In vivo polymerization and manufacturing of wires and supercapacitors in plants

Abstract

Electronic plants, e-Plants, are an organic bioelectronic platform that allows electronic interfacing with plants. Recently we have demonstrated plants with augmented electronic functionality. Using the vascular system and organs of a plant, we manufactured organic electronic devices and circuits in vivo, leveraging the internal structure and physiology of the plant as the template, and an integral part of the devices. However, this electronic functionality was only achieved in localized regions, whereas new electronic materials that could be distributed to every part of the plant would provide versatility in device and circuit fabrication and create possibilities for new device concepts. Here we report the synthesis of such a conjugated oligomer that can be distributed and form longer oligomers and polymer in every part of the xylem vascular tissue of a Rosa floribunda cutting, forming long-range conducting wires. The plant's structure acts as a physical template, whereas the plant's biochemical response mechanism acts as the catalyst for polymerization. In addition, the oligomer can cross through the veins and enter the apoplastic space in the leaves. Finally, using the plant's natural architecture we manufacture supercapacitors along the stem. Our results are preludes to autonomous energy systems integrated within plants and distribute interconnected sensor-actuator systems for plant control and optimization.

Keywords: conjugated oligomers; electronic plants; in vivo polymerization; supercapacitor.

Fig. 1.

ETE-S distribution and polymerization in a rose cutting. (A) Synthetic route/polymerization of ETE-S in vivo. (B, i) Rose after immersion in ETE-S aqueous solution for 24 h. (B, ii–iii) Bottom and top cross-section of stem with vascular bundles darkened due to polymer deposition. (Scale bar, 1 mm.) (B, iv) White rose petal with polymer-darkened veins. (Scale bar, 1 mm.) (B, v–vi) Leaf stem and petiole with polymer-darkened vascular bundles. (Scale bar, 0.5 mm and 1 mm, respectively.) (C) Absorption and emission spectra of polymer-filled xylem (after DMSO extraction), the latter using laser excitation at 355 nm. (D) Theoretical calculation of absorption and emission spectra for ETE-S molecule, hexamer (2 ETE-S units) and dodecamer (4 ETE-S units) (from dark to light color). (Inset) Structure of the hexamer.

Fig. 2.

Distribution of ETE-S from the stem to the veins and extracellular space of leaves. (A) Schematic showing the transport path from the xylem vessels in the leaf to the apoplast and spongy mesophyll. (B) Confocal fluorescent image of leaf functionalized with ETE-S and (C) without functionalization (negative control). (D) Spectra from selected locations on a leaf with (blue) and without (green) ETE-S upon excitation with 405-nm laser.

Fig. 3.

Plant supercapacitor. (A) Simplified schematic and wiring of a plant supercapacitor where the xylem wires comprise the electrodes, and the plant tissue in between comprises the electrolytic spacer. (B) Optical micrograph of a rose supercapacitor. (Scale bar, 1 mm.) (C) Typical charging–discharging curves for a rose supercapacitor. (D) Capacitance and equivalent series resistance and (E) CE of a typical supercapacitor over galvanostatic cycling of the device, for I = 0.5 µA and V_max = 0.25 V. (F) Capacitance per area versus length of xylem limiting wire.