Nano-sensors detect pesticides on fruit

The technique uses flame-sprayed nanoparticles made from silver to increase the signal of chemicals.

“Reports show that up to half of all fruits sold in the EU contain pesticide residues that in larger quantities have been linked to human health problems,” said Georgios Sotiriou, the study’s corresponding author.

“However, current techniques for detecting pesticides on single products before consumption are restricted in practice by the high cost and cumbersome manufacturing of its sensors. To overcome this, we 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 employ a 1970s discovery known as surface-enhanced Raman scattering (SERS), a powerful sensing technique that can increase the diagnostic signals of biomolecules on metal surfaces by more than a million times.

High production costs and limited batch-to-batch reproducibility have so far hindered widespread application of SERS in food safety diagnostics.

In the current study, the researchers created a SERS nano-sensor by using flame spray – a cost-effective technique for depositing metallic coating – to deliver small droplets of silver nanoparticles onto a glass surface.

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

The researchers then fine-tuned the distance between the individual silver nanoparticles to enhance their sensitivity.

To test their substance-detecting ability, they applied a thin layer of tracer dye on top of the sensors and used a spectrometer to uncover their molecular fingerprints. The sensors reliably detected the molecular signals and their performance remained intact when tested again after 2.5 months, which underscores their shelf life potential and feasibility for large-scale production, according to the researchers.

To test the sensors’ practical application, the researchers calibrated them to detect low concentrations of parathion-ethyl, a toxic agricultural insecticide that is banned or restricted in most countries.

A small amount of parathion-ethyl was placed on part of an apple. The residues were later collected with a cotton swab that was immersed in a solution to dissolve the pesticide molecules. The solution was dropped on the sensor, which confirmed the presence of pesticides.

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

The researchers now want to explore whether the nano-sensors can be applied to other areas such as discovering biomarkers for specific diseases at the point of care in resource-limited settings.