Researchers at Sweden’s Karolinska Institutet have created a small sensor that can detect pesticides on fruit in just a few minutes.

The approach, which was described as a proof-of-concept in the journal Advanced Science, uses flame-sprayed silver nanoparticles to boost the chemical signals.

While the research is still in its early stages, the researchers believe that these nano-sensors will be able to detect pesticides in food before they are consumed.

Up to half of all fruits marketed in the EU have pesticide residues that in bigger proportions have been related to human health concerns, says Georgios Sotiriou, the study’s corresponding author.

However, present methods for detecting pesticides on specific products prior to consumption are limited in practice due to the high cost and time-consuming fabrication of its sensors.

“To overcome this,” adds Sotiriou, they have “developed inexpensive and reproducible nano-sensors that could be used to monitor traces of fruit pesticides at, for example, the store.”

The new nano-sensors utilize a discovery from the 1970s known as surface-enhanced Raman scattering, or SERS, a potent sensing technology capable of amplifying diagnostic signals of biomolecules on metal surfaces by more than one million times. Chemical and environmental studies, as well as the detection of biomarkers for various diseases, have all benefited from the method. High production costs and limited batch-to-batch consistency have, however, limited their use in food safety diagnostics so far.

The use of a flame spray

The researchers used flame spray to deposit small droplets of silver nanoparticles onto a glass surface to build a SERS nano-sensor in this study. Flame spray is a well-established and cost-effective approach for depositing metallic coatings.

According to Haipeng Li, the study’s first author, “The flame spray can be used to quickly produce uniform SERS films across large areas, removing one of the key barriers to scalability.”

Then, to make the silver nanoparticles more sensitive, the researchers adjusted the distance between each one. They employed a spectrometer to expose their molecular fingerprints after applying a tiny layer of tracer dye on top of the sensors to test their substance-detecting ability. According to the researchers, the sensors accurately and uniformly detected chemical signals, and their function remained unchanged when tested again after 2,5 months, demonstrating their shelf life potential and viability for large-scale manufacture.

Apple Test

The researchers calibrated the sensors to detect low quantities of parathion-ethyl, a hazardous agricultural insecticide that is prohibited or restricted in most countries, to evaluate their practical application. On a portion of an apple, a small amount of parathion-ethyl was applied. Later, the residues were collected using a cotton swab soaked in a solution to break down the pesticide molecules. Dropping the fluid onto the sensor revealed the presence of pesticides.

These “sensors can detect pesticide residues on apple surfaces in a short time of five minutes without destroying the fruit,” adds Haipeng Li.

“While they need to be validated in larger studies, we offer a proof-of-concept practical application for food safety testing at scale before consumption.”

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