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BEIJING, June 8 (Xinhua) -- Researchers at Sweden's Karolinska Institutet have developed a miniature sensor that can detect pesticides on fruits within minutes. The proof-of-concept technology, described in a paper in the journal Advanced Science, uses flame-sprayed nanoparticles made of silver to enhance the signal of chemicals. Researchers hope these nanosensors will help people detect pesticide residues before they eat them.

Up to half of all fruits sold in the European Union contain significant amounts of pesticide residues linked to human health problems, according to George Sotterio, principal investigator in the Department of Microbiology, Oncology and Cell Biology at Karolinska Medical School. However, the current technology used to detect pesticide residues on a single product before consumption, with associated sensors that are costly and cumbersome to manufacture, is limited in practice. To overcome this problem, researchers have developed inexpensive and reusable nanosensors for monitoring pesticide residues in fruits on sale.

The new nanosensor employs surface-enhanced Raman scattering (SERS) technology, which can enhance the signal of biomolecules on metal surfaces by more than one million times. The researchers created a SERS nanosensor this time by using flame spraying, a well-established and cost-effective technique for depositing metal coatings, to deliver small droplets of silver nanoparticles to a glass surface. Flame spraying rapidly produces uniform SERS films over large areas, eliminating one of the key barriers to scalability.

The researchers then fine-tuned the distance between individual silver nanoparticles to improve their sensitivity. To test their detection capabilities, they coated the top of the sensors with a thin layer of tracer dye and used a spectrometer to reveal their molecular fingerprints. The study showed that the sensors reliably and uniformly detected molecular signals and that their performance remained unchanged when tested again after 2.5 months, demonstrating their durability and the feasibility of mass production.

To test the sensors for practical applications, the researchers calibrated them to detect low concentrations of parathion-ethyl, a toxic agricultural pesticide that is banned or restricted in most countries. The researchers placed a small amount of parathion-ethyl on an apple and subsequently collected the residue with a cotton swab that was dipped into the solution to dissolve the pesticide molecules. After the solution was dropped on the sensor, the sensor could detect the pesticide residue within five minutes without damaging the fruit.

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