The Role of MXene Surface Terminations on Peptide Transportation in Nanopore Sensing.

Nanopores with two-dimensional materials have various advantages in sensing, but the fast translocation of molecules hinders their scale-up applications. In this work, we investigate the influence of -F, -O, and -OH surface terminations on the translocation of peptides through MXene nanopores. We find that the longest dwell time always occurs when peptides pass through the Ti3C2O2 nanopores. This elongated dwell time is induced by the strongest interaction between peptides and the Ti3C2O2 membrane, in which the van der Waals interactions dominate. Compared to the other two MXene nanopores, the braking effect is indicated during the whole translocation process, which evidence the advantage of Ti3C2O2 in nanopore sensing. Our work demonstrates that membrane surface chemistry has a great influence on the translocation of peptides, which can be introduced in the design of nanopores for a better performance.

From salt water to bioceramics: Mimic nature through pressure-controlled hydration and crystallization.

Modern synthetic technology generally invokes high temperatures to control the hydration level of ceramics, but even the state-of-the-art technology can still only control the overall hydration content. Magically, natural organisms can produce bioceramics with tailorable hydration profiles and crystallization traits solely from amorphous precursors under physiological conditions. To mimic the biomineralization tactic, here, we report pressure-controlled hydration and crystallization in fabricated ceramics, solely from the amorphous precursors of purely inorganic gels (PIGs) synthesized from biocompatible aqueous solutions with most common ions in organisms (Ca2+, Mg2+, CO32-, and PO43-). Transparent ceramic tablets are directly produced by compressing the PIGs under mild pressure, while the pressure regulates the hydration characteristics and the subsequent crystallization behaviors of the synthesized ceramics. Among the various hydration species, the moderately bound and ordered water appears to be a key in regulating the crystallization rate. This nature-inspired study offers deeper insights into the magic behind biomineralization.

Two Detection Modes of Nanoslit Sensing Based on Planar Heterostructure of Graphene/Hexagonal Boron Nitride.

Solid-state nanopore sequencing is now confronted with problems of stochastic pore clogging and too fast speed during the DNA permeation through a nanopore, although this technique is revolutionary with long readability and high efficiency. These two problems are related to controlling molecular transportation during sequencing. To control the DNA motion and identify the four bases, we propose nanoslit sensing based on the planar heterostructure of two-dimensional graphene and hexagonal boron nitride. Molecular dynamics simulations are performed on investigating the motion of DNA molecules on the heterostructure with a nanoslit sensor. Results show that the DNA molecules are confined within the hexagonal boron nitride (HBN) domain of the heterostructure. And the confinement effects of the heterostructure can be optimized by tailoring the stripe length. Besides, there are two ways of DNA permeation through nanoslits: the DNA can cross or translocate the nanoslit under applied voltages along the y and z directions. The two detection modes are named cross-slit and trans-slit, respectively. In both modes, the ionic current drops can be observed when the nanoslit is occupied by the DNA. And the ionic currents and dwell times can be simultaneously detected to identify the four different DNA bases. This study can shed light on the sensing mechanism based on the nanoslit sensor of a planar heterostructure and provide theoretical guidance on designing devices controlling molecular transportation during nanopore sequencing.

Distinct roles of graphene and graphene oxide nanosheets in regulating phospholipid flip-flop.

Two-dimensional (2D) nanomaterials, such as graphene nanosheets (GNs) and graphene oxide nanosheets (GOs), could adhere onto or insert into a biological membrane, leading to a change in membrane properties and biological activities. Consequently, GN and GO become potential candidates for mediating interleaflet phospholipid transfer. In this work, molecular dynamics (MD) simulations were employed to investigate the effects of GN and GO on lipid flip-flop behavior and the underlying molecular mechanisms. Of great interest is that GN and GO work in opposite directions. The inserted GN can induce the formation of an ordered nanodomain, which dramatically elevates the free energy barrier of flipping phospholipids from one leaflet to the other, thus leading to a decreased lipid flip-flop rate. In contrast, the embedded GO can catalyze the transport of phospholipids between membrane leaflets by facilitating the formation of water pores. These results suggest that GN may work as an inhibitor of the interleaflet lipid translocation, while GO may play the role of scramblases. These findings are expected to expand promising biomedical applications of 2D nanomaterials.

Molecular mechanisms underlying the role of the puckered surface in the biocompatibility of black phosphorus.

