Researchers at the São Carlos Institute of Physics at the University of São Paulo (IFSC-USP) in Brazil, led by Paulo Augusto Raymundo-Pereira , have created biodegradable, "wearable" sensors for plants to monitor their health, including the presence of pesticides. The sensors are made from carbon ink and are screen-printed onto transparent cellulose acetate bioplastics.
The study was published in Biosensors and Bioelectronics: X. The World Economic Forum selected wearable sensor engineering as one of the top ten emerging technologies of 2023 for its potential to improve plant health and increase agricultural productivity. However, most wearable devices today are made from non-renewable plastic polymers derived from petroleum and have poor adhesion to uneven, wavy, and curved surfaces.
"Our sensor, on the other hand, is made of cellulose acetate, a flexible, plant-based material that can be produced from various agricultural waste streams. Cellulose is the most abundant natural polysaccharide on Earth. It offers exceptional biocompatibility, high thermal stability, and flexibility. It's non-toxic, economical, affordable, biodegradable, lightweight, and easy to handle," Raymundo-Pereira summarizes.
According to him, these miniaturized sensors can be attached directly to various parts of plants, including stems, bark, and leaves, to monitor temperature, humidity, dehydration, biomarkers, diseases, nutrient levels, and the presence of pesticides. "They enable non-destructive, rapid, on-site, and decentralized detection, providing real-time bioinformation on the health of the plant and environmental factors."
Each cellulose acetate platform has two sensor units that use different analytical techniques to detect three classes of pesticides (diquat, carbendazim, and diphenylamine) in a single analysis. One sensor unit uses square-wave voltammetry (SWV) to detect diquat, and the other uses differential pulse voltammetry (DPV) to analyze carbendazim and diphenylamine.
According to Raymundo-Pereira, each sensor costs 0.077 cents. "The sensors are single-use. Therefore, they must be inexpensive and biodegradable. Considering the operation of the two sensors in sequence on the same sample, the device takes three minutes and twenty-eight seconds to perform all measurements."
Identification is performed on the surface of the plant, but in an aqueous medium (a drop of water) since the measurements are taken at the interface between the electrode and the medium. "We need this aqueous solution for conductivity. In the case of wearable sensors, the drop of water is placed in the spots where it's easiest to take the measurement. In the center of the leaves, in the small depression that forms on the stem of a tomato or apple, in the lateral grooves of a bell pepper, where water can also accumulate. Then, simply place the sensors, position them over the droplet, and measure."
The platform containing the dual wearable sensor is integrated with a commercial wireless portable potentiostat, enabling rapid pesticide assessment and real-time analysis display on a cell phone via bluetooth. The team had already created a glove with sensors on the fingertips for the same purpose in 2022 (read more at agencia.fapesp.br/37874 ).
"The wearable sensor has the advantage of being applied directly to the sample, since the acetate can take on the shape of the surface on which it's placed, whereas the glove must be handled. Furthermore, the glove is made of a material that isn't biodegradable, while the wearable sensor is fully biodegradable – and reusable for making new sensors," the scientist explains. According to him, it is possible to burn used sensors under specific conditions and thus obtain the carbon ink to produce new devices.
FAPESP supported the work through a Postdoctoral Fellowship awarded to Nathália Oeazu Gomes , a Regular Research Grant awarded to Sergio Antônio Espínola Machado , and Fellowship for Fixating Young Doctors awarded to Raymundo-Pereira.
Other uses
The wearable sensors were tested on plants after a 1,000 μM agrochemical solution was sprayed onto the skin of apples and bell peppers. The fruits were then left to dry for five hours. This procedure simulated real-world applications. On-site analyses of the pesticide were performed by attaching the sensor directly to the surface of the fruit with the addition of 500 μL of phosphate buffer solution.
As Raymundo-Pereira points out, wearable sensor technology lends itself to a multitude of applications. "It's possible to detect the presence of pesticides in people's saliva, or even in tap water. We did the tests. Samples of human saliva and tap water were spiked with pesticides and analyzed with the sensor to predict residue levels. The technology is very useful in the health sector and can, for example, be used to analyze components present in urine and sweat," the researcher reveals.
Raymundo-Pereira had the idea to adapt the technology for agricultural use after an internship with Professor Joseph Wang at the Center for Wearable Sensors at the University of California, San Diego (United States). "Since a large portion of Brazil's GDP is concentrated in the agricultural sector, I thought, 'Why not adapt the technology?' Abroad, its use is focused on humans. It's applied to the skin to determine what's in people's sweat, for example. It can detect lactic acid, uric acid, glucose, cortisol, sodium ions, potassium ions, chloride ions, hormones, and medications. But these sensors used on humans are made of petrochemical-based plastic. The first biodegradable ones made from natural sources are ours, and they can be adapted for human use."
Patent applications for the glove and wearable sensor have been filed with the National Institute of Intellectual Property (INPI).
The multidisciplinary team that developed the device also includes researchers Samiris Teixeira, Nilda de F. F. Soares, and Taíla de Oliveira from the Federal University of Viçosa.
About São Paulo Research Foundation (FAPESP)
The São Paulo Research Foundation (FAPESP) is a public institution with the mission of supporting scientific research in all fields of knowledge by awarding scholarships, fellowships and grants to investigators linked with higher education and research institutions in the State of São Paulo, Brazil. FAPESP is aware that the very best research can only be done by working with the best researchers internationally. Therefore, it has established partnerships with funding agencies, higher education, private companies, and research organizations in other countries known for the quality of their research and has been encouraging scientists funded by its grants to further develop their international collaboration. You can learn more about FAPESP at www.fapesp.br/en and visit FAPESP news agency at www.agencia.fapesp.br/en to keep updated with the latest scientific breakthroughs FAPESP helps achieve through its many programs, awards and research centers. You may also subscribe to FAPESP news agency at http://agencia.fapesp.br/subscribe.
