Micro-SORS, diffusion processes and heritage science: a non-destructive and systematic investigation

Abstract: In this paper, a systematic investigation is carried out to test micro-SORS capability to non-destructively characterize a system where an agent diffuses into a turbid matrix with potential applications in heritage science and elsewhere. Defocusing micro-SORS experiments were performed on two specially designed sets of samples with controlled characteristics. Three parameters have been considered, namely penetration depth, concentration of the agent and its profile within the matrix. A relative agent/matrix Raman intensity decay rate is observed when the microscope objective is moved away from the sample surface, and the slope of this ratio trend was found to correlate with the penetration depth of the agent involved in the diffusion process. In situations where the concentration profile is known, different penetration depths of the agent can be discriminated from each other using the slope of the normalized agent/matrix Raman intensity decay rate. This outcome opens prospects for non-destructively monitoring the efficacy of conservation treatments, based on the penetration depth of the products as well as it provides an analytical tool for other applications where the penetration of an agent into a diffusely scattering matrix is involved such as drug perfusion through skin, pharmaceutical tablet dissolution process and numerous others. Graphic abstract: [Figure not available: see fulltext.].