An iso-structural series of 1e^--reduced alpha-Keggin heteropolytungstate anions, alpha -Xⁿ⁺W₁₂O₄₀^(9-n)-, Xⁿ⁺ = Al³⁺, Si⁴⁺, P⁵⁺ (1e^- donors), have been developed for use as physicochemical "probes" of electron-transfer processes.  This series of cluster anions has recently provided new information about outer-sphere electron to O₂ in water.  Here, these anions are used to investigate the activation barriers and other fundamental parameters associated with electron-transfer between ligand-protected metal nanoparticles.   In preliminary data presented here, 2-nm core, octanethiol-capped Au nanoparticles serve as versatile and kinetically addressable models for structures that impart functionality to nanoscale materials and devices.  Kinetic interrogation of these soluble nanoparticles by the polyoxometalate (POM) probes provides rate constants (k) and reorganization energies (lambda), while theoretical models relate these parameters to the physics of materials engineering and molecular electronics.