The extent of the depletion layer is determined by synthetically controlled physical attributes such as the doping percentage, radial dopant distribution, size and shape of the NCs. Therefore, synthetic conditions must be optimized to yield NCs with precise control over these parameters to set the stage for a reliable quantitative assessment of electron transfer. Thus, by adapting a continuous injection procedure developed by the Hutchison group, we first synthesized highly monodisperse spherical Sn:In2O3 NCs with different sizes and Sn doping percentages and uniform dopant distribution. More precisely, by adjusting the injection volume and ratio of the metal ion precursors (see experimental section for more details), NCs with average diameter between 8-21 nm and Sn doping percentage between 4.5-13% were synthesized. A summary of synthesized NCs listing the doping percentages obtained from inductively coupled plasma atomic emission spectroscopy (ICP-AES) and the average diameter from scanning transmission electron microscopy (STEM) is provided in Table . All NCs exhibit spherical morphology with low polydispersity (~10%) in their diameter (Figure and). Across the sample series, an increase in the NC diameter leads to a progressive increase of the LSPR peak energy, because of higher dopant activation and a decrease in surface scattering, both of which contribute to a higher electron density (Figure and S4). For a given size, the LSPR peak shifts to higher frequency as Sn doping percentage increases, owing to a progressively higher electron concentration (Figure and S4). To study the effects of depletion on LSPR modulation through chemical doping, the as-synthesized NCs were dispersed in anhydrous toluene/tetrahydrofuran (THF) (1:1 ratio) mixture anaerobically. 50 µL of 0.02 M [H(OEt2)] + [BAr -(also known as Brookhart's acid) in THF was subsequently added to the NC dispersion and this mixture was titrated with 5 µL aliquots of 0.02 M CoCp*2 solution in THF : toluene (1:1) while extinction measurements were performed continuously through an optical fiber assembly (see experimental section for details). -acid solution to the NC dispersion preserves the original LSPR frequency and peak width (Figure ), which suggests that addition of protons doesn't deteriorate the colloidal stability of NCs or initiate any electron transfer. This observation is consistent with the previous assessment that proton-coupled electron transfer occurs only upon addition of a reducing agent such as CoCp*2, to [H(OEt2)] + [BAr F