In Vitro Detection of S100B and Severity Evaluation of Traumatic Brain Injury Based on Biomimetic Peptide-Modified Nanochannels

The diagnosis and evaluation of traumatic brain injury (TBI) are crucial steps toward the treatment and prognosis of patients. A common question remains as to whether it is possible to introduce an ideal device for signal detection and evaluation that can directly connect digital signals with TBI, thereby enabling prompt response of the evaluation signal and sensitive and specific functioning of the detection process. Herein, a method is presented utilizing polymetric porous membranes with TRTK-12 peptide-modified nanochannels for the detection of S100B (a TBI biomarker) and assessment of TBI severity. The method leverages the specific bonding force between TRTK-12 peptide and S100B protein, along with the nanoconfinement effect of nanochannels, to achieve high sensitivity (LOD: 0.002 ng mL-1) and specificity (∆I/I0: 44.7%), utilizing ionic current change as an indicator. The proposed method, which is both sensitive and specific, offers a simple yet responsive approach for real-time evaluation of TBI severity. This innovative technique provides valuable scientific insights into the advancement of future diagnostic and therapeutic integration devices.

Asymmetric Nanoporous Alumina Membranes for Nanofluidic Osmotic Energy Conversion

The potential of harnessing osmotic energy from the interaction between seawater and river water has been recognized as a promising, eco-friendly, renewable, and sustainable source of power. The reverse electrodialysis (RED) technology has gained significant interest for its ability to generate electricity by combining concentrated and diluted streams with different levels of salinity. Nanofluidic membranes with tailored ion transport dynamics enable efficient harvesting of renewable osmotic energy. In this regard, anodic aluminum oxide (AAO) membranes with abundant nanochannels provide a cost-effective nanofluidic platform to obtain structures with a high density of ordered pores. AAO can be utilized in constructing asymmetric composite membranes with enhanced ion flux and selectivity to improve output power generation. In this review, we first present the fundamental structure and properties of AAO, followed by summarizing the fabrication techniques for asymmetric membranes using AAO and other nanostructured materials. Subsequently, we discuss the materials employed in constructing asymmetric structures incorporating AAO while emphasizing how material selection and design can resist and promote efficient energy conversion. Finally, we provide an outlook on future applications and address the challenges that need to be overcome for successful osmotic energy conversion.

Bioinspired Artificial Ion Pumps

Ion pumps are important membrane-spanning transporters that pump ions against the electrochemical gradient across the cell membrane. In biological systems, ion pumping is essential to maintain intracellular osmotic pressure, to respond to external stimuli, and to regulate physiological activities by consuming adenosine triphosphate. In recent decades, artificial ion pumping systems with diverse geometric structures and functions have been developing rapidly with the progress of advanced materials and nanotechnology. In this Review, bioinspired artificial ion pumps, including four categories: asymmetric structure-driven ion pumps, pH gradient-driven ion pumps, light-driven ion pumps, and electron-driven ion pumps, are summarized. The working mechanisms, functions, and applications of those artificial ion pumping systems are discussed. Finally, a brief conclusion of underpinning challenges and outlook for future research are tentatively discussed.

Ultrathin and Ultrastrong Kevlar Aramid Nanofiber Membranes for Highly Stable Osmotic Energy Conversion

An ion-selective membrane can directly convert the osmotic energy to electricity through reverse electrodialysis. However, developing an advanced membrane that simultaneously possesses high power density, excellent mechanical strength, and convenient large-scale production for practical osmotic energy conversion, remains challenging. Here, the fabrication of ultrathin and ultrastrong Kevlar aramid nanofiber (KANF) membranes with interconnected three-dimensional (3D) nanofluidic channels via a simple blade coating method is reported. The negatively charged 3D nanochannels show typical surface-charge-governed nanofluidic ion transport and exhibit excellent cation selectivity. When applied to osmotic energy conversion, the power density of the KANF membrane-based generator reaches 4.8 W m^-2 (seawater/river water) and can be further increased to 13.8 W m^-2 at 328 K, which are higher than most of the state-of-the-art membranes. Importantly, a 4-µm-thickness KANF membrane shows ultrahigh tensile strength (565 MPa) and Young's modulus (25 GPa). This generator also exhibits ultralong stability over 120 days, showing great potential in practical energy conversions.

