Determination of inclusion depth in ex vivo animal tissues using surface enhanced deep Raman spectroscopy

Abstract

This work presents recent developments in spatially offset and transmission Raman spectroscopy for noninvasive detection and depth prediction of a single SERS inclusion located deep inside ex vivo biological tissues. The concept exploits the differential attenuation of Raman bands brought about by their different absorption due to tissue constituents enabling to predict the inclusion depth. Four different calibration models are tested and evaluated to predict the depth of surface enhanced Raman scattering labelled nanoparticles, within an up to 40 mm slab of porcine tissue. An external measurement carried out in transmission mode, with a noninvasively built model on the analysed sample, is shown to be insensitive to variations of the overall thickness of the tissue yielding an average root‐mean‐square error of prediction of 6.7%. The results pave the way for future noninvasive deep Raman spectroscopy in vivo enabling to localise cancer biomarkers for an early diagnosis of multiple diseases.

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.…”

“…The second type of multi-layer phantom was made of ex vivo animal tissue (turbid matrix) and SERS nanoparticles (NPs) (inclusion). 13 The ex vivo tissue consisted of a stack of sliced back bacon from pork loin (45 × 45 × 2 mm or 45 × 45 × 3 mm per slice) purchased fresh from a local store and frozen until used. The SERS NPs used as an inclusion consisted of gold NPs (approximately 100 nm diameter) labelled with Raman reporters (d8-4,40-dipyridyl-d8DIPY) and coated with a silica shell (acquired from Oxonica 25 ) already characterised and used previously.…”

“…The SERS NPs used as an inclusion consisted of gold NPs (approximately 100 nm diameter) labelled with Raman reporters (d8-4,40-dipyridyl-d8DIPY) and coated with a silica shell (acquired from Oxonica 25 ) already characterised and used previously. 13,16 The SERS NPs were transferred into a quartz cuvette (2 mm optical path length; H × W × D = 2 × 10 × 2 mm 3 ) and then multiple layers of porcine tissue were added either side of the cuvette. The sample used for the study consisted of approximately 2.8 × 10 14 NPs ml −1 .…”

“…8 Recent medically-oriented research has also demonstrated the use of SORS and TRS for monitoring physical information such as pH 9 and temperature 10 and localising and predicting the depth of an inclusion (target) within turbid media. [11][12][13] Moreover, surface-enhanced Raman spectroscopy (SERS) nanoparticles (NPs) can be used to target specific biomarkers of interest at depth by combining SERS and SORS techniques (i.e. SESORS) permitting, for example, effective in vivo imaging of cancer lesions [14][15][16] or neurotransmitters through skull.…”

“…Recent research has proposed and demonstrated the use of SORS to retrieve the depth information of a single inclusion buried within a diffusively scattering synthetic phantom 12 and ex vivo tissues. 13 The method relies on there being a difference in the optical properties (e.g. absorption coefficient μ a and scattering coefficient μ′ s ) of the diffusive medium as a function of wavelength over the acquired Raman spectral range.…”