Tuning Particle Velocity and Measurement Sensitivity by Changing Pore Sensor Dimensions

Abstract

Tuning the size of an elastic pore sensor enables the control of both the measurement sensitivity and particle velocity through the pore. Increasing the pore size by stretching the pore membrane reduced the magnitude of the resistive pulse signal generated by 330 nm polystyrene particles by 24% while simultaneously increasing their velocity through the pore, as shown by the 68% shorter pulse durations. These effects are due to the reduced excluded particle volume and increased fluid velocity through the larger pore, respectively.The ability to measure individual particles, molecules, or DNA base pairs has generated considerable interest in pore sensors that measure dispersion properties using the Coulter principle.1 These sensors have been used to measure the concentration, size, 2 and ¦-potential, 3 and even to infer information about the conductivity 4 of objects in a dispersion. Compared to traditional fixed-pore sensors, new size-tunable elastic pore sensors have the advantage of increasing analysis size range, measurement sensitivity, and even selective gating of particles by tuning the pore dimensions to a particulate system. 5 As demonstrated in this paper, tuning the pore dimensions also controls the electrokinetic and fluidic forces that act to drive particles through the pore. Understanding this relationship is critical to pore sensor design and accurate particle analysis.Objects traversing a pore sensor, which in simple terms consists of two electrolyte chambers separated by a membrane with a hole, give rise to an increased resistance through the pore that is proportional to the excluded volume of the particle. 2,6 Typically recorded as a change in ionic current-in-time (i t ), theses brief "pulses" contain information on particle size (pulse magnitude, ¦i max ) and velocity (pulse duration, measured here at the full width at half-maximum (FWHM) of the pulse signal). The collation of hundreds to thousands of pulses, which can often be achieved over a short analysis duration (i.e., on the order of seconds; inset of Figure 1), enables not only particleby-particle characterization but also analysis of the overall distribution of the suspension. The key to extracting this information from the generated pulse signals are knowledge of the pore dimensions and appropriate theoretical models.The dimensions of elastic pore sensors are dependent on the pore puncturing process and the applied membrane stretch. Typically, these pores are conical and have the characteristic geometric terms A, B, and L, which correspond to the small and large pore opening diameters and the pore length, respectively. Stretching or relaxing the elastic membrane enables the dimensions to be altered or "tuned." The dimensions of the pore used in this study were measured, at 2 mm stretch increments going from 44 to 52 mm (Table 1), according to our previously described methodology.8 Stretching the membrane was found to increase A and B from 0.80 to 1.69¯m and from 33 to 58¯m, respectively, and to decrease L from 230 to 169¯m.As shown in ...

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