Non-invasive imaging of skin physiology and percutaneous penetration using fluorescence spectral and lifetime imaging with multiphoton and confocal microscopy

An example of multichannel FLIM data from endogenous fluorophores at the stratum granulosum level in human epidermis, recorded in three wavelength channels (350-450 nm, 450-515 nm, 515-620 nm) with excitation at 740 nm. The lower panel shows decay curves from a selected pixel fitted with a bi-exponential model. The three lifetime images in the upper panel show, from left to right, mainly NAD(P)H, both NAD(P)H and FAD and FAD only. The weak FAD signal and lack of cellular definition seen in the right FAD image indicates that 740 nm is not the optimal excitation wavelength for FAD.