STRaman Technology: Raman for See Through Material Identification

Importance of the Topic

Raman spectroscopy is a powerful analytical tool for material identification, yet its application is limited when samples are enclosed within diffusely scattering or opaque media. Innovations in probe design and sampling strategies are critical to extend Raman capabilities to thermolabile, photolabile, heterogeneous, or packaged samples without invasive preparation. The See Through STRaman™ approach addresses these challenges by increasing sampling depth and area while reducing power density, enabling rapid, non-destructive analysis across a wide range of real-world scenarios.

Objectives and Article Overview

• Introduce a novel Raman probe design—STRaman™—optimized for materials inside diffusely scattering containers.
• Compare performance against standard confocal Raman configurations through multiple case studies.
• Demonstrate advantages in sensitivity, reproducibility, and sample safety.

Methodology and Instrumentation

• Instrument: i-Raman® Pro ST Analyzer equipped with a 785 nm, 450 mW excitation laser.
• Signal correction: Intensity axis calibration using NIST SRMs for relative intensity correction.
• Probing modes: See Through configuration for large-area illumination; standard confocal configuration for comparison.
• Sampling kits: Focus Adaptor and Surface Regulator allow conversion between large-area and tight-focus modes, supporting standoff, contact, and microscopy measurements.

Main Results and Discussion

• Through white plastic bottles, STRaman clearly resolved sodium benzoate signals that were otherwise masked by the container material in confocal mode. A subtraction algorithm isolates and enhances the content spectrum.
• D-glucose identification through manila envelopes was feasible with STRaman; standard Raman yielded only cellulose signals and fluorescence background.
• Coated pharmaceutical tablets (Advil®) displayed dominant coating features under confocal measurement, while STRaman recovered the active drug signature matching the pure compound spectrum.
• Dark and sensitive samples (gun powder, biological tissues) were measured with full laser power without sample damage due to reduced power density across a larger area. Transcutaneous bone and muscle measurements distinguished phosphate and protein signatures non-invasively.
• Heterogeneous and crystalline materials exhibited large spectral variability under a ~100 µm spot size. STRaman’s millimeter-scale sampling reduced this variability significantly, achieving near-perfect hit quality indices (HQI) and eliminating false negatives in tablet and xylitol bag studies.

Benefits and Practical Applications

• Non-destructive identification through opaque or scattering packaging—valuable for incoming material inspection and quality control.
• Enhanced reproducibility for heterogeneous, crystalline, and bulk samples by averaging over larger sampling areas.
• Reduced risk of photothermal damage, enabling analysis of thermolabile, photolabile, and biological specimens.
• Portable, flexible platform suited for fieldwork, laboratory QC, and research environments.

Future Trends and Potential Applications

• Integration of machine learning algorithms for automated container-content deconvolution and spectral classification.
• Miniaturization and fiber-optic adaptations for endoscopic or remote sensing in clinical and industrial settings.
• Expansion to near-infrared or UV excitation for deeper penetration or selective fluorescence suppression.
• High-throughput screening in pharmaceutical manufacturing and customs inspection for rapid, contactless verification.

Conclusion

The See Through STRaman™ technology significantly extends the scope of Raman spectroscopy by enabling reliable material identification through diffusely scattering and opaque media. By combining a large sampling area with high throughput optics, this approach enhances sensitivity, reproducibility, and sample safety. The ability to switch seamlessly between bulk sampling and confocal modes further increases versatility, making the i-Raman Pro ST Analyzer an adaptable solution for diverse analytical challenges.

Reference

1. P. Matousek et al. “Subsurface Probing in Diffusely Scattering Media Using Spatially Offset Raman Spectroscopy”. Appl. Spectrosc. 59, 393 (2005).
2. S.J. Choquette et al. “Relative Intensity Correction of Raman Spectrometers: NIST SRMs 2241–2243 for 785 nm, 532 nm, and 488/514.5 nm Excitation”. Appl. Spectrosc. 61(2):117–129 (2007).
3. P. Matousek et al. “Noninvasive Raman Spectroscopy of Human Tissue In Vivo”. Appl. Spectrosc. 60, 758–763 (2006).
4. X.-F. Ling et al. “Investigation of Normal and Malignant Tissue Samples from the Human Stomach Using Fourier Transform Raman Spectroscopy”. Appl. Spectrosc. 56, 570–573 (2002).