EP1281062A1

EP1281062A1 - Plasmon resonance sensor

Info

Publication number: EP1281062A1
Application number: EP01940431A
Authority: EP
Inventors: Andreas Hofmann
Original assignee: Jandratek GmbH
Current assignee: BIOSCIENCE VENTURES GROUP AG
Priority date: 2000-05-12
Filing date: 2001-05-09
Publication date: 2003-02-05
Also published as: WO2001086262A1; US20030076501A1; US6801317B2; AU2001274010A1; DE10023363C1

Abstract

The invention relates to a plasmon resonance sensor that comprises collimator optics (13) in the form of a cylindrical lens that is interposed between the laser diode (7) and the prism (1), said prism being provided with a reflective metal layer (5). This arrangement preserves the beam divergence in the plane of incidence that comprises all angles of incidence that are potentially possible for a resonance and that are detected by the detector (8). In a plane perpendicular to the plane of incidence the beam path is collimated, thereby allowing for a compact design and for the simultaneous arrangement of a plurality of measuring cells that are arranged perpendicular to the plane of incidence one behind the other.

Description

Patent application

Name: plasmon resonance sensor

Description

The invention relates to a plasmon resonance sensor for biological, biochemical or chemical tests with a translucent body, in particular glass prism, a reflective metal layer or semiconductor layer applied to a surface of the body with a surface sensitive to molecules to be detected in a sample, which in connection with a cuvette forms a measuring cell, a monochromatic light source, in particular a laser diode, for emitting a diverging light beam or beam path through the translucent body onto the inner surface of the layer and a detector which is assigned to the outgoing beam path reflected by the layer and which is dependent on time and which is sensitive to molecular deposits Surface-changing angle of reflection of the light, at which due to the resonance, an intensity minimum of incident light occurs. Such a plasmon resonance sensor with a glass prism, a thin gold layer from 40 to 70 nm and a light source in the form of a laser diode is known from US 4,844,613.

The phenomenon of surface plasmon resonance (SPR) is a collective excitation of the electrons on the surface of a layer having free electrons. The resonance frequency of the surface plasmon is very sensitive to the refractive index of the medium that is adjacent to the sensitive surface. This can be used to measure thin layers (refractive index or layer thickness). This effect is used in particular in biosensors to investigate the attachment kinetics of biomolecules to a functionalized metal surface. For this purpose, the resonance condition of the surface plasmons is detected in a time-resolved manner. The surface plasmons of the thin metal layer are excited by light that shines through the glass onto the metal layer at a certain angle or range of angles. The resonance condition is then fulfilled for a certain combination of wavelength and angle of incidence. Under this resonance condition, the intensity of the light reflected on the metal layer is significantly reduced due to the generation of the surface plasmon. To find the resonance condition, either the angle of incidence (at constant wavelength) or the wavelength (at constant angle of incidence) can be scanned and the intensity of the reflected light can be detected.

In the case of the plasmon resonance sensor described at the outset, it is expedient to work with a fixed wavelength and to determine the angle of incidence at which the resonance condition is fulfilled. A laser diode is used which emits an elliptical beam cone. The opening angles are typically 22 ° in one dimension and 9 ° in the other - half of the intensity maximum (FWHM). This beam divergence is used to illuminate the light source with different angles of incidence within a win- ding without any beam shaping optics and without changing the orientation of the light source. to illuminate the range that is considered for the occurrence of the resonance condition. Accordingly, an elongated detector arrangement is provided which records the diverging beam path across its entire dimension in the plane of incidence of light and can thus determine the angle of incidence at which the resonance condition is met at the time of measurement.

This known plasmon resonance sensor, because it does not require any beam shaping optics and devices for changing the angle of incidence, is comparatively simple and therefore inexpensive to manufacture. However, light rays with different angles of incidence hit different points of the reflective metal layer, so that high demands must be placed on their homogeneity in order to prevent falsifications of the measurement results. In this sense, however, sufficiently homogeneous metal layers can be applied.

The main disadvantage of the known design is therefore seen in the fact that the performance of the plasmon resonance sensor equipped with a single measuring cell, based on the number of tests that can be carried out, is low and that this does not permit simultaneous reference measurements in order to eliminate the influence, for example, of the heating of the reflective metal layer. Precisely because of the strong temperature dependence of the refractive index of liquids and since the samples to be examined are usually examined dissolved in liquid, reference measurements are particularly useful. In this context, it should also be borne in mind that, because of the diverging beam path, additional measuring cells must be arranged at a greater distance from one another so that different beam cones do not overlap and thus lead to falsifications. Such a distance would run counter to the desired compact design and also significantly increase the costs for correspondingly large parts.

From EP 305 109 B1 it is already known to work with a comparable plasmon resonance sensor for carrying out biological tests with a light source emitting in parallel and to produce a convergent beam fan with all necessary angles of incidence therefrom by means of an optical system, with an optical system also being provided in the diverging beam path that aligns the beam path again in parallel before it hits the detector. In this plasmon resonance sensor, the light is focused on a point on the metal layer, so that the influence of inhomogeneities in the metal layer is largely eliminated. However, increased heating of the metal layer and falsified results must be expected. Another disadvantage of the known plasmon resonance sensor can be seen in the comparatively expensive beam shaping optics. In addition, additional measuring cells to increase performance and for reference measurements would also require additional corresponding beam shaping optics and thus make the plasmon resonance sensor considerably more expensive.

