8 research outputs found
Concentration-Gradient-Dependent Ion Current Rectification in Charged Conical Nanopores
Ion current rectification (ICR) in negatively charged
conical nanopores
is shown to be controlled by the electrolyte concentration gradient
depending on the direction of ion diffusion. The degree of ICR is
enhanced with the increasing forward concentration difference. An
unusual rectification inversion is observed when the concentration
gradient is reversely applied. A numerical simulation based on the
coupled Poisson and Nernst–Planck (PNP) equations is proposed
to solve the ion distribution and ionic flux in the charged and structurally
asymmetric nanofluidic channel with diffusive ion flow. Simulation
results qualitatively describe the diffusion-induced ICR behavior
in conical nanopores suggested by the experimental data. The concentration-gradient-dependent
ICR enhancement and inversion is attributed to the cooperation and
competition between geometry-induced asymmetric ion transport and
the diffusive ion flow. The present study improves our understanding
of the ICR in asymmetric nanofluidic channels associated with the
ion concentration difference and provides insight into the rectifying
biological ion channels
The Selective Transport of Ions in Charged Nanopore with Combined Multi-Physics Fields
The selective transport of ions in nanopores attracts broad interest due to their potential applications in chemical separation, ion filtration, seawater desalination, and energy conversion. The ion selectivity based on the ion dehydration and steric hindrance is still limited by the very similar diameter between different hydrated ions. The selectivity can only separate specific ion species, lacking a general separation effect. Herein, we report the highly ionic selective transport in charged nanopore through the combination of hydraulic pressure and electric field. Based on the coupled Poisson–Nernst–Planck (PNP) and Navier–Stokes (NS) equations, the calculation results suggest that the coupling of hydraulic pressure and electric field can significantly enhance the ion selectivity compared to the results under the single driven force of hydraulic pressure or electric field. Different from the material-property-based ion selective transport, this method endows the general separation effect between different kinds of ions. Through the appropriate combination of hydraulic pressure and electric field, an extremely high selectivity ratio can be achieved. Further in-depth analysis reveals the influence of nanopore diameter, surface charge density and ionic strength on the selectivity ratio. These findings provide a potential route for high-performance ionic selective transport and separation in nanofluidic systems
The Optimization of the Transition Zone of the Planar Heterogeneous Interface for High-Performance Seawater Desalination
Reverse osmosis has become the most prevalent approach to seawater desalination. It is still limited by the permeability-selectivity trade-off of the membranes and the energy consumption in the operation process. Recently, an efficient ionic sieving with high performance was realized by utilizing the bi-unipolar transport behaviour and strong ion depletion of heterogeneous structures in 2D materials. A perfect salt rejection rate of 97.0% and a near-maximum water flux of 1529 L m−2 h−1 bar−1 were obtained. However, the energy consumption of the heterogeneous desalination setup is a very important factor, and it remains largely unexplored. Here, the geometric-dimension-dependent ion transport in planar heterogeneous structures is reported. The two competitive ion migration behaviours during the desalination process, ion-depletion-dominated and electric-field-dominated ion transport, are identified for the first time. More importantly, these two ion-transport behaviours can be regulated. The excellent performance of combined high rejection rate, high water flux and low energy consumption can be obtained under the synergy of voltage, pressure and geometric dimension. With the appropriate optimization, the energy consumption can be reduced by 2 orders of magnitude, which is 50% of the industrial energy consumption. These findings provide beneficial insight for the application and optimized design of low-energy-consumption and portable water desalination devices
Nanofluidic Pulser Based on Polymer Conical Nanopores
