Detection and quantitation of unlabeled nucleic acids in polyacrylamide gels

A method for the detection and quantitation of unlabeled nucleic acids in polyacrylamide gels is presented. The technique is a variation on UV shadowing. The technique is based on the observation that some storage phosphor screens (Kodak in this case) are sensitive to UV light in the range where nucleic acids absorb most strongly. Nucleic acid present in a gel resting on the screen absorbs the UV light and casts an ultraviolet shadow on the storage phosphor screen. The amount of nucleic acid in a particular area of the polyacrylamide gel is inversely proportional to the average pixel intensity in the corresponding area of the image. The technique therefore provides an electronic record of the gel in addition to the ability to quantitate the amount of nucleic acid present in any particular band. The storage phosphor screen images are erased by visible light. If the passage of that light to the screen is blocked by the presence of solid objects or images, the reverse process can be achieved, i.e., the recording of positive images by visible light etching of a uniformly charged background. By this method, we are able to transform old autoradiographic data into digital form for easy storage, computerized manipulation and distribution.