Protecting food crops is vital to the world’s food chain, and pesticides are a critical tool to kill, repel and control pests. Two million tonnes of pesticides are used annually worldwide, with this value predicted to increase over time. However, pesticides can cause severe environmental issues to aquatic systems, wildlife (e.g., bees), air and soil. Additionally, the reported effects of pesticides on human health range from short-term, such as skin irritation and headaches, to chronic effects, such as asthma and cancer. There are also concerns about the consequences of consuming pesticides from the small, but repetitive, doses in our diet.
One method to reduce the dangers of pesticides is limiting the allowed concentration used on crops. This is controlled by analysing the crop and determining the level of pesticide present. Apples are one of the most pesticide-treated fruits and as such producers have a list of regulations they must abide by for sale to the public.
Phosmet is an organophosphate insecticide used on apple trees to control codling moths, the 2018 Code of Federal Regulations set the pesticide residue tolerance on apples of phosmet as 10 ppm. High-performance liquid chromatography, mass spectrometry and gas chromatography are currently the most used techniques for testing down to low concentrations. However, these are time-consuming and costly, and Raman spectroscopy offers several advantages such as rapid and non-destructive fingerprint-like identification with little to no sample preparation.
Surface enhanced Raman scattering (SERS) is an enhancement technique used with Raman spectroscopy to provide lower limits of detection. SERS offers a signal enhancement of up to 1010‒1015 and also advantageously quenches the fluorescence of analytes. Commercial SERS substrates are readily available, making SERS an accessible technique for low-concentration detection. In this application note, residual phosmet insecticide on apple skin is detected using SERS.