Trace Detection of Auramine O in Curry Powder

Importance of the Topic

Curry powder is widely used and valued for its bright yellow coloration derived from natural spices. However, the addition of synthetic dyes like Auramine O (AO) poses serious health risks, including carcinogenic effects and organ toxicity. Despite regulatory bans, AO continues to appear as an illicit additive in food products. Rapid, on-site screening methods are therefore critical to protect consumer safety and ensure compliance in food supply chains.

Objectives and Study Overview

This study demonstrates a streamlined approach for detecting trace levels of Auramine O in adulterated curry powder using surface-enhanced Raman spectroscopy (SERS). The goals were to:

• Establish a SERS reference spectrum for AO
• Develop a simple liquid-liquid extraction protocol compatible with field conditions
• Evaluate the sensitivity and reliability of the Metrohm Instant SERS Analyzer (MISA) for detecting AO across a range of concentrations
• Provide a practical workflow for on-site testing

Methodology and Instrumentation

A formative extraction was performed by mixing 100 mg of spiked curry powder with 1 mL of 0.1 mol/L NaOH, followed by addition of ethyl acetate and NaCl. After phase separation, a small aliquot of the organic layer was combined with gold nanoparticle colloid and NaCl to induce SERS enhancement. Measurements were conducted immediately on the portable MISA Advanced system. Key experimental parameters included:

• Laser wavelength and power optimized for gold colloids
• Integration time of 10 s with 10 averages
• Orbital-Raster-Scan (ORS) enabled to improve spectral reproducibility

Used Instrumentation

The analytical setup comprised:

• MISA Advanced portable SERS analyzer with ORS spectrograph
• Au NP ID Kit containing gold colloid, pipettes, spatulas, and sample vials
• MISA Vial Attachment for reproducible sample placement
• Standard laboratory reagents: NaOH, NaCl, ethyl acetate

Main Results and Discussion

Baseline-corrected SERS spectra of curry powder spiked at concentrations from 1 to 1000 µg/g show clear AO marker peaks even at the lowest level. Solvent and pH conditions caused minor Raman band shifts, but key vibrational features remained identifiable. The system reliably distinguished AO signals from background spice matrix, confirming a detection limit of approximately 1 µg/g under field-friendly conditions.

Benefits and Practical Applications

By combining a minimal-step extraction with a handheld SERS analyzer, this method offers:

• Rapid turnaround: results in under 15 minutes
• Minimal consumable use and training requirements
• Portability for on-site quality control in manufacturing, shipping, and customs inspections
• High sensitivity to low-level contamination

Future Trends and Potential Applications

Advances in SERS substrate design and data analysis software could expand this approach to other banned dyes or contaminants in a variety of food matrices. Integration with machine learning for automated spectral interpretation and the development of multiplex assays are promising directions. Future portable systems may incorporate wireless data reporting and cloud-based libraries for real-time monitoring across supply chains.

Conclusion

The described SERS-based assay using MISA demonstrates a robust, sensitive, and user-friendly protocol for detecting Auramine O adulteration in curry powder. Its portability and straightforward workflow make it an effective tool for on-site food safety screening and regulatory compliance.