Two-step spatially offset Raman spectroscopy technique for rapid and non-invasive detection of drugs in containers—simulation and experiment

Abstract

Spatially offset Raman spectroscopy (SORS) provides a new powerful method for non-invasive detecting of the substance in containers. However, it takes a long time to collect spectra at different offset distances and needs multivariate analysis, which is not suitable for rapid on-site detection. In this paper, a rapid two-step SORS detection method based on the Raman scattering photons transmission and distribution simulated by Monte Carlo is proposed. Commonly used packaging materials such as plastic and glass are considered, the ‘plastic/glass-drug’ double-layer samples were constructed and the Raman intensities of each layer of samples at different offset distances were simulated. The Raman spectra of actual samples at different offset distances were collected by a self-developed portable confocal Raman spectrometer with additional collection probe. The relationship between the optimal offset distance of two-step SORS and the thickness of different materials container wall was investigated. Actual measurement results are consistent with simulation results. The feasibility of decreasing the detection steps and shortening the detection time by pre-selecting the optimal offset distance was studied. Based on this, we propose the two-step SORS technique that only needs to collect spectra at two pre-selected locations with a simple data processing method to quickly obtain the Raman spectrum of the substance in the container. Two-step SORS technique can greatly reduce the detection steps, improve the detection efficiency, and achieve non-invasive rapid detection.