Shifted excitation resonance Raman difference spectroscopy system suitable for the quantitative in vivo detection of carotenoids in human skin

A system for shifted excitation resonance Raman spectroscopy (SERRDS) suitable for the application in medical practice for the in vivo detection of carotenoids in human skin is presented. This system comprises a miniaturized (150 mm × 27 mm × 12 mm) handheld probe and a wavelength-tunable diode laser-based 488 nm SHG light source. The diode laser provides two closely spaced excitation wavelengths. In parallel with the resonance excitation of carotenoids in the skin, SERRDS separates the fluorescence background from the Raman peaks. Inhomogeneities of human skin are averaged by the applied spot diameter of 3 mm. The implemented optics are designed for a detection of carotenoids over the whole excitation spot area. The system was calibrated using skin phantoms, resulting in a detection limit of 0.03 nmol g−1 (beta-carotene per gram of skin/tissue) which is more than one order of magnitude below the average beta-carotene concentration in human skin.