Comprehensive Analysis of Electrostatic Gating in Nanofluidic Systems

Molecular transport in nanofluidic systems exhibits properties that are unique to the nanoscale. Here, the electrostatic and steric interactions between particle and surfaces become dominant in determining particle transport. At the solid-liquid interface of charged surfaces an electric double layer (EDL) forms due to electrostatic interactions between surfaces and charged particles. In these systems, tunable charge-selective nanochannels can be generated by manipulating electrostatic gating via co-ions exclusion and counterions enrichment of the EDL at the solid-liquid interface. In this context, electrostatic gating has been used to modulate the selectivity of nanofluidic membranes for drug delivery, nanofluidic transistors, and FlowFET, among other applications. While an extensive body of literature investigating nanofluidic systems exists, there is a lack of a comprehensive analysis accounting for all major parameters involved in these systems. Here we performed an all-encompassing modeling investigation corroborated by experimental analysis to assess the influence of nanochannel size, electrolyte properties, surface chemistry, gate voltage, dielectric properties, and molecular charge and size on the exclusion and enrichment of charged analytes in nanochannels. We found that the leakage current in electrostatic gating, often overlooked, plays a dominant role in molecular exclusion. Importantly, by independently considering all ionic species, we found that counterions compete for EDL formation at the surface proximity, resulting in concentration distributions that are nearly impossible to predict with analytical models. Achieving a deeper understanding of these nanofluidic phenomena will help the development of innovative miniaturized systems for both medical and industrial applications.

Nanoionics from Biological to Artificial Systems: An Alternative Beyond Nanoelectronics

Ion transport under nanoconfined spaces is a ubiquitous phenomenon in nature and plays an important role in the energy conversion and signal transduction processes of both biological and artificial systems. Unlike the free diffusion in continuum media, anomalous behaviors of ions are often observed in nanostructured systems, which is governed by the complex interplay between various interfacial interactions. Conventionally, nanoionics mainly refers to the study of ion transport in solid-state nanosystems. In this review, to extent this concept is proposed and a new framework to understand the phenomena, mechanism, methodology, and application associated with ion transport at the nanoscale is put forward. Specifically, here nanoionics is summarized into three categories, i.e., biological, artificial, and hybrid, and discussed the characteristics of each system. Compared with nanoelectronics, nanoionics is an emerging research field with many theoretical and practical challenges. With this forward-looking perspective, it is hoped that nanoionics can attract increasing attention and find wide range of applications as nanoelectronics.

Spontaneous and Selective Potassium Transport through a Suspended Tailor-Cut Ti3C2Tx MXene Film

Biological ion pumps selectively transport target ions against the concentration gradient, a process that is crucial to maintaining the out-of-equilibrium states of cells. Building an ion pump with ion selectivity has been challenging. Here we show that a Ti₃C₂T_x MXene film suspended in air with a trapezoidal shape spontaneously pumps K⁺ ions from the base end to the tip end and exhibits a K⁺/Na⁺ selectivity of 4. Such a phenomenon is attributed to a range of properties of MXene. Thanks to the high stability of MXene in water and the dynamic equilibrium between evaporation and swelling, the film keeps a narrow interlayer spacing of ∼0.3 nm when its two ends are connected to reservoirs. Because of the polar electrical structure and hydrophilicity of the MXene nanosheet, K⁺ ions experience a low energy barrier of ∼4.6 k_BT when entering these narrow interlayer spacings. Through quantitative simulations and consistent experimental results, we further show that the narrow spacings exhibit a higher energy barrier to Na⁺, resulting in K⁺/Na⁺ selectivity. Finally, we show that the spontaneous ion transport is driven by the asymmetric evaporation of the interlayer water across the film, a mechanism that is similar to pressure driven streaming current. This work shows how ion transport properties can be facilely manipulated by tuning the macroscopic shape of nanofluidic materials, which may attract interest in the interface of kirigami technologies and nanofluidics and show potential in energy and separation applications.

