The absorption maxima (max) of the solutions were analyzed by means of ultraviolet/visible spec-troscopy (UV/VIS) using a NanoDrop ND-1000 spectrophotometer (NanoDrop Technologies, Wilmington, DE, USA) to determine the approximate particle sizes, which were confirmed by transmission electron microscopy (TEM) measurements using a JEM-1230 transmission electron microscope (TEM; JEOL, Tokyo, Japan)