Improving sensitivity in Raman imaging for thin layered and powdered food analysis utilizing a reflection mirror

Authors: LOHUMI, SANTOSH - Chungnam National University; Kim, Moon; Qin, Jianwei - Tony Qin; CHO, BYOUNG-KWAN - Chungnam National University

Submitted to: Sensors
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/13/2019
Publication Date: 6/15/2019
Citation: Lohumi, S., Kim, M.S., Qin, J., Cho, B. 2019. Improving sensitivity in Raman imaging for thin layered and powdered food analysis utilizing a reflection mirror. Sensors. 19(12):2698. https://doi.org/10.3390/s19122698.
DOI: https://doi.org/10.3390/s19122698

Interpretive Summary: Although conventional backscattering-based Raman imaging has been an established method for effective characterization and visualization of materials such as chemical or food powders, samples that include two or more constituent materials presented in layers still pose challenges for effective measurement of the deeper subsurface constituents. This study investigated the use of a background mirror for sample presentation to improve subsurface chemical detection, and results showed that the Raman signals for subsurface constituents could be increased by 1.6 to 2 times when using the mirrored sample holder. The samples tested included starch and melamine powders presented under a 1-mm layer of Teflon, and also polystyrene particles placed under a 2-mm layer of wheat flour to mimic real-world occurrences of food adulteration. These results show that the mirrored background may be an effective way to improve Raman spectral imaging for food safety and quality inspection as well as other disciplines such as pharmaceuticals.

Technical Abstract: Raman imaging has been proven to be a powerful analytical technique for the characterization and visualization of chemical components in a range of products, particularly in the food and pharmaceutical industries. The conventional backscattering Raman imaging technique for the spatial analysis of deep layer suffer from presence of intense fluorescent and Raman signals originating from the surface layer which mask the weaker subsurface signals. Here we demonstrated the application of a new reflection amplifying method using a background mirror as a sample holder to increase the Raman signals from deep layer. The approach is conceptually demonstrated on enhancing the Raman signals from the subsurface layer. Results show that when bilayer samples scanned on reflection mirror, the average signals increase of 1.62 times for intense band at 476 cm-1 of starch powder, and average increase of 2.04 times (for band at 612 cm-1) for a subsurface layer of high Raman sensitive melamine powder under 1 mm thick teflon sheet. The method was then applied successfully to detect noninvasively the presence of small polystyrene pieces buried under 2 mm thick layer of food powder (a case of powdered food adulteration) which otherwise are inaccessible to conventional backscattering Raman imaging. In addition, the increase in Raman signal to noise ratio when measuring samples on mirror, a feature important in many applications where high-throughput imaging is of interest. This concept is also applicable in an analogous manner to other discipline such as pharmaceutical and artwork where the Raman signals from deeper zones are typically, substantially diluted due to the interference from surface layer.