The disclosure relates to an apparatus and associated method for concentration of polarizable molecules within a fluid medium. The apparatus comprising a structure defining a cavity, having a cross-sectional dimension of 200 nm or less; at least two translocation electrodes positioned relative to the structure to enable generation of a DC electric field passing through the cavity; and at least two trapping electrodes positioned relative to the structure to enable generation of a time-varying electric field proximal to the cavity inlet.
