Supercoiled DNA-modified mercury electrode: A highly sensitive tool for the detection of DNA damage

A fast method for the detection of small damage in DNA is presented. The method is based on the appearance of an a.c. voltammetric peak (peak 3) resulting from the introduction of a single-strand scission into the covalently closed circular (supercoiled) DNA molecule. Peak 3 is absent in an intact supercoiled DNA. DNA is immobilized by short incubation of a hanging mercury drop electrode in 5 mu l of the DNA solution followed by washing and transfer of the DNA-modified electrode in a voltammetric cell containing blank background electrolyte. This makes it possible to determine one strand scission in < 2% of the DNA molecules or among > 2.5 x 10(-5) phosphodiesteric bonds. The amount of DNA required for the analysis is below 10 ng. The DNA damage can be studied either in solution or the electrode modified with intact supercoiled DNA can be used as a sensor to detect the DNA damaging agent (e.g. hydroxyl radical) in the environment. In the latter case the response can be obtained in seconds. The method is faster than the currently applied gel electrophoresis.