Molecular sieving using nanofilters: past, present and future

Ion Selectivity in Multilayered Stacked Nanoporous Graphene

Nanoporous graphene is an ideal candidate for molecular filtration as it can potentially combine high permeability with high selectivity at molecular levels. To make use of graphene in filtration setups, the defects formed during its growth and during the transfer of graphene to the carrier support pose a challenge. These uncontrolled pores can be avoided by stacking graphene layers, and then, controlled pores can be initiated with oxygen plasma. Here, we show that two-layer stacks provide the best balance of defect coverage and high selectivity compared with other stacks. Using the electrical characterization of ionic solutions in the standard diffusion cell, we compare the ionic transport and ionic selectivity of up to three-layered stacks of graphene that have been plasma-treated. We find that there is a decrease in the ionic selectivity of a two-layered stack as one more layer of graphene is added. We provide a model for this occurrence. Our results will be helpful for making practical and high-performance filtration systems from two-dimensional materials.

A superstable, flexible, and scalable nanofluidic ion regulation composite membrane

Two-dimensional layered membranes with high and stable ion transport properties have various applications in nanofluidic devices; however, their construction remains a considerable challenge. Herein, we develop a superstable aramid nanofiber/graphite composite membrane with numerous one-dimensional and two-dimensional nano-confined interspaces for ultrafast ion transport. The fabricated flexible and scalable membrane exhibits high tensile strength (∼115.3 MPa) even after immersion in water for 90 days. Further, the aramid nanofiber/graphite conductor features the surface-charge-governed ion transport behavior. The ionic conductivity of the membrane at a low potassium chloride concentration of 10-4 mol/L can be enhanced by 16 times that of the bulk counterpart. More importantly, its structure and ionic conductivity remain unchanged even after immersion in different harsh solutions (e.g., acid, base, and ethanol) for over 30 days. Molecular dynamics simulations reveal that the superstability of the membrane is attributable to the robust interchain interactions within the aramid nanofibers and the strong interfacial interactions between the aramid nanofibers and graphite nanosheets. This study highlights the superior structural stability of the proposed flexible and scalable aramid nanofiber/graphite composite membrane, which could be employed in advanced nanofluidic devices for application under extreme working environments.

Continuous-flow macromolecular sieving in slanted nanofilter array: stochastic model and coupling effect of electrostatic and steric hindrance

Microfabricated slanted nanofilter arrays are a promising technology for integrated biomolecule analysis systems such as online monitoring and point-of-care quality validation, due to their continuous-flow and one-step operation capability. However, an incomplete understanding of the system limits the performance and wider applications of slanted nanofilter arrays. In this paper, we present rigorous theoretical and experimental studies on macromolecule sieving in a slanted nanofilter array. From both stochastic and kinetic models, an explicit theoretical solution describing size-dependent molecule sieving was derived, which was validated using experimental sieving results obtained for various sieving conditions. Our results not only detail the relationship between sieving conditions and sieving efficiency but also demonstrate that sieving is affected by multiple hindrance effects (electrostatic hindrance), not steric hindrance alone. There is an optimal sieving condition for achieving the greatest separation efficiency for DNAs of a certain size range. Small DNA has great size selectivity in small nanofilters and in weak electric fields, whereas large DNA is present in large nanofilters and in strong electric fields. This study provides insights into designing a slanted nanofilter array for particular target applications and understanding the sieving principles in the nanofilter array.

Continuous Online Titer Monitoring in CHO Cell Culture Supernatant Using a Herringbone Nanofluidic Filter Array

Online monitoring of monoclonal antibody product titers throughout biologics process development and production enables rapid bioprocess decision-making and process optimization. Conventional analytical methods, including high-performance liquid chromatography and turbidimetry, typically require interfacing with an automated sampling system capable of online sampling and fractionation, which suffers from increased cost, a higher risk of failure, and a higher mechanical complexity of the system. In this study, a novel nanofluidic system for continuous direct (no sample preparation) IgG titer measurements was investigated. Tumor necrosis factor α (TNF-α), conjugated with fluorophores, was utilized as a selective binder for adalimumab in the unprocessed cell culture supernatant. The nanofluidic device can separate the bound complex from unbound TNF-α and selectively concentrate the bound complex for high-sensitivity detection. Based on the fluorescence intensity from the concentrated bound complex, a fluorescence intensity versus titer curve can be generated, which was used to determine the titer of samples from filtered, unpurified Chinese hamster ovary cell cultures continuously. The system performed direct monitoring of IgG titers with nanomolar resolution and showed a good correlation with the biolayer interferometry assays. Furthermore, by variation of the concentration of the indicator (TNF-α), the dynamic range of the system can be tuned and further expanded.

Nanostructured Material and its Application in Membrane Separation Technology

Abstract:

Nanomaterials are classified with their at least one dimension in the range of 1-100 nm, which offers new innovative solutions for membrane development. These are included as nanosized adsorbents, nanomembranes, nanocomposites, photocatalysts, nanotubes, nanoclays, etc. Nanomaterials are promising, exceptional properties for one of the opportunity is to prevent the global water crisis with their extraordinary performance as their usage for membrane development, particularly for water treatment process. Nanomaterial based membranes that include nanoparticles, nanofibers, 2D layered materials, and their nanostructured composites which provide superior permeation characteristics besides their antifouling, antibacterial and photodegradation properties. They are enable for providing the extraordinary properties to be used as ultrafast and ultimately selective membranes for water purification. In this review, recently developed nanomaterial based membranes and their applications for water treatment process were summarized. The main attention is given to the nanomaterial based membrane structure design. The variety in terms of constituent structure and alterations provide nanomaterial based membranes which will be expected to be a perfect separation membrane in the future.

