Planar homogeneous light source
The invention relates to a light source for irradiating, generally using light, an object or preparation for analysis, comprising at least one lamp.
For the purpose of analysing DNA and RNA structures, proteins etc., use is made of camera systems (also designated as "imaging systems"). In such a camera system is placed an object, normally in gel-form, such as a gel with nucleic acid or a gel with protein. The object is irradiated, usually with light and preferably from the underside. The object can be treated with a fluorophore, whereby an object radiated with a preferably monochromatic light produces a determined emission as a result of fluorescence. In a large number of fluorophores the optimal wavelengths for radiation ("excitation maximum") and of the emission ("emission maximum") are very close to each other. According to the prior art an object with a size lying generally between 100 and 400 cm2 is illuminated by means of a fluorescent tube over which a filtering glass plate is placed. A drawback of such an existing excitation source is that the bandwidth of the emitted light is not precisely limited, with the result that a part of the excitation light has an overlap with the emission bandwidth. The accuracy and sensitivity of an emission measurement is adversely affected hereby. In order to at least partly neutralize this disturbing effect of the light source not being precisely limited, use could be made in practice of an interference wave band filter. Drawbacks of applying an interference wave band filter with a surface area greater than 100 cm2 is that such a filter is bulky and very expensive. Another drawback of a prior art light source is that it has a non- homogeneous distribution of the light intensity over the surface for illuminating, as well as that a different filter plate is required each time for each different measurement (with for instance different fluorophores).
The international patent application WO 97/48977 describes a method and apparatus for measuring ligand interaction with DNA or protein on the basis of changes in the mechanical properties of the DNA or the protein. The ligand interaction can be determined inter alia by measuring a physical (for instance an optical or chemical) property of a sample. Described in the publication is a light source which can comprise a light conductor connecting to the light source and a magnifying or converging lens connecting to the light conductor. The lens can also be adjustable to different external light sources.
The present invention has for its object to provide a planar and homogeneous light source which can be embodied in relatively inexpensive and compact manner and which is suitable for application in a detection device wherein an object is irradiated.
The invention provides for this purpose a light source with a bandwidth to be defined (for instance a bandwidth of less than 60 nm), as according to claim 1. The choice of lamp in such a light source is free. In a preferred embodiment a halogen lamp can thus be chosen such as a xenon or krypton lamp, which already has a spectrum favourable for the excitation of for instance many fluorophores, The drawback that such a lamp produces a relatively large amount of heat is obviated by the presence of the conducting means for light; the lamp can be placed at a distance from the surface for illuminating so that this surface is not heated, or hardly so. Another advantage of the light source according to the invention is that the filtering means can also be placed at a distance from the surface for illuminating. The filtering means can hereby be given a compact form and can be selected with fewer limitations from the large variety of filters already available commercially. It is also possible for the filter to be readily exchanged for a filter with a filtering action differing from that of the first filter; it is thus possible to achieve in simple manner with a single lamp that the light source can produce varying bandwidths, which makes it possible to perform a plurality of measurements on the same object and/or measurements with diverse fluorophores.
The conducting means for light can comprise optical fibres. Optical fibres, such as glass fibres, are available as standard on the market and provide a great freedom in the design of the light source because they can be flexible. Since the objects for illuminating are generally larger than 100 cm2, the emitting element preferably also has a surface area for illuminating with a size of a minimum of 100 cm2. The maximum size is not limited but surface areas larger than 600 cm2 are among the possibilities. Surface areas smaller than 100 cm2, such as microscope slides of for instance 6 by 2.5 cm, can however also be irradiated using a light source according to the present invention.
In a particular preferred embodiment the emitting element is formed by a transparent body with a surface for illuminating which is provided with irregularities for emitting the light cast into the transparent body by the conducting means. Such a body can be realized simply and inexpensively in any desired dimension. The light can be cast into the body in simple manner, for instance by arranging in one side openings in which optical fibres are arranged. The irregularities can be arranged in or on the surface in the form of pits, scratches, lines, protrusions and so on. For a uniform distribution of the light intensity the irregularities of the surface for illuminating are arranged such that the density of the irregularities increases at greater distance from the connection of the conducting means to the emitting element. Compensation is thus made for the emission
in that the light intensity in the transparent body decreases at greater distance from the connection(s) of the conducting means.
For a homogeneous illumination of the side for lighting, the conducting means for the light connect to the emitting element at a distance from the side to be illuminated of the emitting element. The conducting means can moreover be concealed by such a method of connection such that they do not form an obstacle during use of the light source. When the conducting means for the light connect to a plurality of sides of the emitting element, it is also possible in effective manner to homogeneously illuminate emitting elements with a larger surface area for lighting. When the side for illuminating is defined as upper side, it is possible to introduce the light on a plurality of sides of the emitting element and/or on the underside of the emitting element.
In yet another preferred embodiment the present light source is provided with a plurality of lamps connecting to the emitting element via individual filtering means. Using a plurality of light sources and filtering means associated individually with each light source, it is for instance possible to cast light of different (for instance two) colours into the emitting element so that a multiple measurement can be performed. It is of course also possible to vary the intensity in a single light colour by varying the number of lamps with which light of a determined colour (wavelength range) is cast into the emitting element.
In order to optimize the controllability of the bandwidth of the light entering the emitting element, the filtering means for selecting a bandwidth of light to be transmitted which are disposed between the lamp and the emitting element are preferably situated between the conducting means and the emitting element. The fluorescence occurring in the conducting means during the light transport can thus be filtered out before the light is cast into the emitting element. Fluorescence in the conducting means can impede or even make impossible the analysis of an object. In order to also limit the fluorescence occurring in the emitting element for light, this latter is preferably manufactured from a low-fluorescent material such as PMMA or, when even better specifications are desired, a borosilicate glass (boron/silicon), which is for instance commercially available under the trade name Borofloat®.
