Our manuscript addresses the issue of probing an effective surface charge that any surface can acquire at the solid/liquid interface. Even if a particle is predicted to be neutral based on its chemical structure, the particle can carry finite surface charges when placed in a solution. We present tools to probe the presence of surface charge densities of meso-particles, characterized with zeta potentials below 10 mV. The tools are based on the resistive-pulse technique, which uses single pores to probe properties of individual objects including molecules, particles, and cells. The presented experiments were performed with particles 280 and 400 nm in diameter and single pores with opening diameter tuned between ∼ 200 nm and one micron. Surface charge properties were probed in two modes: (i) the passage of the particles through pores of diameters larger than the particles, as well as (ii) an approach curve of a particle to a pore that is smaller than the particle diameter. The curve in the latter mode has a biphasic character starting with a low-amplitude current decrease, followed by a current enhancement reaching an amplitude of ∼10% of the baseline current. The current increase was long-lasting and stable, and shown to strongly depend on the particle surface charge density. The results are explained via voltage-modulation of ionic concentrations in the pore.

中文翻译：

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用电阻脉冲技术探测固液界面上的电荷

我们的手稿解决了探测有效表面电荷的问题，该表面电荷可以在固/液界面获得。即使根据其化学结构预测颗粒为中性，当将其置于溶液中时，该颗粒也可以携带有限的表面电荷。我们目前提供工具来探测介电粒子表面电荷密度的存在，其特征在于zeta电位低于10 mV。这些工具基于电阻脉冲技术，该技术使用单个孔来探测包括分子，粒子和细胞在内的单个对象的属性。提出的实验是用直径为280和400 nm的颗粒以及开口直径在〜200 nm和1微米之间调节的单个孔进行的。表面电荷特性以两种模式进行探测：（i）颗粒通过直径大于颗粒直径的孔，以及（ii）颗粒到小于颗粒直径的孔的接近曲线。后一种模式下的曲线具有双相特性，首先是低幅度电流减小，然后是电流增强，幅度达到基线电流的〜10％。电流增加是持久且稳定的，并且显示出强烈依赖于颗粒表面电荷密度。结果说明 电流增加是持久且稳定的，并且显示出强烈依赖于颗粒表面电荷密度。结果说明 电流增加是持久且稳定的，并且显示出强烈依赖于颗粒表面电荷密度。结果说明通过孔隙中离子浓度的电压调制。