Influence of hydrophobic moieties on the crystallization of amphiphilic DNA nanostructures

Three-dimensional crystalline frameworks with nanoscale periodicity are valuable for many emerging technologies, from nanophotonics to nanomedicine. DNA nanotechnology has emerged as a prime route for constructing these materials, with most approaches taking advantage of the structural rigidity and bond directionality programmable for DNA building blocks. Recently, we have introduced an alternative strategy reliant on flexible, amphiphilic DNA junctions dubbed C-stars, whose ability to crystallize is modulated by design parameters, such as nanostructure topology, conformation, rigidity, and size. While C-stars have been shown to form ordered phases with controllable lattice parameter, response to stimuli, and embedded functionalities, much of their vast design space remains unexplored. Here, we investigate the effect of changing the chemical nature of the hydrophobic modifications and the structure of the DNA motifs in the vicinity of these moieties. While similar design variations should strongly alter key properties of the hydrophobic interactions between C-stars, such as strength and valency, only limited differences in self-assembly behavior are observed. This finding suggests that long-range order in C-star crystals is likely imposed by structural features of the building block itself rather than the specific characteristics of the hydrophobic tags. Nonetheless, we find that altering the hydrophobic regions influences the ability of C-star crystals to uptake hydrophobic molecular cargoes, which we exemplify by studying the encapsulation of antibiotic penicillin V. Besides advancing our understanding of the principles governing the self-assembly of amphiphilic DNA building blocks, our observations thus open up new routes to chemically program the materials without affecting their structure.

Interlayer spacing in pillared and grafted MCM-22 type silicas: density functional theory analysis versus experiment

Pillaring of synthetic layered crystalline silicates and aluminosilicates provides a strategy to enhance their adsorption and separation performance, and can facilitate the understanding of such behavior in more complex natural clays. We perform the first-principles density functional theory calculations for the pillaring of the pure silica polymorph of an MCM-22 type molecular sieve. Starting with a precursor material MCM-22P with fully hydroxylated layers, a pillaring agent, (EtO)₃SiR, can react with hydroxyl groups (-OH) on adjacent internal surfaces, 2(-OH) + (EtO)₃SiR + H₂O → (-O)₂SiOHR + 3EtOH, to form a pillar bridging these surfaces, or with a single hydroxyl, -OH + (EtO)₃SiR + 2H₂O → (-O)Si(OH)₂R + 3EtOH, grafting to one surface. For computational efficiency, we replace the experimental organic ligand, R, by a methyl group. We find that the interlayer spacing in MCM-22 is reduced by 2.66 Å relative to weakly bound layers in the precursor MCM-22P. Including (-O)₂SiR bridges for 50% (100%) of the hydroxyl sites in MCM-22P increases the interlayer spacing relative to MCM-22 by 2.52 Å (2.46 Å). For comparison, we also analyze the system where all -OH groups in MCM-22P are replaced by non-bridging grafted (-O)Si(OH)₂R which results in a smaller interlayer spacing expansion of 2.17 Å relative to MCM-22. Our results for the interlayer spacing in the pillared materials are compatible with experimental observations for a similar MCM-22 type material with low Al content (Si : Al = 51 : 1) of an expansion relative to MCM-22 of roughly 2.8 Å and 2.5 Å from our x-ray diffraction and scanning transmission electron microscopy analyses, respectively. The latter analysis reveals significant variation in individual layer spacings.

Double-sided plasmonic metasurface for simultaneous biomolecular separation and SERS detection

Porous membrane-based nanofiltration separation of small biomolecules is a widely used biotechnology for which size-based selectivity is a critical parameter of technological relevance. Efficient determination of size selectivity calls for an advanced detection method capable of performing sensitive, rapid, and on-membrane examination. Surface-enhanced Raman spectroscopy (SERS) is such a detection method that has been widely recognized as an ultrasensitive technique for trace-level detection with sensitivity down to the single-molecule level. In this work, we for the first time develop a double-sided hierarchical porous membrane-like plasmonic metasurface to realize high-selectivity bimolecular separation and simultaneous ultrasensitive SERS detection. This highly flexible device, consisting of subwavelength nanocone pairs surrounded by randomly orientated sub-5 nm nanogrooves, was prepared by combining customized "top-down" fabrication of conical nanopores in an ion-track registered polycarbonate membrane and self-assembly of nanogrooves on the membrane surface through physical vapor deposition. The unique tip-to-tip oriented conical nanopores in the device enables excellent size-based molecular selectivity; the hierarchical groove-pore structure supports a peculiar cascaded electromagnetic near-field enhancement mechanism, endowing the device with SERS-based molecular detection of ultrahigh sensitivity, uniformity, repeatability, and polarization independence. With such dual structural merits and performance enhancement, we demonstrate effective nanofiltration separation of small-sized adenine from big-sized ss-DNA and synergistic SERS determination of their species. We experimentally demonstrate an ultrasensitive detection of 4-mercaptopyridine down to 10 pM. Together with its unparalleled mechanical flexibility, this double-side-responsive plasmonic metasurface membrane can find great potential in real-world molecular filtration and detection under extremely complex working conditions.

