Tunable aqueous virtual micropore

A charged microparticle can be trapped in an aqueous environment by forming a narrow virtual pore-a cylindrical space region in which the particle motion in the radial direction is limited by forces emerging from dynamical interactions of the particle charge and dipole moment with an external radiofrequency quadrupole electric field. If the particle satisfies the trap stability criteria, its mean motion is reduced exponentially with time due to the viscosity of the aqueous environment; thereafter the long-time motion of particle is subject only to random, Brownian fluctuations, whose magnitude, influenced by the electrophoretic and dielectrophoretic effects and added to the particle size, determines the radius of the virtual pore, which is demonstrated by comparison of computer simulations and experiment. The measured size of the virtual nanopore could be utilized to estimate the charge of a trapped micro-object. Charged microparticles in an aqueous environment are trapped in microsized tunable aqueous virtual pores (AVP) formed by quadrupole electric fields of a linear Paul microtrap. The AVP is controlled by the electrophoretic and dielectrophoretic forces, and its main advantage over a physical nanopore is relaxation of critical dimension control, which simplifies device fabrication. The radial dimension of the desired trapping region could be significantly smaller than the actual fabricated dimensions.