This Low-Cost Paper-Based Sensor Provides a Warning About Pesticides on Your Fruit and Vegetables

Researchers from the University of São Paulo (USP) have developed a paper-based sensor which, they say, can help detect pesticides on fruits and vegetables before they're consumed — proving the concept by applying the smart label sensor to apples and cabbages.

"Wearable sensors such as those made with paper are needed for non-destructive routine analysis of pesticides on plants, fruits, and vegetables," the researchers explain in the abstract to their paper on the topic. "Herein we report on electrochemical sensors made with screen-printed carbon electrodes on kraft and parchment papers to detect the fungicide carbendazim."

Frequently used to protect cereal and fruit crops around the world, as well as for treating non-edible plants including elm trees and lawns, carbendazim has been shown to cause infertility and even destroy the testicles of lab animals in high doses — meaning that cutting down on its consumption is advisable. Knowing what fruit still contains high doses of carbendazim at the point of sale or consumption is tricky without destroying the fruit for testing — which is where the team's paper-based sensor comes in.

"To find out whether a food sample contains traces of pesticides by conventional methods, you must grind up the sample and submit it to time-consuming chemical processes before any such substances can be detected," co-author Osvaldo Novais de Oliveira Junior explains in an interview with Maria Fernanda Ziegler of Agência FAPESP, which supported the research. "Wearable sensors like the one we developed for continuous monitoring of pesticides in agriculture and the food industry eliminate the need for these complex processes. Inspection is much easier, cheaper and reliable for a supermarket, restaurant or importer, for example."

The sensor developed by the researchers uses a kraft or parchment paper substrate which is screen-printed with carbon electrodes to form an electrochemical sensor then treated in an acidic medium to improve its response. Once treated, the kraft paper variant of the sensor proved capable of detecting carbendazim levels as low as 0.06µM — well below the common maximum pesticide residue limit of 0.1mg/kg for citrus and pome fruits, and on a par with gold-standard destructive approaches — with the results read via smartphone app.

The team's work has been published in the journal Food Chemistry under closed-access terms, with more information available in the Agência FAPESP announcement.