Figure 13.

Smoothing fitted function of the reflectance of GNP-hydrogel with ${\mathrm{ND}}_{03}$ at $1.7\times {10}^{11}$ particles/mL at pH 4.4 with the corresponding first derivative. The minimum of the first derivative of the reflectance of GNP-hydrogel determines the baseline used for computing the FWHM.