We have developed a facile method to rapidly synthesize the monodisperse silver nanowire-DNA conjugates with a constant diameter and systematically controllable lengths in the range of 0.5-2.5 mu m. The synthesis of silver nanowires takes advantage of poly(sodium 4-styrenesulfonate) as a structure-directing reagent and is performed under very mild conditions such as room temperature and aqueous media. The nanowires are densely conjugated with DNA sequences enough to exhibit the cooperative properties for the sensitive and selective detection of DNA targets. The limit of detection is 50 pM.