A Critical Review on the Sensing, Control, and Manipulation of Single Molecules on Optofluidic Devices

Single-molecule techniques have shifted the paradigm of biological measurements from ensemble measurements to probing individual molecules and propelled a rapid revolution in related fields. Compared to ensemble measurements of biomolecules, single-molecule techniques provide a breadth of information with a high spatial and temporal resolution at the molecular level. Usually, optical and electrical methods are two commonly employed methods for probing single molecules, and some platforms even offer the integration of these two methods such as optofluidics. The recent spark in technological advancement and the tremendous leap in fabrication techniques, microfluidics, and integrated optofluidics are paving the way toward low cost, chip-scale, portable, and point-of-care diagnostic and single-molecule analysis tools. This review provides the fundamentals and overview of commonly employed single-molecule methods including optical methods, electrical methods, force-based methods, combinatorial integrated methods, etc. In most single-molecule experiments, the ability to manipulate and exercise precise control over individual molecules plays a vital role, which sometimes defines the capabilities and limits of the operation. This review discusses different manipulation techniques including sorting and trapping individual particles. An insight into the control of single molecules is provided that mainly discusses the recent development of electrical control over single molecules. Overall, this review is designed to provide the fundamentals and recent advancements in different single-molecule techniques and their applications, with a special focus on the detection, manipulation, and control of single molecules on chip-scale devices.

Wireless bipolar electrode-based textile electrofluidics: towards novel micro-total-analysis systems

Point of care testing using micro-total-analysis systems (μTAS) is critical to emergent healthcare devices with rapid and robust responses. However, two major barriers to the success of this approach are the prohibitive cost of microchip fabrication and poor sensitivity due to small sample volumes in a microfluidic format. Here, we aimed to replace the complex microchip format with a low-cost textile substrate with inherently built microchannels using the fibers' spaces. Secondly, by integrating this textile-based microfluidics with electrophoresis and wireless bipolar electrochemistry, we can significantly improve solute detection by focusing and concentrating the analytes of interest. Herein, we demonstrated that an in situ metal electrode simply inserted inside the textile-based electrophoretic system can act as a wireless bipolar electrode (BPE) that generates localized electric field and pH gradients adjacent to the BPE and extended along the length of the textile construct. As a result, charged analytes were not only separated electrophoretically but also focused where their electrophoretic migration and counter flow (EOF) balances due to redox reactions proceeding at the BPE edges. The developed wireless redox focusing technique on textile constructs was shown to achieve a 242-fold enrichment of anionically charged solute over an extended time of 3000 s. These findings suggest a simple route that achieves separation and analyte focusing on low-cost surface-accessible inverted substrates, which is far simpler than the more complex ITP on conventional closed and inaccessible capillary channels.

Wood Ionic Cable

The combination of good stability, biocompatibility, and high mechanical strength is attractive for bio-related material applications, but it remains challenging to simultaneously achieve these properties in a single, ionically conductive material. Here a "wood" ionic cable, made of aligned wood nanofibrils, demonstrating a combination of biocompatibility, high mechanical strength, high ionic conductivity, and excellent stability is reported. The wood ionic cable possesses excellent flexibility and exhibits high tensile strength up to 260 MPa (in the dry state) and ≈80 MPa (in the wet state). The nanochannels within the highly aligned cellulose nanofibrils and the presence of negative charges on the surfaces of these nanochannels, originating from the cellulose hydroxyl groups, provide new opportunities for ion regulation at low salt concentrations. Ion regulation in turn enables the wood ionic cable to have unique nanofluidic ionic behaviors. The Na⁺ ion conductivity of the wood ionic cable can reach up to ≈1.5 × 10^-4 S cm^-1 at low Na⁺ ion concentration (1.0 × 10^-5 mol L^-1 ), which is an order of magnitude higher than that of bulk NaCl solution at the same concentration. The scalable, biocompatible wood ionic cable enables novel ionic device designs for potential ion-regulation applications.

Artificial sodium-selective ionic device based on crown-ether crystals with subnanometer pores

Biological sodium channels ferry sodium ions across the lipid membrane while rejecting potassium ions and other metal ions. Realizing such ion selectivity in an artificial solid-state ionic device will enable new separation technologies but remains highly challenging. In this work, we report an artificial sodium-selective ionic device, built on synthesized porous crown-ether crystals which consist of densely packed 0.26-nm-wide pores. The Na⁺ selectivity of the artificial sodium-selective ionic device reached 15 against K⁺, which is comparable to the biological counterpart, 523 against Ca^2 +, which is nearly two orders of magnitude higher than the biological one, and 1128 against Mg^2 +. The selectivity may arise from the size effect and molecular recognition effect. This work may contribute to the understanding of the structure-performance relationship of ion selective nanopores.

Biomimetic N-Doped Graphene Membrane for Proton Exchange Membranes

Proton exchange membranes (PEMs) with both high selectivity and high permeance are of great demand in hydrogen-based applications, especially in fuel cells. Although graphene membranes have shown high selectivity of protons over other ions and molecules, the relatively low permeance of protons through perfect pristine graphene restricts its practical applications. Inspired by the nitrogen-assisted proton transport in biological systems, we introduced N-doping to increase the proton permeance and proposed a type of N-doped graphene membranes (NGMs) for proton exchange, which have both high proton permeance and high selectivity. Compared to the state-of-the-art commercial PEMs, the NGMs show significant increases in both areal proton conductivity (2-3 orders of magnitude) and selectivity of proton to methanol (1-2 orders of magnitude). The work realized the controllable tuning of proton permeance of the graphene membrane with N-doping and developed a new type of graphene-based PEMs with high performance for practical applications.