Accordingly, the object of the invention is to create a plasmon resonance sensor which, with a compact and inexpensive design, enables high test performance with error-free results at the same time.

Starting from the plasmon resonance sensor described at the outset, this object is achieved according to the invention in that a collimation lens is arranged between the light source and the translucent body, which collimates the incident beam path perpendicular to the plane of incidence, but still leaves it diverging in the plane of incidence.

Expedient refinements and developments of the invention result from the subclaims.

The plasmon resonance sensor according to the invention manages with simple beam shape optics in the form of a cylindrical lens, and therefore requires only a small amount of construction. Although the original beam divergence, for example of a laser diode, is used to cover the entire range of angles of incidence of interest, the targeted parallel alignment of the beam path in the direction perpendicular to the plane of incidence In this direction, a narrow beam path is created, which enables a compact juxtaposition of several identical plasmon resonance sensors and, accordingly, of several measuring cells, which leads to a powerful device with the possibility of advantageous reference measurements.

However, this result is expediently not achieved by stringing together several complete plasmon resonance sensors, but rather by arranging two or more measuring cells for different samples on a common translucent body or prism, which are aligned in a row perpendicular to the plane of incidence, with each measuring cell being one own detector is assigned. Such a design with a common translucent body or prism and possibly only one light source and one collimation lens leads to particularly low costs in relation to performance.

Exemplary embodiments of the invention are explained in more detail below with the aid of a schematic drawing. In it show:

Figure 1 is a side view of a plasmon resonance sensor;

Figure 2 is a top view of a plasmon resonance sensor with four measuring cells;

3 shows a plasmon resonance sensor similar to the embodiment according to FIG. 2, but in which each measuring cell is assigned its own light source; and

Figure 4 shows a further modification compared to the embodiment of Figure 3, according to which each measuring cell and light source is assigned its own collimation optics.

According to FIG. 1, a translucent body 1 in the form of a glass prism with a triangular cross-sectional shape is provided. This prism has a light incident side 2, a light incident side 3 and a horizontally oriented upper reflection side 4. On this reflection side 4 is a reflective measurement tallschicht 5 applied, which consists for example of gold in a thickness of 50 nm. A sensitive coating 6 is also applied to the metal layer 5, as is indicated schematically. This sensitive coating is matched, for example, to the biomolecules to be detected in the sample to be examined, so that the biomolecules in question attach to the sensitive coating. Such coatings and their regeneration, for example by means of a hydrochloric acid solution, are familiar to the person skilled in the art.

A monochromatic light source 7 in the form of a laser diode is assigned to the light incidence side 2, and in a corresponding manner the detector 3 is at a distance from the light exit side 3 of the prism 1. Thus, as shown in FIG. 1, a divergent beam path 9 is generated by the laser diode 7, which is reflected on the metal layer 5 and is directed onto the detector 8. The beam path 9 is divided into an incident beam path 10 in front and an outgoing beam path 11 behind the metal layer 5, the plane of incidence 12 (FIG. 2) running parallel to the plane of the drawing in FIG. 1.

In the incident beam path 10, collimation optics 13 are arranged in the form of a cylindrical lens, which is arranged inclined in the plane of incidence 12 in accordance with the incident beam path. This cylindrical lens 13 brings about collimation or parallel alignment of the light beams only in a direction perpendicular to the plane of incidence 12 (FIG. 2), while the beam divergence is retained in the plane of incidence, as shown in FIG. 1. As a result of the effect of the collimation optics 13, the beam path 9 runs through the prism 1 within a comparatively narrow area with a small dimension perpendicular to the plane of incidence 12.

The occurring plasmon resonance, on which the test method carried out with the plasmon resonance sensor according to the invention is based, is indicated schematically in FIG. 1. The divergence of the beam path 9 in the plane of incidence 12 is sufficiently large to cover the range of angles of incidence within which the resonance phenomenon occurs. The reso- Specifically leading angles of incidence change as a result of the attachment of molecules from the sample to be examined to the sensitive coating 6. The incident light beam is noticeably weakened at the respectively resonant angle of incidence, and this angle of incidence is determined by the detector 8 in a time-resolved manner. Accordingly, 11 steps or areas with different light intensity are indicated in the emerging beam path, the area with the highest degree of blackening corresponding to the weakest light failure and thus illustrating the time-dependent sample-specific resonance angle of incidence. Thus, according to FIG. 1, the resonance occurs at an average angle of incidence. The relationships explained with reference to FIG. 1 apply generally to all of the exemplary embodiments described below.

In the embodiment according to FIG. 2, a laser diode 15, a cylindrical lens 16 and a prism 17 are provided in accordance with the description of FIG. 1, which likewise has a triangular cross section and extends perpendicular to the plane of incidence 12 of the light, four measuring cells 18 on the prism 17, 19, 20 and 21 are formed, on each of which the metal layer 5 and the sensitive coating 6 are present. Each measuring point is assigned its own detector 22, 23, 24 or 25.

