Trace Detection of Malathion on Corn

Significance of the Topic

Malathion is a commonly used organophosphate insecticide that can pose health risks even at low residue levels. Regulatory agencies worldwide enforce stringent maximum residue limits in food products to protect consumers. Rapid, sensitive detection methods for malathion on produce surfaces are essential for ensuring compliance and public safety.

Objectives and Study Overview

This study evaluates the performance of the Metrohm Instant SERS Analyzer (MISA) for trace detection of malathion on corn kernels. The main goals are to establish a reference SERS spectrum for malathion, determine detection limits on real samples, and validate a field‐deployable protocol using gold nanoparticle substrates.

Methodology and Used Instrumentation

The analysis employs a MISA Advanced system equipped with Orbital‐Raster‐Scan technology and a vial attachment. Gold colloid (ID Kit – Au NP) serves as the SERS substrate. Key steps include:

1. Preparation of a pure malathion standard (100 µg/mL) in ethanol to build a spectral library entry.
2. Spiking of field corn kernels with malathion in acetone to achieve concentrations from 1 to 20 µg/g.
3. Extraction by adding 0.25 mL acetone, swirling for 10 minutes, transferring 100 µL extract, and evaporating to dryness.
4. Reconstitution of residue in 450 µL Au NP solution and 50 µL 0.5 M NaCl, followed by SERS measurement on MISA.
5. Instrument settings: firmware 0.9.33; laser power 5 mW; integration time 10 s; 10 averages; raster scan ON.

Main Results and Discussion

Overlayed, baseline‐corrected SERS spectra demonstrate clear detection of malathion on corn down to 5 µg/g. Spectral features correspond to the reference library entry, confirming compound identity. At low concentrations, the method remains sensitive but can be affected by co‐extracted organic materials and substrate background.

Benefits and Practical Applications

• High sensitivity at or below regulatory limits (US MRL ~8 µg/g, EU MRL ~20 ng/g).
• Portable, battery‐powered instrument ideal for on‐site or mobile laboratory use.
• Minimal consumables and reagents, supporting a green analytical approach.
• User‐friendly software and rapid data analysis streamline field testing protocols.

Future Trends and Applications

Advancements may include the development of multiplexed SERS assays for simultaneous detection of multiple pesticides, incorporation of AI‐driven spectral interpretation, and greener nanoparticle substrates. Integration with cloud‐based databases could further enhance real‐time monitoring and compliance reporting.

Conclusion

The MISA platform provides a robust, sensitive, and portable solution for trace detection of malathion on corn. The unoptimized protocol already achieves detection limits relevant to food safety regulations, demonstrating its practical utility in both laboratory and field settings.