The study of voltage-dependent ion current fluctuation phenomena in synthetic nanopores is important as it is helpful to investigate the mechanism of mass transport in nanoscale systems, which have similarities with natural ion channels in the biological cell membrane. Moreover, we could fabricate some high-performance nanofluidic devices through clearly understanding ion current fluctuation behavior. In this paper, we report a nanofluidic pulser induced by formation and dissolution of weakly soluble salts in conical nanopores. The current fluctuation signals are easily controllable in 1 M KCl electrolyte. Amplitude, frequency, and waveform of ion fluctuation current of the nanofluidic pulser could be controlled by changing the applied negative voltage, and the time ratio of pore opening/closing could be simply manipulated by the concentration of the bivalent cation. A high-quality square wave of ion current signal is found, especially when the negative voltage is below 300 mV. Additionally, we developed a new model about the formation and dissolution process of precipitation. Our work is helpful for the design of nanoscale ion current waveform generators in the future
Lactobacillus gasseri LGV03 isolated from the cervico-vagina of HPV-cleared women modulates epithelial innate immune responses and suppresses the growth of HPV-positive human cervical cancer cells
Persistent human papillomavirus (HPV) infections is necessary for the development of cervical cancers. An increasing number of retrospective studies have found the depletion of Lactobacillus microbiota in the cervico-vagina facilitate HPV infection and might be involved in viral persistence and cancer development. However, there have been no reports confirming the immunomodulatory effects of Lactobacillus microbiota isolated from cervico-vaginal samples of HPV clearance in women. Using cervico-vaginal samples from HPV persistent infection and clearance in women, this study investigated the local immune properties in cervical mucosa. As expected, type I interferons, such as IFN-α and IFN-β, and TLR3 globally downregulated in HPV+ persistence group. Luminex cytokine/chemokine panel analysis revealed that L. jannaschii LJV03, L. vaginalis LVV03, L. reuteri LRV03, and L. gasseri LGV03 isolated from cervicovaginal samples of HPV clearance in women altered the host's epithelial immune response, particularly L. gasseri LGV03. Furthermore, L. gasseri LGV03 enhanced the poly (I:C)-induced production of IFN by modulating the IRF3 pathway and attenuating poly (I:C)-induced production of proinflammatory mediators by regulating the NF-κB pathway in Ect1/E6E7 cells, indicating that L. gasseri LGV03 keeps the innate system alert to potential pathogens and reduces the inflammatory effects during persistent pathogen infection. L. gasseri LGV03 also markedly inhibited the proliferation of Ect1/E6E7 cells in a zebrafish xenograft model, which may be attributed to an increased immune response mediated by L. gasseri LGV03
On the Origin of Ionic Rectification in DNA-Stuffed Nanopores: The Breaking and Retrieving Symmetry
The discovery of ionic current rectification (ICR) phenomena in
synthetic nanofluidic systems elicits broad interest from interdisciplinary
fields of chemistry, physics, materials science, and nanotechnology;
and thus, boosts their applications in, for example, chemical sensing,
fluidic pumping, and energy related aspects. So far, it is generally
accepted that the ICR effect stems from the broken symmetry either
in the nanofluidic structures, or in the environmental conditions.
Although this empirical regularity is supported by numerous experimental
and theoretical results, great challenge still remains to precisely
figure out the correlation between the asymmetric ion transport properties
and the degree of symmetry breaking. An appropriate and quantified
measure is therefore highly demanded. Herein, taking DNA-stuffed nanopores
as a model system, we systematically investigate the evolution of
dynamic ICR in between two symmetric states. The fully stuffed and
fully opened nanopores are symmetric; therefore, they exhibit linear
ion transport behaviors. Once the stuffed DNA superstructures are
asymmetrically removed from one end of the nanopore via aptamer-target
interaction, the nanofluidic system becomes asymmetric and starts
to rectify ionic current. The peak of ICR is found right before the
breakthrough of the stuffed DNA forest. After that, the nanofluidic
system gradually retrieves symmetry, and becomes non-rectified. Theoretical
results by both the coarse-grained Poisson-Nernst–Planck model
and the 1D statistic model excellently support the experimental observations,
and further establish a quantified correlation between the ICR effect
and the degree of asymmetry for different molecular filling configurations.
Based on the ICR properties, we develop a proof-of-concept demonstration
for sensing ATP, termed the ATP balance. These findings help to clarify
the origin of ICR, and show implications to other asymmetric transport
phenomena for future innovative nanofluidic devices and materials