The incident beam path 10 corresponds to the description with reference to FIG. 1. Accordingly, there is divergence between the laser diode 15 and the cylindrical lens 16 both in the plane of incidence 12 and perpendicular to it, while behind the cylindrical lens 16 there is only divergence in the plane of incidence 12 and perpendicular to the Plane of incidence there is a parallel beam path. Accordingly, the various measuring cells 18 to 21 and the associated detectors 22 to 25 are not only spaced apart from one another, but in particular are radially decoupled from one another, as illustrated by the outgoing beam paths 26, 27, 28 and 29, and this even with a small distance between the measuring cells 18 to 21 and accordingly between the detectors 22 to 25 and despite the intended divergence in the emerging beam paths 26 to 29, which is only present in the direction of the plane of incidence 12. A compact arrangement with four measuring cells 18 to 21 with only one laser diode 15, a cylindrical lens 16 and a prism 17 can thus be achieved.

With the four measuring cells 18 to 21, four samples can be examined simultaneously, or three samples in connection with a reference measurement based on a known reference sample. The increase in performance by additional measuring cells is particularly valuable because the individual measurements can be comparatively time-consuming, depending on the samples to be examined or the molecules to be detected. For example, the duration of the examination or measurement, in particular in the case of biological or biochemical tests, can be up to one hour.

The embodiments according to FIGS. 3 and 4 also provide a common prism 17 with four measuring cells and detectors assigned to them. The differences relate to the beam path in each case, without however changing the beam divergence in the plane of incidence and the collimation in the direction perpendicular to the plane of incidence.

According to FIG. 3, the measuring cells 30 to 33 are assigned their own laser diodes 34 to 37. Nevertheless, a common cylindrical lens 38 can be used, which collimates the four differently directed beam paths 39 to 42. Corresponding to the fan-shaped beam paths 39 to 45, the arrangement of the detectors 43 to 46 is spread out in a somewhat more space-consuming manner.

This can be dispensed with if, according to FIG. 4, each of the laser diodes 51 to 54 assigned to a measuring cell 47 to 50 is assigned its own cylindrical lens 55 to 58. In this case, the individual beam paths 59 to 62 run parallel to one another until they strike the detectors 63 to 66 assigned to the measuring cells 47 to 50.

Claims

Patent claims

1. plasmon resonance sensor for biological, biochemical or chemical tests with a translucent body (1, 17), in particular glass prism, a reflective metal layer (5) or semiconductor layer applied to a surface (4) of the body (1, 17) with one for molecules to be detected in a sample-sensitive surface (6), which forms a measuring cell in connection with a cuvette, a monochromatic light source (7, 15, 34 to 37, 51 to 54), in particular a laser diode, for emitting a diverging light beam or beam path (9, 26 to 29, 39 to 42, 59 to 62) through the translucent body (1, 17) onto the inner surface of the layer (5) and a detector (8, 22 to 25, 43 to 46, 63 to 66) which corresponds to that of the layer (5) is assigned to reflecting the outgoing beam path (11) and, as a function of time, determines the angle of reflection of the light which changes due to molecular deposits on the sensitive surface (6), in the case of the resonance condition t there is an intensity minimum of light falling out, characterized in that between the light source (7, 15, 34 to 37, 51 to 54) and the translucent body (1, 17) a collimation lens (13, 16, 38, 55 to 58) is arranged, which collimates the incident beam path (10) perpendicular to the plane of incidence (12), but still leaves diverging in the plane of incidence (12).

2. plasmon resonance sensor according to claim 1, characterized in that a cylindrical lens is provided as collimation optics (13, 16, 38, 55 to 58).

3. plasmon resonance sensor according to claim 1 or 2, characterized in that the sensitive surface is formed by a sensitive coating (6) of the reflective layer (5).

4. plasmon resonance sensor according to one of claims 1 to 3, characterized in that the translucent body (1, 17) two or more measuring cells (18 to 21, 30 to 33, 47 to 50) are assigned for different samples, which are in a row are aligned perpendicular to the plane of incidence (12), each measuring cell being assigned its own detector (22 to 25, 43 to 46, 63 to 66).

5. plasmon resonance sensor according to claim 4, characterized in that a single reflective layer (5) is provided which extends perpendicular to the plane of incidence (12) over all measuring cells (18 to 21, 30 to 33, 47 to 50).

6. plasmon resonance sensor according to claim 4 or 5, characterized in that each measuring cell (30 to 33, 47 to 50) is assigned its own light source (34 to 37, 51 to 54).

7. plasmon resonance sensor according to claim 6, characterized in that the light sources (34 to 37) is associated with a common collimation optics (38).

8. plasmon resonance sensor according to claim 6, characterized in that each light source (51 to 54) is assigned its own collimation optics (55 to 58).

9. plasmon resonance sensor according to one of claims 4 to 8, characterized in that the measuring cells are separated from one another by diaphragms.