Fibers comprising the hydrophilic polymer polyvinylpyrrolidone K90, cetyltrimethylammonium bromide, tetraethyl orthosilicate and Fe3O4 were fabricated using an electrospinning process. Silica coated magnetite (Fe3O4@SiO2) core-shell nanoparticles (NPs) with high magnetic sensitivity were spontaneously formed through molecular self-assembly when the fibers were added to 80% aqueous ethanol (pH 9.0). The sizes of the Fe3O4@SiO2 particles could be manipulated from 30 nm to 83 nm by varying the Fe3O4 content in the fibers. A possible mechanism for the formation of templated Fe3O4@SiO2 NPs is proposed. Since the nanoparticles have high magnetic sensitivity and controllable particle size (<100 nm), and are prepared via a facile and convenient strategy, they have much promise in a range of practical applications. (C) 2013 Elsevier Ltd. All rights reserved.