The 'plant-wearable' pesticide sensor

Researchers at the University of São Paulo (USP) and the Federal University of Viçosa (UFV) in Brazil have developed a ‘plant-wearable’ sensor that can be placed directly on the surface of a vegetable or fruit to detect the presence of pesticides.

The analytical tools most often used to monitor pesticide levels in food use chromatographic techniques, which are effective but have drawbacks such as the need for pretreatment of samples, expensive equipment and qualified laboratory specialists, as well as the long time taken to complete the analysis and lack of portability. The residues produced by organic solvents are also a problem under present-day conditions.

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

The researchers used cellulose-acetate, a plant-derived material that is biodegradable and has little impact on the environment. Derived from wood pulp, the cellulose acetate substrate was produced by a casting method in which the material was placed in a space with the required shape and the full electrochemical system with three electrodes was deposited by screen printing.

To simulate a real-world example, a solution containing carbendazim (a fungicide) and paraquat (a herbicide) was sprayed on lettuce and tomatoes. The sensor was then directly attached to the lettuce and tomatoes and measurements showed a level of detection compatible with those obtained with polyethylene terephthalate, the material most frequently used for this purpose.

The researchers also washed the vegetables in water for two hours to test whether it was effective to remove pesticide residues. Water was found to remove 40% of the carbendazim and 60% of the paraquat from lettuce and 64% of both from tomatoes.

The technology has potential applications for sanitary surveillance agencies and sellers of organic produce to certify the absence of pesticides. Farmers could also use it to monitor levels of pesticides in the field.

An article on the results of the study has been published in Biomaterials Advances.

Image credit: Paulo Augusto Raymundo Pereira