Screening for pesticides using magnetic nanoparticles

Materials World magazine
1 Apr 2018

The use of magnetic nanoparticles to extract synthetic pesticides can reduce the screening process by four hours. Khai Trung Le talks to Assistant Professor Yang Hongshun about his team’s new method.

A new method of screening for pesticides takes an unusual angle through the use of bespoke magnetic nanoparticles to simplify the extraction of pesticides, which lend the process high sensitivity and speed.

The technique, developed by scientists from the Food Science and Technology Programme at the National University of Singapore (NUS), focuses on synthetic pesticides, specifically pyrethorids, that are commonly used in vegetable farming. Synthetic pesticides are extensively used to control agricultural pests and thus improve crop yield, but the long-term effects of human ingestion may lead to adverse health.

Yang Hongshun, Assistant Professor at the NUS Food Science and Technology Programme, told Materials World, ‘Pyrethorids have carcinogenic and teratogenic effects on mammals, if they are exposed to certain amounts. To the best of our knowledge, no synthetic pesticide is 100% safe, although the harm depends on the amount of exposure and other properties,’ including long-term ingestion of excess residues. Yang points to numerous studies, including Mammal Toxicology of Synthetic Pyrethorids, published by Springer, and Studies on the teratogenic effects of deltamethrin in rats, published by Europe PMC, among others.

Nanoparticles with a Fe3O4 magnetic core and polystyrene coating layer capable of attracting chemicals with benzene rings, such as pyrethorids, are used to extract the pyrethorid via magnetic separation. The pyrethorids are then washed off with organic solvents for analysis.

Yang said, ‘Substances with similar chemical structure can be attracted to each other. Since polystyrene and pyrethorids share the structural properties – both highly conjugated – they can attract each other.’ The team claims that this allows the nanoparticles to extract pyrethorids from the bulk samples used during tests more easily and specifically and at low concentrations – as little as 0.02 nanograms per gram of vegetables – compared to general extraction techniques.’

More greens

Common techniques for pyrethorid screening involve lengthy and costly procedures, including column filtration and centrifugation, which the team states can take up to six hours to process and analyse a sample. Yang added that the NUS technique is not only far more rapid, taking under two hours, but is more cost effective. ‘Because our magnetic nano adsorbants can be recycled after use,’ said Yang. ‘After each extraction procedure is finished, we can complete our nanoparticles using magnets and, after an easy wash and dry process, they can be reused up to 30 times. Additionally, since we are using solid phase adsorbants, the consumption of organic solvents is being reduced significantly too, further reducing the cost.’

With small modifications, the nanoparticle can detect pyrethorids in a variety of vegetables, fruits, and vegetable oils, which Yang said demonstrates ‘the method is reliable and versatile for different food items. The same principle can be applied for detecting other chemical hazards in food systems. With small modifications, we are going to expand its application to make it suitable for detecting different hazardous chemicals in various samples’. The NUS team is also exploring using alternative magnetic nanoparticles with different coatings to extract other chemicals of concern.