Barbosa Júlia A, Freitas Vitoria M S, Vidotto Lourenço H B, Schleder Gabriel R, de Oliveira Ricardo A G, da Rocha Jaqueline F, Kubota Lauro T, Vieira Luis C S, Tolentino Hélio C N, Neckel Itamar T, Gobbi Angelo L, Santhiago Murilo, Lima Renato S
Brazilian Nanotechnology National Laboratory, Brazilian Center for Research in Energy and Materials, Campinas, São Paulo 13083-970, Brazil.
São Carlos Institute of Chemistry, University of São Paulo, São Carlos, São Paulo 09210-580, Brazil.
ACS Appl Mater Interfaces. 2022 Mar 21. doi: 10.1021/acsami.2c02943.
Impedimetric wearable sensors are a promising strategy for determining the loss of water content (LWC) from leaves because they can afford on-site and nondestructive quantification of cellular water from a single measurement. Because the water content is a key marker of leaf health, monitoring of the LWC can lend key insights into daily practice in precision agriculture, toxicity studies, and the development of agricultural inputs. Ongoing challenges with this monitoring are the on-leaf adhesion, compatibility, scalability, and reproducibility of the electrodes, especially when subjected to long-term measurements. This paper introduces a set of sensing material, technological, and data processing solutions that overwhelm such obstacles. Mass-production-suitable electrodes consisting of stand-alone Ni films obtained by well-established microfabrication methods or ecofriendly pyrolyzed paper enabled reproducible determination of the LWC from soy leaves with optimized sensibilities of 27.0 (Ni) and 17.5 kΩ % (paper). The freestanding design of the Ni electrodes was further key to delivering high on-leaf adhesion and long-term compatibility. Their impedances remained unchanged under the action of wind at velocities of up to 2.00 m s, whereas X-ray nanoprobe fluorescence assays allowed us to confirm the Ni sensor compatibility by the monitoring of the soy leaf health in an electrode-exposed area. Both electrodes operated through direct transfer of the conductive materials on hairy soy leaves using an ordinary adhesive tape. We used a hand-held and low-power potentiostat with wireless connection to a smartphone to determine the LWC over 24 h. Impressively, a machine-learning model was able to convert the sensing responses into a simple mathematical equation that gauged the impairments on the water content at two temperatures (30 and 20 °C) with reduced root-mean-square errors (0.1% up to 0.3%). These data suggest broad applicability of the platform by enabling direct determination of the LWC from leaves even at variable temperatures. Overall, our findings may help to pave the way for translating "sense-act" technologies into practice toward the on-site and remote investigation of plant drought stress. These platforms can provide key information for aiding efficient data-driven management and guiding decision-making steps.
阻抗式可穿戴传感器是一种很有前景的用于测定叶片水分含量损失（LWC）的策略，因为它们能够通过单次测量对细胞水分进行现场且无损的定量分析。由于水分含量是叶片健康的关键指标，监测LWC能够为精准农业、毒性研究以及农业投入品开发的日常实践提供关键见解。这种监测目前面临的挑战包括电极在叶片上的附着力、兼容性、可扩展性和可重复性，尤其是在进行长期测量时。本文介绍了一系列能够克服这些障碍的传感材料、技术和数据处理解决方案。通过成熟的微加工方法获得的独立镍膜或环保型热解纸制成的适合大规模生产的电极，能够以优化后的灵敏度27.0（镍）和17.5 kΩ %（纸）对大豆叶片的LWC进行可重复测定。镍电极的独立式设计对于实现高叶片附着力和长期兼容性至关重要。在风速高达2.00 m/s的风作用下，它们的阻抗保持不变，而X射线纳米探针荧光分析使我们能够通过监测电极暴露区域的大豆叶片健康状况来确认镍传感器的兼容性。两种电极都是通过使用普通胶带将导电材料直接转移到多毛大豆叶片上来操作的。我们使用了一种手持且低功率的恒电位仪，并通过无线连接到智能手机来在24小时内测定LWC。令人印象深刻的是，一个机器学习模型能够将传感响应转化为一个简单的数学方程，该方程能够在两个温度（30和20°C）下测量水分含量的损伤情况，且均方根误差降低（0.1%至0.3%）。这些数据表明该平台具有广泛的适用性，即使在不同温度下也能直接测定叶片的LWC。总体而言，我们的研究结果可能有助于为将“传感 - 行动”技术转化为实践铺平道路，以实现对植物干旱胁迫的现场和远程调查。这些平台可以提供关键信息，以帮助进行高效的数据驱动管理并指导决策步骤。
