Relevance of empirical optimization for cross-linking DNA by using an ordinary ultraviolet-light source

For cross-linking DNA onto nitrocellulose or nylon membranes by using ordinary ultraviolet (UV) light, empirical optimization with respect to exposure time is crucial for obtaining complete hybridization signals. Longer than optimal UV exposure reduces the signal intensity particularly in the larger DNA fragments, whereas shorter exposure due to insufficient immobilization produces incomplete signals. Relevance of using ordinary source of UV light with respect to fixing DNA on a large number of circular filters during library screening is discussed.