Time-Correlated Single Photon Counting For Simultaneous Monitoring Of Zinc Oxide Nanoparticles And NAD(P)H In Intact And Barrier-Disrupted Volunteer Skin
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There is a lack of relevant, non-animal alternatives for assessing exposure and toxicity of nanoparticle-containing cosmetics, e.g. sunscreens. Our goal was to evaluate timecorrelated single photon counting (TCSPC) for simultaneous monitoring of zinc oxide nanoparticles (ZnO-NP) and the metabolic state of volunteer skin.
We separated the fluorescence lifetime signatures of endogenous fluorophore signals (i.e. nicotinamide adenine dinucleotide phosphate, NAD(P)H and keratin) and the ZnO-NP signal using advanced TCSPC to simultaneously determine ZnO-NP penetration profiles and NAD(P)H changes in subjects with altered barrier function, including tape-stripped skin and in psoriasis or atopic dermatitis lesions.
We detected no ZnO-NP penetration into viable human skin in any group. ZnO-NP signal was significantly increased (p < 0.01) on the surface of tape-stripped and lesional skin after 4 and 2 h of treatment, respectively. Free NAD(P)H signal significantly increased in tape-stripped viable epidermis treated for 4 h of ZnO-NP compared to vehicle control. No significant NAD(P)H changes were noted in the lesional study.
TCSPC techniques enabled simultaneous, real-time quantification of ZnO-NP concentration and NAD(P)H via non-invasive imaging in the stratum corneum and viable epidermis of volunteers.
KEY WORDShuman skin metabolism multiphoton microscopy sunscreen zinc oxide nanoparticle
atomic absorption spectroscopy
fluorescence lifetime imaging microscopy
inductively coupled plasma-optical emission spectroscopy
instrument response function
potassium di-hydrogen phosphate
multiphoton tomography with fluorescence lifetime imaging microscopy
nicotinamide adenine dinucleotide phosphate
second harmonic generation
time-correlated single photon counting
transmission electron microscope
transepidermal Water Loss
zinc oxide nanoparticles
ACKNOWLEDGMENTS & DISCLOSURES
We would like to thank the National Health and Medical Research Council of Australia (ID# 569694) and the United States Air Force Asian Office of Aerospace Research and Development for funding. We also thank Corinne Yoong for recruiting volunteers for the lesion studies.
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