In order to further optimize the efficiency of the light source it is recommended that on at least one side the emitting element abuts a light-reflecting surface. Light exiting in an undesired direction can thus be returned to the emitting element. Particularly favourable
results are achieved when the reflecting surface lies immediately abutting the emitting element.
In order to prevent the filters and possibly other components of the light source and the immediate surroundings of the light source becoming overheated, heat filter means are preferably placed between the lamp and the emitting element. Such emitting means are also known under the name "hot mirror". The filters can for instance be manually exchangeable but it is also possible to integrate into the light source a mechanical exchange mechanism for filters (for instance a rotating disc with filters) .
For a simple and interchangeable coupling of the light source according to the invention to a detection device the light source is combined with a housing substantially enclosing the light source, which housing is provided on the outside with coupling means for fixing the module in a detection device. Such a housing also forms a protection of the light source. Such a housing can optionally also be provided with a control panel for the lighting source. Another option for the lighting source is coupling thereof to the control of an apparatus in which the lighting source is arranged.
The present invention will be further elucidated on the basis of the non-limitative embodiments shown in the following figures. Herein: figure 1 shows a schematic view of the light source according to the invention, figure 2 A shows a cut-away view of the elementary components of a light source according to the invention in modular form, figure 2B is a side view of the modular light source shown in figure 2b, figure 3 A shows a cut-away view of the elementary components of an alternative embodiment variant of a light source according to the invention in modular form, and figure 3B is a side view of the modular light source shown in figure 3b. Figure 1 shows a homogeneous light source 1 provided with two lamps 2, the radiation of which is cast through a heat filter 4 by means of reflectors 3. The heat from lamps 2 is discharged as according to arrows PI. The remaining light is passed through a colour filter 5. Due to the presence of a plurality of alternative colour filters 6 a colour filtering can be adjusted as required, for instance by rotating filtering discs 7. The light thus limited in bandwidth by filter 5 is introduced into a bundle of fibres 8, the fibres 9 of which lead to two sides 10, 11 to a transparent plastic plate 12. On the upper side 13 of plate 12 is arranged a pattern of pits 14 through which is emitted the light carried into plate 12 from fibres 9. The density of pit pattern 14 increases at a greater distance from the sides 10,11 onto which the fibres 9 connect.
Figure 2 A shows a light source 15 in modular form with a housing 16 provided with a plug 17 with which the modular light source 15 can be coupled to a detection device functioning by means of irradiation of a preparation (which can also be designated an object), for instance for detecting fluorescent excitation. Shown are an emitting element 18 and, disposed on either side of this element 18, lamps 19 from which radiation beams 20 are cast through "hot mirrors" 21. Also shown are drives 22 with which a filter of choice can be placed in radiation beams 20. The thus coloured light is caught in introducing elements 23 and carried to emitting elements 18 by means of the fibres (not shown).
Figure 2B shows the light source 15 in modular form with housing 16 in side view. Externally visible is plug 17 as well as protruding parts 24 (these are not shown in figure 2a) for a simple coupling to a detection device (not shown).
Figure 3 A shows an embodiment variant as alternative to figures 2A and 2B of a light source 25 in modular form, which for the time being is preferred in practice to the embodiment variant shown in figures 2A and 2B of modular light source 15, with a housing 26 provided with a plug 27 with which the modular light source 25 can be coupled to a detection device making use of irradiation of a preparation. Shown are an emitting element 28 and lamps 29 disposed on either side of this element 28, the radiation beams 30 from which lamps are cast through "hot mirrors" 31. Other than in the embodiment variant shown in figure 2A, the radiation beams 30 are fed directly into introducing elements 32. By means of fibre bundles 33 the intercepted light is carried to heads 34 where the wavelength of the light is reduced to a limited bandwidth by filters 35. The light filtered through filters 35 enters protruding parts 36 of emitting element 28. The advantage of the embodiment variant of the modular light source 25 shown in this figure 3 A over the embodiment variant of modular light source 15 shown in figure 2 A is that changes in wavelength of the light during the transport of the light through fibre bundles 33 do not have a disturbing effect on the controllability of the bandwidth of the light exiting the emitting element 28; possible wavelength shifts in fibre bundles 33 are filtered by filters 35.
Figure 3B shows a part of the light source 25 in modular form, shown in side view in figure 3 A. A carriage 37 which is linearly displaceable in housing 26 by means of a linear drive member (not shown) is provided with a plurality of filters 35. A filter 35 of choice with a desired limited bandwidth can be placed above a lifting arm 38. A motor 39 provided with a cam disc 40 is driven to place the desired filter 35 between head 34 and the protruding part 36 of emitting element 28 counter to the bias of a compression
spring 41. For a close fitting of head 34, filter 35 and the protruding part 36, the head 34 is mounted on a displaceable support 42. The displaceable support 42 is provided with a cam following arm 43 which is displaced by cam disc 40 (or a separate second cam disc driven for this purpose by motor 39). Filter 35 can thus be enclosed in exchangeable manner between head 34 and the protruding part 36 so as to thus minimize possible light losses. It is noted that in the close fitting of head 34, filter 35 and the protruding part 36, light-proof abutting gaskets (not shown) are preferably provided. The emission side of light source 25 is covered by means of a diffuse light-transmitting plate 44.