Development of electrical conductivity measurement technology for key plant physiological information using microneedle sensor

Abstract

Impedance measurement is a widely used technique for monitoring ion species in various applications. In plant cultivation, the impedance system is used to measure the electrical conductivity (EC) of nutrient solutions. Recent research has shown that the quality and quantity of horticultural crops, e.g. tomato, can be optimized by controlling the salinity of nutrient solutions. However, understanding the detailed response of a plant to a nutrient solution is not possible until the fruit is fully grown or by sacrificing the stem. To overcome this issue, horticultural crop cultivation requires real-time monitoring of the EC inside the stem. Using this data, the growth model of a plant could be constructed, and the response of the plant to external environment determined. In this paper, we propose an implantable microneedle device equipped with a micro-patterned impedance measurement system for direct measurement of the EC inside the tomato stem. The fabrication process includes silicon-based steps such as microscale deposition, photolithography, and a deep etching process. Further, microscale fabrication enables all functional elements to fulfill the area budget and be very accurate with minimal plant invasion. A two-electrode geometry is used to match the measurement condition of the tomato stem. Real-time measurement of local sap condition inside the plant in which real-time data for tomato sap EC is obtained after calibration at various concentrations of standard solution demonstrate the efficacy of the proposed device.

Emerging Technologies for Monitoring Plant Health in Vivo

“…A study by Jeon et al looked at measuring salinity, an important factor in plant health and crop yield. 24 They developed a real-time monitoring system to detect salinity in a nondestructive manner through electrical conductivity inside the stems of tomato plants. They designed a self-contained unit, including a microneedle electrode and electrode pad, that can be inserted into the stem of a tomato plant.…”

Design of composite microneedle sensor systems for the measurement of transdermal pH

“…Microneedle systems have been employed for various sensing purposes within plant physiology [31,32] but, this is the first report highlighting the use of composite patches for voltammetric sensing. While the work detailed here has demonstrated the capability of the MN systems for measuring pH, it is clear that the electroanalytical capabilities go beyond this initial…”

Robust, Long‐Term, and Exceptionally Sensitive Microneedle‐Based Bioimpedance Sensor for Precision Farming

“…[7] Borrowing a page from medicine, [8] minimally invasive microneedles (MNs) were developed to directly probe the relevant plant tissue, thereby bypassing the cuticle. As this approach gained traction, MNs were used for DNA extraction from leaves, [9] EIS measurement of plant tissue to probe the content of the EF [10,11] and to assess sap flow through the plant's stem. [12] Due to the breadth of their applications, several MN fabrication techniques were devised.…”