Abstract
The boom of plant phenotype highlights the need to measure the physiological characteristics of an individual plant. However, continuous real‐time monitoring of a plant's internal physiological status remains challenging using traditional silicon‐based sensor technology, due to the fundamental mismatch between rigid sensors and soft and curved plant surfaces. Here, the first flexible electronic sensing device is reported that can harmlessly cohabitate with the plant and continuously monitor its stem sap flow, a critical plant physiological characteristic for analyzing plant health, water consumption, and nutrient distribution. Due to a special design and the materials chosen, the realized plant‐wearable sensor is thin, soft, lightweight, air/water/light‐permeable, and shows excellent biocompatibility, therefore enabling the sap flow detection in a continuous and non‐destructive manner. The sensor can serve as a noninvasive, high‐throughput, low‐cost toolbox, and holds excellent potentials in phenotyping. Furthermore, the real‐time investigation on stem flow insides watermelon reveals a previously unknown day/night shift pattern of water allocation between fruit and its adjacent branch, which has not been reported before.
Highlights
In this work, monitoring the sap flow is based on measurements of spatial anisotropy in thermal transport along the plant stem resulted from the flow
When there is a sap flow in the stem, since thermal transport is more efficient along the flow direction, an anisotropic temperature distribution occurs, which can be monitored by the two temperature sensors, thereby allowing the analysis of the sap flow rate
Sap flow symbolizes the translocation of plant food, including water, nutrition, and photosynthetic product, which contributes largely to the growth of plant shoot parts.[9,39]
Summary
In this work, monitoring the sap flow is based on measurements of spatial anisotropy in thermal transport along the plant stem resulted from the flow. The whole multilayer structure with serpentine Cu tracks is very thin (≈20 μm), provides an extremely low effective elastic moduli, large deformability, and stretchability, allowing the sap flow sensor to adapt to the contour surfaces and time-variate growth of the plant. A thin Cu film (6 μm) supported by a glass slide was pattern into the serpentine tracks via a direct laser cutting technique. The above fabrication based on direct laser cutting technique is more efficient and faster than the conventional photolithography approach in preparing flexible electronic devices. Further information about the sensing system’s integration is provided in the Supporting Information (Figure S2, Supporting Information)
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