Scaled-Up Synthesis of Freestanding Molybdenum Disulfide Membranes for Nanopore Sensing

Synthesis of Nanographene-DNA Conjugates and Their Profiling with MoS2 Nanopores

We demonstrate the possibility of covalently bonded hybrid DNA-graphene materials by synthesizing a model DNA-polycyclic aromatic hydrocarbon (PAH) conjugate comprising a 33mer oligonucleotide containing thymine and uridine modified with bispyrenyl benzene. This DNA-PAH conjugate (T13UPAHT19; T = thymine, UPAH = PAH-modified uridine) has an atomically thin nanographene protrusion extending by only about 1 nm from the single-stranded DNA (ssDNA). We show that DNA-PAH conjugates can be characterized with high resolution by profiling with a nanopore in a monolayer MoS2 membrane. The profiling experiments provided sufficient resolution to distinguish the thymine and PAH-modified regions of T13UPAHT19 and confirm the asymmetry of the PAH attachment relative to the 3' and 5' ends of the ssDNA due to different lengths of the T13 and T19 segments. This work provides the foundation for further exploration of DNA-graphene hybrids, demonstrating an example of their synthesis and the utility of nanopore profiling for their structural characterization with an ∼1 nm resolution.

Single-molecule resolution of macromolecules with nanopore devices

Nanopore-based electrical detection technology holds single-molecule resolution and combines the advantages of high sensitivity, high throughput, rapid analysis, and label-free detection. It is widely applied in the determination of organic and biological macromolecules, small molecules, and nanomaterials, as well as in nucleic acid and protein sequencing. There are a wide variety of organic polymers and biopolymers, and their chemical structures, and conformation in solution directly affect their ensemble properties. Currently, there is limited approach available for the analysis of single-molecule conformation and self-assembled topologies of polymers, dendrimers and biopolymers. Nanopore single-molecule platform offers unique advantages over other sensing technologies, particularly in molecular size differentiation of macromolecules and complex conformation analysis. In this review, the classification of nanopore devices, including solid-state nanopores (SSNs), biological nanopores, and hybrid nanopores is introduced. The recent developments and applications of nanopore devices are summarized, with a focus on the applications of nanopore platform in the resolution of the structures of synthetic polymer, including dendritic, star-shaped, block copolymers, as well as biopolymers, including polysaccharides, nucleic acids and proteins. The future prospects of nanopore sensing technique are ultimately discussed.

Tuning the Sensitivity of MoS2 Nanopores: From Labeling to Labeling-Free Detection of DNA Methylation

DNA methylation discrimination is often challenged by complicated pretreatment, insufficient sensitivity, and suboptimal accuracy. Here, single-molecule readout of DNA methylation is reported using single-layer MoS2 nanopores. By tuning pore dimension, the sensitivity of MoS2 nanopores is manipulated, empowering both labeling and labeling-free strategies for DNA methylation discrimination. With methyl-CpG-binding domain protein 1 (MBD1)-labeled methylated DNA translocation in customized nanopores, multiple methylated sites with distance as short as 70 bp in double strand DNA can be resolved. To further improve spatial resolution, small MoS2 nanopores are engineered with single-nucleotide sensitivity, realizing labeling-free methylation detection with single-nucleotide resolution to recognize two nucleotides with only one methyl difference. This study demonstrates the availability of engineered MoS2 nanopores in DNA methylation detection, underscoring their potential for epigenetic alteration research at the single-molecule level.

Molecular sandwich-based DNAzyme catalytic reaction towards transducing efficient nanopore electrical detection of antigen proteins

Despite significant advances in nanopore nucleic acid sequencing and sensing, protein detection remains challenging due to the inherent complexity of protein molecular properties (i.e., net charges, polarity, molecular conformation & dimension) and sophisticated environmental parameters (i.e., biofluids), resulting in unsatisfactory electrical signal resolution for protein detection such as poor accessibility, selectivity and sensitivity. The selection of an appropriate electroanalytical approach is strongly desired which should be capable of offering easily detectable and readable signals regarding proteins particularly depending on the practical application. Herein, a molecular sandwich-based cooperative DNAzyme catalytic reaction nanopore detecting approach was designed. Specifically, this approach uses Mg2+ catalyzed DNAzyme (10-23) toward nucleic acids digestion for efficient antigen protein examination. The proposed strategy operates by initial formation of a molecular sandwich containing capture antibody-antigen-detection antibody for efficient entrapment of target proteins (herein taking the HIV p24 antigen for example) and immobilization on magnetic beads surfaces. After that, the DNAzyme was linked to the detection antibody via a biotin-streptavidin interaction. In the presence of Mg2+, the DNAzyme catalytic reaction was triggered to digest nucleic acid substrates and release unique cleavage fragments as reporters capable of transducing more easily detectable nucleic acids as a substitute for the complicated and hard to yield protein signals, in a nanopore. Notably, experimental validation confirms the detecting stability and sensitivity for the target antigen referenced with other antigen proteins, meanwhile it demonstrates a detection efficacy in a human serum environment at very low concentration (LoD ∼1.24 pM). This cooperative DNAzyme nanopore electroanalytical approach denotes an advance in protein examination, and may benefit in vitro testing of proteinic biomarkers for disease diagnosis and prognosis assessment.

