This paper describes a new, organic-soluble 4-tert-butylbenzyl mercaptan (BBT) monolayer-protected silver cluster (AgBBT MPC) as the first example of a dissolved silver nanoparticle that exhibits quantized one-electron double layer charging (QDL) voltammetry. Polydisperse AgBBT MPCs made by two different synthetic protocols, but with similar average core diameters (2.1 nm), exhibit sharply differing electrochemistry and optical absorbance spectra. A twophase procedure (organic/aqueous, termed Prep A-AgBBT) produced MPCs exhibiting a 475 nm surface plasmon absorbance and QDL voltammetry. Neither property was seen for MPCs made by a single-phase procedure, termed Prep B-AgBBT. The difference is thought to reflect poor passivation to oxide formation in the latter Prep B procedure, which is supported by X-ray photoelectron spectroscopy results. Thermogravimetry, mass spectra, and electrochemistry results suggest an a Verage stoichiometric formula of Ag140BBT53, but transmission electron microscopy shows that the products are also polydisperse and include polycrystalline aggregates. Dry, cast films of both Ag MPC preparations on interdigitated array electrodes exhibit low electron hopping conductivity, compared to Au MPCs.