title: Highly Charged Particles Cause a Larger Current Blockage in Micropores Compared to Neutral Particles.
abstract: Single pores in the resistive-pulse technique are used as an analytics tool to detect, size, and characterize physical as well as chemical properties of individual objects such as molecules and particles. Each object passing through a pore causes a transient change of the transmembrane current called a resistive pulse. In high salt concentrations when the pore diameter is significantly larger than the screening Debye length, it is assumed that the particle size and surface charge can be determined independently from the same experiment. In this article we challenge this assumption and show that highly charged hard spheres can cause a significant increase of the resistive-pulse amplitude compared to neutral particles of a similar diameter. As a result, resistive pulses overestimate the size of charged particles by even 20%. The observation is explained by the effect of concentration polarization created across particles in a pore, revealed by numerical modeling of ionic concentrations, ion current, and local electric fields. It is notable that in resistive-pulse experiments with cylindrical pores, concentration polarization was previously shown to influence ionic concentrations only at pore entrances; consequently, additional and transient modulation of resistive pulses was observed when a particle entered or left the pore. Here we postulate that concentration polarization can occur across transported particles at any particle position along the pore axis and affect the magnitude of the entire resistive pulse. Consequently, the recorded resistive pulses of highly charged particles reflect not only the particles' volume but also the size of the depletion zone created in front of the moving particle. Moreover, the modeling identified that the effective surface charge density of particles depended not only on the density of functional groups on the particle but also on the capacitance of the Stern layer. The findings are of crucial importance for sizing particles and characterizing their surface charge properties.
authors.affiliation: School of Mechanical Engineering and Jiangsu Key Laboratory for Design and Manufacture of Micro-Nano Biomedical Instruments, Southeast University , Nanjing 211189, China.
authors.forename: Yinghua
authors.initials: Y
authors.lastname: Qiu
authors.affiliation: Department of Chemical Engineering, National Taiwan University , Taipei 10617, Taiwan.
authors.forename: Chih-Yuan
authors.initials: CY
authors.lastname: Lin
authors.forename: Preston
authors.initials: P
authors.lastname: Hinkle
authors.forename: Timothy S
authors.initials: TS
authors.lastname: Plett
authors.forename: Crystal
authors.initials: C
authors.lastname: Yang
authors.forename: Jenu Varghese
authors.initials: JV
authors.lastname: Chacko
authors.forename: Michelle A
authors.initials: MA
authors.lastname: Digman
authors.affiliation: Department of Chemical and Materials Engineering, National Yunlin University of Science and Technology , Yunlin 64002, Taiwan.
authors.forename: Li-Hsien
authors.initials: LH
authors.lastname: Yeh
authors.affiliation: Department of Chemical Engineering, National Taiwan University , Taipei 10617, Taiwan.
authors.forename: Jyh-Ping
authors.initials: JP
authors.lastname: Hsu
authors.forename: Zuzanna S
authors.initials: ZS
authors.lastname: Siwy
keywords: concentration polarization; particles; resistive pulse