Biodegradable sensor monitors pesticide levels through direct contact with the surface of fruits and vegetables

Researchers from the University of São Paulo (USP) and the Federal University of Viçosa (UFV) in Brazil have developed a durable sensor that can be placed directly on the surface of a vegetable or fruit to detect the presence of pesticides. Known for this reason as “plantable”, it is made of cellulose acetate, a material derived from wood pulp.

This system has the potential to help ensure food security in a world that is increasingly suffering from food shortages and environmental and health problems caused by excessive use of agrochemicals.

The study is published in the journal Advances in biomaterials.

Pesticides are widely used to increase crop yields and are usually applied by spraying, but only 50% achieve their goal. The rest ends up in soil, groundwater, surface water, raw drinking water, wastewater and food products. Monitoring pesticide levels in water, soil and food is therefore essential to avoid any contact between these toxic substances and the public via the skin, lungs or digestive system.

The analytical tools most often used for this purpose are chromatographic techniques, which are effective but have disadvantages such as the need for sample pretreatment, expensive equipment and trained laboratory specialists, and the time required to perform the analysis and the lack of portability. . Hazardous residues produced by organic solvents are also a significant problem under current conditions.

“As an alternative, electrochemical sensors can combine affordability, rapid detection, miniaturization, large-scale production, convenience, ease of use, high selectivity and in situ pesticide detection. Our invention has all these characteristics. The analysis is carried out directly on the surface of fruits, vegetables or leaves. Hence the term “portable plant,” said Paulo Augusto Raymundo-Pereira, last author of the paper and researcher at the Institute of Physics of São Carlos ( IFSC-USP).

“However, instead of the usual environmentally unsustainable and slow-to-degrade materials like ceramic or petroleum-derived plastic polymers, we used cellulose acetate, a plant-derived material that has little environmental impact and disintegrates completely in 340 days or less depending on local conditions.Of course, it must have suitable characteristics for any sensor, including low cost, portability and flexibility.

The biodegradable cellulose acetate substrate was produced by a casting process in which the material was placed in a space with the required shape, and the complete three-electrode electrochemical system was deposited by screen printing.

The researchers conducted laboratory tests in which a solution containing carbendazim, a fungicide, and paraquat, a herbicide, was sprayed on lettuce and tomatoes in a simulation of real-world use. Paraquat was banned by the European Union in 2003 due to its harmful effects on humans, but it is still used in Brazil. The sensor was then attached directly to lettuce and tomatoes, and measurements showed a detection level consistent with those obtained with polyethylene terephthalate, the sensor material most frequently used for this purpose.

Excessive levels of pesticides

The study also examined whether washing and submerging vegetables in a liter of water for two hours was effective in removing pesticide residue. Results showed the removal of 40% of carbendazim and 60% of paraquat from lettuce, and 64% of both from tomatoes.

“Washing and immersion were clearly insufficient to remove pesticide residue. At least 10% remained in the leaves or skin,” Raymundo-Pereira said.

The technology can be useful to health monitoring agencies around the world, he added, as well as sellers of organic produce to certify the absence of pesticides. Farmers can generally use it to monitor pesticide levels in the field and be sure to apply only the required dose to each crop or part of a planting. Pesticide use could therefore decrease, while yields would continue to increase, leading to lower consumer prices.