Imaging of zinc oxide nanoparticle penetration in human skin in vitro and in vivo

Abstract

Abstract. Zinc oxide ͑ZnO-nano͒ and titanium dioxide nanoparticles ͑20 to 30 nm͒ are widely used in several topical skin care products, such as sunscreens. However, relatively few studies have addressed the subdermal absorption of these nanoparticles in vivo. We report on investigation of the distribution of topically applied ZnO in excised and in vivo human skin, using multiphoton microscopy ͑MPM͒ imaging with a combination of scanning electron microscopy ͑SEM͒ and an energy-dispersive x-ray ͑EDX͒ technique to determine the level of penetration of nanoparticles into the sub-dermal layers of the skin. The good visualization of ZnO in skin achieved appeared to result from two factors. First, the ZnO principal photoluminescence at 385 nm is in the "quiet" spectral band of skin autofluorescence dominated by the endogenous skin fluorophores, i.e., NAD͓P͔H and FAD. Second, the two-photon action cross section of ZnO-nano ͓ ZnO ͑TPEF͒ ϳ 0.26 GM; diameter, 18 nm͔ is high: ϳ500-fold of that inferred from its bulk third-order nonlinear susceptibility ͓Im ZnO ͑3͒ ͔, and is favorably compared to that of NAD͓P͔H and FAD. The overall outcome from MPM, SEM, and EDX studies was that, in humans in vivo, ZnO nanoparticles stayed in the stratum corneum ͑SC͒ and accumulated into skin folds and/or hair follicle roots of human skin. Given the lack of penetration of these nanoparticles past the SC and that the outermost layers of SC have a good turnover rate, these data suggest that the form of ZnO-nano studied here is unlikely to result in safety concerns.

Confocal laser scanning microscopy to estimate nanoparticles’ human skin penetration in vitro

“…Permeability of each sized NP made no difference in excised human skin, and no "viable" epidermal penetration was observed. The results were consistent with some reports using human skin 8,18,21 and animal skin. 16,17 Barrier function of SC against molecule penetration in general depends on its protein, lipid and water compartments.…”

“…8 Zvyagin et al 18 suggested that animal skin represents a poor model for human skin for the studies on NP transdermal penetrability. Differences between these skins, especially hair follicle density, SC thickness, whole skin and skin lipid mass, 19 could lead to different results.…”

Nano-zinc oxide damages spatial cognition capability via over-enhanced long-term potentiation in hippocamus of Wistar rats

“…In humans, environmental exposure to nano-ZnO has shown that it stayed in the stratum corneum and accumulated in skin folds and/or hair follicle roots of the skin. 5 Also, exposure to low concentrations of nano-ZnO indicates a genotoxic potential mediated by lipid peroxidation and oxidative stress in epidermal cells. …”

Optical imaging to trace near infrared fluorescent zinc oxide nanoparticles following oral exposure

“…The main drawback of tagging with traceable molecules is potential detachment from the nanoparticles via spontaneous or enzyme-catalyzed reactions in vivo. [17][18][19][20] The dissociation of Cy5.5 from nanoscaled ZnO nanoparticles after 3 hours is inconsequential because the gastric emptying rate is faster than the time needed to dissociate Cy5.5.…”