AbstractsPhysics

Porphyrins produced by Propionibacterium acnes represent the principal fluorophore associated with acne, and appear as orange-red luminescence under the Wood’s lamp. Assessment of acne based on Wood’s lamp (UV) or visible (VIS) light illumination is limited by photon penetration depth and has limited sensitivity for earlier stage lesions. Inducing fluorescence with near infrared (NIR) excitation may provide an alternative way to assess porphyrin-related skin disorders. The objectives of this thesis are (1) to design and develop an optical instrument that perform anti-Stokes fluorescence spectroscopy and imaging measurements under continuous wave CW laser excitation as well as multiphoton fluorescence spectroscopy and imaging under femtosecond (fs) pulsed laser excitation; and (2) using this system for regular (Stokes) fluorescence measurements to evaluate and compare sebum-associated porphyrin fluorescence properties. A NIR multi-modality fluorescence imaging system with fluorescence spectroscopy capability was constructed. The switchable output from a tunable Ti : Sapphire femtosecond (fs) laser (720-950nm) or a (CW) laser (785nm) was scanned over the objective lens. Co-registered confocal imaging and fluorescence (anti-stokes fluorescence & two-photon fluorescence) imaging were acquired in video rate. Under 785 nm CW laser excitation PpIX powder exhibited anti-Stokes fluorescence with an intensity that was linearly dependent on the excitation power and a red spectral emission of 650-720 nm, while the fs laser excited two-photon excitation fluorescence showed a quadratic dependency. Anti-Stokes fluorescence of psoriasis scale image and ex vivo human nasal skin, skin surface smears from the nose, and ex vivo sebum secretions was obtained by the same system configuration. Regular (Stokes) fluorescence was presented under UV and visible light excitation on ex vivo nasal skin and sebum secretions from non-inflamed acne, but not on skin surface smears from the nose or sebum secretions from inflamed acne. In conclusion, anti-Stokes fluorescence under NIR CW excitation is more sensitive and specific for porphyrins than UV or visible light-excited regular (Stokes) fluorescence and fs laser-excited multi-photon fluorescence. The anti-Stokes fluorescence of porphyrins within sebum could potentially be applied to detecting and targeting acne lesions for treatment via fluorescence image guidance.