Assembly of Nanofluidic MXene Fibers with Enhanced Ionic Transport and Capacitive Charge Storage by Flake Orientation

MXenes are an emerging class of highly conductive two-dimensional (2D) materials with electrochemical storage features. Oriented macroscopic Ti₃C₂T_x fibers can be fabricated from a colloidal 2D nematic phase dispersion. The layered conductive Ti₃C₂T_x fibers are ideal candidates for constructing high-speed ionic transport channels to enhance the electrochemical capacitive charge storage performance. In this work, we assemble Ti₃C₂T_x fibers with a high degree of flake orientation by a wet spinning process with controlled spinning speeds and morphology of the spinneret. In addition to the effects of cross-linking of magnesium ions between Ti₃C₂T_x flakes, the electronic conductivity and mechanical strength of the as-prepared fibers have been improved to 7200 S cm^-1 and 118 MPa, respectively. The oriented Ti₃C₂T_x fibers present a volumetric capacitive charge storage capability of up to 1360 F cm^-3 even in a Mg-ion based neutral electrolyte, with contributions from both nanofluidic ion transport and Mg-ion intercalation pseudocapacitance. The oriented 2D Ti₃C₂T_x driven nanofluidic channels with great electronic conductivity and mechanical strength endows the MXene fibers with attributes for serving as conductive ionic cables and active materials for fiber-type capacitive electrochemical energy storage, biosensors, and potentially biocompatible fibrillar tissues.

An integrated microfluidic system for early detection of sepsis-inducing bacteria

Since early diagnosis of sepsis may assist clinicians in initiating timely, effective, and prognosis-improving antibiotic therapy, we developed an integrated microfluidic chip (IMC) for rapid isolation of both Gram-positive and Gram-negative bacteria from blood. The device comprised a membrane-based filtration module (90 min operating time), a bacteria-capturing module using a micro-mixer containing magnetic beads coated with "flexible neck" regions of mannose-binding lectin proteins for bacteria capture (20 min), and a miniature polymerase chain reaction (PCR) module for bacteria identification (90 min via TaqMan® probe technology). The filter separated all white blood cells and 99.5% of red blood cells from bacteria, which were captured at rates approaching 85%. The PCR assay's limit of detection was 5 colony-forming units (CFU) per reaction, and the entire process was completed in only 4 h. Since this is far less than that for culture-based approaches, this IMC may serve as a promising device for detection of sepsis.

Comparison of separation modes for microchip electrophoresis of proteins

Separation of a set of model proteins was tested on a microchip electrophoresis analytical platform capable of sample injection by two different electrokinetic mechanisms. A range of separation modes-microchip capillary zone electrophoresis, microchip micellar electrokinetic chromatography, and nanoparticle-based sieving-was tested on glass and polydimethylsiloxane/glass microchips and with silica-nanoparticle colloidal arrays. The model proteins calmodulin (18 kiloDalton), bovine serum albumin (66 kDa), and concanavalin (106 kDa) were labeled with Alexa Fluor 647 for laser-induced fluorescence detection. The best separation and resolution were obtained in a silica-nanoparticle colloidal array chip.

Continuous and spontaneous nanoparticle separation by diffusiophoresis

The separation of nanoparticles has drawn critical attention in various microfluidic applications including chemical analysis, diagnostics and environmental monitoring. Thus, a number of nanoparticle separation methods have been extensively proposed. However, most of the conventional methods require complicated structured devices, expensive manufacturing processes, and external power sources. While a spontaneous diffusiophoretic separation device based on an ion exchange mechanism could overcome such drawbacks, the recovery of separated particles and the inevitable development of an acidic environment due to the release of H+ from the cation exchange membrane limit its practical applicability. Therefore, in this work, we present a simple but robust nanoparticle separation method based on spontaneously induced diffusiophoresis, which is operated in a continuous manner to overcome the limitations of conventional methods. First, we confirmed that the particle exclusion distance followed the previously developed scaling law of diffusiophoresis. Consequently, we demonstrated the separation of nanoparticles of 40 nm, 200 nm and 2 μm diameter by utilizing the fact that the exclusion distances of various particles were proportional to their diffusiophoretic mobility. Furthermore, the use of Tris buffer increased the diffusiophoretic migration of nanoparticles due to the enhanced concentration gradient, and enabled the produced solution to be compatible with pH-sensitive bio-samples. Therefore, we expect this continuous and spontaneous diffusiophoretic separation platform to be useful in practical applications for analyzing various nano-meter scale bio-particles.

