Inverse SORS for detecting a low Raman-active turbid sample placed inside a highly Raman-active diffusely scattering matrix – A feasibility study

The broad range of applications of spatially-offset Raman spectroscopy (SORS) were found to involve samples having only marginal differences in Raman cross-sections between the surface and subsurface targets. We report the results of a feasibility study to evaluate the potential of the approach to identify the presence of a very low Raman-active turbid sample placed inside a highly Raman-active diffusely scattering matrix. Paraffin sandwiched tissue blocks prepared by embedding slices of chicken muscle tissue into solid paraffin blocks were employed as representative samples for the study. It was found that in contrast to the several millimetres of probing depth reported in the earlier applications, the Raman signatures of tissue were best recovered when it was located beneath the surface of the paraffin block at a depth of around a millimetre, beyond which the quality of recovery was increasingly poorer. However, the probing depth could be further increased by increasing the thickness of the embedded tissue sections. The results clearly suggest that though the probing depth achievable under the current condition is less than that found in previous applications, nevertheless it is sufficient for various other applications that would not require probing as deep as was required earlier.

The paper reports a feasibility study aimed to evaluate the potential of inverse SORS in the identification of a very low Raman active sample placed under a highly Raman active compound. The results suggest though the probing depth achieved is much less than that reported earlier, inverse SORS is a promising candidate for a potentially broad range of applications requiring non-invasive SORS measurement of a weak Raman scattering layer below a strongly Raman scattering overlayer

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