University of São Paulo (USP) researchers have developed a kraft paper-based electrochemical sensor that can detect traces of pesticides in fruit and vegetables.

This innovation works in “real time” when linked to an electronic device and the researchers say that, using an apple or cabbage as an example, the device can detect carbendazim, a banned fungicide that they claim is still used in Brazil.

“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,” said Osvaldo Novais de Oliveira Junior, an author of the article and a professor at IFSC-USP.

“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.”

The researchers claim that the new device is highly sensitive and resembles the glucometers used by diabetics to measure blood sugar, except that the results of food scanning for pesticides are displayed on a smartphone.

“In the tests we performed, its sensitivity was similar to the conventional methods. Plus, it’s fast and inexpensive,” said José Luiz Bott Neto, corresponding author of the article and a postdoctoral fellow at IFSC-USP.

The device itself consists of a paper substrate modified with carbon ink which is submitted to electrochemical treatment in an acid medium to activate carboxyl groups which makes detection possible.

“We use the silkscreen process to transfer carbon-conducting ink to a strip of kraft paper, thereby creating a device based on electrochemistry. It has three carbon electrodes and is immersed in an acidic solution to activate the carboxyl groups. In other words, oxygen atoms are added to the structure of the carbon electrode.

“When it comes into contact with a sample contaminated with carbendazim, the sensor induces an electrochemical oxidation reaction that permits detection of the fungicide. The quantity of carbendazim is measured via electrical current,” explained Bott Neto.

After developing the tool, the researchers evaluated the stability and structure of the paper substrate. Looking at kraft paper and parchment, the researchers found that both types of paper were “stable enough” to be used as a substrate for the sensor.

However, they noted that the porousness of kraft paper allowed for more sensitivity on the sensor and the carboxyl groups formed during electrochemical activation. Meanwhile more they found that paper-based electrodes could be used in “many applications”.

“There are commercial electrodes made of plastic or ceramic material. We successfully developed electrochemical sensors based on paper, a much more malleable material and therefore potentially useful in many areas, not just on farms or in supermarkets, but also in healthcare,” concluded Thiago Serafim Martins, first author of the article and a postdoctoral fellow at IFSC-USP