Fouling Analysis and the Recovery of Phytosterols from Orange Juice Using Regenerated Cellulose Ultrafiltration Membranes

This study describes the use of regenerated cellulose (RCA) membranes with molecular weight cut-off (MWCO) values of 10, 30, and 100 kDa, respectively, to separate phytosterols from orange juice for possible nutraceutical production. A desirable membrane separation rejects protein whilst transmitting phytosterols and other low molecular mass compounds such as sugars. The ultrafiltration was performed in a cross-flow membrane system with a total filtration area of 336 cm2. Total phytosterol analysis was carried out by using a Liebermann-Buchard-based method. Protein concentration was quantified by the Bradford method. The effects of three different membranes upon the rejection of total phytosterol content, proteins, sugar, and antioxidant activity were studied. Of the membranes tested, the 10-kDa membrane displayed the highest concentration of phytosterols in the permeate. The 30-kDa and 100-kDa membranes gave comparatively higher phytosterol rejection. The membrane surface roughness and corresponding pure water flux values varied as a function of MWCO such that RCA30 > RCA100 > RCA10. Membranes with rougher surfaces displayed higher fouling than those with smoother surfaces. Hydrophobicity and surface roughness both influenced filtration performance, by controlling the development of the protein-based foulant which modified membrane selectivity.

Electrokinetic stacking of particle zones in confined channels enabling their UV absorbance detection on microchips

In this article, we report a simple approach to stacking micro- and nanoparticle zones by electrokinetically migrating them through moderately confined channels of uniform cross-section. Experiments show the reported pre-concentration process to initiate at the tail end of the zone following its electrokinetic injection, with the stacked region migrating faster than the rest of the sample band. This effect causes the particles traveling in front to merge into the stacked region making it grow both in size and concentration. Because the stacked zone also gradually loses particles from its trailing edge, it eventually disintegrates upon running out of particles at its front end. Nevertheless, enhancements in peak height by over 100-fold were recorded using the reported approach for polystyrene beads with diameters comparable to the channel depth. This enhancement however, exhibited a temporal variation as the particle band migrated through the analysis column reaching a maximum value that depended on the particle diameter, particle concentration, channel depth, electric field strength, electroosmotic mobility, etc. Interestingly, the peak area recorded by the detector remained relatively constant during this particle migration period allowing reliable sample quantitation. Moreover, upon incubating antibody-coated particles against an antigen sample, the peak area for the particle zone was seen to scale linearly with the antigen concentration establishing the utility of the reported focusing phenomenon for chemical/biochemical analysis. The noted stacking technique was further applied to enabling UV absorbance detection of particle zones on microchips which then allowed us to determine the colloidal content in actual natural water samples. .

Finite-Size Charged Species Diffusion and pH Change in Nanochannels

Molecular transport through nanofluidic structures exhibits properties that are unique at the nanoscale. The high surface-to-volume ratio of nanometer-sized confined spaces renders particle interactions with the surface of central importance. The electrical double layer (EDL) at the solid-liquid interface of charged surfaces generates an enrichment of counterions and the exclusion of co-ions that lead to a change in their diffusivity. In addition, the diffusive transport is altered by steric and hydrodynamic interactions between fluid molecules and the boundaries. An extensive body of literature investigates molecular transport at the nanoscale. However, most studies account for ionic species as point charges, severely limiting the applicability of the results to "large" nanofluidic systems. Moreover, and even more importantly, the change of pH in the nanoconfined region inside nanochannels has been completely overlooked. Corroborated by experimental data, here we present an all-encompassing analysis of molecular diffusion from the micro- to the ultra-nanoscale. While accounting for finite-size ions, we compute self-consistently the pH inside the channels. Surprisingly, we found that the concentration of ions H⁺ can change by more than 2 orders of magnitude compared to the bulk, hugely affecting molecular transport. Further, we found that counterions exhibit both enrichment and exclusion, depending on the size of nanochannels. Achieving a greater understanding of the effective transport properties of fluids at the nanoscale will fill the gap in knowledge that still limits development of innovative systems for medicine and industrial applications alike.

Direct electrophoretic microRNA preparation from clinical samples using nanofilter membrane

A method to directly collect negatively charged nucleic acids, such as DNA and RNA, in the biosamples simply by applying an electric field in between the sample and collection buffer separated by the nanofilter membrane is proposed. The nanofilter membrane was made of low-stress silicon nitride with a thickness of 100 nm, and multiple pores were perforated in a highly arranged pattern using nanoimprint technology with a pore size of 200 nm and a pore density of 7.22 × 10⁸/cm². The electrophoretic transport of hsa-mir-93-5p across the membrane was confirmed in pure microRNA (miRNA) mimic solution using quantitative reverse transcription-polymerase chain reactions (qRT-PCR). Consistency of the collected miRNA quantity, stability of the system during the experiment, and yield and purity of the prepared sample were discussed in detail to validate the effectiveness of the electrical protocol. Finally, in order to check the applicability of this method to clinical samples, liquid biopsy process was demonstrated by evaluating the miRNA levels in sera of hepatocellular carcinoma patients and healthy controls. This efficient system proposed a simple, physical idea in preparation of nucleic acid from biosamples, and demonstrated its compatibility to biological downstream applications such as qRT-PCR as the conventional nucleic acid extraction protocols.

Slot Self-Allocation Based MAC Protocol for Energy Harvesting Nano-Networks

Nano-networks are composed of interconnected nano-nodes and can enable unprecedented applications in various fields. Due to the peculiarities of nano-networks, such as high density, extremely limited energy and computational resources, traditional carrier-sensing based Media Access Control (MAC) protocols are not suitable for nano-networks. In this paper, a Slot Self-Allocation based MAC protocol (SSA-MAC) is proposed for energy harvesting nano-networks. Two transmission schemes for centralized and distributed nano-networks are designed, respectively. In centralized nano-networks, nano-nodes can only send packets to the nano-controller in their Self-Allocation Slots (SASs), while, in distributed nano-networks, nano-nodes can only receive packets from surrounding nano-nodes in their SASs. Extensive simulations were conducted to compare the proposed SSA-MAC with PHysical LAyer aware MAC (PHLAME), Receiver-Initiated Harvesting-aware MAC (RIH-MAC) and Energy Efficient Wireless NanoSensor Network MAC (EEWNSN). From the results, it can be concluded that the proposed SSA-MAC achieves better performance and can reduce the collision probability, while improving the energy efficiency of nano-networks.

