Perspective on Nanofluidic Memristors: From Mechanism to Application.

Nanofluidic memristors are memory resistors based on nanoconfined fluidic systems exhibiting history-dependent ion conductivity. Toward establishing powerful computing systems beyond the Harvard architecture, these ion-based neuromorphic devices attracted enormous research attention owing to the unique characteristics of ion-based conductors. However, the design of nanofluidic memristor is still at a primary state and a systematic guidance on the rational design of nanofluidic system is desperately required for the development of nanofluidic-based neuromorphic devices. Herein, we proposed a systematic review on the history, main mechanism and potential application of nanofluidic memristors in order to give a prospective view on the design principle of memristors based on nanofluidic systems. Furthermore, based on the present status of these devices, some fundamental challenges for this promising area were further discussed to show the possible application of these ion-based devices.

Insights into Surface Charge of Single Particles at the Orifice of a Nanopipette.

The dynamic behaviors of particles in various physical fields are related to the physicochemical properties of particles. Herein, we focus on the relationship between surface charge and dynamic behaviors of particles at the orifice of a nanopipette. We interestingly find that angle θ, a parameter related to the asymmetric degree of current spike, exhibits a strong relationship with surface charge of the particles. Both theoretical derivation and finite element simulation validate this relationship and thus could be used for quantifying the surface charge of single particles. Moreover, the gold and silica nanoparticles with the same size but different surface charges could be well distinguished and identified based on this relationship. This study not only gives a comprehensive understanding on the dynamic behaviors of particles outside the nanopipette but also opens a new way for investigating the surface charge of single particles.

Label-Free Resistance Cytometry at the Orifice of a Nanopipette.

Development of new principles and techniques at the single-cell level is significantly important since cells as basic units of living organisms always bear large heterogeneity. Herein, we demonstrate a new electrochemical principle for single-cell analysis based on an ion current blockage at the orifice of a nanopipette, defined as resistance cytometry. The amplitude and the frequency of ion current transients show strong dependence on the size and the concentration of cells, which could be used for in situ cell sizing and counting. This technique shows good ability to detect the size change of RBCs under stimulations of different pH and osmotic pressure values. More importantly, the as-presented resistance cytometry can distinguish lymphoma blood cells from normal blood cells for patient blood samples. The as-presented resistance cytometry is label-free, non-invasive, and non-destructive, which not only opens new opportunities for single-cell analysis but also provides a new platform for cell-related medical diagnostic technologies.

Sizing Single Particles at the Orifice of a Nanopipette.

Developing new methods and techniques for the size analysis of particles in a solution is highly desirable not only for the industrial screening of particles but also for single biological entity analysis (e.g., single cells or single vesicles). Herein, we report a new technique for sizing single particles in a solution with a nanopipette. The rationale is essentially based on ion-current blockage when the particles approach the proximity of a nanopipette orifice. By rationally controlling the geometry of the nanopipette and the applied potential, the spike-type ion current transient generated from the motion of particles in the process of "collision and departure" is employed for sizing single particles. The results show that both the relative ion-current change (ΔI/I0) and the dwell time (Δt) of spike-type transient are dependent on particle size. Differently, Δt is also related to an externally applied voltage. Statistical analysis shows that ΔI/I0 is proportional to the particle diameter, and this linear relationship is further understood by finite-element simulations. This study not only provides a new principle for sizing single particles in a solution but also is helpful to understand the motion of a particle near the orifice of the nanopipette.