Oleogel-mediated transdermal delivery of white emitting NaYF4 conjugated with Rose Bengal for the generation of reactive oxygen species through NIR-upconversion.

The transdermal route for the delivery of therapeutic agents to the inner skin tissues for non-invasive photodynamic therapy; though constitutes a desired modality for treating skin cancer, the success has been limited due to the insurmountable nature of the stratum corneum (SC). In this context, for the first time we report the localization of photosensitizer-conjugated upconversion (UC) particles to the deeper dermal region by overcoming SC through an oleogel-mediated transport mechanism for NIR-induced photodynamic production of reactive oxygen species (ROS). We developed soybean oil and stearic acid based oleogels by incorporating photoluminescent white light emitting NaYF4 (WEN) upconversion (UC) particles conjugated with Rose Bengal (RB), termed as WEN-RB-G. Similarly, we fabricated another type of oleogel by incorporating Li+ doped WEN based UC particles (RB conjugated), with 10 times more photoluminescence intensity, termed as LiWEN-RB-G. Based on the skin permeation enhancing effect of the constituents of the oleogels, we demonstrated the permeation of these two types of conjugated particles in microgram scale through the full thickness of the pig ear skin model within 48 h. The localization of the conjugated particles throughout the skin tissue including dermal and epidermal region was confirmed by confocal microscopy. We also conducted a comparative assessment on WEN-RB-G and LiWEN-RB-G for the suitability of ROS generation and bioimaging under NIR activation. The 'proof of principle' concept reported here is expected to frame a gateway in future for NIR-induced photo-theranostics targeting skin cancer.