Trace Detection of Acetamiprid on Raisins

Significance of the Topic

Raisins are a widely consumed fruit product, yet recent studies indicate they frequently carry multiple pesticide residues. Prolonged intake of these compounds poses unknown health risks, particularly to vulnerable populations such as children. Rapid on-site screening methods are essential to ensure consumer safety and to prevent contaminated batches from entering the supply chain.

Objectives and Study Overview

This study evaluates the capability of the Metrohm Instant SERS Analyzer (MISA) to detect trace levels of the neonicotinoid insecticide acetamiprid on commercial raisins. Key goals include establishing detection limits, comparing spectral signatures to reference standards, and proposing strategies to enhance sensitivity.

Methodology

Raisin samples were spiked with known concentrations of acetamiprid (ranging from 100 µg/mL down to 500 ng/mL). The pesticide was extracted using dichloromethane (DCM), vortexed, allowed to settle, and evaporatively dried. Silver colloid and NaCl were added to promote SERS enhancement before spectral acquisition.

Instrumentation Used

• MISA Advanced: A portable SERS analyzer with Orbital-Raster-Scan technology, equipped with vial and P-SERS attachments.
• MIRA XTR DS Advanced: A bench-top Raman system with a 785 nm laser and AI-driven fluorescence mitigation, featuring multiple sampling attachments and spectral libraries.
• Silver colloidal solution: SERS-active enhancer for trace analyte detection.

Results and Discussion

SERS spectra of acetamiprid-spiked raisin extracts matched reference peaks, with intensity correlating to pesticide concentration. Detection down to 500 ng/mL (ppb) was achieved, aligning with European maximum residue limits. Sensitivity improvement was demonstrated by combining multiple extract aliquots, resulting in enhanced signal at low analyte levels. Nonlinear intensity response and extraction variability were identified as influencing factors.

Benefits and Practical Applications

• Rapid, portable testing suitable for field inspections and mobile laboratories.
• Trace-level detection of pesticide residues without complex sample preparation.
• Informed decision-making to prevent contaminated food from reaching consumers.

Future Trends and Opportunities

Emerging developments include integration of machine learning algorithms to automate spectral interpretation, advanced SERS substrates to boost sensitivity, and extension of the method to a broader range of contaminants. Miniaturized devices coupled with cloud-based spectral libraries may further streamline routine food screening.

Conclusion

The MISA SERS platform offers a fast, sensitive, and user-friendly solution for monitoring acetamiprid residues on raisins. Its portability and proven detection limits support proactive food safety protocols, minimizing risks to public health.

References

• USDA Agricultural Marketing Service. Raisin Grades & Standards. 2022.
• Environmental Working Group. Shopper’s Guide to Pesticides in Produce. 2022.
• EFSA. National Summary Reports on Pesticide Residue Analysis Performed in 2020. EFSA Supporting Publications. 2022.