Additional file 1:
A scan area of head and midpiece region of human sperm cell. (A) 3D SNOM topography, (B) SNOM reflection and (C) transmission. (D) longitudinal profile along the head. Black arrows in (B) indicate the ends of post-acrosomial part, while red arrows in (C) indicate the ends of the bright layer partially surrounding the head and that includes the acrosome. In (E) cross section profile along the white line in (C) allows evaluating the width of this layer (266 nm).