Effect of Ionic Constituents on the Propagation of Charged Nanospheres in Passivated Gel Electrophoresis

We explore the types and concentrations of ionic constituents in aqueous buffer solutions that largely determine their conductivities. These constituents, in turn, directly influence the electric field E acting on charged sulfate-stabilized polystyrene nanospheres, having diameters ranging from ≈40 nm to ≈200 nm, that propagate at velocities v through large-pore, passivated agarose gels in a sodium borate buffer. Conductivity measurements near the center of the gel region show that predictions of E based on a constitutive conductivity model closely correlate with v of propagating bands of nanospheres, as measured using time-lapse optical video recording of scattered light. Additionally, we explore v(E) influenced by two different passivation agents: nonionic polyethylene glycol (PEG) and anionic sodium dodecyl sulfate (SDS). The conductivity model leads to a refined and more accurate estimate of E as compared to the standard method of dividing applied voltage by an inter-electrode separation. Moreover, this conductivity model provides a good starting point for interpreting the complicated effects of amphiphilic ionic passivation agents, such as dodecyl sulfate anions, on the velocities of propagating nanospheres in gel electrophoresis.