1. Field of the Invention
The present invention relates generally to an imaging screen for electrophoresis applications and, more particularly, to an imaging screen for detecting and recording the impingement of beta particles or visible light emitted from electrophoresis gels.
2. Description of the Related Art
In order to sequence deoxyribonucleic acid (DNA), it is necessary to chemically treat and label DNA fragments prior to performing electrophoresis. Specifically terminated fragments of the DNA are placed in wells in a gel and an electric field applied, resulting in the motion along well-defined lanes in the gel. Depending on the length of the fragments and the time for performing the electrophoresis, they will travel more or less far along the lanes. The result of the electrophoresis operation is a pattern of bands of DNA fragments.
If the fragments have been labelled with a beta particle emitter, it is possible to obtain a two-dimensional map of the pattern by placing X-ray film in relatively intimate contact to the gel. The X-ray film is somewhat sensitive to the beta particle radiation, and generally after long exposure will record the pattern. Unfortunately, such a procedure typically requires a time period on the order of days for the film to register a sufficient number of emitted beta particles to provide an accurate representation of the pattern of bands.
Another drawback to this method is associated with the properties of X-ray film. Because of its limited dynamic range, and the complexity of obtaining quantitative information using such film, efforts have been undertaken to develop simpler, speedier and more accurate methodologies to detect radioactively labelled DNA fragments in electrophoresis gels.
Four beta emitters are typically employed for tagging DNA fragments--i.e., .sup.32 P, .sup.35 S, .sup.14 C, and .sup.3 H. The beta particles end point energies are 1.71 MeV, 168 keV, 156 keV, and 18.6 keV, respectively. The electron ranges vary greatly, with .sup.32 P having the longest range, and .sup.3 H having the shortest range.
Recently developed devices for obtaining quantitative information from radioactively labelled DNA, RNA or protein fragments in electrophoresis gels generally utilize two coincident grids which sense the beta emissions from the gels. Such a device is marketed as the Betascope 603 Blot Analyzer. That device can perform an analysis of the emitted beta particles in a number of hours. However, the Betascope device, and similar such devices, cannot readily detect the shorter range and lower energy beta particles. In addition, its spatial resolution is poor.
Fuji has developed a BaFBr imaging screen system which can work with .sup.32 P, .sub.35 S, and .sup.14 C, but is at least 1-2 orders of magnitude slower then the Betascope Blot Analyzer in processing the information contained in the radioactively labelled DNA, RNA or protein carrying electrophoresis gel.
Accordingly, there is a need for a simple, speedy and accurate methodology for detecting radioactive tracers emitted from electrophoresis gels. It would be additionally advantageous if such methodology could also be utilized to detect dye-tagged and chemiluminescent tracers which emit visible light, which the Fuji BaFBr system cannot detect.