Light-driven directional ion transport for enhanced osmotic energy harvesting

Light-driven ion (proton) transport is a crucial process both for photosynthesis of green plants and solar energy harvesting of some archaea. Here, we describe use of a TiO₂/C₃N₄ semiconductor heterojunction nanotube membrane to realize similar light-driven directional ion transport performance to that of biological systems. This heterojunction system can be fabricated by two simple deposition steps. Under unilateral illumination, the TiO₂/C₃N₄ heterojunction nanotube membrane can generate a photocurrent of about 9 μA/cm², corresponding to a pumping stream of ∼5500 ions per second per nanotube. By changing the position of TiO₂ and C₃N₄, a reverse equivalent ionic current can also be realized. Directional transport of photogenerated electrons and holes results in a transmembrane potential, which is the basis of the light-driven ion transport phenomenon. As a proof of concept, we also show that this system can be used for enhanced osmotic energy generation. The artificial light-driven ion transport system proposed here offers a further step forward on the roadmap for development of ionic photoelectric conversion and integration into other applications, for example water desalination.

Numerical Simulation of Continuous Extraction of Li+ from High Mg2+/Li+ Ratio Brines Based on Free Flow Ion Concentration Polarization Microfluidic System

Ion concentration polarization (ICP) is a promising mechanism for concentrating and/or separating charged molecules. This work simulates the extraction of Li⁺ ions in a diluted high Mg²⁺/Li⁺ ratio salt lake brines based on free flow ICP focusing (FF-ICPF). The model solution of diluted brine continuously flows through the system with Li⁺ slightly concentrated and Mg²⁺ significantly removed by ICP driven by external pressure and perpendicular electric field. In a typical case, our results showed that this system could focus Li⁺ concentration by ~1.28 times while decreasing the Mg²⁺/Li⁺ ratio by about 85% (from 40 to 5.85). Although Li⁺ and Mg²⁺ ions are not separated as an end product, which is preferably required by the lithium industry, this method is capable of decreasing the Mg²⁺/Li⁺ ratio significantly and has great potential as a preprocessing technology for lithium extraction from salt lake brines.

Unidirectionally Driving Nanofluidic Transportation via an Asymmetric Textile Pump for Simultaneous Salt-Resistant Solar Desalination and Drenching-Induced Power Generation

Solar-driven seawater desalination provides a promising technology for sustainable water energy harvesting. Although tremendous efforts have been dedicated to developing efficient evaporators, the challenge of preventing salt accumulation while simultaneously realizing high-performance steam-electricity cogeneration remains to be addressed. In this work, inspired by the water and solute transportation in plants via the wicking mechanism, a one-way asymmetric nanofluidic photothermal evaporator fabricated by disproportionately depositing photothermal MXene nanosheets on a hydrophilic cotton textile is reported for simultaneous freshwater and power production. By unidirectionally driving dynamic saline transportation via this photothermal cotton textile pump, this evaporator not only enables self-operating salt rejection for stable steam generation but also affords continuous electric power generation induced by the formation of an asymmetric double electrode layer within MXene nanochannels under the drenching state. Specifically, the solar-driven evaporation rate and voltage generation reach 1.38 kg/m²/h (with a conversion efficiency of 83.1%) and 363 mV under 1 sun irradiation, respectively. Notably, this designed nanofluidic system suffers negligible performance depreciation after 30 h of operation and washing 15 times, which indicates its outstanding stability and reusability. This facile design of the asymmetric nanofluidic photothermal system may provide prospective opportunities for scaling up sustainable freshwater and electric power production.

Devices for Nanoscale Guiding of DNA through a 2D Nanopore

We fabricate on-chip solid-state nanofluidic-2D nanopore systems that can limit the range of motion for DNA in the sensing region of a nanopore. We do so by creating devices containing one or more silicon nitride pores and silicon nitride pillars supporting a 2D pore that orient DNA within a nanopore device to a restricted geometry, yet allow the free motion of ions to maintain a high signal-to-noise ratio. We discuss two concepts with two and three independent electrical connections and corresponding nanopore chip device architectures to achieve this goal in practice. Here, we describe device fabrication and transmission electron microscope (TEM) images, and provide simulated translocations based on the finite element analysis in 3D to demonstrate its merit. In both methods, there is a main 2D nanopore which we refer to as a "sensing" nanopore (monolayer MoS₂ in this paper). A secondary layer is either an array of guiding pores sharing the same electrode pair as the sensing pore (Method 1) or a single, independently contacted, guiding pore (Method 2). These pores are constructed parallel to the "sensing" pore and serve as "guiding" elements to stretch and feed DNA into the atomically thin sensing pore. We discuss the practical implementation of these concepts with nanofluidic and Si-based technology, including detailed fabrication steps and challenges involved for DNA applications in solution.

