Researchers at Karolinska Institutet in Sweden have developed a tiny sensor to detect pesticides in fruits in just a few minutes. The approach, described as a proof-of-concept in the journal Advanced Science, uses flame-sprayed silver nanoparticles to amplify the chemical signal. While the research is still in its infancy, the researchers believe these nano-sensors could detect pesticides in foods before they're consumed.
"Reports show that more than half of all fruits sold in the EU contain pesticide residues that are more linked to human health problems," explains Georgios Sotiriou, principal investigator in Karolinska Institutet's Department of Microbiology, Tumor and Cell Biology.
“On the other hand, current methods for detecting pesticides in single crops before consumption are limited in practice due to the high cost and time-consuming manufacture of sensors. To address this, we have created low-cost, repeatable nano-sensors. For example, it can be used to monitor pesticide residues in fruit in a supermarket.”
The new nanosensors use surface-enhanced Raman scattering, or SERS, a powerful sensing technology that can amplify the diagnostic signals of biomolecules on metal surfaces by more than 1 million times. In addition to chemical and environmental studies, the detection of biomarkers for various diseases has also benefited from the method. However, high production costs and limited batch-to-batch consistency have so far limited their use in food safety diagnostics.
Use of Flame Spray Technologies
In this study, the researchers used a flame spray to deposit tiny droplets of silver nanoparticles on a glass surface to create a SERS nanosensor. Flame spraying is an established and cost-effective approach to coating metallic coatings.
“Flame spray can be used to rapidly produce coherent SERS films over large areas, removing one of the main barriers to scalability,” says Haipeng Li, first author of the study and postdoctoral researcher on Sotiriou's team.
To increase the sensitivity of the silver nanoparticles, the researchers fine-tuned the spacing between them. To test their substance-detection abilities, they applied a small layer of tracer paint over the sensors and then used a spectrometer to reveal their molecular fingerprints. According to the researchers, the sensors correctly and properly identified the chemical signals, and their function remained unchanged after 2,5 months of testing, indicating that they have a long shelf life and are suitable for large-scale production.
Pesticides Discovered in Apples
The researchers calibrated the sensors to detect low amounts of parathion-ethyl, a dangerous agricultural insecticide that has been banned or restricted in most countries to evaluate its practical applications. A small amount of parathion-ethyl was applied to a portion of the apple. The residues were then collected using a cotton swab dipped in a solution to break up the pesticide molecules. Pesticide was detected when the solution was sprayed on the sensor.
“Without damaging the fruit, our sensors can detect pesticide residues on the apple surface within five minutes,” says Haipeng Li. “Although larger studies are needed to validate them, we provide a viable application of proof-of-concept for food safety testing at scale before consumption.”
The researchers now want to see if nano-sensors can be used in other areas, such as finding biomarkers for certain diseases at the point-of-care in resource-constrained environments.