For in vivo extraction of trace and polar components in tissues, extraction materials should be biocompatible, highly permeable to matrix and have high extraction capacity for polar and ionic compounds. In this study, nanofibers (similar to 200 nm) with rough polyaniline (PAn) sheath were prepared successfully for the first time by coaxial electrospinning and coelectrospun polymer sacrificing method. The nanofibers (0.5 mg) were then compressed into tiny bar (Phi 1 mm x 2 mm) and inserted directly into the aloe leaf for in vivo extraction of trace phytohormones. Due to the large surface area (13.97 m(2)/g) of nanofibers and large through pores formed between fibers, high extraction capacity (up to 10 mu g/bar) and permeability to tissue matrix of the tiny bar can be obtained. Moreover, PAn sheath has high adsorption equilibrium constants (10(7)-10(8) mL/mol) for acidic phytohormones in aloe leaf. Four phytohormones were detected by in vivo extraction with a spatial resolution of 3-8 mm(3), temporal resolution of 20 min, and limit of detection down to 60 pg/g. The quantification results were well met with that by traditional in vitro organic solvent extraction. (C) 2014 Elsevier B.V. All rights reserved.