Efficient mitigation of fluorescence in Raman spectroscopy using SSE

Significance of the Topic

Raman spectroscopy is a cornerstone technique for material characterization across pharmaceutical, polymeric, and chemical industries. However, the presence of fluorescence often overwhelms weak Raman signals, limiting reproducibility and hampering reliable identification and quantification. Mitigating this fluorescence interference expands the applicability of handheld Raman instruments for in-field analysis, quality control, and rapid screening tasks.

Objectives and Study Overview

This product note presents the BRAVO handheld Raman spectrometer by Bruker, which incorporates a patented Sequentially Shifted Excitation (SSETM) method to suppress fluorescence. The goals are to demonstrate:

• Improved wavelength accuracy and data consistency compared to competing devices.
• Effective fluorescence removal without post-acquisition baseline corrections.
• Preservation of intrinsic Raman band shape and position for confident material identification.

Methodology and Instrumentation

• Sequentially Shifted Excitation (SSETM): Three excitation wavelengths are alternated during acquisition so that Raman peaks shift on the detector while fluorescence remains stationary. A dedicated algorithm isolates the moving components (Raman) and discards the fixed background.
• Laser Source: Class 1M safe lasers with finely controlled emission wavelengths to ensure high spectral accuracy and user safety.
• Spectrometer Design: Compact, handheld format optimized for field use, offering guided workflows for automated data capture and analysis.

Key Results and Discussion

• Figure 1 (Talc in PE bag): Raw spectra display intense fluorescence masking talc features. After SSETM processing, only the shifted Raman bands remain, clearly identifying talc.
• Figure 2 (Sodium Alginate): Conventional 785 nm Raman shows dominant fluorescence background. BRAVO with SSETM reveals clean alginate peaks without additional baseline correction.
• Comparison with 1064 nm NIR Raman: While 1064 nm excitation reduces fluorescence naturally, it suffers from low scattering efficiency and potential thermal effects. SSETM retains high sensitivity under safe, low-power conditions.

Benefits and Practical Applications

• Fluorescence-free spectra ready for direct library matching and quantification.
• Elimination of data pretreatment steps reduces risk of information loss and misidentification.
• Maintains native Raman band shapes, supporting trace contaminant detection and detailed spectral interpretation.
• Enables rapid, portable analysis in QA/QC, counterfeit screening, environmental monitoring, and forensic investigations.

Future Trends and Potential Applications

Adoption of SSETM in other handheld and benchtop Raman platforms is expected to grow, enhancing robustness for in situ process monitoring and real-time decision making. Integration with machine learning and cloud-based spectral libraries will further streamline automated identification workflows. Advances in multi-wavelength shifting schemes may enable even faster acquisitions and broader spectral coverage.

Conclusion

The BRAVO handheld Raman spectrometer, equipped with Sequentially Shifted Excitation (SSETM), delivers reliable fluorescence suppression, exceptional wavelength accuracy, and uncompromised sensitivity. This innovation empowers users to perform confident material identification and quantification in challenging fluorescence-rich environments without extensive post-processing.

Reference

[1] S. Assi et al., Eur. Pharm. Rev. 20 (2015)
[2] Product Note T30, Bruker Optics
[3] J. B. Cooper et al., Appl. Spectrosc. 67, 973 (2013)
[4] J. B. Cooper et al., Appl. Opt. 53, 3333 (2014)
[5] J. Kauffmann et al., Amer. Pharm. Rev. 14 (2011)