Controlling Nanoparticle Dynamics in Conical Nanopores

Conical nanopores are a powerful tool for characterizing nanoscale particles and even small molecules. Although the technique provides a wealth of information, such pores are limited in their ability to investigate particle dynamics due to high particle velocities through a very short sensing zone. In this report, we demonstrate the use of applied pressure to balance electrokinetic forces acting on 8 nm diameter Au nanoparticles as they translocate through a ∼10 nm diameter orifice. This force balance provides a means to vary nanoparticle velocity by 3 orders of magnitude, allowing for their detection and characterization on time scales as long as 100 ms. We studied nanoparticles having different zeta potentials by varying salt concentration, applied pressure, and voltage to reveal the point at which forces are balanced and the particle velocities approach zero. Variation of the voltage around this force balance point provides a means to precisely control the magnitude and direction of the particle translocation velocity. Nanoparticle velocities computed from finite-element simulations as a function of applied pressure and voltage yield predictions in semiquantitative agreement with the experimental results. Optimizing the conditions of these techniques will allow the characterization of particles and their dynamics down to the smallest end of the nanoscale range.