Study on a Non-Destructive Drug Testing Method Based on Spatially Offset Raman Spectroscopy

The identification of counterfeit medicines has been a serious problem confronted by the contemporary world, particularly for the developing countries. Thus, anti-counterfeit innovations can help find solutions on avoiding the hazards to health and lives, as well as for the harmful effects on social morality and commercial culture. In this work, a modular Inverse Spatially Offset Raman Spectroscopy (Inverse SORS) system was built for overcoming the limitations of traditional Raman spectroscopy whose detection depth is confined to a few hundred micrometers. Besides, it can also effectively avoid the background of the container for realizing the detection and analysis of deep chemical components in a non-destructive and non-intrusive way by using different spatially offset values (Delta s), which will lay the foundation for a simple and efficient method for direct detection of drugs. A 785 nm diode laser and WITec UHTS300 Raman spectrometer were employed to construct Inverse SORS system. During the experiments, a collimated beam passed through an axicon lens to form a ring beam, and its radius was adjusted by controlling the distance between the cone lens and sample. The Raman spectra of paracetamol and metronidazole in polyethylene (PE)bottles (with a 1. 5 mm thickness) and polytetrafluoroelene (PTFE) centrifuge tubes (with a 4 mm thickness) were respectively measured by using a built-in spectral detection device. One of the container's Raman peaks was selected as the reference peak for normalizing and processing acquired results. The featured Raman spectra of drugs were obtained by a scaled subtraction of the two spectra (Ring-Spot). The experimental results showed that the Inverse SORS not only avoided the optical background from the opaque container, but also truly presented the molecular fingerprint information of the sample inside. When the radius of the ring beam doubled its size, the intensity of acquired paracetamol spectra increased by six times, whereas the characteristics of Raman peaks of metronidazole in the PTFE tube increased by 100%. The above results showed that the inverse SORS can accurately detect the fingerprint spectrum of the chemical components inside the opaque/translucent container. Moreover, by optimizing system performance and adopting a variety of data processing methods, inverse SORS technology, which is expected to be a fast, accurate and convenient detection method, will be an indispensable complement to the existing pharmaceutical analysis technologies.