Dodecyl-dimethyl-amine-oxide (DDAO) is an amphiphile that may exist either in a neutral or cationic protonated form depending on the pH of aqueous solutions. Thus it realizes ionic or non-ionic micelles of easily controlled composition. These micelles, partially charged, realize an efficient support on which DNA can be linked in a controlled manner. In this Letter we report a study on DNA/DDAO complex formation using two physical techniques, dielectric spectroscopy (DS) and circular dichroism (CD). At pH 8, where the micelle is in a neutral state, no formation of a complex DNA/DDAO is evident. At pH 7, where the degree of ionization of the micelle is very low, the formation of the complex has been observed by the two techniques. Coherent results on the formation of the complex as a function of DDAO concentration and its influence on DNA conformation. are presented. (C) 2003 Elsevier Science B.V. All rights reserved.