SERS Detection of Metanil Yellow in Turmeric

Importance of the Topic

Metanil Yellow (MY) is a toxic azo dye banned as a food additive in many countries due to its adverse neurological and multi-organ effects. Despite regulatory restrictions, MY is illicitly employed to enhance the yellow color of spices such as turmeric. Given turmeric’s growing use in dietary supplements and functional foods, rapid and reliable on-site testing methods are essential to protect consumer safety and maintain product integrity.

Objectives and Study Overview

This application describes the development of a straightforward Surface-Enhanced Raman Spectroscopy (SERS) assay using the Metrohm Instant SERS Analyzer (MISA) for detection of Metanil Yellow in turmeric. The aim is to demonstrate a sensitive, selective, and portable workflow suitable for routine quality control in food processing and distribution environments.

Used Instrumentation

The primary analytical platform comprises:

• MISA Advanced (Cat. No. 2.950.0020): a portable SERS analyzer with Orbital-Raster-Scan (ORS) technology, Bluetooth/USB connectivity, and various sampling attachments.
• ID Kit – Au NP (Cat. No. 6.07506.440): gold nanoparticle colloid, disposable spatula, pipettes, and sample vials for SERS measurements.

Methodology

Sample Preparation:

• Spike turmeric powder with MY at concentrations of 0.1 to 10 mg/g.
• Extract 100 mg of each spiked sample with 1 mL of 0.5 mol/L HCl, shake, and settle 10 minutes.

Assay Assembly:

• Combine 100 μL of HCl extract with 800 μL Au NP solution and 100 μL 0.5 mol/L NaCl in a vial.
• Invert to mix and insert into the MISA vial attachment.

Instrument Settings:

• Firmware: 0.9.33; Software: Misa Cal V1.0.15
• Laser power: 5; Integration time: 10 s; Averages: 10; Raster scan: ON

Main Results and Discussion

Baseline-corrected SERS spectra reveal clear detection of MY down to 0.1 mg/g in turmeric. Characteristic Raman peaks at 504, 1176, 1383, and 1588 cm⁻¹ enable reliable identification. The method displayed good reproducibility across replicate measurements and minimal interference from the turmeric matrix.

Benefits and Practical Applications

• Rapid, on-site screening requiring minimal sample preparation.
• Portable instrumentation suitable for processing plants, distribution centers, and field inspections.
• Cost-effective assay with user-friendly software and minimal operator training.

Future Trends and Potential Applications

• Extension of the SERS assay to other adulterated spices and legumes (e.g., dal).
• Development of advanced nanoparticle substrates for enhanced sensitivity.
• Integration with cloud-based spectral libraries and machine-learning algorithms for automated contaminant identification.
• Combination with other portable spectroscopic techniques for multi-compound screening.

Conclusion

The MISA-based SERS assay provides a rapid, sensitive, and field-deployable solution for detecting Metanil Yellow in turmeric. Its simplicity, portability, and robustness make it a valuable tool for ensuring food safety and regulatory compliance in the spice industry.

References

• No external references cited in the original text.