An Experimental Test of the Ion Condensation Theory for Spherical Colloidal Particles

Quesada‐Pérez, Manuel; Callejas-Fernández, J.; Hidalgo‐Álvarez, R.

doi:10.1006/jcis.2000.7265

Cited by 16 publications

(17 citation statements)

References 19 publications

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“…Figure compares experimental data of pulse amplitude recorded at two values of pH, 8 and 5.5. At the weakly acidic solution, the surface charge density is expected to be lower due to lower degree of carboxyl groups’ deprotonation . Our experiments (Figures and ) confirm the predictions: at the solution with higher pH, the difference in the magnitude of Δ I / I measured in the directions from base to tip and tip-to-base is higher than at pH 5.5.…”

Section: Resultssupporting

confidence: 84%

“…At the weakly acidic solution, the surface charge density is expected to be lower due to lower degree of carboxyl groups' deprotonation. 55 Our experiments (Figures 3 and 6) confirm the predictions: at the solution with higher pH, the difference in the magnitude of ΔI/I measured in the directions from base to tip and tip-to-base is higher than at pH 5.5. Note that the modeling shown in Figure 5a also provides an explanation for the weak pH dependence of the current blockage in the direction from base to tip (Figure 3b); when the surface charge density increased from 0 to −0.04 C/m 2 , the predicted blockage increased only from ∼0.065 to 0.075.…”

Section: ■ Results and Discussionsupporting

confidence: 84%

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Direction Dependence of Resistive-Pulse Amplitude in Conically Shaped Mesopores

et al. 2016

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Conically shaped pores such as glass pipets as well as asymmetric pores in polymers became an important analytics tool used for the detection of molecules, viruses, and particles. Electrokinetic or pressure driven passage of single particles through a single pore causes a transient change of the transmembrane current, called a resistive-pulse, whose amplitude is the measure of the particle volume. The shape of the pulse reflects the pore topography, and in a conical pore, resistive pulses have a shape of a tick point. Passage of particles in both directions was reported to produce pulses of the same amplitude and shapes that are mirror images of each other. In this manuscript we identify conditions at which the amplitude of resistive-pulses in a conical mesopore is direction dependent. Neutral particles entering the pore from the larger entrance of a conical pore, called the base, block the current to a larger extent than the particles traveling in the opposite direction. Negatively charged particles on the other hand size larger when being transported in the direction from tip to base. The findings are explained via voltage-regulated ionic concentrations in the pore such that for one voltage polarity a weak depletion zone is formed, which increases the current blockage caused by a particle. For the opposite polarity, an enhancement of ionic concentrations was predicted. The findings reported here are of crucial importance for the resistive-pulse technique, which relates the current blockage with the size of the passing object.

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Section: Resultssupporting

confidence: 84%

Section: ■ Results and Discussionsupporting

confidence: 84%

Direction Dependence of Resistive-Pulse Amplitude in Conically Shaped Mesopores

et al. 2016

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“…Since the two types of studied particles were carboxylated, the increase of pH was expected to lead to the increase of their surface charge density. 38 However, we were surprised to observe that the highly charged particles (400 nm in diameter, red traces in Figure 1) caused a larger current decrease than the weakly charged or uncharged particles (blue and green traces in Figure 1). The difference was especially pronounced at pH 10.…”

Section: Resultsmentioning

confidence: 91%

Highly Charged Particles Cause a Larger Current Blockage in Micropores Compared to Neutral Particles

Qiu

Lin

Hinkle³

et al. 2016

ACS Nano

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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.

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“…Experiments were performed with two types of charged colloids that differed in their surface charge density by a factor of 3. The more charged colloids were previously reported to undergo the effect of ion condensation, − leading to lowering the particle zeta potential and significant slowing down of the translocation . Here we present experimental data claiming that the kinetics of deprotonation/protonation of the colloids with condensed ions is significantly slower than what could be predicted based on previous experiments , and can exceed 100 ms.…”

Section: Introductionmentioning

confidence: 51%

Experimental Investigation of Dynamic Deprotonation/Protonation of Highly Charged Particles

2017

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Single pores have found application in detecting and characterizing individual objects such as cells, particles, and even individual molecules. The experimental approach, called resistive-pulse technique, is often performed at symmetric electrolyte conditions so that the properties of the passing object remain constant in the course of measurement and translocation. Here we report experiments with highly charged mesoparticles passing through pores placed in contact with a pH gradient and demonstrate that this setup allows probing protonation and deprotonation of the particles. On the basis of fast diffusion of protons and submillisecond deprotonation/protonation kinetics of carboxyl groups, we expected that the particles would change their ionization state within a few milliseconds. However, our results show that the kinetics of protonation and deprotonation of the highly charged particles is significantly slower and exceeds 100 ms. We hypothesize that condensation of counterions that occurs on the particles at higher pH is responsible for the modified rates of protonation. The slowed-down deprotonation is attributed to modified local pH of the solution next to a highly charged surface. In addition, we show how electroosmotic flow of neutral particles through a pore in contact with pH gradient can probe modulations of local surface charge properties of the pore by voltage polarity.

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An Experimental Test of the Ion Condensation Theory for Spherical Colloidal Particles

Cited by 16 publications

References 19 publications

Direction Dependence of Resistive-Pulse Amplitude in Conically Shaped Mesopores

Direction Dependence of Resistive-Pulse Amplitude in Conically Shaped Mesopores

Highly Charged Particles Cause a Larger Current Blockage in Micropores Compared to Neutral Particles

Experimental Investigation of Dynamic Deprotonation/Protonation of Highly Charged Particles

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