Ionic liquids are described that contain duplex DNA as the anion and polyether-decorated transition metal complexes based on M(MePEG-bpy)(3)(2+) as the cation (M = Fe, Co; MePEG-bpy = 4,4'-(CH3(OCH2CH2)(7)OCO)(2)-2,2'-bipyridine). When the undiluted liquid DNA-or molten salt-is interrogated electrochemically by a microelectrode, the molten salts exhibit cyclic voltammograms due to the physical diffusion (D-PHYS) Of the polyether-transition metal complex. When M = Co(II), the cyclic voltammogram of the melt shows an oxidative wave due to the co(mm) couple at E-1/2 = 0 40 V (versus Ag/AgCl) and a DPHYS Of 6 x 10(-12) cm(2)/s, which is significantly lower than that for Co(MePEG-bpy)(3)(ClO4)(2) (D-PHYS = 2.6 x 10(-10) cm(2)/s) due to greater viscosity provoked by the DNA polymer. When a 1:1 mixture is made of the Co(MePEG-bpy)(3). DNA and Fe(MePEG-bpy)(3)(ClO4)(2) melts, two redox waves are observed. The first is due to the Co(III/II) couple, and the second is a catalytic wave due to oxidation of guanine in DNA by electrogenerated Fe(III) in the undiluted melt. Independent experiments show that the Fe(III) form of the complex selectively oxidizes guanine in duplex DNA. These DNA molten salts constitute a new class of materials whose properties can be controlled by nucleic acid sequence and that can be interrogated in undiluted form on microelectrode arrays.