Figure 1.

A microstructural cross-section of a human finger pad (middle finger) obtained using Optical Coherence Tomography (Spectral Radar OCT – OCP930SR, ex Thorlabs). Typical fingerprint height and spacing are shown with four (spiral) sweat ducts (filled circles) and a drop of sweat (open circle) emerging from a pore on a ridge surface. The sweat ducts are visible within the stratum corneum layer which is relatively dark. The thickness of the stratum corneum is estimated to be approximately 300 µm. This is based on the difference of 400 µm in the optical depth between the light skin surface and the upper boundary of the intermediate light layer, which is the remainder of the epidermis [48,49], and using an assumed value of the refractive index for skin of 1.4. The inset photograph shows the same skin region from above, bounded top and bottom by the edges of the OCT contact probe. (Online version in colour.)