(320e) Electrokinetic Translocation of Nanoparticles Through Nanopores Under Concentration Gradients

We present experimental and theoretical studies of electrokinetic translocation of nanoparticles through solid-state nanopores with/without concentration gradients. Firstly, we used the Coulter counter principle (also known as resistive pulse method) to investigate the electrokinetic translocation of charged polystyrene (PS) nanoparticles (50- and 100-nm-diameter) through solid-state silicon nitride nanopores with diameters from 80 nm to 200 nm, respectively. The time-dependent electric current was recorded as the nanoparticles were driven across nanopores by externally applied voltages. The size of nanoparticles can be discriminated by the different magnitudes of current whereas the mean velocity of particle translocation can be estimated by measuring the duration of the current pulse. The translocation phenomena were further studied under different operating conditions, by changing salt concentrations, pH values, and salt types. In addition to electrophoresis and electroosmosis, a charged particle is also supposed to experience diffusiophoresis arising from the salt concentration gradients. Therefore, we conducted experiments to study how concentration gradients affect the particle translocation. The experiments were carried out at different salt concentration gradients, different sizes of the nanopores and the nanoparticles, and different types of the salts. In order to better understand the mechanisms of particle translocation through nanopores subject to concentration gradients, we further developed a continuum model that consists of the Poisson equation for the electric potential distribution, the Nernst-Planck equations for the ionic mass transport, and the Navier-Stokes equations for the fluid flow. We computed the position-dependent nanoparticle velocity as the nanoparticle moves through the nanopores. The resistive pulse of computational results is in good agreement with the corresponding experimental observations. Both the experimental measurements and computational results indicate that imposing a concentration gradient is an effective way to regulate translocation velocity of nanoparticles through solid-state nanopores. This technique can also be used to regulate the DNA translocation through nanopores for a better DNA detection.