Electronic plants

Abstract

The roots, stems, leaves, and vascular circuitry of higher plants are responsible for conveying the chemical signals that regulate growth and functions. From a certain perspective, these features are analogous to the contacts, interconnections, devices, and wires of discrete and integrated electronic circuits. Although many attempts have been made to augment plant function with electroactive materials, plants' "circuitry" has never been directly merged with electronics. We report analog and digital organic electronic circuits and devices manufactured in living plants. The four key components of a circuit have been achieved using the xylem, leaves, veins, and signals of the plant as the template and integral part of the circuit elements and functions. With integrated and distributed electronics in plants, one can envisage a range of applications including precision recording and regulation of physiology, energy harvesting from photosynthesis, and alternatives to genetic modification for plant optimization.

Keywords: conducting polymers; organic bioelectronics; plants.

Fig. 1. Basic plant physiology and analogy to electronics.

(A and B) A plant (A), such as a rose, consists of roots, branches, leaves, and flowers similar to (B) electrical circuits with contacts, interconnects, wires, and devices. (C) Cross section of the rose leaf. (D) Vascular system of the rose stem. (E) Chemical structures of PEDOT derivatives used.

Fig. 2. Electronically conducting xylem wires.

(A) Forming PEDOT-S:H wires in the xylem. A cut rose is immersed in PEDOT-S:H aqueous solution, and PEDOT-S:H is taken up and self-organizes along the xylem forming conducting wires. The optical micrographs show the wires 1 and 30 mm above the bottom of the stem (bark and phloem were peeled off to reveal the xylem). (B) Scanning electron microscopy (SEM) image of the cross section of a freeze-dried rose stem showing the xylem (1 to 5) filled with PEDOT-S:H. The inset shows the corresponding optical micrograph, where the filled xylem has the distinctive dark blue color of PEDOT. (C) SEM images (with corresponding micrograph on the left) of the xylem of a freeze-dried stem, which shows a hydrogel-like PEDOT-S structure.

Fig. 3. Electrical characterization of xylem wires.

(A) Schematic of conductivity measurement using Au probes as contacts. (B) I-V characteristics of PEDOT-S xylem wires of different lengths: L₁ = 2.15 mm, L₂ = 0.9 mm, and L₃ = 0.17 mm. The inset shows resistance versus length/area and linear fit, yielding a conductivity of 0.13 S/cm.

Fig. 4. Xylem transistors and digital logic.

(A) Output characteristics of the xylem-OECT. The inset shows the xylem wire as source (S) and drain (D) with gate (G) contacted through the plant tissue. (B) Transfer curve of a typical xylem-OECT for V_D = −0.3 V (solid line, linear axis; dashed line, log axis). (C) Temporal response of I_D and I_G relative to increasing V_G. (D) Logical NOR gate constructed along a single xylem wire. The circuit diagram indicates the location of the two xylem-OECTs and external connections (compare with circuit in Fig. 1B). Voltage traces for V_in1, V_in2, and V_out illustrate NOR function. The dashed lines on the V_out plot indicate thresholds for defining logical 0 and 1.

Fig. 5. PEDOT-infused leaves.

(A) Vacuum infiltration. Leaf placed in PEDOT:PSS–NFC solution in a syringe with air removed. The syringe is pulled up, creating negative pressure and causing the gas inside the spongy mesophyll to be expelled. (B) When the syringe returns to standard pressure, PEDOT:PSS–NFC is infused through the stomata, filling the spongy mesophyll between the veins. (C and D) Photograph of the bottom (C) and cross section (D) of a pristine rose leaf before infiltration. (E and F) Photograph of the bottom (E) and cross section (F) of leaf after PEDOT:PSS–NFC infusion.

Fig. 6. Electrochromism in PEDOT:PSS–NFC–infused leaf.

(A and B) Optical micrographs of the infused leaf upon application of (A) +15 V and (B) −15 V. Movie S1 shows a video recording of these results. (C and D) False color map of change in grayscale intensity between application of (C) +15 V and (D) −15 V. Green represents a positive increase in grayscale value (light to dark). (E and F) Grayscale values of pixel intensity along the lines indicated in (C) and (D) showing successive oxidation/reduction gradients. A plot of the change in grayscale intensity over a fixed line showing the change and oxidation/reduction gradations versus distance. a.u., arbitrary unit.

Fig. 7. Leaf OECD.

(A) Visualization of the electric field in the leaf-OECD via the induced electrochromic gradient directions [cf. study by Said et al. (30)]. (B) Electrical schematic representation of n-compartments modeling both electronic and ionic components of the current.