Rapid detection of illegal adulterants in dietary supplements with Raman

Importance of the Topic

Dietary supplements are often marketed with unverified health claims and classified as foods rather than pharmaceuticals, resulting in minimal regulatory oversight. Illegal adulteration with undeclared pharmaceuticals or analogues can pose serious health risks, including cardiovascular events and acute toxicity. Rapid, on-site screening methods are therefore critical for protecting consumers and ensuring product integrity.

Objectives and Overview

This application note demonstrates a surface-enhanced Raman scattering (SERS) approach for the rapid detection of illicit adulterants in dietary supplements, with a focus on so-called “hot honey” products. The study aims to provide a qualitative, field-deployable screening method capable of identifying trace levels of undeclared erectile dysfunction drugs, weight-loss stimulants, and other active compounds.

Methodology

• SERS substrates: Metrohm silver and gold P-SERS paper strips and colloidal nanoparticle solutions
• Analyzer: Metrohm Instant SERS Analyzer (MISA) with Orbital-Raster-Scan technology and MISA Cal software
• Sample preparation for tablets: 10 mg of supplement mixed with excipient matrix, extracted in ethanol, vortexed, centrifuged, and 10 µL supernatant applied to P-SERS strip
• Sample preparation for honey: Dissolution in NaOH, salting out with sodium chloride and isopropyl alcohol, separation of organic layer, direct application to SERS substrate
• Library matching: Custom reference library of 23 analytes; Hit Quality Index (HQI) threshold ≥ 0.70 for positive identification

Used Instrumentation

• Metrohm Instant SERS Analyzer (MISA) with Vial and P-SERS attachments
• Silver and gold nanoparticle substrates (P-SERS strips and colloids)
• Standard laboratory equipment: vortex mixer, centrifuge

Main Results and Discussion

• Eleven target adulterants (e.g., sildenafil analogues, vardenafil, acetildenafil, phenethylamine, vinpocetine) produced strong SERS signals (HQI 0.60–0.99) on silver P-SERS substrates
• Limits of identification (LOI) ranged from 0.1% w/w for erectile dysfunction drugs to 5.0% w/w for less Raman-active compounds like fluoxetine and melatonin
• Common excipients (cellulose, magnesium stearate, silicon dioxide, hydroxypropyl methylcellulose, titanium oxide) exhibited negligible interference
• Commercial tablets spiked with 0.1–5.0% w/w adulterants were correctly identified within seconds
• In real honey samples, sildenafil (20–50 mg/15 g) was detected with both silver P-SERS and gold colloid, while tadalafil (20–50 mg/15 g) required gold colloid for reliable detection

Benefits and Practical Applications

• High sensitivity for trace adulterants with minimal sample preparation
• Insensitivity to complex sample matrices reduces false positives
• Rapid results (<10 sec per analysis) enabling on-site screening without laboratory infrastructure
• Low operational costs and portability support law enforcement, customs, and quality-control labs

Future Trends and Opportunities

Advances in nanoparticle design and portable spectrometer miniaturization will further enhance sensitivity and ease of use. Integration with automated data analysis and expanding spectral libraries can enable quantitative measurements and broader applications, including food fraud detection and environmental monitoring.

Conclusion

Surface-enhanced Raman scattering using Metrohm’s P-SERS substrates and MISA analyzer provides a fast, sensitive, and cost-effective solution for detecting illegal adulterants in dietary supplements. Its portability and minimal sample prep make it ideal for on-site screening, safeguarding public health by revealing undeclared pharmaceutical contaminants.

References

1. Rizzo S.; Weesepoel Y.; Erasmus S.; Sinkeldam J.; Piccinelli A. L.; van Ruth S. A Multi-Analyte Screening Method for the Rapid Detection of Illicit Adulterants in Dietary Supplements Using a Portable SERS Analyzer. Heliyon 2023, 9(8), e18509.
2. U.S. Food & Drug Administration. Tainted Honey-Based Products with Hidden Active Drug Ingredients. 2025-07-09.