Fig. 7: In vivo OPTM imaging of human skin.

a Schematic and photo of in vivo OPTM imaging of a human’s forearm skin. b Photothermal phase gradient images of endogenous proteins and lipids in the viable epidermis layer with a depth of 40 µm without topical drug administration. c Phase gradient DC image of the stratum corneum showing a hair on the skin surface and the hair follicle opening. d–g Photothermal phase gradient images of protein (d 1553 cm⁻¹), fatty acid (e 1704 cm⁻¹), lipid ester (f 1742 cm⁻¹), and benzoyl peroxide (g 1760 cm⁻¹) in the stratum corneum layer with a depth of 8 µm after topical drug administration. h An overlap image of phase gradient DC and drug distribution. i An overlap image of endogenous lipid and administrated drug contents. FA fatty acid, LE lipid ester. BPO benzoyl peroxide. Scale bar 50 µm. Field of view was 120\(\times\)120 µm². Probe power on sample was 10 mW. IR power on sample was ~2 mW with repetition rate of 390 kHz and pulse width of 100 ns. The imaging speed was 2 frame per second with a pixel dwell time of 8 µs. PG phase gradient, FA fatty acid, LE lipid ester, BPO benzoyl peroxide.