Two-Dimensional Material-Based Nanofluidic Devices and Their Applications

Nanofluidics is an interdisciplinary field of study that bridges hydrodynamics, statistical physics, chemistry, materials science, biology, and other fields to investigate the transport of fluids and ions on the nanometric scale. The progress in this field, however, has been constrained by challenges in fabricating nanofluidic devices suitable for systematic investigations. Recent advances in two-dimensional (2D) materials have revolutionized the development of nanofluids. Their ultrathin structure and photothermoelectric response make it possible to achieve the scale control, friction limitation, and regulatory response, all of which are challenging to achieve with traditional solid materials. In this review, we provide a comprehensive overview of the preparation methods and corresponding structures of three types of 2D material-based nanofluidic devices, including nanopores, nanochannels, and membranes. We highlight their applications and recent advances in exploring physical mechanisms, detecting biomolecules (DNA, protein), developing iontronics devices, improving ion/gas selectivity, and generating osmotic energy. We discuss the challenges facing 2D material-based nanofluidic devices and the prospects for future advancements in this field.

Coupled nanopores for single-molecule detection

Rapid sensing of molecules is increasingly important in many studies and applications, such as DNA sequencing and protein identification. Here, beyond atomically thin 2D nanopores, we conceptualize, simulate and experimentally demonstrate coupled, guiding and reusable bilayer nanopore platforms, enabling advanced ultrafast detection of unmodified molecules. The bottom layer can collimate and decelerate the molecule before it enters the sensing zone, and the top 2D pore (~2 nm) enables position sensing. We varied the number of pores in the bottom layer from one to nine while fixing one 2D pore in the top layer. When the number of pores in the bottom layer is reduced to one, sensing is performed by both layers, and distinct T- and W-shaped translocation signals indicate the precise position of molecules and are sensitive to fragment lengths. This is uniquely enabled by microsecond resolution capabilities and precision nanofabrication. Coupled nanopores represent configurable multifunctional systems with inter- and intralayer structures for improved electromechanical control and prolonged dwell times in a 2D sensing zone.

Large-Area Epitaxial Growth of Transition Metal Dichalcogenides

Over the past decade, research on atomically thin two-dimensional (2D) transition metal dichalcogenides (TMDs) has expanded rapidly due to their unique properties such as high carrier mobility, significant excitonic effects, and strong spin-orbit couplings. Considerable attention from both scientific and industrial communities has fully fueled the exploration of TMDs toward practical applications. Proposed scenarios, such as ultrascaled transistors, on-chip photonics, flexible optoelectronics, and efficient electrocatalysis, critically depend on the scalable production of large-area TMD films. Correspondingly, substantial efforts have been devoted to refining the synthesizing methodology of 2D TMDs, which brought the field to a stage that necessitates a comprehensive summary. In this Review, we give a systematic overview of the basic designs and significant advancements in large-area epitaxial growth of TMDs. We first sketch out their fundamental structures and diverse properties. Subsequent discussion encompasses the state-of-the-art wafer-scale production designs, single-crystal epitaxial strategies, and techniques for structure modification and postprocessing. Additionally, we highlight the future directions for application-driven material fabrication and persistent challenges, aiming to inspire ongoing exploration along a revolution in the modern semiconductor industry.

Light-Driven Ionic and Molecular Transport through Atomically Thin Single Nanopores in MoS2/WS2 Heterobilayers

Nanofluidic ionic and molecular transport through atomically thin nanopore membranes attracts broad research interest from both scientific and industrial communities for environmental, healthcare, and energy-related technologies. To mimic the biological ion pumping functions, recently, light-induced and quantum effect-facilitated charge separation in heterogeneous 2D-material assemblies is proposed as the fourth type of driving force to achieve active and noninvasive transport of ionic species through synthetic membrane materials. However, to date, engineering versatile van der Waals heterostructures into 2D nanopore membranes remains largely unexplored. Herein, we fabricate single nanopores in heterobilayer transition metal dichalcogenide membranes with helium ion beam irradiation and demonstrate the light-driven ionic transport and molecular translocation phenomena through the atomically thin nanopores. Experimental and simulation results further elucidate the driving mechanism as the photoinduced near-pore electric potential difference due to type II band alignment of the semiconducting WS2 and MoS2 monolayers. The strength of the photoinduced localized electric field near the pore region can be approximately 1.5 times stronger than that of its counterpart under the conventional voltage-driven mode. Consequently, the light-driven mode offers better spatial resolution for single-molecule detection. Light-driven ionic and molecular transport through nanopores in van der Waals heterojunction membranes anticipates transformative working principles for next-generation biomolecular sequencing and gives rise to fascinating opportunities for light-to-chemical energy harvesting nanosystems.

