Translocation of a Charged Nanoparticle Through a Fluidic Nanochannel: The Interplay of Nanoparticle and Ions

Confinement effects and mechanistic aspects for montmorillonite nanopores

Owing to the ubiquity, critical importance and special properties, confined microenvironments have recently triggered overwhelming interest. In this work, all-atom molecular dynamics simulations have been conducted to address the confinement effects and ion-specific effects for electrolyte solutions within montmorillonite nanopores, where the pore widths vary with a wide range. The adsorption number, structure, dynamics and stability of inner- and outer-sphere metal ions are affected by the change of pore widths (confinement effects), while the extents are significantly dependent on the type of adsorbed species. The type of adsorbed species is, however, not altered by the magnitude of confinement effects, and confinement effects are similar for different electrolyte concentrations. Ion-specific effects are pronounced for all magnitudes of confinement effects (from non- to strong confined conditions), and Hofmeister sequences of outer-sphere species are closely associated with the magnitude of confinement effects while those of inner-sphere species remain consistent. In addition, mechanistic aspects of confinement have been posed using the electrical double layer theories, and the results can be generalized to other confined systems that are ubiquitous in biology, chemistry, geology and nanotechnology.

Interface nanoparticle control of a nanometer water pump

A nanoparticle is forced to move on a membrane surface, inducing considerable water flux through a carbon nanotube, suggesting a controllable nanometer water pump.

A current-driven nanometer water pump

The design of a water pump, which has huge potential for applications in nanotechnology and daily life, is the dream of many scientists. In this paper, we successfully design a nanometer water pump by using molecular dynamics simulations. Ions of either sodium or chlorine in a narrow channel will generate electric current under electric fields, which then drives the water through a wider channel, similar to recent experimental setups. Considerable water flux is achieved within small field strengths that are accessible by experimentation. Of particular interest, is that for sodium the water flux increases almost linearly with field strengths; while for chlorine there exists a critical field strength, the water flux exhibits a plateau before the critical value and increases linearly after it. This result follows the behavior of ion velocity, which is related to friction behavior. We also estimate the power and energy consumption for such a pump, and compare it to the macroscopic mechanical pumps. A further comparison suggests that different ions will have different pumping abilities. This study not only provides new, significant results with possible connection to existing research, but has tremendous potential application in the design of nanofluidic devices.

Sensitive Detection of a Modified Base in Single-Stranded DNA by a Single-Walled Carbon Nanotube

In this work, we use molecular dynamics simulations to study the responses of the configuration of single-strand DNA (ssDNA) within a carbon nanotube (CNT) and the concomitant ion flow to a single modified base, i.e., benzoimidazole (Bzim)-modified 5-hydroxymethyl cytosine (5hmC). Our simulation results show the Bzim-modified 5hmC can considerably increase the ion flow through a single-walled carbon nanotube (SWCNT), despite its larger size, which is consistent with prior experimental results. This phenomenon is attributed to enhanced adsorption of DNA to the interior wall of the CNT driven by the Bzim-modified 5hmC, leading to a reduced steric effect on ion transport through the CNT. As revealed in this work, the distribution of ssDNA can be affected by limited change in the interactions with the CNT surface. Such behavior of ssDNA within small-sized CNTs can be exploited to further improve the sensitivity of nanopore detection.

Pumping of water by rotating chiral carbon nanotube

Water transportation inside carbon nanotubes is of great importance for designing novel nanodevices. In this article, by using molecular dynamics simulations, we systematically investigate the pumping of water by rotating carbon nanotube (CNT). It is found that the chirality and rotation of the CNT are two preconditions for stable water flux inside it. Besides, we find that the water flux shows an approximately logarithmic dependence on the angular velocity of the rotation, a linear dependence on the radius of the CNT, and interestingly, independence of its length within a certain range of CNT size and angular velocity. Further, we also use a dragging theory which successfully describes the water flux behaviors inside the CNT and can fit well with the results obtained from simulations. The present study provides insight into the designing of nanodevices based on the CNT for real applications.

Translocation of a nanoparticle through a fluidic channel: the role of grafted polymers

The surface properties of nanoparticles (NPs) are key factors for their design and use in biomedicine; however, our understanding of the effect of surface properties on the translocation of NPs through membranes is still rather poor. Herein, we have used molecular dynamics simulations to study the translocation of a polymer-grafted NP through a fluidic channel. We change the length, number, amount of charge and the charge position of grafted polymers. With the increase of polymer length, the NP flux decreases as a whole due to the increase of NP size, where the -NP translocation fails at the smallest polymer length, because of the strong binding of Na(+). Surprisingly, the NP flux exhibits a maximum with the increase of the polymer number or charge amount, which is co-determined by the NP net charge and size. Owing to the NP-membrane adsorption and NP-ion binding, the NP flux decreases with the decrease of charge position. We also analyze the transport of counterions, which depends on both the NP-ion binding and NP dynamics. Finally, we investigate the effect of electric fields for a given NP type. Our results reveal the important role of grafted polymers in the NP translocation and may have implications in the design of highly efficient NP delivery.