Nanoparticle size distributions measured by optical adaptive-deconvolution passivated-gel electrophoresis

We image visible light scattered from dispersions of charged spherical nanoparticles propagating through a passivated agarose gel during electrophoresis. By analyzing one-dimensional light intensities along different lanes, we measure the mobility distributions of the nanoparticles and thereby infer their size distributions, which become time-independent after adequate propagation and separation have occurred. For a given large-pore passivated agarose gel, experiments using monodisperse, surfactant-free, sulfate-stabilized, polystyrene nanopheres establish the propagation distance as a function of time for a range of different sphere radii having known surface charges. As bands of monodisperse nanospheres propagate through the gel, the bands become smeared, developing asymmetric tails as some nanospheres experience additional delays compared to others of the same size. After background subtraction, these bands, including their tails, can be fit well using a modified log-normal distribution, yielding deconvolution parameters that vary with propagation distance and transit time. To demonstrate the approach for complex nanosphere dispersions, such as a multi-modal mixture or a broadly polydisperse nanoemulsion, we measure scattered light intensities as a function of propagation distance and time during gel-EP. Iterative deconvolution using a modified log-normal point-spread function, which changes shape according to propagation distance and time, directly yields unsmeared, high-resolution electrophoretic mobility distributions, from which detailed particle size distributions are inferred.