Patent Application
20060227328
Embodiments in accordance with the invention pertain to light sensors.
In surface plasmon resonance (SPR) spectroscopy, light from a light source is directed onto a metal film and the intensity of the light reflected from the metal film is measured. The intensity of light reflected from the metal film depends on the angle of incidence or the wavelength of light from the light source, and also depends on the refractive index of a substance on the side of the metal film that is opposite the side facing the light source.
SPR can be used to perform highly sensitive measurements of chemical and biological substances. For example, SPR can be used to measure interactions between proteins. A first protein (e.g., a ligand) is attached to the metal film on the side of the film not facing the light source, and a second protein (e.g., an analyte) is placed in solution and flowed over the first protein. If the first and second proteins bind to some degree, a composition of the first and second proteins is formed on the surface of the metal film away from the light source. The refractive index of the composition depends on the relative amounts of the first and second proteins, and will vary with time if the relative amounts of the first and second proteins change with time. The metal film is illuminated with light at different wavelengths or different angles of incidence. By measuring the intensity of the reflected light at those different angles of incidence or wavelengths, the amount of binding can be derived. The measurements can be repeated so that the amount of binding as a function of time can be plotted. Association and dissociation rates for the two proteins can be determined in this manner. These rates are of key interest in the field of drug discovery, for example.
Multiple experiments can be conducted at the same time by arraying a number of samples on the surface of the metal film. For example, different types of ligands can be tested at the same time to measure binding affinity with a particular analyte. Light reflected from the samples can be imaged using a camera. In essence, the camera takes pictures of the array of samples at a frequency that corresponds to the frame rate of the camera. The images are then processed to measure the intensity of light reflected from each sample versus time.
A camera used for SPR may use an imager consisting of a 320×256 array of pixels. For each image frame, the digital values of the pixels (e.g., 81,920 pixel values for a 320×256 array of pixels) are transferred to a computer system for processing. For each sample tested, the pixel values that correspond to that sample are extracted from the other values. The pixel values extracted for a sample are then averaged to provide a data point for that sample.
It is desirable to increase the number of samples that can be tested at a time, so that testing can be completed more efficiently. It is also desirable to increase the rate at which data is collected, allowing information about the interaction between substances (e.g., proteins) to be captured in more detail. The data collection rate can be increased by increasing the rate at which the samples are imaged. This can be achieved using a camera capable of operating at higher frame rates.
However, increasing the number of samples and the frame rate increases the amount of data that needs to be transferred and processed. Tests may be conducted over a period of days, so a tremendous amount of data can be collected, placing a heavy burden on the resources used to transfer and process the data. Additional computational resources can be used to alleviate data handling and processing loads, but that can increase the cost of testing.
Also, cameras that operate at higher frame rates are quite expensive. For example, a camera that operates at 60 frames per second (fps) may cost around $20,000, while a camera that operates at 400 fps may cost around $50,000. Cameras can have other shortcomings as well. For example, cameras have a limited full well capacity (that is, they can only store a limited number of electrons per pixel before becoming saturated). Also, cameras have a relatively low quantum efficiency (the rate at which photons are converted to electrons) of less than 20 percent.
Accordingly, a system and/or method that can be used with a sufficiently large number of samples and that can permit higher data collection rates, without substantially increasing either cost or data handling and processing loads, would be valuable.
Embodiments in accordance with the invention pertain to light-sensing systems and methods thereof. In one embodiment, a light source illuminates target areas arrayed on a surface. Light guides receive light reflected from the target areas. The amount of light reflected from a target area corresponds at least in part to the composition of a substance associated with that target area. Detectors receive reflected light carried by the light guides.
The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. The drawings referred to in this description should not be understood as being drawn to scale except if specifically noted.
Reference will now be made in detail to various embodiments in accordance with the invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with these embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of the invention, numerous specific details are set forth in order to provide a thorough understanding of the invention. In other instances, well known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the invention.
