Development of portable defocusing micro-scale spatially offset Raman spectroscopy

Abstract

We present, for the first time, portable defocusing micro-Spatially Offset Raman Spectroscopy (micro-SORS). Micro-SORS is a concept permitting the analysis of thin, highly turbid stratified layers beyond the reach of conventional Raman microscopy. The technique is applicable to the analysis of painted layers in cultural heritage (panels, canvases and mural paintings, painted statues and decorated objects in general) as well as in many other areas including polymer, biological and biomedical applications, catalytic and forensics sciences where highly turbid stratified layers are present and where invasive analysis is undesirable or impossible. So far the technique has been demonstrated only on benchtop Raman microscopes precluding the non-invasive analysis of larger samples and samples in situ. The new set-up is characterised conceptually on a range of artificially assembled two-layer systems demonstrating its benefits and performance across several application areas. These included stratified polymer sample, pharmaceutical tablet and layered paint samples. The same samples were also analysed by a high performance (non-portable) benchtop Raman microscope to provide benchmarking against our earlier research. The realisation of the vision of delivering portability to micro-SORS has a transformative potential spanning across multiple disciplines as it fully unlocks, for the first time, the non-invasive and non-destructive aspects of micro-SORS enabling it to be applied also to large and non-portable samples in situ without recourse to removing samples, or their fragments, for laboratory analysis on benchtop Raman microscopes.

SERS detection of food contaminants by means of portable Raman instruments

“…Variations of Raman spectroscopy. Spatially offset Raman spectroscopy and portable sequentially shifted excitation Raman spectroscopy have been also implemented in portable devices. The former allows one to record spectra through obscuring surfaces (e.g., explosives inside containers and pharmaceutical products inside plastic bottles) avoiding (or minimizing) the contribution of the surface; the latter instead reduces the unwanted contribution of fluorescence by combining the Raman spectra acquired at two slightly different excitation wavelengths.…”

Methodological evolutions of Raman spectroscopy in art and archaeology

“…To enable micro-SORS to perform in situ measurements, a conventional portable Raman equipped with 785 nm excitation wavelength was adapted for defocusing micro-SORS analysis. 140 The new set-up allowed obtaining signicant results on articial micrometric layer systems consisting of spray paint on stone and painted stratigraphy. Given the wide applicability of the technique and potential for further improvements by developing portable full micro-SORS, the concept is expected to nd a number of application niches in several areas providing a benecial complementary analytical capability to conventional Raman microscopy in situations where its accessible depths are inadequate.…”

Non‐invasive and in situ investigation of layers sequence in panel paintings by portable micro‐spatially offset Raman spectroscopy

“…[12] Micro-SORS has been developed on conventional benchtop Raman microscopes, and a large body of literature exists reporting on data from layered systems in polymers and industrial paper, [11] in biomedical area, [13][14][15] and in micro-samples taken from art objects. [12,16,17] Because of the importance of avoiding the invasive sampling and analyzing the artworks in situ, two portable micro-SORS prototypes, set-up according to the defocusing and full micro-SORS variants, [18,19] were developed and tested using laboratory mock-up samples. Here, a micro-SORS portable device was applied, for the first time, to a study of layered makeup of artworks in situ.…”