Fig. 2.

Schematic depiction of the phantom measurement setup at four axial positions (a) 9.5  mm, (b) 7.5 mm, (c) 5.5 mm, and (d) 3.5 mm along a single lateral position (top); representative spectra collected at the four axial positions (bottom left); and the resultant abundance map (bottom right). The shaded peak in the Raman spectra corresponds to the major peak of the SERS nanoparticle solution. The focal distance of the probe is 7.5 mm.