Light-Controlled Selective Collection-and-Release of Biomolecules by an On-Chip Nanostructured Device

The analysis of biosamples, e.g., blood, is a ubiquitous task of proteomics, genomics, and biosensing fields; yet, it still faces multiple challenges, one of the greatest being the selective separation and detection of target proteins from these complex biosamples. Here, we demonstrate the development of an on-chip light-triggered reusable nanostructured selective and quantitative protein separation and preconcentration platform for the direct analysis of complex biosamples. The on-chip selective separation of required protein analytes from raw biosamples is performed using antibody-photoacid-modified Si nanopillars vertical arrays (SiNPs) of ultralarge binding surface area and enormously high binding affinity, followed by the light-controlled rapid release of the tightly bound target proteins in a controlled liquid media. Two important experimental observations are presented: (1) the first demonstration on the control of biological reaction binding affinity by the nanostructuring of the capturing surface, leading to highly efficient protein collection capabilities, and (2) the light-triggered switching of the highly sticky binding surfaces into highly reflective nonbinding surfaces, leading to the rapid and quantitative release of the originally tightly bound protein species. Both of these two novel behaviors were theoretically and experimentally investigated. Importantly, this is the first demonstration of a three-dimensional (3D) SiNPs on-chip filter with ultralarge binding surface area and reversible light-controlled quantitative release of adsorbed biomolecules for direct purification of blood samples, able to selectively collect and separate specific low abundant proteins, while easily removing unwanted blood components (proteins, cells) and achieving desalting results, without the requirement of time-consuming centrifugation steps, the use of desalting membranes, or affinity columns.

Anomalous transport in the soft-sphere Lorentz model

The sensitivity of anomalous transport in crowded media to the form of the inter-particle interactions is investigated through computer simulations. We extend the highly simplified Lorentz model towards realistic natural systems by modeling the interactions between the tracer and the obstacles with a smooth potential. We find that the anomalous transport at the critical point happens to be governed by the same universal exponent as for hard exclusion interactions, although the mechanism of how narrow channels are probed is rather different. The scaling behavior of simulations close to the critical point confirm this exponent. Our result indicates that the simple Lorentz model may be applicable to describing the fundamental properties of long-range transport in real crowded environments.

Flexibility defines structure in crystals of amphiphilic DNA nanostars

DNA nanostructures with programmable shape and interactions can be used as building blocks for the self-assembly of crystalline materials with prescribed nanoscale features, holding a vast technological potential. Structural rigidity and bond directionality have been recognised as key design features for DNA motifs to sustain long-range order in 3D, but the practical challenges associated with prescribing building-block geometry with sufficient accuracy have limited the variety of available designs. We have recently introduced a novel platform for the one-pot preparation of crystalline DNA frameworks supported by a combination of Watson-Crick base pairing and hydrophobic forces (Brady et al 2017 Nano Lett. 17 3276-81). Here we use small angle x-ray scattering and coarse-grained molecular simulations to demonstrate that, as opposed to available all-DNA approaches, amphiphilic motifs do not rely on structural rigidity to support long-range order. Instead, the flexibility of amphiphilic DNA building-blocks is a crucial feature for successful crystallisation.

Fabrication and application of nanoporous polymer ion-track membranes

With the development of the nano-fabrication and nanofluidics, nanoporous membranes have shown great potential in applications such as molecular separation, energy conversion, and molecular sensing. However, their performance has often been limited by the trade-off between selectivity and permeability and the lack of scalability. The prospect of overcoming these problems with nanoporous polymer ion-track membranes is promising. Focusing on these membranes, this review provides a comprehensive overview of fabrication methods, including the traditional track-etching technique and the recently developed track-UV technique; characterization methods; transport mechanisms; and major properties and applications.

Amphiphilic-DNA Platform for the Design of Crystalline Frameworks with Programmable Structure and Functionality

The reliable preparation of functional, ordered, nanostructured frameworks would be a game changer for many emerging technologies, from energy storage to nanomedicine. Underpinned by the excellent molecular recognition of nucleic acids, along with their facile synthesis and breadth of available functionalizations, DNA nanotechnology is widely acknowledged as a prime route for the rational design of nanostructured materials. Yet, the preparation of crystalline DNA frameworks with programmable structure and functionality remains a challenge. Here we demonstrate the potential of simple amphiphilic DNA motifs, dubbed "C-stars", as a versatile platform for the design of programmable DNA crystals. In contrast to all-DNA materials, in which structure depends on the precise molecular details of individual building blocks, the self-assembly of C-stars is controlled uniquely by their topology and symmetry. Exploiting this robust self-assembly principle, we design a range of topologically identical, but structurally and chemically distinct C-stars that following a one-pot reaction self-assemble into highly porous, functional, crystalline frameworks. Simple design variations allow us to fine-tune the lattice parameter and thus control the partitioning of macromolecules within the frameworks, embed responsive motifs that can induce isothermal disassembly, and include chemical moieties to capture target proteins specifically and reversibly.

