In summary, it was demonstrated that mean free path corrected
Mie theory affords a quantitative description of the absorbance
of GNPs in the size range from 5 to 100 nm where a good
agreement with the experimental data was found. It was shown
that both the size and the concentration of GNPs can be
determined directly from UV-vis spectra using eqs 10-13 for
the calculation of d and eq 14 for the calculation of N together
with the corresponding fit parameters stated in the text. Tabular
material presented in the Supporting Information allows the reader
to determine size and concentration of GNPs without the need to
perform calculations.