Determination of Depth in Transmission Raman Spectroscopy in Turbid Media Using a Beam Enhancing Element

Abstract

This study demonstrates experimentally a method to enable prediction of depth of a chemical species buried in a turbid medium by using transmission Raman spectroscopy alone. The method allows the prediction of the depth of a single, chemically distinct layer within a turbid matrix by performing two measurements, with and without a beam enhancing element, or "photon diode." The samples employed consisted of two different polymers, of total thickness 3.6 mm, whose optical properties are loosely relevant to pharmaceutical applications. A polymer layer of low-density polyethylene (LDPE) was placed at different positions within multiple layers of the polytetrafluoroethylene (PTFE) matrix and Raman spectra were recorded in each case. Both univariate and multivariate analyses were utilized to determine whether the depth of the LDPE layer could be predicted using the obtained data. The best-achieved RMSE of prediction was 4.2% of the total sample size (i.e., +/- 0.15 mm) with the multivariate approach.

Noninvasive simultaneous monitoring of pH and depth using surface‐enhanced deep Raman spectroscopy

“…To date, SESORS has mostly been used to either show conceptually a SERS signal can be recovered at depth in the range of millimetre to centimetre 10, 11 to monitor specific compounds at depth, be that glucose 12 or neurotransmitters, 13, 14 or finally to inform on other physical properties of the environment, for example, temperature or pH 15–17 . However, in these cases, the SERS reporter has been used for one function at a time, as has been a limitation in our previous studies to date 8, 16, 18 . Here we demonstrate how the spectra can be used in a multiplexed fashion to retrieve information on multiple properties simultaneously, be that the identification of SERS nanoparticles, as well as the depth and the pH using transmission Raman.…”

“…[15][16][17] However, in these cases, the SERS reporter has been used for one function at a time, as has been a limitation in our previous studies to date. 8,16,18 Here we demonstrate how the spectra can be used in a multiplexed fashion to retrieve information on multiple properties simultaneously, be that the identification of SERS nanoparticles, as well as the depth and the pH using transmission Raman. This is an important step change for the field of SEDRS.…”

Self-absorption corrected non-invasive transmission Raman spectroscopy (of biological tissue)

“…[12][13][14] Over time the sophistication of signal retrieval has increased from identifying a single compound, 5,15 to multiplexed signal recovery, 13 physical property signal recovery 16 and depth localisation. [17][18][19][20][21] A number of publications have demonstrated how differential optical properties in a scattering medium, i.e. tissue, between different Raman components can also be exploited for depth localisation.…”

Non-invasive depth determination of inclusion in biological tissues using spatially offset Raman spectroscopy with external calibration

“…Any smaller distortion observed for this inclusion when located inside the matrix a specific depth can then be assigned to it based on the above calibration measurement using a proportionality relationship. In contrast to TRS, 10,13,22 placing the inclusion into the laser illumination and Raman collection cannot be assigned straightforwardly any specific depth in SORS as the spatial offset does not equate directly to depthalthough it is related to it by some scaling factor. To find this relationship and specifically the scaling factor, we have carried out Monte Carlo (MC) simulations for medically relevant scenarios.…”