Approach to classify, separate, and enrich objects in groups using ensemble sorting

The sorting of objects into groups is a fundamental operation, critical in the preparation and purification of populations of cells, crystals, beads, or droplets, necessary for research and applications in biology, chemistry, and materials science. Most of the efforts exploring such purification have focused on two areas: the degree of separation and the measurement precision required for effective separation. Conventionally, achieving good separation ultimately requires that the objects are considered one by one (which can be both slow and expensive), and the ability to measure the sorted objects by increasing sensitivity as well as reducing sorting errors. Here we present an approach to sorting that addresses both critical limitations with a scheme that allows us to approach the theoretical limit for the accuracy of sorting decisions. Rather than sorting individual objects, we sort the objects in ensembles, via a set of registers which are then in turn sorted themselves into a second symmetric set of registers in a lossless manner. By repeating this process, we can arrive at high sorting purity with a low set of constraints. We demonstrate both the theory behind this idea and identify the critical parameters (ensemble population and sorting time), and show the utility and robustness of our method with simulations and experimental systems spanning several orders of scale, sorting populations of macroscopic beads and microfluidic droplets. Our method is general in nature and simplifies the sorting process, and thus stands to enhance many different areas of science, such as purification, enrichment of rare objects, and separation of dynamic populations.

Entropic trap purification of long DNA

Long-read genomic applications, such as genome mapping in nanochannels, require long DNA that is free of small-DNA impurities. We have developed a chip-based system based on entropic trapping that can simultaneously concentrate and purify a long DNA sample under the alternating application of an applied pressure (for sample injection) and an electric field (for filtration and concentration). In contrast, short DNA tends to pass through the filter owing to its comparatively weak entropic penalty for entering the nanoslit. The single-stage prototype developed here, which operates in a continuous pulsatile manner, achieves selectivities of up to 3.5 for λ-phage DNA (48.5 kilobase pairs) compared to a 2 kilobase pair standard based on experimental data for the fraction filtered using pure samples of each species. The device is fabricated in fused silica using standard clean-room methods, making it compatible for integration with long-read genomics technologies.

Nanotechnology Applications in Medicine

In recent years there has been a rapid increase in nanotechnology applications to medicine in order to prevent and treat diseases in the human body. The established and future applications have the potential to dramatically change medical science. The present paper will give a few examples that could transform common medical procedures.

Intrusion of polyethylene glycol into solid-state nanopores

The mechanism of PEG molecule penetration into nanopores upon mechanical pressure is understood.

Fabrication techniques enabling ultrathin nanostructured membranes for separations

The fabrication of nanostructured materials is an area of continuous improvement and innovative techniques that fulfill the demand of many fields of research and development. The continuously decreasing size of the smallest patternable feature has expanded the catalog of methods enabling the fabrication of nanostructured materials. Several of these nanofabrication techniques have sprouted from applications requiring nanoporous membranes such as molecular separations, cell culture, and plasmonics. This review summarizes methods that successfully produce through-pores in ultrathin films exhibiting an approximate pore size to thickness ratio of one, which has been shown to be beneficial due to high permeability and improved separation potential. The material reviewed includes large-area, parallel, and affordable approaches such as self-organizing polymers, nanosphere lithography, anodization, nanoimprint lithography as well as others such as solid phase crystallization and nanosphere lens lithography. The aim of this review is to provide a set of inexpensive fabrication techniques to produce nanostructured materials exhibiting pores ranging from 10 to 350 nm and a pore size to thickness ratio close to one. The fabrication methods described in this work have reported the successful manufacture of nanoporous membranes exhibiting the ideal characteristics to improve selectivity and permeability when applied as separation media in ultrafiltration.

The Emerging Role of Nanotechnology in Cell and Organ Transplantation

Transplantation is often the only choice many patients have when suffering from end-stage organ failure. Although the quality of life improves after transplantation, challenges, such as organ shortages, necessary immunosuppression with associated complications, and chronic graft rejection, limit its wide clinical application. Nanotechnology has emerged in the past 2 decades as a field with the potential to satisfy clinical needs in the area of targeted and sustained drug delivery, noninvasive imaging, and tissue engineering. In this article, we provide an overview of popular nanotechnologies and a summary of the current and potential uses of nanotechnology in cell and organ transplantation.

Crystallization of Amphiphilic DNA C-Stars

Many emerging technologies require materials with well-defined three-dimensional nanoscale architectures. Production of these structures is currently underpinned by self-assembling amphiphilic macromolecules or engineered all-DNA building blocks. Both of these approaches produce restricted ranges of crystal geometries due to synthetic amphiphiles' simple shape and limited specificity, or the technical difficulties in designing space-filling DNA motifs with targeted shapes. We have overcome these limitations with amphiphilic DNA nanostructures, or "C-Stars", that combine the design freedom and facile functionalization of DNA-based materials with robust hydrophobic interactions. C-Stars self-assemble into single crystals exceeding 40 μm in size with lattice parameters exceeding 20 nm.

