SERS Detection of Brilliant Blue

Significance of the Topic

Detecting synthetic dyes such as Brilliant Blue FCF (FD&C Blue #1) in food and beverage products is crucial for consumer safety, regulatory compliance and quality control. Conventional Raman spectroscopy often fails due to strong fluorescence from these dyes. Surface-enhanced Raman spectroscopy (SERS) offers enhanced sensitivity, but fluorescent targets with weak intrinsic SERS signals require optimized sample preparation and instrumentation.

Objectives and Overview of the Study

This application note demonstrates a rapid, on-site method for identifying Brilliant Blue in a complex flavored drink mix using the Metrohm Instant SERS Analyzer (MISA). The study aims to overcome fluorescence interference and weak SERS response through a simple liquid-liquid extraction combined with gold nanoparticle enhancement.

Methodology

A flavored “blue raspberry” drink powder was first analyzed directly by dissolving 100 mg in 1 mL water, mixing aliquots with gold nanoparticles (Au NPs) and NaCl, and measuring the SERS spectrum on MISA. To improve spectral clarity, 40 mg of sample was extracted with an aqueous benzethonium chloride surfactant, followed by chloroform partitioning. The organic layer was evaporated, and the residue was re-suspended in Au NPs and NaCl for measurement.

Used Instrumentation

• MISA Advanced (Metrohm Instant SERS Analyzer) with Orbital-Raster-Scan technology
• ID Kit – Au NP containing gold colloid, vials, pipettes and disposable spatulas
• Benzethonium chloride surfactant, chloroform and NaCl solution

Main Results and Discussion

The direct measurement produced a distorted SERS spectrum due to matrix fluorescence and overlapping signals. After simple chloroform extraction with benzethonium chloride, the extracted sample generated a SERS profile closely matching the reference spectrum of pure Brilliant Blue at 500 µg/mL. The extraction step effectively concentrated the anionic dye and removed interfering matrix components, yielding enhanced peak intensity and improved library matching.

Benefits and Practical Applications

• Rapid, on-site screening of fluorescent dyes in food and beverage matrices without extensive laboratory infrastructure
• Simple liquid-liquid extraction requires minimal reagents and equipment, reducing analysis time
• High specificity through SERS spectral library matching, supporting regulatory compliance and quality assurance

Future Trends and Applications

Advancements in portable SERS platforms and novel nanoparticle substrates will extend capabilities to multiplexed detection of food additives and contaminants. Integration of automated sample prep modules, machine-learning spectral interpretation and field-deployable workflows will further streamline on-site chemical analysis across the food, pharmaceutical and environmental sectors.

Conclusion

The MISA system, combined with a straightforward chloroform extraction protocol, successfully overcomes fluorescence and weak SERS signals to detect Brilliant Blue in a complex sample matrix. This method delivers a practical, cost-effective solution for rapid field testing of fluorescent dyes.