Stable Ti3C2Tx MXene-Boron Nitride Membranes with Low Internal Resistance for Enhanced Salinity Gradient Energy Harvesting

Extracting salinity gradient energy through a nanomembrane is an efficient way to obtain clean and renewable energy. However, the membranes with undesirable properties, such as low stability, high internal resistance, and low selectivity, would limit the output performance. Herein, we report two-dimensional (2D) laminar nanochannels in the hybrid Ti₃C₂T_x MXene/boron nitride (MXBN) membrane with excellent stability and reduced internal resistance for enhanced salinity gradient energy harvesting. The internal resistance of the MXBN membrane is significantly reduced after adding BN in a pristine MXene membrane, due to the small size and high surface charge density of BN nanosheets. The output power density of the MXBN membrane with 44 wt % BN nanosheets reaches 2.3 W/m², almost twice that of a pristine MXene membrane. Besides, the output power density can be further increased to 6.2 W/m² at 336 K and stabilizes for 10 h at 321 K, revealing excellent structure stability of the membrane in long-term aqueous conditions. This work presents a feasible method for improving the channel properties, which provides 2D layered composite membranes in ion transport, energy extraction, and other nanofluidic applications.

Engineering a Smart Nanofluidic Sensor for High-Performance Peroxynitrite Sensing through a Spirocyclic Ring Open/Close Reaction Strategy

Peroxynitrite (ONOO^-) is an important reactive oxygen/nitrogen species that participates in a range of physiological and pathological processes by modulating ion flux through biological channels. Inspired by a ONOO^--regulated K⁺ channel in vivo, herein, we describe the construction of a smart ONOO^--driven nanosensor using a spirocyclic ring open/close reaction approach. The prepared nanosensor possessed a prominent ONOO^- selectivity and sensitivity and rapid response (∼90 s) owing to the specific reaction between ONOO^- and ligands on the nanosensor surface with a high ion rectification ratio (∼10) and ion gating ratio (∼4). Moreover, this nanosensor system also exhibits excellent stability and recyclability. Thus, these results will provide a new direction for the design of nanochannel-based sensors for future practical and biological applications.

Novel Application of Nanofluidic Chip Digital PCR for Detection of African Swine Fever Virus

African swine fever virus (ASFV) gives rise to a grievous transboundary and infectious disease, African swine fever (ASF), which has caused a great economic loss in the swine industry. To prevent and control ASF, once suspicious symptoms have presented, the movement of animal and pork products should be stopped, and then, laboratory testing should be adopted to diagnose ASF. A method for ASFV DNA quantification is presented in this research, which utilizes the next-generation PCR platform, nanofluidic chip digital PCR (cdPCR). The cdPCR detection showed good linearity and repeatability. The limit of detection for cdPCR is 30.1995 copies per reaction, whereas no non-specific amplification curve was found with other swine viruses. In the detection of 69 clinical samples, the cdPCR showed significant consistency [91.30% (63/69)] to the Office International des Epizooties-approved quantitative PCR. Compared with the commercial quantitative PCR kit, the sensitivity of the cdPCR assay was 86.27% (44/50), and the specificity was 94.44% (17/18). The positive coincidence rate of the cdPCR assay was 88% (44/50). The total coincidence rate of the cdPCR and kit was 89.86% (62/69), and the kappa value reached 0.800 (P < 0.0001). This is the first time that cdPCR has been applied to detecting ASFV successfully.

