Raman Spectroscopy Peers Through Packaging

Significance of the Topic

Raman spectroscopy is a powerful tool for noninvasive chemical identification. The newly developed see-through Raman (STRaman) method extends its application to samples hidden beneath diffusely scattering materials such as plastics, paper and tablet coatings. This capability addresses critical needs in pharmaceutical quality control, security screening and non-destructive testing.

Goals and Study Overview

The study aims to demonstrate STRaman's ability to recover Raman signals from substances obscured by strongly scattering containers. By comparing STRaman with conventional confocal Raman and spatially offset Raman spectroscopy (SORS), the authors evaluate sampling depth, signal strength and reproducibility across multiple scenarios.

Methodology and Instrumentation

• Instrument: i-Raman Pro ST spectrometer (B&W Tek) with 785 nm laser at 450 mW output.
• STRaman probe: large sampling area (~4 mm diameter) to reduce power density and increase penetration depth.
• Data processing: baseline correction, intensity normalization and spectral subtraction to isolate sample signatures.
• Comparison setups: standard confocal probe (~100 µm spot) and STRaman configurations including liquid focus adaptor, surface regulator, standoff lens and microscope mount.

Main Results and Discussion

• Plastic containers: STRaman identified sodium benzoate inside titanium dioxide-filled polyethylene bottles by isolating its spectrum from container background, whereas conventional Raman was dominated by container peaks.
• Envelope screening: D-(+) glucose was successfully detected through a manila envelope despite strong paper fluorescence that overwhelms confocal Raman signals.
• Tablet coatings: STRaman penetrated sucrose/TiO₂ coatings to reveal ibuprofen peaks matching pure drug spectra, avoiding the need to remove coatings.
• Heterogeneous samples: A larger sampling area improved reproducibility for pharmaceutical blends of acetaminophen, aspirin and caffeine; standard confocal measurements yielded variable hit quality indices (HQI), while STRaman eliminated false negatives.
• Sensitive materials: Reduced power density enabled safe measurement of photolabile samples, gunpowder and in vivo bone tissue without damage or ignition risk.
• Accessory versatility: A modular kit allows rapid switching between STRaman and confocal modes, liquid container focus, standoff analysis and Raman microscopy.

Benefits and Practical Applications

STRaman enhances Raman spectroscopy by offering:

• Non-destructive testing of packaged pharmaceuticals and chemicals.
• Rapid, on-site screening for security, customs and law enforcement.
• Improved reproducibility for heterogeneous and crystalline materials.
• Safe interrogation of sensitive or energetic samples.
• Integration into process analytical technology workflows.

Future Trends and Opportunities

• Development of handheld and standoff STRaman systems for field deployment.
• Advanced chemometric algorithms and machine learning for automated identification beneath complex matrices.
• Integration with manufacturing lines for real-time quality assurance.
• Extension to biomedical imaging and in vivo diagnostics.

Conclusion

STRaman spectroscopy significantly expands the capabilities of conventional Raman analysis by enabling clear chemical identification through diffusely scattering barriers. Its large sampling depth, low power density and modular design make it a versatile tool for pharmaceutical QC, security screening and sensitive sample analysis.

Used Instrumentation

• B&W Tek i-Raman Pro ST spectrometer with 785 nm, 450 mW laser.
• STRaman fiber probe, focus adaptor, surface regulator, standoff lens, microscope mount.

Reference

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