Remote in vivo imaging of human skin corneocytes by means of an optical fiber bundle

Human corneocytes forming the outermost layer of the epidermis (stratum corneum) were imaged in vivo by epifluorescence through a coherent optical fiber bundle. A very simple and rapid method to remotely visualize the cells forming this protective layer of the skin is presented. After the topical application of fluorescein, the distal face of an optical fiber bundle is gently applied perpendicularly onto the labeled skin (contact mode). Remote fluorescence images of the corneocytes are acquired in 50ms through the bundle comprising 30 000 individually cladded 3.5μm diameter optical fibers. The very short focal distance which is an intrinsic characteristic of such bundles, allows visualizing only the most superficial monolayer of cells in contact with the external environment. An image displays about 400–500 cells directly on the human body. The size and the arrangement of the corneocytes can thus be acquired and analyzed in a very simple and easy way. The method is flexible and can be used for any location on the human body. Using a gradient-index lens objective (magnification 2.8×) fused to the distal face of the bundle allows the shape of the corneocytes to be better resolved. In addition, the working distance is 300μm and hence this second approach works in a noncontact imaging mode. Both approaches are complementary and allow providing instantaneously either a global view of the cells with a possible statistical determination of their area or morphological information, which are essential for dermatology and cosmetic sciences. Finally, to improve the quality and the contrast of the recorded images, we tested silica nanoparticles containing fluorescein. In brief, this diagnostic method is nontoxic, painless, easy to use, noninvasive, and nondestructive.