Issue 23, 2020

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

Abstract

Spatially offset Raman spectroscopy (SORS) allows chemical characterisation of biological tissues at depths of up to two orders of magnitude greater than conventional Raman spectroscopy. In this study, we demonstrate the use of SORS for the non-invasive prediction of depth of an inclusion within turbid media (e.g. biological tissues) using only external calibration data sets, thus extending our previous approach that required internal calibration. As with the previous methodology, the concept is based on relative changes in Raman band intensities of the inclusion that are directly related to the path length of Raman photons travelling through the medium thereby encoding the information of depth of the inclusion. However, here the calibration model is created using data only from external measurements performed at the tissue surface. This new approach facilitates a fully non-invasive methodology applicable potentially to in vivo medical diagnosis without any a priori knowledge. Monte Carlo simulations of photon propagation have been used to provide insight into the relationship between the spatial offset and the photon path lengths inside the tissues enabling one to derive a general scaling factor permitting the use of spatial offset measurements for the depth prediction. The approach was validated by predicting the depth of surface-enhanced Raman scattering (SERS) labelled nanoparticles (NPs) acting as inclusions inside a slab of ex vivo porcine tissue yielding an average root mean square error of prediction of 7.3% with respect to the overall tissue thickness. Our results pave the way for future non-invasive deep Raman spectroscopy in vivo by enabling, for example, the localisation of cancer lesions or cancer biomarkers in early disease diagnosis and targeted treatments.

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

Supplementary files

Article information

Article type
Paper
Submitted
29 6 2020
Accepted
21 9 2020
First published
22 9 2020
This article is Open Access
Creative Commons BY license

Analyst, 2020,145, 7623-7629

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

S. Mosca, P. Dey, M. Salimi, F. Palombo, N. Stone and P. Matousek, Analyst, 2020, 145, 7623 DOI: 10.1039/D0AN01292K

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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