Multiphoton microscopy for the investigation of dermal penetration of nanoparticle-borne drugs

Abstract

Multiphoton microscopy of a dually fluorescence-labeled model system in excised human skin is employed for high resolution three dimensional visualization in order to study the release, accumulation and penetration properties of drugs released from nanoscale carrier particles in dermal administration. Polymer particles were covalently labeled with fluorescein while Texas Red as a drug-model was dissolved in the particle to be released to the formulation matrix. Single nanoparticles on skin could easily be localized and imaged with diffraction limited resolution. The temporal evolution of the fluorescent drug-model concentration in various skin compartments over more than five hours was investigated by multiphoton spectral imaging of the same area of the specimen. The three dimensional penetration profile of the drug-model in correlation with skin morphology and particle localization information are obtained by a multiple laser line excitation experiment. Multiphoton microscopy combined with spectral imaging was found to allow non invasive long term studies of particle-borne drug-model penetration into the skin with sub cellular resolution. By dual color labeling a clear discrimination between particle-bound and released drug-model was possible. The introduced technique was shown to be a powerful tool in revealing the dermal penetration properties and pathways of drugs and nanoscale drug vehicles on microscopic level.