where 𝜔 𝑝 is the bulk plasma frequency that governs the LSPR, 𝑛 𝑒 is the carrier density, 𝑒 is the elementary charge, 𝜀 𝑜 is the dielectric constant of free space, and 𝑚 * is the effective carrier mass. While many reports have focused on modifying carrier density through intrinsic doping (vacancy generation) and extrinsic doping (aliovalent doping), a distinctive advantage of LSPR in doped semiconductor NCs is the opportunity for substantial dynamic post-synthetic modulation of the carrier density. This post-synthetic modification of the carrier density can be achieved using an external source of carriers, such as an electrochemical potential, light-activated reduction, or a chemical redox agent. For instance, addition of an aliovalent dopant during In2O3 NC synthesis leads to degenerate doping of the semiconductor and consequently, doped In2O3 NCs exhibit LSPR in the near-infrared region. The electrons provided by post-synthetic doping are expected to have a chemical potential above the Fermi level potential. However, due to the presence of surface states, the Fermi level is pinned to the surface potential, triggering the formation of a depletion (low carrier density) region at the surface of the NC. Therefore, modulation of surface sensitive properties like LSPR, catalysis, sensing and electrical conductivity in degenerately doped materials such as doped In2O3 NCs becomes inherently dependent on the presence of this surface depletion layer. Indeed, studying electrochemical modulation of LSPR in thin films of Sn-doped In2O3 (Sn:In2O3) NCs showed that the extent to which the LSPR shifts during charging is controlled by the fraction of the NC volume occupied by the depletion layer at the surface, which depends on both NC size and Sn dopant concentration. However, in electrochemically charged thin films, net LSPR shift of doped metal oxide NCs is dependent on a competition between depletion effects and changes in plasmonic coupling between NCs, which makes it difficult to precisely identify the contribution of depletion effects in controlling LSPR modulation of doped metal oxide NCs. Performing spectroelectrochemical investigations on colloidal dispersions of polymer-wrapped Sn-doped In2O3 NCs circumvents LSPR coupling effects, but it's difficult to stabilize colloidal dispersions over a wide range of electrochemical conditions, limiting the range of information that has been gleaned by this approach. Thus, we sought a method of post-synthetic doping in colloidal dispersions of Sn:In2O3 NCs that maintained NC stability, in order to isolate the effects of the depletion layer on the LSPR modulation. In that respect, chemical doping can be performed on stable colloidal dispersions of NCs and with an appropriate reducing (oxidizing) reagent, it also enables facile transfer of electrons to (from) the NCs. Thus, to deconvolute the contribution of depletion effects in governing the extent of LSPR modulation, we carried out chemical doping on Sn:In2O3 NCs of varying sizes and doping concentrations. In addition, this also allowed us to systematically investigate the effects of chemical doping on LSPR of NCs with different size and doping percentage to compare with earlier electrochemical studies carried out on similar NCs. Chemical doping has been extensively utilized in dispersions of metal oxide NCs to reveal information about electronic energy levels and their relationship to their chemical environment and to other NCs. The optical band gap energy and magnitude of near-infrared absorption due to free electrons increases in undoped ZnO NCs when decamethylcobaltocene (CoCp*2) is added to a dispersion, signifying electron transfer to the ZnO NCs. CoCp*2 is an ideal reductant to use because it is highly soluble in nonpolar solvents typically used to disperse NCs. CoCp*2 has a high standard reduction potential of -1.95 V vs Fc +/0 (ferrocenium/ferrocene redox pair), high enough to reduce ZnO and presumably other metal oxide NCs. Further, the magnitude of electron transfer from CoCp*2 to NCs is increased substantially by addition of an acid to facilitate proton-coupled electron transfer. Given that ZnO and In2O3 have similar band gap energy and band-edge positions, we hypothesized that CoCp*2 should also be able to spontaneously reduce Sn:In2O3 NCs.