Pierceable, Water-Resistant, and Transparent Nanofilm Electrodes Comprising Carbon Nanotubes for Long-Term Monitoring of Plant Electrophysiology.

Trichomes are found on the surfaces of many crops, making it challenging to design sensors that monitor plant conditions without interfering with their natural functions. Notably, conventional and advanced electrodes developed for plant electrophysiology have not overcome this challenge. Herein, we present thin-film composite electrodes that are transparent, water-vapor-permeable, water-resistant, non-invasive, pierceable by trichomes, and conformal to the complex surfaces of leaves, ensuring low contact impedance without the need for adhesives. The bilayer electrodes (referred to as "nanofilm electrodes") are composed of single-walled carbon nanotubes (SWCNTs) deposited on poly(styrene-b-butadiene-b-styrene), and the thickness is varied (70-480 nm) to evaluate its influence. Furthermore, the sensing performance and long-term stability are compared with those of commercial wet electrodes and conventional poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) electrodes. The proposed SWCNT nanofilm electrodes enable stable detection of electrophysiological changes in leaves for over 2 months, as well as light-induced biopotential signals under chemical stress, highlighting their potential for long-term, real-time plant health monitoring in smart agriculture systems.