Transdermal delivery is a useful and attractive method for drug delivery, even though the stratum corneum is a major barrier of protein translocation into the skin. To achieve protein delivery through the stratum corneum, we first cast gold nanorods, acting as a heating device in response to near-infrared light irradiation, onto the skin surface. After applying an aqueous solution of ovalbumin to the skin, the skin was irradiated by near-infrared laser light. Irradiation of the skin using a continuous-wave laser increased the skin temperature resulting in an efficient translocation of ovalbumin into the skin. Furthermore, migration of inflammation cells and induction heat shock protein 70 (HSP70) were observed. Irradiation of the skin using a pulsed laser caused an enhanced permeability of the stratum corneum without an increase in skin temperature, migration of inflammation cells, or HSP70 induction. This effect is due to the pulsed-laser irradiation increasing the temperature of a limited part of the skin surface. Thus, the physiological response of skin is dependent on the type of laser light used. It is anticipated that this phenomenon will find wide application in such applications as, for example, general transdermal protein delivery and transdermal vaccination.
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