1 research outputs found
Highly Charged Particles Cause a Larger Current Blockage in Micropores Compared to Neutral Particles
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