A New Procedure for Measuring Particle Length using the Resistive Pulse Technique with Irregular Single Micropores

Abstract

Application of the resistive pulse technique using single micro- and nanopores is an effective way of characterizing the physical properties of nanoparticles. It has been demonstrated that application of the technique to pores with radial irregularities can distinguish aspherical particles by aspect ratio. We expand the technique by defining a procedure for measuring the length of microscale rod-shaped particles; this allows for rapid length measurements of individual particles as well as statistical information about an ensemble of particles with a distribution of lengths. The technique can also reveal information about the dynamics of particle rotation during pore translocation, about which much remains to be understood. The method works by translocating small spherical “tracer” particles through an irregular pore, providing a one-to-one mapping of the local pore radius to the position-dependent pulse amplitude. By calculating a weighted moving average of the tracer's pulse over a varying number of ion current-position data points, the signal becomes convoluted in the same way a rod's signal is the convolution of the local pore radius along the rod's length. The measured length of the rod is then determined from the number of points such that the difference between the sphere's convoluted signal and the rod's signal is minimized. We give a physical justification for the technique, and provide experimental results that demonstrate the efficacy of the technique to measuring particle lengths. We also provide a quantitative analysis of the accuracy of the technique to the various regions of parameter space constituting the microscale. Finally, we discuss the possibility of extending the technique to nano-sized systems, and address the additional challenges that exist at that scale.