Diverging Time Scale in the Dimensional Crossover for Liquids in Strong Confinement

We study a strongly interacting dense hard-sphere system confined between two parallel plates by event-driven molecular dynamics simulations to address the fundamental question of the nature of the 3D to 2D crossover. As the fluid becomes more and more confined the dynamics of the transverse and lateral degrees of freedom decouple, which is accompanied by a diverging time scale separating 2D from 3D behavior. Relying on the time-correlation function of the transversal kinetic energy, the scaling behavior and its density dependence is explored. Surprisingly, our simulations reveal that its time dependence becomes purely exponential such that memory effects can be ignored. We rationalize our findings quantitatively in terms of an analytic theory which becomes exact in the limit of strong confinement.

Nanofluidics in two-dimensional layered materials: inspirations from nature

This review highlights the recent progress, current challenges, and future perspectives in the design and application of 2D layered materials for nanofluidic research, with emphasis on the thought of bio-inspiration.

Continuous high throughput nanofluidic separation through tangential-flow vertical nanoslit arrays

Nanofluidic devices exhibit unique, tunable transport properties that may lead to breakthroughs in molecular separations and sensing. However, the throughput of these devices is orders of magnitude too small for the processing of macroscopic samples. Here we overcome this problem by combining two technological innovations. First, nanofluidic channels are made as vertical slits connecting the two sides of a silicon nitride membrane. Arbitrary arrays of such nanoslits down to 15 nm wide with <6 Å uniformity were made by merging the idea of templating with chemical mechanical polishing to create a scalable, nanolithography-free wafer level process. Second, we provide for efficient solute transport to and from the openings of the nanoslits by incorporating the nanofluidic membrane into a microfluidic tangential-flow system, which is also fabricated at wafer level. As an exemplary application, we demonstrate charge-based continuous flow separation of small molecules with a selectivity of 100 and constant flux over more than 100 hours of operation. This proves the exciting possibility of exploiting transport phenomena governed by precision-engineered nanofluidic devices at a macroscopic scale.

Update on Renal Replacement Therapy: Implantable Artificial Devices and Bioengineered Organs

Recent advances in the fields of artificial organs and regenerative medicine are now joining forces in the areas of organ transplantation and bioengineering to solve continued challenges for patients with end-stage renal disease. The waiting lists for those needing a transplant continue to exceed demand. Dialysis, while effective, brings different challenges, including quality of life and susceptibility to infection. Unfortunately, the majority of research outputs are far from delivering satisfactory solutions. Current efforts are focused on providing a self-standing device able to recapitulate kidney function. In this review, we focus on two remarkable innovations that may offer significant clinical impact in the field of renal replacement therapy: the implantable artificial renal assist device (RAD) and the transplantable bioengineered kidney. The artificial RAD strategy utilizes micromachining techniques to fabricate a biohybrid system able to mimic renal morphology and function. The current trend in kidney bioengineering exploits the structure of the native organ to produce a kidney that is ready to be transplanted. Although these two systems stem from different technological approaches, they are both designed to be implantable, long lasting, and free standing to allow patients with kidney failure to be autonomous. However, for both of them, there are relevant issues that must be addressed before translation into clinical use and these are discussed in this review.

Numerical investigation of molecular nano-array in potential-energy profile for a single dsDNA

A Rigorous numerical investigation on dsDNA translocation in quasi-2-dimensional nano-array filter is performed using Molecular Dynamics (MD) method. Various dsDNA molecules with different sizes are chosen in order to model Ogston sieving in a nano-array filter. The radius of gyration of dsDNA molecule is less than the characteristic length of the shallow region in nano-array. The dsDNA molecule is assumed to be in the 0.05M NaCl electrolyte. MD shows acceptable results for potential-energy profile for nano-array filter. According to the MD outcomes, the dsDNA electrophoretic mobility decreases almost linearly with dsDNA size and show the same trend as Ogston sieving for gel electrophoresis. In addition, different shapes for nano-array filter are studied for a unique dsDNA molecule. It is concluded that steeping the nano-array wall can cause the retardation of dsDNA translocation and decreases dsDNA electrophoretic mobility.

Splitting of the Universality Class of Anomalous Transport in Crowded Media

We investigate the emergence of subdiffusive transport by obstruction in continuum models for molecular crowding. While the underlying percolation transition for the accessible space displays universal behavior, the dynamic properties depend in a subtle nonuniversal way on the transport through narrow channels. At the same time, the different universality classes are robust with respect to introducing correlations in the obstacle matrix as we demonstrate for quenched hard-sphere liquids as underlying structures. Our results confirm that the microscopic dynamics can dominate the relaxational behavior even at long times, in striking contrast to glassy dynamics.

Ionic liquid prolongs DNA translocation through graphene nanopores

Ionic liquid molecules interact strongly with DNA and effectively reduce its translocation speed via graphene nanopore.

Wetting Driven by Thermal Fluctuations on Terraced Nanostructures

Theoretical analysis and fully atomistic molecular dynamics simulations reveal a Brownian ratchet mechanism by which thermal fluctuations drive the net displacement of immiscible liquids confined in channels or pores with micro- or nanoscale dimensions. The thermally driven displacement is induced by surface nanostructures with directional asymmetry and can occur against the direction of action of wetting or capillary forces. Mean displacement rates in molecular dynamics simulations are predicted via analytical solution of a Smoluchowski diffusion equation for the position probability density. The proposed physical mechanisms and derived analytical expressions can be applied to engineer surface nanostructures for controlling the dynamics of diverse wetting processes such as capillary filling, wicking, and imbibition in micro- or nanoscale systems.