Application of multiphoton microscopy to study of nanoparticle penetration through skin in vitro and in vivo

Convergence of nanotechnology and biomedicine provides new opportunities. It appears that nanoparticles can carry drug cargo to a targeted cell population, with exciting prospects of side-effect-free medical treatment. Their potential cytotoxic effects, however, must be avoided. Also, widespread application of zinc oxide nanoparticles (ZnO-nano) in pharmacy and cosmetic care raises concerns due to the reported cytotoxicity of ZnO-nano (Nohynek et al.).  It is safer if ZnO-nano stays on the topmost layer of skin.

Together with the medical researchers, we have visualised ZnO-nano distribution in skin, including live skin.  The key technique is multiphoton microscopy (MPM) that can produce clear subsurface images of skin at the sub-cellular resolution (see Figure).  Although exquisite imaging capabilities of MPM have been demonstrated (Xu et al.), strong contrast of ZnO-nano on skin autofluorescence background was remarkable and surprising (see Figure, left panel). We now aim to address an important question on the skin penetrability to nanoparticles taking into account skin type, treatment, and nanoparticle size.

G. J. Nohynek, J. Lademann, C. Ribaud, M. S. Roberts, “Grey goo on the skin? Nanotechnology, cosmetic and sunscreen safety”, Critical Rev. Toxicol. 37 251 (2007).
C. Xu, W. Zphel, J. B. Shear, R. M. Williams, and W. W. Webb, “Multiphoton fluorescence excitation: New spectral windows for biological nonlinear microscopy”, Proc. Natl. Acad. Sci. USA 93, 10763 (1996).

A multiphoton micorscope system "DermaInspect" for imaging in vivo comprising box on the left of the optical table with a pulsed femtosecond laser (box on the right of the optical table), and with a bedside.	An MPM subsurface image of human skin in vivo at a depth of 26 mm. Epidermis layer cells are clearly observable, with dark nuclei (bottom part of the image). Image of ZnO-nano distributino is overlaid (red colour). It is evident that ZnO-nano falls in skin folds, but does not penetrate to the epidermis. Scale bar 30 mm.

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Last modified: 14 August, 2007