Optically transmissive element (e.g., prism) 13 is made up of a transparent material. In the example of
In one embodiment, optically transmissive element 14 is a transparent plate or slide that supports the metal film 15. Metal film 15 may be embodied as a coating that is applied to optically transmissive element 14. In one embodiment, metal film 15 is a thin film of gold; silver can also be used.
Coupled to the surface of the metal film 15, on the side of the film facing away from light source 11, are sample areas exemplified by sample area 16. In the present embodiment, sample area 16 and the other sample areas identify the positions at which ligands can be placed. Different ligands may be used in different sample areas. One or more types of analytes can be presented to the ligands in buffer chamber 17. In one embodiment, an analyte is placed in solution and flowed through buffer chamber 17 over the sample areas.
Light source 11 can be an ordinary light source with suitable filters and collimators. Alternatively, light source 11 can be a laser or a superluminescent light emitting diode (SLD). Other types of light sources may be used.
Also, multiple light sources may be used, with each light source placing a beam of light on each area of the surface of metal film 15 that corresponds to a respective sample area (e.g., there may be one light source per sample area). Alternatively, a diffractive plate can be placed between light source 11 and the sample areas, so that the light from the light source is split into multiple beams of light, each beam of light illuminating an area on the surface of metal film 15 that corresponds to a respective sample area.
In one embodiment, the wavelength of light emitted by light source 11 can be varied. In another embodiment, light source 11 can be moved so that the angle of incidence θ (the angle formed by incident light 12 and a vector that is normal to the plane of metal film 15) can be varied.
Light source 11 transmits light 12 onto and through optically transmissive elements 13 and 14 to metal film 15. In the embodiment of
In one embodiment, detector array 18 is a linear array. In one embodiment, a V-groove assembly with a pitch that corresponds to the pitch of the detectors in detector array 18 is used to align the light guides with the detectors. In one embodiment, the detectors (e.g., detector 19) are photodiodes. In one embodiment, the light guides (e.g., light guide 20) are optical fibers. The use of a system such as system 10 instead of a system that uses a camera, for example, can result in significant cost savings because the cost of a detector array may be orders of magnitude less than the cost of a suitable camera. As will be discussed further below, embodiments in accordance with the invention provide other advantages as well.
The number of light guides generally corresponds to the number of sample areas, and the number of detectors generally corresponds to the number of light guides; however, the invention is not so limited. In one embodiment, each light guide is associated with a single sample area, and each detector in detector array 18 is associated with a single light guide (and hence with a single sample area). In such an embodiment, the light reflected from the area of metal film 15 that corresponds to sample area 16 will be captured by light guide 20, and carried by light guide 20 to detector 19, for example. Light reflected from other areas on metal film 15, corresponding to other sample areas, will be similarly captured by a corresponding light guide and carried to a respective detector.
The light guides can be placed sufficiently close to metal film 15 so that the light reflected from an area on metal film 15 can be coupled into a respective light guide without significant crosstalk with light reflected from other areas. For example, the light guides can be pressed against or nearly against optically transmissive element 13.
In one embodiment, the cross-sectional area of a light guide (e.g., light guide 20) is not more than the size of a sample area (e.g., sample area 16). More precisely, the cross-sectional area of a light guide is less than the size of the area on metal film 15 from which light associated with a particular sample area is reflected. In general, a light guide is sized and positioned so that it does not capture light reflected from outside a defined area on metal film 15. For example, light guide 20 is sized and positioned so that it does not capture light reflected from metal film 15 outside of the area on metal film 15 associated with sample area 16.
System 10 is now described in operation for SPR spectroscopy. Ligands are coupled to metal film 15 (e.g., at sample area 16). An analyte solution is flowed past sample area 16 in buffer channel 17. Light from light source 11 is incident on metal film 15, having passed through optically transmissive elements 13 and 14. Light reflected from the area on metal film 15 that corresponds to sample area 16 is coupled into light guide 20. Light carried by light guide 20 is received at detector 19. This process continues over time until the test is completed.
