Wearable sensors are increasingly present in the lives of people who use electronic devices to monitor heart rate during physical activities and sleep quality, among many other patterns sensitive to human health.

Similar devices are being designed to deepen plant health monitoring in search of useful applications for precision farming.

This type of technology is a promising strategy to determine the loss of water content of the leaves, as they can provide on-site and nondestructive quantification of the liquid inside the cells from a single measurement.

Because water content is an important marker of leaf health, real-time monitoring can provide valuable data to guide management in precision agriculture, as well as for toxicity studies and development of new agricultural insums.

"Conventional methods have limitations because they are based on imaging systems, satellites and drones. They need the plant attacked by a disease to show phenotypic signs or visual cues to generate alerts in monitoring. In crops such as soybeans, for example, the change in color can signal an irreversible stage of diseases such as rust," explains Renato Sousa Lima, a researcher at the National Nanotechnology Laboratory (LNNano), an agency that is part of the National Center for Research in Energy and Materials (CNPEM), based in Campinas.

Complex sensor manufacturing

Despite technological advances in this area, the manufacture of suitable electrodes for plant monitoring carries challenges. The materials need to be light, flexible and able to adhere to the surface of the leaves, covered with trichas, by which they protect against insects and contribute to reduce water loss. In addition, they need to be biocompatible, that is, they cannot harm the biological processes of plant development.

Overcoming all these challenges from a device was described in the article Biocompatible Wearable Electrodes on Leaves toward the On-Site Monitoring of Water Loss from Plants, recently published in the journal ACS Applied Materials & Interfaces.

The study, which used as samples soybean and sugarcane plants, is the result of a project supported by Fapesp. The investigation mobilized a multidisciplinary team, which includes researchers from the State universities of Campinas (Unicamp), Federal abc (UFABC) and Harvard (United States), as well as specialists and resources from LNNano, the National Biorenewable Laboratory (LNBR) and the Carnaúba research station of Sirius.

The project also had resources from the Ministry of Science, Technology and Innovations (MCTI) and the National Council for Scientific and Technological Development (CNPq).

How the sensor works

The device developed in Campinas uses an electrode obtained by lithography. A single piece covered by a thin nickel film fixed with the help of a micropore adhesive. By this electrode is applied an electric field generated by a capacitor.

The polarization of nutrient ions present in water reveals with great sensitivity minimal variations in impedance, or electrical resistance, which are related to the plant's hydration levels.

"If there's more water, there's more ions, you load the system more, then the impedance decreases. If you have less water, less ions, you carry less system and impedance increases," lima explains.

Machine learning tools – an artificial intelligence technique – have helped to select, within a wide spectrum of frequencies, the most suitable for monitoring references. Between temperatures of 30 and 20°C, the precise parameters of quantification of water loss in leaves under different microclimate conditions were also used to determine, between temperatures of 30 and 20°C.

The acquisition of data collected by the devices is done by bluetooth, with the help of a smartphone, which allows automation of readings and remote monitoring over the Internet.

Patented innovation

The main advantages of the device developed in CNPEM are portability, battery life (ten days), sensitivity, biocompatibility and data acquisition security, which allow essential automations for remote monitoring. As there are no similar sensors on the market, the patent filing is already underway.

The manufacturing methods of the device are well known and are already available even in small industries, which creates conditions for scalability of production and potential reduction of the final price if any company is interested in the technology and decides to turn it into a product.

Sirius

In the study, techniques that make use of synchrotron radiation were used to evaluate in depth the biocompatibility conditions of the sensors in the leaves.

At Sirius's Carnaúba research station – the state-of-the-art electron accelerator installed at CNPEM – spectrometry measurements attest to the device's non-interference in the metabolism of soybean leaves and sugarcane.

Conventional techniques would not allow measuring nutrient concentrations with the sensitivity and accuracy necessary to ensure biocompatibility.

"In healthy leaves, zinc, manganese, calcium and iron ions, which are fundamental nutrients for both the structural part and transport, obey a morphological structure similar to that of capillaries, xylems and phloems. When the leaf is affected, the cells break and there is no more pattern," lima explains.

Next steps

At the current stage of development, the device proves to be quite efficient for use in controlled environments, but is also very promising for monitoring in outdoor environments. Partnerships with the industry can bring different demands for improvement.

"The device demonstrated high sensitivity for assessing the efficiency of the use of some management techniques or impact of the use of insums, as well as to potentially monitor crop productivity conditions. We believe that, with small adaptations, it could also contribute as an additional resource in monitoring the toxicological conditions of the field", says Julia Adorno Barbosa, phD and phD of LNNano and first author of the article.

Watch the technology illustrative video:

Source: Canal Rural