Fast and Selective Detection of Trigonelline, a Coffee Quality Marker, Using a Portable Raman Spectrometer

Importance of the Topic

Rapid, efficient, and selective analytical methods are essential for food quality control, detection of adulteration, and monitoring of key biomarkers. Surface-enhanced Raman spectroscopy (SERS) leverages metallic nanostructures to amplify Raman signals, offering lower detection limits, shorter acquisition times, and minimal sample volumes. This study applies a portable Raman spectrometer coupled with gold nanotriangles to quantify trigonelline, a coffee quality marker.

Objectives and Study Overview

The primary goal is to develop and validate a SERS-based technique using the i-Raman Plus 785S device for accurate trigonelline quantification. The method aims to provide a practical alternative to conventional Raman analysis for routine quality assessment in foods such as coffee and quinoa.

Methodology and Instrumentation Used

• Instrumentation: i-Raman Plus 785S portable Raman spectrometer with 785 nm laser, 150–2800 cm⁻¹ range, 50 s integration time, 10 scans, and a 10 mm liquid cuvette holder.
• Nanoantennas: Gold nanotriangles functionalized with mercaptopropionic acid dispersed in deionized water.
• Samples: Aqueous trigonelline standards from 0.5 to 10 mM. For SERS measurements, samples were mixed with gold nanotriangles at a 15:2 ratio prior to analysis.
• Data Analysis: Monitoring the 1034 cm⁻¹ pyridine ring breathing mode; the peak area between 1010–1045 cm⁻¹ was integrated to construct calibration curves.

Main Results and Discussion

Conventional Raman analysis of a 250 mM trigonelline solution exhibited a strong 1034 cm⁻¹ peak. Comparative measurements of 0.5–10 mM standards revealed a significant improvement in signal-to-noise ratio with SERS. Calibration curves demonstrated linear responses for both approaches, while SERS achieved reliable detection below 0.5 mM and reduced measurement times with lower sample requirements.

Benefits and Practical Applications

• Enhanced Sensitivity: SERS provides lower detection limits compared to standard Raman spectroscopy.
• Portability: The handheld system enables on-site, real-time monitoring of trigonelline in coffee, quinoa, and similar matrices.
• Operational Efficiency: Shorter acquisition times and minimal sample volumes streamline quality control workflows.

Future Trends and Potential Applications

Advancements in portable SERS platforms and customized nanoantennas are likely to broaden applications in food authentication, environmental monitoring, and point-of-care diagnostics. Progress in nanostructure design and miniaturized detectors may facilitate multiplexed biomarker screening and non-invasive packaging analysis.

Conclusion

This work presents a straightforward SERS-based method using a portable Raman spectrometer and gold nanotriangles for sensitive trigonelline quantification. The approach offers lower detection limits, operational flexibility, and strong potential for field-based quality assurance in the food industry.

References

• Galarreta B.C., Hernandez Y., Saldana Ramos A. (2016) Synthesis and application of gold nanotriangles for quantification of trigonelline. PUCP.
• Galarreta B.C., Maruenda H. (2014) Vibrational and NMR spectroscopy in quality control of Peruvian organic and instant coffee. PUCP.
• Aroca R. (2016) Surface-enhanced vibrational spectroscopy. John Wiley & Sons.
• Jaworska A., Malek K., Marzec K.M., Baranska M. (2012) Nicotinamide and trigonelline studied with surface-enhanced FT-Raman spectroscopy. Vibrational Spectroscopy, 63, 469–476.