to any one of the preceding claims, characterized by , that the width (x) of the grid bars (6a) in the plane of their coating (7) on their surface / uppermost plateau, viewed in the direction of the spacing of the grid bars (6a) is in the range of 150 to 300 nanometers. [11] Device according to any one of the preceding claims, characterized by, that the distance (z) between adjacent grid webs (6a), in particular in the plane of their coating (7) on their surface / uppermost plateau or in the area of ​​the bottom surface of the grid grooves (6b), is in the range of 150 to 250 nanometers, preferably 150 to 200 nanometers. [12] Device according to any one of the preceding claims, characterized by , that the substrate (1) is formed from a flexible polymer, in particular from polyimide. [13] Device according to any one of the preceding claims, characterized bythat it comprises a light coupling element (8), in particular a prism (8) with which the light beam (3) can be coupled into the substrate (1), in particular wherein the surface of the substrate (1) with the grid structure (6a, 6b) indirectly contacts the light coupling element (8) via a means for refractive index matching, in particular a liquid, in particular wherein the means for refractive index matching is arranged above the coated surface of the grid webs (6a) and between them in the grid grooves (6b).

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