Procedures for collecting
DNA from dilute solutions as small spots of the insoluble cetyltrimethylammonium
salt deposited on either glass fiber or Millipore filters are described. This method of concentration facilitates the fluorescent assay of
DNA, either by a microreaction in which the spots on glass fiber are punched out, reacted with a small volume of
3,5-diaminobenzoic acid, and then assayed in a microcuvette or, alternatively, by
spotting the
DNA onto black Millipore filters and soaking these in
ethidium bromide so that the fluorescence of each spot can be measured by direct scanning. These methods are capable of detecting
DNA amounts as low as, respectively, 50 and 10 ng. The most important advantage in this procedure is not, however, its intrinsic sensitivity but, rather, the ability to recover and assay
DNA from very dilute solutions. The use of
silver both to
stain DNA on filters and to enhance the sensitivity of the
4',6-diamidino-2-phenylindole fluorescence method of estimating
DNA is also briefly described.