Improving Sensitivity in Raman Imaging for Thin Layered and Powdered Food Analysis Utilizing a Reflection Mirror

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 a deep layer suffers from the 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 a deep layer. The approach is conceptually demonstrated on enhancing the Raman signals from the subsurface layer. Results show that when bilayer samples are scanned on a reflection mirror, the average signals increase 1.62 times for the intense band at 476 cm−1 of starch powder, and average increases of 2.04 times (for the band at 672 cm−1) for a subsurface layer of high Raman sensitive melamine powder under a 1 mm thick teflon sheet. The method was then applied successfully to detect noninvasively the presence of small polystyrene pieces buried under a 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 the Raman signal to noise ratio when measuring samples on a mirror is an important feature in many applications where high-throughput imaging is of interest. This concept is also applicable in an analogous manner to other disciplines, such as pharmaceutical where the Raman signals from deeper zones are typically, substantially diluted due to the interference from the surface layer.

Interband electronic transitions and optical phonon modes in size-dependent multiferroic BiFeO3 nanoparticles

“…The intensity of the Raman modes increases with increasing calcination temperature, and this is attributed to (i) enhanced crystallinity and (ii) the resonance with laser excitation matching with the electronic absorption bands in the BiFeO 3 nanoparticles. 40,41 The observed vibrational modes are also in agreement with the reported literature. 39,42,43 Table S4 (ESI †) lists all the fitted Raman modes for the 350, 400, 500, and 600 1C annealed BiFeO 3 nanoparticle samples.…”

Improved performance of near infrared excitation Raman spectroscopy using reflective thin-film gold on glass substrates for cytology samples

“…Other related work includes the demonstration of enhancements in Raman spectra for chemical samples placed on a reective substrate 21 and in Ref. 22 it was shown that a re ective silver-coated substrate o ered an enhancement of the signal from uorescently labelled dog-kidney cells with an enhancement of 3-4, which is similar to the level of enhancement of intensity determined in this paper with respect to the Raman spectrum.…”

Quartz Tube Enhanced Raman Scattering Spectroscopy

“…Peter J. Larkin et al [15] proposed increasing the path of action between the laser and the sample by drilling a conical/cylindrical hole in the tablet, thereby provided 3-5 times enhancement of Raman signal and 2 times increase of the accuracy. Lohumi S et al [16] proposed a mirror was used to improve the detection sensitivity of Raman imaging spectroscopy, which increased the Raman signal intensity of powder samples by 2 times. Besides, it verified the feasibility of the technique used for food adulteration in the paper.…”