Raman Spectroscopy Peers Through Packaging

Importance of Topic

Raman spectroscopy is a powerful noninvasive technique widely used for molecular identification in pharmaceuticals, security screening, art conservation and materials science. Traditional confocal Raman is limited by its shallow sampling depth and sensitivity to diffusely scattering or opaque packaging layers.

Objectives and Study Overview

This study introduces see-through Raman spectroscopy (STRaman), an approach designed to detect chemical species beneath diffusely scattering barriers such as plastic containers, tablet coatings and paper envelopes. The authors compare STRaman against conventional confocal Raman and spatially offset Raman spectroscopy (SORS) to highlight its enhanced depth penetration, sampling area and reproducibility.

Methodology and Instrumentation

An i-Raman Pro ST spectrometer (785 nm, 450 mW) equipped with a large-area fiber probe (4 mm spot) forms the core of STRaman. Modular accessories—including a focus adaptor, surface regulator, telescope lens and industrial probe—enable configurations for bulk, confocal, standoff and microscopic measurements. Spectral calibration follows NIST SRM 2241 protocols.

Main Results and Discussion

STRaman successfully identified sodium benzoate through white polyethylene, D-(+)-glucose through manila envelopes and active ingredients beneath tablet coatings, where traditional confocal measurements failed or yielded weak signals. Sampling over a larger area drastically improved measurement reproducibility and eliminated false negatives seen with small-spot sampling. Reduced power density prevented sample damage, making STRaman suitable for photolabile, thermolabile and energetic materials.

Benefits and Practical Applications

STRaman offers rapid, nondestructive screening for raw material inspection and quality control in pharmaceutical production, safe package inspection in security and customs applications, and in situ analysis in art and archaeological studies. Its plug-and-play probe accessories provide a versatile, multi-mode platform without changing the core instrument.

Future Trends and Opportunities

Continued miniaturization and integration of STRaman into handheld and portable Raman systems will expand field deployment. Advanced probe designs, coupled with machine learning–driven spectral libraries, may improve detection limits and automate complex sample identification. Hybrid approaches combining STRaman with complementary techniques could further enhance subsurface analysis capabilities.

Conclusion

STRaman overcomes conventional depth and sampling limitations by using large-area excitation and specialized optics, enabling reliable, nondestructive Raman analysis through diffusely scattering packaging. This versatile technique enhances reproducibility and sample safety across diverse analytical challenges.

Reference

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