Exposure to engineered nanoparticles (NPs) is becoming near-inescapable as their unique size dependent properties have ensured integration into a wide range of consumer products and research tools. One of the most biologically impactful of these applications is in consumer products such as sunscreens and other cosmetics. where consumer use commonly consists of topical application to UVB damaged skin. A number of studies have investigated the ability of NPs to penetrate the skin barrier, but very few are available on NP permeation differences that result from clinically relevant skin barrier disruptions such as UVB. This thesis uses semiconductor quantum dots (QDs) as a model nanoparticle to investigate the impact of UVB on skin permeability. QDs are NPs with advantageous fluorescence properties including high quantum yield, broad excitability, and narrow emission bandwidth. This doctoral dissertation evaluates the impact of UVB on QD skin penetration, investigates the effects of UVB primary keratinocyte QD cellular interaction, and expands the technical palette with whole tissue confocal imaging development.;UVB radiation causes a host of biological changes in the skin, one of which is epidermal barrier disruption. In the first portion of this thesis, the skin penetration of carboxylated QD through the skin of SKH-1 mice with and without UVB exposure was evaluated immediately after irradiation. Skin samples collected at 8 and 24 hours after QD application demonstrated low levels of penetration in non-UVB exposed mice and qualitatively higher but still low levels of QD penetration in the UVB exposed mice. To approach a quantitative evaluation of both UVB-induced defect and QD skin penetration, this dissertation next used a designed experiment approach to evaluate the effects of UVB on skin barrier function as measured by transepidermal water loss and the impact of UVB on skin penetration of QDs with atomic absorption spectroscopy. UVB induced a strong defect that peaked 4--6 days after exposure. Carboxylic acid coated QDs were applied to SKH-1 mice over the peak barrier disruption 24 hours, and both a qualitative increase in skin penetration after UVB exposure using microscopy and a low-level quantitative increase in Cd levels in the liver were found, suggesting increased systemic access. Interestingly, experiments found statistically significant but still low levels of QD collection in the lymph nodes without UVB exposure whose magnitude decreased with UVB.;Increased QD skin penetration with UVB exposure suggests that topically applied QDs will be able to interact with local cells in the epidermis. To investigate this possibility, differences in acute QD cytotoxicity and uptake of carboxylated QDs between proliferative and differentiated primary keratinocytes with and without UVB exposure have been evaluated. Despite similarities between proliferative and differentiated keratinocytes in UVB and QD cytotoxicity, the proliferative cells have a much greater ability to endocytose QDs than differentiated cells. These results suggest the greater potential for QD interaction with proliferative basal and suprabasal cells in the epidermis which could potentiate a higher risk of possible long-term effects from NP contact with UVB exposed skin.;A challenge in the evaluation of NP skin penetration is sampling error and other problems associated with histological processing. Current literature suggests the usefulness of confocal or tnultiphoton microscopies to address these issues. The final portion of this thesis introduces the design, implementation; and validation of a fluorescence and reflectance confocal microscopy system that utilizes far-red excitation to detect near-IR lead sulfide QDs through ex vivo human stratum corneum and in the epidermis. The tested system achieves QD sensitivity measures on par with those reported in the literature for other techniques, and is demonstrated to detect QDs permeating skin.;This dissertation presents the first published results to evaluate the impact of UVB on skin penetration of QDs and keratinocyte interaction with QDs, and has advanced technology for whole-tissue confocal microscopic evaluation of QD skin penetration. Important advancements have been made, suggesting that UVB may increase risk of systemic exposure to NPs, and that the lymphatic system may play an important role in the translocation of topically applied NPs.
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