Cutaneous Porphyrin Exhibits Anti-Stokes Fluorescence Emission Under Continuous Wave Laser Excitation

We report the discovery that anti-Stokes fluorescence emission can be induced from porphyrins by continuous wave (cw) laser excitation. An anti-Stokes spectroscopy and imaging technique with an integrated multimodal imaging system was developed to study cutaneous porphyrin in psoriasis, acne, and nasal skin. We experimentally demonstrated that under 785 nm cw laser excitation, photoporphyrin IX (PpIX) powder exhibited anti-Stokes fluorescence with its intensity linearly depending on the excitation power, confirmed that it is a single-photon process. Anti-Stokes fluorescence imaging of psoriasis scale, acne sebum smear, and nasal skin was performed. The results showed that Anti-Stokes fluorescence is sensitive and also specific for porphyrin detection without interference from other skin fluorophores.