"Effects of topical creams containing vitamin C, a copper-binding peptide cream and melatonin compared with tretinoin on the ultrastructure of normal skin - A pilot clinical, histologic, and ultrastructural study"
In this assay, the 30 min incubation duration was chosen to be optimal because of the inherently cytotoxic nature of CuCl 2 and Cu(OAc) 2 towards HaCaT keratinocytes, as they were observed to cause substantial cell death at a duration longer than 30 mins
If you cant do that, just flip on as many artificial lights as you can
Wang S, Yang H, Fu Y, Teng X, Wang C, Xu W
Naturwissenschaften 66:377382 Kwak JM, Mori IC, Pei ZM, Leonhardt N, Torres MA, Dangl JL, Bloom RE, Bodde S, Jones JD, Schroeder JI (2003) NADPH oxidase AtrbohD and AtrbohF genes function in ROS-dependent ABA signaling in Arabidopsis