1. Field of the Invention
This invention lies in the field of illumination systems such as those used for machine vision or illumination or for biological or chemical assays in multiple reaction systems.
2. Description of the Prior Art
Advances in microbiology, and particularly in the study and use of nucleic acids for diagnostic, clinical, and research purposes, have led to the development of complex automated equipment in which large numbers of procedures are performed simultaneously. The typical procedure is a sequence of reaction steps, each performed at a specified temperature. The sequence is typically repeated, as many as 30-40 times, with thermal cycling and with detection of the progress of the reaction at each stage of a cycle. Among the procedures that have been performed in this manner are polymerase chain reactions, strand displacement amplifications, ligase chain reactions, self-sustained sequence replication, enzyme kinetic studies, and certain ligand binding assays. Monitoring of the reactions and control of the reaction conditions in each stage of the sequence is essential to the achievement of reliable and meaningful results.
A particularly effective means of reaction monitoring for these systems is the use of optical readers and scanners. Light sources described in the literature for use in these scanners range from incandescent bulbs and fluorescent tubes to xenon flash tubes, lasers, light-emitting diodes and x-ray tubes. Light-emitting diodes (LEDs) emitting either ultraviolet, infrared, or visible-range light offer durability, low power dissipation, and a rapid switching speed. These attributes, coupled with the small size of the typical LED, make these devices the light source of choice for many operations. A particularly convenient detection method is fluorescence, which offers a high degree of control and specificity plus ease of quantification. Means of detecting fluorescence are varied, and examples are photomultiplier tubes, CCD cameras, SMOS detectors, and photodiodes.
In typical procedures, a multitude of samples, up to several hundred in some cases, are processed simultaneously in individual reaction wells arranged in two-dimensional arrays such as microplates. The optimal system is therefore one that provides uniformity and reproducibility among each of the wells or reaction systems as well as a reliable means for monitoring the progress of the reactions in each well. The factors that tend to prevent these systems from performing at their optima are sensitivity of the detecting systems and crosstalk between signals from adjacent samples. In systems that utilize LEDs, these difficulties have been attributable in part to the LEDs themselves due to variances in the internal construction of the LEDs. To compensate for these variances, individual adjustments and normalizations of the LEDs are often made. Examples of methods that have been developed to make these adjustments are the use of curable adhesives as disclosed by Thrailkill, W., in U.S. Pat. No. 5,822,053 (issued Oct. 13, 1998), the use of a controller to adjust power levels to individual LEDs as disclosed by Goldman, J. A., et al., in U.S. Pat. No. 6,825,927 B1, issued Nov. 30, 2004, and the use of either silicon photodiodes with associated feedback circuitry or calibration phosphors, as disclosed by Lee, J. D., et al., in United States Pre-Grant Patent Publication No. US 2004/0222384 A1, published Nov. 11, 2004.
It has now been discovered that an array of reaction wells can be illuminated with excitation light from individual LEDs with a high level of accuracy and uniformity among the wells by the use of a specially engineered support block to serve as a holding plate for positioning the LEDs. The support block has an array of apertures extending through the block, each aperture having a longitudinal axis and contoured to receive a single LED in a fixed orientation along the axis. In certain embodiments of the invention, the axes are oriented to converge at a location between the LED support block and the reaction well array, preferably passing through a common point at the site of convergence. The light beams from the LEDs likewise converge at approximately the same point, and both the axes and the light beams diverge before reaching the multi-well array. A lens is preferably positioned between the convergence of the beams and the multi-well array to orient the light beam axes in a direction normal to the wells, thereby directing excitation light to each well from a direction approximately normal to the mouth of the well. In other embodiments, the apertures and hence the LEDs are oriented either to diverge or to be parallel. Features of the apertures and the support block and further objects, aspects, and advantages of the invention will be apparent from the description that follows.
While the present invention is susceptible to a wide range of configurations, a detailed review of one particular configuration that exemplifies the invention will provide an understanding of the function and operation of the invention as a whole. The figures hereto depict one such configuration and are explained below.
While LEDs can assume a variety of shapes and sizes, the exterior of a typical LED 11 for which the present invention is designed is shown in
The side view of the LED holder plate in
The orientation of the axes in the presented embodiment is further illustrated in
Returning to
To assemble the illumination system, i.e., to secure the LEDs in the LED holder plate fully connected with the circuitry in the printed circuit board, the following procedure can be used. The LEDs, which have been pre-sorted according to intensity, can first be attached to the printed circuit board by means of conventional spring contact pins, and the circuit board can then be attached to the LED holder plate through the spacers mentioned above, while the lower ends of the LEDs are lowered into the apertures in the holder plate. Thus lowered, the LEDs can be pressed into the apertures in a tight fit by a tool inserted through access holes 25 (
A side elevation of a multi-receptacle reaction system incorporating the illumination system of the preceding figures is shown in
The foregoing is offered for purposes of illustration. The principles of this invention are similarly applicable to uses other than directing excitation light to planar arrays of reaction wells, such as machine vision or illumination. It will be apparent to those skilled in the art that further modifications and substitutions can be made without departing from the spirit and scope of the invention.