Fig. 4. NO permeation through ex vivo human skin sections upon treatment with GSNO–CS NPs (GSNO concentration of 100 mmol L^–1) for 6 h, followed by 20 min of UV irradiation, compared with those in the dark. Confocal florescence microscopy images of human skin were acquired through incubation of the skin sections with the NO fluorochrome 4,5-diaminofluorescein diacetate (DAF-2DA) for 24 h prior to the addition of: GSNO–CS NPs, GSH–CS NPs, and no treatment (untreated skin sections). Representative images of human skin sections: (A) untreated skin in the dark; and (B) skin treated with GSNO–CS NPs in the dark. (C) Means of fluorescence intensities due to the presence of NO in the epidermis of skin sections (n = 6) of: (i) untreated skin in the dark; (ii) pre-treated skin with GSH–CS NPs in the dark; (iii) pre-treated skin with GSNO–CS NPs in the dark; (iv) untreated skin under UV irradiation for 20 min; (v) pre-treated skin with GSH–CS NPs followed by UV-irradiation for 20 min and (vi) pre-treated skin with GSNO–CS NPs followed by UV-irradiation for 20 min. UV irradiation with 290 nm. *P < 0.05 and AU, arbitrary units.