Photothermal imaging in 3D surface analysis of membrane drug delivery

Various methods exist for research into the penetration process in the human nail plate and for investigation of dermal drug delivery. Application of spectroscopic methods in this scientific field is gaining importance. However, no method meets all demands of the large variety of applications. An alternative optical technique for the characterisation of samples is the photothermal spectroscopy. Photoacoustic techniques, photothermal radiometry, and photothermal beam deflection spectroscopy (PDS) are non-destructive analytical techniques that take advantage of the so-called photoacoustic and photothermal phenomena. PDS, in conjunction with an appropriate scanner, allows for depth profiling and is a promising technique for studies of three-dimensional drug diffusion into artificial and biological membranes. The objective of this article is to demonstrate the use of PDS imaging for pharmaceutical applications and drug delivery studies, with two experiments being used as examples: the follow-up of lateral dithranol penetration into an artificial membrane and depth-resolved measurement of the distribution of a model drug within a keratin membrane from bovine hoof.