The amount of light reflected from metal film 15 is a function of the refractive index of the substance at sample area 16 and the wavelength or angle of incidence of the incident light 12. The refractive index of the substance at sample area 16 is in turn a function of the degree to which the ligand and the analyte interact (e.g., the degree to which the analyte and the ligand bind). The angle of incidence θ or the wavelength of the incident light 12 can be varied to produce a condition that resonates the free electrons at the reflecting surface of metal film 15. At the SPR condition, the intensity or amount of light reflected by metal film 15 is decreased. The amount of reflected light received at detector 19, along with the angle of incidence or the wavelength of the incident light 12, can be used to determine the amount of interaction between the ligand and the analyte at sample area 16. System 10 functions in a similar manner with regard to the other sample areas, light guides and detectors.
In the present embodiment, system 30 includes light source 11, optically transmissive element (e.g., slide or plate) 14, metal film 15, detector array 18, exemplary detector 19, and light guides (exemplified by light guide 20) between metal film 15 and detector array 18, previously described herein.
System 30 also incorporates a group 31 of light guides (exemplified by light guide 32) that carry light from light source 11 to the sample areas. In one embodiment, the light guides are optical fibers. The light guides in the group 31 can be pressed against or nearly against the areas on metal film 15 that correspond to the sample areas. In an SPR application, a collimator can be placed between the light guides and the metal film 15.
The light guides that receive reflected light (e.g., light guide 20) can also be pressed against or nearly against areas of metal film 15 corresponding to the sample areas. In one embodiment, a block 33 (e.g., a plastic block) can be used to hold the light guides that deliver light to metal film 15 and the light guides that receive light reflected from metal film 15 in place relative to the areas on metal film 15 that correspond to the sample areas. The group 31 of light guides can be moved within block 33 so that the angle of incidence of the incident light can be varied.
The number of light guides in the group 31 of light guides generally corresponds to the number of sample areas; however, the invention is not so limited. In one embodiment, each of the light guides in the group 31 of light guides is associated with a single sample area. For example, light guide 32 is associated with sample area 16.
In another embodiment, in place of block 33, an optically transmissive element 13 (
In the present embodiment, system 40 includes light source 11, optically transmissive element (e.g., slide or plate) 14, metal film 15, detector array 18, exemplary detector 19, and light guides (exemplified by light guide 20) between metal film 15 and detector array 18, previously described herein. System 40 also includes a group 41 of optically transmissive elements (exemplified by prism 43) composed of a transparent material. In general, the number of elements in the group 41 corresponds to the number of sample areas; however, the invention is not so limited. In one embodiment, each of the optically transmissive elements in the group 41 is associated with a single sample area. For example, prism 43 may be associated only with sample area 16.
The optically transmissive elements (e.g., prism 43) in the group 41 are smaller than optically transmissive element 13 of
In one embodiment, each light guide is associated with a single optically transmissive element in the group 41 of optically transmissive elements. For example, light guide 20 may be associated only with prism 43.
In the present embodiment, system 50 includes light source 11, optically transmissive element (e.g., slide or plate) 14, metal film 15, detector array 18, exemplary detector 19, and light guides (exemplified by light guide 20) between metal film 15 and detector array 18, previously described herein.
System 50 also includes a group 51 of optically transmissive elements (exemplified by prisms 53 and 55) composed of a transparent material. In general, the number of these elements corresponds to the number of sample areas; however, the invention is not so limited. In one embodiment, each of the optically transmissive elements in the group 51 is associated with a single sample area. For example, prism 53 may be associated only with sample area 54, and prism 55 may be associated only with sample area 16.
System 50 also includes a group 56 of light guides (exemplified by light guide 52) that carry light from light source 11 to the optically transmissive elements (exemplified by prism 53). In one embodiment, these light guides are optical fibers. The light guides in the group 56 can be pressed against or nearly against the optically transmissive elements in the group 51. For example, light guide 52 can be pressed against or nearly against prism 53. In one embodiment, each of the light guides in the group 56 is associated with a single optically transmissive element in the group 51. That is, for example, light guide 52 may be associated only with prism 53. In an SPR application, a collimator can be placed between the light guides and the group 51 of optically transmissive elements.
