Efficient mitigation of fluorescence in Raman spectroscopy using SSE

Significance of the Topic

Raman spectroscopy is a cornerstone technique for non-destructive materials analysis across pharmaceuticals, polymers, and forensic science. Its rapid molecular fingerprinting capability makes it ideal for field and laboratory use. However, fluorescence interference often limits sensitivity, reproducibility, and identification accuracy. The development of robust fluorescence mitigation methods is critical to extend Raman’s applicability to colored or fluorescent samples in handheld configurations.

Objectives and Study Overview

This work presents the BRAVO handheld Raman spectrometer by Bruker, featuring the patented Sequentially Shifted Excitation (SSE TM) method for fluorescence suppression. The primary goals are to enhance wavelength accuracy, ensure eye-safe operation, and automatically remove fluorescence background to yield clear Raman spectra for reliable material identification and quantification.

Methodology and Instrumentation

The BRAVO integrates three diode lasers whose excitation wavelengths are sequentially shifted by small increments during acquisition. The SSE TM algorithm exploits the fact that Raman peaks shift position on the detector while fluorescence remains stationary. By comparing successive spectra, the software isolates moving components (Raman signals) and constructs a clean, fluorescence-free spectrum. Key instrument features include class 1M laser safety, improved wavelength calibration over competing devices, and an intuitive guided workflow for automated data collection and analysis.

Main Results and Discussion

Experimental demonstrations with talc in a polyethylene bag show that raw spectra dominated by fluorescence yield misleading baselines. After SSE TM processing, the talc Raman bands emerge without baseline artifacts, preserving intrinsic peak shapes and positions. In another example, sodium alginate excited at 785 nm exhibits a strong fluorescence background that overwhelms the Raman signature. Application of SSE TM recovers clear polymer bands, facilitating unambiguous compound identification.

Benefits and Practical Applications

The SSE TM approach offers several advantages:

• Fluorescence removal without baseline correction preserves true spectral features
• Improved reproducibility and data consistency through enhanced wavelength accuracy
• Safe operation under class 1M certification at moderate laser power
• Rapid, automated analysis ideal for field deployment in QA/QC, anti-counterfeiting, and environmental monitoring

Future Trends and Applications

Further integration with machine learning algorithms may enable real-time spectral library matching and anomaly detection. Advances in hybrid excitation schemes could expand chemical coverage, while miniaturization of multiwavelength sources will drive broader adoption in point-of-need diagnostics and homeland security.

Conclusion

The BRAVO handheld Raman spectrometer coupled with Sequentially Shifted Excitation technology effectively mitigates fluorescence interference, delivering high-quality Raman spectra with minimal user intervention. This innovation enhances the reliability and versatility of handheld Raman analysis for a wide range of applications.

References

1. S. Assi Identification of counterfeit drugs using dual laser handheld Raman Eur Pharm Rev 20 20 (2015)
2. Product Note T30 BRAVO Accuracy is crucial The starting point for a robust transfer of methods
3. J B Cooper et al Sequentially Shifted Excitation Raman Spectroscopy Novel Algorithm and Instrumentation for Fluorescence-Free Raman Spectroscopy in Spectral Space Appl Spectrosc 67 973 (2013)
4. J B Cooper et al Spatially compressed dual-wavelength excitation Raman spectrometer Appl Opt 53 3333 (2014)
5. J Kauffmann et al Spectral Preprocessing for Raman Library Searching Amer Pharm Rev 14 (2011)