14 August 2023

Inexpensive nanosensors can detect pesticides in orange juice, explain researchers at Karolinska Institutet in Stockholm. Experimentation has shown their efficacy and the possibility of massive production

by Matteo Cavallito


Is it possible to use nanosensors to detect the presence of pesticides or other harmful substances in food? And is it possible, at the same time, to make this technology widely available to the public by drastically reducing its production costs? Surely it is, say Georgios Sotiriou and Haipeng Li, two researchers from the Department of Microbiology at Karolinska Institutet of Stockholm who, in a recent study, outlined a new system for making a large number of decidedlyeffective detectors in the laboratory.

The investigation, explains a statement from the Swedish university, thus demonstrated “the scalability and cost-effectiveness of the aerosol manufacturing strategy democratizing these sensors for practical applications.”

A system based on nanoparticles

The two scientists’ study follows a previous work in which they demonstrated the theoretical validity of a production method based on the “flame aerosol deposition” technique. The researchers, on that occasion, had pointed out how it was possible to atomize a solution based on silver and silicon into droplets. Subsequent combustion of the droplets themselves generated the nanoparticles, which were deposited directly on a glass substrate.

Such a substrate, enriched by the new nanostructure, can be used for a spectroscopic analysis known as SERS (surface-enhanced Raman scattering), This investigation, oversimplifying as much as possible, allows for the detection of the chemical composition of a substance i.e., the presence of certain specific molecules. Including those of pesticides.

Production runs at the rate of more than one sample per minute

“Although surface-enhanced Raman scattering (SERS) technique can rapidly and reliably detect pesticide residues, its application in food safety diagnostics is restricted by its high expense, low scalability, and low reproducibility of the necessary sensors,” the study says. “Herein, we present a low-cost, large-scale, and highly reproducible nanofabrication route for SERS nano-sensors.”

The authors tested the creation of the substrates through the aerosol deposition technique by achieving an extremely favorable production rate: 100 samples per hour. Even more important are the results that emerged from the tests. “Our highly sensitive SERS substrates rapidly and quantitatively detected pesticide residues in fresh orange, indicating their practical applicability for food safety diagnostics,” the researchers explain.

Pesticides in oranges do not escape detection

To evaluate the effectiveness of detection, the authors dissolved a particularly toxic (and today banned in many countries) pesticide known as Parathion in orange juice. The substance was added at various times in widely varying concentrations ranging from 0.1 to 100 parts per million.

“Initially, 2 µL of the orange juice was dropped on the SERS substrate and allowed to dry before the Raman measurements,” the researchers explain. “Raman peaks corresponding to parathion-ethyl were observed, indicating pesticide presence down to 0.1 ppm, demonstrating a SERS sensing performance comparable to that reported in the literature.”

The downward limit is particularly significant. In fact, the minimum detected concentration of 0.1 parts per million is one-tenth of the maximum threshold set by the U.S. Department of Agriculture in regulating the presence of Parathion in food.

Rilevamento rapido e quantitativo dei residui di pesticidi nei succhi di frutta. (a) Deposizione di molecole di pesticidi mirati sulla superficie del substrato SERS. (b) Spettri SERS del Paration nel succo d'arancia fresco alle frazioni volumetriche di 100 ppm, 10 ppm, 1 ppm e 0,1 ppm (dal basso verso l'alto). (c) Grafico Log-Log delle intensità medie dei picchi in funzione della frazione volumetrica di paration-etile nel succo d'arancia. Tutti i dati sono rappresentati come valori medi ± SD. Fonte: Haipeng Li et al., "Democratizing robust SERS nano-sensors for food safety diagnostics" https://www.sciencedirect.com/science/article/pii/S1385894723027547?via%3Dihub, Chemical Engineering Journal Volume 470, 15 August 2023, 144023 Attribuzione 4.0 Internazionale (CC BY 4.0)

Rapid and quantitative detection of pesticide residues in fruit juices. (a) Deposition of targeted pesticide molecules on the SERS substrate surface. (b) SERS spectra of parathion-ethyl in fresh orange juice at the volume fractions of 100 ppm, 10 ppm, 1 ppm, and 0.1 ppm (from bottom to top). (c) Log-Log plot of the averaged peak intensities  as a function of the parathion-ethyl volume fraction in orange juice. All data are represented as mean values ± SD. Source: Haipeng Li et al., “Democratizing robust SERS nano-sensors for food safety diagnostics”, Chemical Engineering Journal Volume 470, 15 August 2023, 144023
Attribuzione 4.0 Internazionale (CC BY 4.0)

Monitoring pesticides is critical for food security

Excessive use of pesticides in agriculture, the authors point out, is still a particularly significant problem with obvious impacts on human health. “As a result,” the authors say, “iit is necessary to control the pesticide residue levels in food below safety limits.” Encouraging the production of low-cost and therefore readily available detectors therefore becomes crucial.

This is also why the scientists said they are seeking new international collaborations. Moreover, they “will also expand the application of our nano-sensors from detecting single pesticides to the mixed pesticides“, i.e., those combinations of multiple chemicals that can increase the toxicity of a product.