Fig. 3: In-tube molecular translocation and current blockade signals received by wireless transmission.

a Schematic representation of an in-tube MPSN device in a centrifuge. The device features a nanopore in a flow cell and two Ag/AgCl electrodes in KCl solution that apply voltage bias (U) and measure current blockade. The rotation speed is denoted by ω and the centrifugal force is defined by f_c = mρω². Here, m is the molecular weight; ρ is distance between the targets and the rotating shaft of the centrifuge, i.e., 25.6 cm in the experiments; and ρω² at rotation speeds ω of 1000, 2000, 3000, and 4000 rpm are 280 g, 1120 g, 2520 g, and 4480 g, respectively. b Illustration of molecular motions in MPSN and associated current blockade signals received via wireless communication. The adjustment of pH value of the analyte medium leads to a counter-balanced electrophoretic force f_EP and electroosmosis force f_EO, the centrifugal force f_c dominates and competes with Brownian motion to drive the outside molecules (i) into the sensing zone (ii) of a sensing length L, defined as the distance between two points where the maximal electric field intensity decays to its e⁻¹ value. Molecules are then translocated through the nanopore (iii) by overcoming the potential barrier ∆U. Each molecular motion is reflected in the recorded current blockade signal, including the current baseline related to stage (i), the first current drop and duration (I₁, t₁) associated with molecular capture in stage (ii), and the second current drop and duration (I₂, t₂) due to molecular translocation in stage (iii). The amplitude of current blockade I is defined as I₁ + I₂ an_d the dwell time t_d is calculated as t₁ + t₂. c–e Schematics (left) illustrating competing forces extorted on BSA at different pH values and corresponding current traces (right) measured at rotation speed of 4000 rpm and voltage bias of 0.6 V. The balanced state of f_EP and f_EO is achieved at pH = 4.3 for BSA.