As a newly emerging two-dimensional material, black phosphorus (BP) has received broad attention in the field of biomedical applications. Prior to its clinical application, its cytotoxicity to cells should be carefully evaluated; however, this field is still in its infancy. Motivated by this, we performed molecular dynamics (MD) simulations to systematically investigate the potential mechanisms of the cytotoxicity of BP to the lipid membrane, including lipid extraction, penetration into the membrane, and the impacts of BP on the physical properties of the membrane. Surprisingly, we observed that BP could not extract lipid molecules from the membrane. The thermodynamic analyses suggested that the puckered surface structure could weaken the interactions between BP and lipid molecules, thus inhibiting the lipid extraction. Additionally, through simulating the spontaneous interaction modes between BP and the lipid membrane, we found that the "passivated" edges of BP prohibited it from penetrating into the membrane. As a result, BP could only spontaneously lie parallel on the surface of the membrane, in which manner BP exerted little influence on the properties of the lipid membrane. To comprehensively appraise the cytotoxicity, we even artificially inserted BP into the membrane and compared the effects of BP and graphene on the properties of the membrane. Simulation results showed that the influences of the inserted BP on the lipid properties were much milder than those of graphene. Overall, the present work suggests that BP possesses distinctive biocompatibility benefiting from its puckered surface structure. This work provides a better understanding of the interactions between BP and the membrane, which may offer some useful suggestions for exploring strategies to improve the biocompatibility of nanomaterials.

Simultaneous Sensing of Force and Current Signals to Recognize Proteinogenic Amino Acids at a Single-Molecule Level.

The identification ability of nanopore sequencing is severely hindered by the diversity of amino acids in a protein. To tackle this problem, a graphene nanoslit sensor is adopted to collect force and current signals to distinguish 20 residues. Extensive molecular dynamics simulations are performed on sequencing peptides under pulling force and applied electric field. Results show that the signals of force and current can be simultaneously collected. Tailoring the geometry of the nanoslit sensor optimizes signal differences between tyrosine and alanine residues. Using the tailored geometry, the characteristic signals of 20 types of residues are detected, enabling excellent distinguishability so that the residues are well-grouped by their properties and signals. The signals reveal a trend in which the larger amino acids have larger pulling forces and lower ionic currents. Generally, the graphene nanoslit sensor can be employed to simultaneously sense two signals, thereby enhancing the identification ability and providing an effective mode of nanopore protein sequencing.

Membrane Perturbation and Lipid Flip-Flop Mediated by Graphene Nanosheet.

Graphene nanosheets (GNs) may spontaneously insert into cell membranes and perturb the dynamic organization of the surrounding lipid bilayer. Understanding the interaction between GNs and cell membranes is vital for learning how to avoid adverse effects and nanomedical applications. To better understand the nature of such perturbations, we performed molecular dynamics simulations to provide molecular details about the molecular mechanism. In this study, we observed two typical interaction states of the GN-membrane systems. Both states have different effects on the cell membrane (lipid density, membrane thickness, and the mobility of phospholipids). Of great interest is that the insertion of GNs could generate a liquid-ordered domain and dramatically reduce the rate of lipid flip-flop. A similar phenomenon could be found in the GN adhesion states. Thus, these results could facilitate molecular-level understanding of the cytotoxicity of nanomaterials and help future studies on designing personalized drugs and therapeutics for diseases.

Lattice constant-dependent anchoring effect of MXenes for lithium-sulfur (Li-S) batteries: a DFT study.

The anchoring effect of the cathode plays a significant role in improving the performance of lithium-sulfur (Li-S) batteries. MXenes, a new class of two-dimensional materials, have been reported to be effective sulfur hosts for Li-S batteries. However, previous studies mainly focused on Ti-based MXenes, while other potential transition metal MXenes have not been systematically explored. In the present work, we thoroughly investigated the interactions between lithium polysulfides (LiPSs) and a Ti2CO2 substrate, as well as six other M3C2O2 (M = Cr, V, Ti, Nb, Hf and Zr) MXenes using density functional theory (DFT) calculations. It is found that all six M3C2O2 systems possess trapping ability towards soluble LiPSs, largely attributed to the strong Li-O interactions between the LiPSs and the surface of the M3C2O2. Among them, Cr3C2O2 exhibited the strongest anchoring effect with the largest Eb. More importantly, a monotonical relationship between the binding energies and the lattice constants of M3C2O2 was identified, which indicated that M3C2O2 MXenes with a smaller lattice constant tend to exhibit a stronger anchoring effect. Furthermore, all six M3C2O2 MXenes showed metallic properties during the whole process. Our results shed light on the future rational selection and design of MXenes acting as sulfur hosts in Li-S batteries and on the potential to improve host-guest interactions in other energy storage systems.