Polyaniline sheathed electrospun nanofiber bar for in vivo extraction of trace acidic phytohormones in plant tissue

• Polyaniline sheathed nanofibers were electrospun for the first time.
• The compressed nanofiber bar was inserted in aloe leaf for in vivo extraction.
• Four phytohormones were detected by in vivo extraction.
• A 3–8 μL spatial resolution and 20-min temporal resolution were obtained.
• The limit of detection was down to 60 pg/g.

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 (∼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 (Φ1 mm × 2 mm) and inserted directly into the aloe leaf for in vivo extraction of trace phytohormones. Due to the large surface area (13.97 m2/g) of nanofibers and large through pores formed between fibers, high extraction capacity (up to 10 μg/bar) and permeability to tissue matrix of the tiny bar can be obtained. Moreover, PAn sheath has high adsorption equilibrium constants (107–108 mL/mol) for acidic phytohormones in aloe leaf. Four phytohormones were detected by in vivo extraction with a spatial resolution of 3–8 mm3, 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.