Due to the insoluble and non-thermoplastic properties, pure electroactive polymers are difficult to be processed into device nano features and thus their performances (e.g., sensitivity, selectivity, and miniaturization) are limited. Here we demonstrate an approach to synthesize highly stable colloidal polypyrrole dispersion or magnetic conductive fluid with excellent processibility. Remarkably, the unique liquid dispersion possesses specific liquid-solid-liquid phase-convertible characteristics, a great improvement from the pure conduttive polymers. Hence the dispersion can be readily converted to device structures of any scale sizes and shapes. Zero to three dimensional magnetic conductive polypyrrole nanostructures are fabricated via novel casting, injecting or coating of the dispersion. With the distinct selective solubility in different solutions and large surface-to-volume ratio, the smart polypyrrole nanostructures can be applied to extremely sensitive, selective, and rapid response nanosensors of solutions/solvents as well as in the detection of liquid N-2. This novel methodology introduces a facile way to enhance the processibility and applications of insoluble conductive polymers by encapsulating them with small bi- or multi-surfactant molecules. (C) 2014 Published by Elsevier B.V.