Ultrafast 2D Nanosheet Assembly via Spontaneous Spreading Phenomenon

In 2D materials, a key engineering challenge is the mass production of large-area thin films without sacrificing their uniform 2D nature and unique properties. Here, it is demonstrated that a simple fluid phenomenon of water/alcohol solvents can become a sophisticated tool for self-assembly and designing organized structures of 2D nanosheets on a water surface. In situ, surface characterizations show that water/alcohol droplets of 2D nanosheets with cationic surfactants exhibit spontaneous spreading of large uniform monolayers within 10 s. Facile transfer of the monolayers onto solid or flexible substrates results in high-quality mono- and multilayer films with high coverages (>95%) and homogeneous electronic/optical properties. This spontaneous spreading is quite general and can be applied to various 2D nanosheets, including metal oxides, graphene oxide, h-BN, MoS2, and transition metal carbides, enabling on-demand smart manufacture of large-size (>4 inchϕ) 2D nanofilms and free-standing membranes.

Bioinspired 2D nanofluidic membranes for energy applications

Bioinspired two-dimensional (2D) nanofluidic membranes have been explored for the creation of high-performance ion transport systems that can mimic the delicate transport functions of living organisms. Advanced energy devices made from these membranes show excellent energy storage and conversion capabilities. Further research and development in this area are essential to unlock the full potential of energy devices and facilitate the development of high-performance equipment toward real-world applications and a sustainable future. However, there has been minimal review and summarization of 2D nanofluidic membranes in recent years. Thus, it is necessary to carry out an extensive review to provide a survey library for researchers in related fields. In this review, the classification and the raw materials that are used to construct 2D nanofluidic membranes are first presented. Second, the top-down and bottom-up methods for constructing 2D membranes are introduced. Next, the applications of bioinspired 2D membranes in osmotic energy, hydraulic energy, mechanical energy, photoelectric conversion, lithium batteries, and flow batteries are discussed in detail. Finally, the opportunities and challenges that 2D nanofluidic membranes are likely to face in the future are envisioned. This review aims to provide a broad knowledge base for constructing high-performance bioinspired 2D nanofluidic membranes for advanced energy applications.

Nanopore Fabrication Made Easy: A Portable, Affordable Microcontroller-Assisted Approach for Tailored Pore Formation via Controlled Breakdown

With growing interest in solid-state nanopore sensing─a single-molecule technique capable of profiling a host of analyte classes─establishing facile and scalable approaches for fabricating molecular-size pores is becoming increasingly important. The introduction of nanopore fabrication by controlled breakdown (CBD) has transformed the economics and accessibility of nanopore fabrication. Here, we introduce the design of an Arduino-based, portable USB-powered CBD device, with an estimated cost of <150 USD, which is ≈10-100× cheaper than most commercial solutions, capable of fabricating single nanopores conducive for single molecule sensing experiments. We demonstrate the facile fabrication of 60 tailored nanopores (∼2.6-12.6 nm) with ∼80% of the pores within 1 nm of the target diameter. Selected pores were then tested with double-stranded DNA, the canonical molecular ruler, demonstrating their performance for single-molecule sensing applications. The device is constructed with off-the-shelf readily available components and controlled using a highly customizable MATLAB application, which has capabilities encompassing pore fabrication, pore enlargement, and current-voltage acquisition for pore size estimation. When combined with a portable amplifier, this device also provides a fully portable sensing platform, an important step toward portable solid-state nanopore sensing applications.

High durability and stability of 2D nanofluidic devices for long-term single-molecule sensing

Nanopores in two-dimensional (2D) membranes hold immense potential in single-molecule sensing, osmotic power generation, and information storage. Recent advances in 2D nanopores, especially on single-layer MoS2, focus on the scalable growth and manufacturing of nanopore devices. However, there still remains a bottleneck in controlling the nanopore stability in atomically thin membranes. Here, we evaluate the major factors responsible for the instability of the monolayer MoS2 nanopores. We identify chemical oxidation and delamination of monolayers from their underlying substrates as the major reasons for the instability of MoS2 nanopores. Surface modification of the substrate and reducing the oxygen from the measurement solution improves nanopore stability and dramatically increases their shelf-life. Understanding nanopore growth and stability can provide insights into controlling the pore size, shape and can enable long-term measurements with a high signal-to-noise ratio and engineering durable nanopore devices.