The light guides (exemplified by light guide 20) that carry light reflected from metal film 15 can also be placed closer to metal film 15. For example, light guide 20 can be pressed against or nearly against prism 55.
In the present embodiment, system 60 includes light source 11, optically transmissive element (e.g., prism) 13, optically transmissive element (e.g., slide or plate) 14, metal film 15, detector array 18, and detector 19, previously described herein.
System 60 also includes a number of light guides (exemplified by light guide 62) coupled to the detector array 18. The number of lights guides generally corresponds to the number of sample areas, and the number of detectors generally corresponds to the number of light guides; however, the invention is not so limited. In one embodiment, each light guide is associated with a single sample area, and each detector in detector array 18 is associated with a single light guide (and hence with a single sample area), as previously described herein.
In contrast to the embodiment of
In the embodiment of
In the present embodiment, system 70 includes light source 11, optically transmissive element (e.g., prism) 13, optically transmissive element (e.g., slide or plate) 14, metal film 15, detector array 18, and detector 19, previously described herein.
System 70 also includes a group 76 of light guides (exemplified by light guide 72) coupled to the detector array 18. The number of lights guides generally corresponds to the number of sample areas, and the number of detectors generally corresponds to the number of light guides; however, the invention is not so limited. In one embodiment, each light guide is associated with a single sample area, and each detector in detector array 18 is associated with a single light guide (and hence with a single sample area), as previously described herein.
Similar to the embodiment of
In one embodiment, an imaging lens 61 is positioned so that light reflected from metal film 15 passes through lens 61 before reaching the group 76 of light guides. In such an embodiment, the group 76 of light guides are situated within the image plane of lens 61.
In the embodiment of
In another embodiment, diffractive optical elements can be used instead of lenses such as lens 71. An array of micro-lenses can be formed on a sheet of plastic, for example, and positioned up against or nearly up against the group 76 of light guides, such that each light guide is aligned with a respective micro-lens.
In the present embodiment, system 80 includes light source 11, metal film 15, detector array 18, and detector 19, previously described herein. System 80 also includes a grating 84 to match the momentum of the light to the momentum of a plasmon wave created in the metal film 15. In one embodiment, grating 84 provides support for metal film 15. In such an embodiment, metal film 15 follows the contours of grating 84. Light passes through the film 15 to the grating 84.
The features of system 80 can be combined with the other features described above. That is,
Also, for example, the features described in conjunction with
In addition to the cost savings mentioned above, embodiments in accordance with the invention provide a number of other advantages. For one, samples can be collected at a faster rate; that is, the sample rate is not limited by frame rate. Sample rates as high as five mega-samples per second are achievable. Thus, more time-wise continuous plots of test results can be generated.
Also, a single data point (e.g., the detector output) is collected for each sample area, eliminating the transfer of large amounts of data for processing. This also eliminates the extraction and averaging of pixel values for each of the samples tested, simplifying processing.
Furthermore, detectors (e.g., photodiodes) are more precise than cameras, measured in terms of the number of output bits. Also, cameras have limited full well capacity and may saturate if too much light is placed on the sample areas. Detectors are not subject to these limitations, in particular for the levels of light used in applications such as SPR.
In addition, the quantum efficiency of detectors (e.g., photodiodes) is on the order of 75 percent, which is greater than the quantum efficiency of cameras. Thus, for a given amount of light, a detector will output a better signal than a camera.
In one embodiment, light is transmitted to an area on the surface through an element (e.g., optically transmissive element 13 of
In yet another embodiment, the light is transmitted to the surface via a plurality of light guides (e.g., light guide 32 of
In step 92 of
In step 93 of
The invention is thus described in various embodiments. While the invention has been described in particular embodiments, it should be appreciated that the present invention should not be construed as limited by such embodiments, but rather construed according to the following claims.