Nanofluidic Immobilization and Growth Detection of Escherichia coli in a Chip for Antibiotic Susceptibility Testing

Infections with antimicrobial resistant bacteria are a rising threat for global healthcare as more and more antibiotics lose their effectiveness against bacterial pathogens. To guarantee the long-term effectiveness of broad-spectrum antibiotics, they may only be prescribed when inevitably required. In order to make a reliable assessment of which antibiotics are effective, rapid point-of-care tests are needed. This can be achieved with fast phenotypic microfluidic tests, which can cope with low bacterial concentrations and work label-free. Here, we present a novel optofluidic chip with a cross-flow immobilization principle using a regular array of nanogaps to concentrate bacteria and detect their growth label-free under the influence of antibiotics. The interferometric measuring principle enabled the detection of the growth of Escherichia coli in under 4 h with a sample volume of 187.2 µL and a doubling time of 79 min. In proof-of-concept experiments, we could show that the method can distinguish between bacterial growth and its inhibition by antibiotics. The results indicate that the nanofluidic chip approach provides a very promising concept for future rapid and label-free antimicrobial susceptibility tests.

Nanometer-Scale Heterogeneous Interfacial Sapphire Wafer Bonding for Enabling Plasmonic-Enhanced Nanofluidic Mid-Infrared Spectroscopy

As one of the most effective surface-enhanced infrared absorption (SEIRA) techniques, metal-insulator-metal structured metamaterial perfect absorbers possess an ultrahigh sensitivity and selectivity in molecular infrared fingerprint detection. However, most of the localized electromagnetic fields (i.e., hotspots) are confined in the dielectric layer, hindering the interaction between analytes and hotspots. By replacing the dielectric layer with the nanofluidic channel, we develop a sapphire (Al₂O₃)-based mid-infrared (MIR) hybrid nanofluidic-SEIRA (HN-SEIRA) platform for liquid sensors with the aid of a low-temperature interfacial heterogeneous sapphire wafer direct bonding technique. The robust atomic bonding interface is confirmed by transmission electron microscope observation. We also establish a design methodology for the HN-SEIRA sensor using coupled-mode theory to carry out the loss engineering and experimentally validate its feasibility through the accurate nanogap control. Thanks to the capillary force, liquid analytes can be driven into sensing hotspots without external actuation systems. Besides, we demonstrate an in situ real-time dynamic monitoring process for the acetone molecular diffusion in deionized water. A small concentration change of 0.29% is distinguished and an ultrahigh sensitivity (0.8364 pmol^-1 %) is achieved. With the aid of IR fingerprint absorption, our HN-SEIRA platform brings the selectivity of liquid molecules with similar refractive indexes. It also resolves water absorption issues in traditional IR liquid sensors thanks to the sub-nm long light path. Considering the wide transparency window of Al₂O₃ in MIR (up to 5.2 μm), the HN-SEIRA platform covers more IR absorption range for liquid sensing compared to fused glass commonly used in micro/nanofluidics. Leveraging the aforementioned advantages, our work provides insights into developing a MIR real-time liquid sensing platform with intrinsic IR fingerprint selectivity, label-free ultrahigh sensitivity, and ultralow analyte volume, demonstrating a way toward quantitative molecule identification and dynamic analysis for the chemical and biological reaction processes.

High-Throughput Quantitative RT-PCR in Single and Bulk C. elegans Samples Using Nanofluidic Technology

This paper presents a high-throughput reverse transcription quantitative PCR (RT-qPCR) assay for Caenorhabditis elegans that is fast, robust, and highly sensitive. This protocol obtains precise measurements of gene expression from single worms or from bulk samples. The protocol presented here provides a novel adaptation of existing methods for complementary DNA (cDNA) preparation coupled to a nanofluidic RT-qPCR platform. The first part of this protocol, named 'Worm-to-CT', allows cDNA production directly from nematodes without the need for prior mRNA isolation. It increases experimental throughput by allowing the preparation of cDNA from 96 worms in 3.5 h. The second part of the protocol uses existing nanofluidic technology to run high-throughput RT-qPCR on the cDNA. This paper evaluates two different nanofluidic chips: the first runs 96 samples and 96 targets, resulting in 9,216 reactions in approximately 1.5 days of benchwork. The second chip type consists of six 12 x 12 arrays, resulting in 864 reactions. Here, the Worm-to-CT method is demonstrated by quantifying mRNA levels of genes encoding heat shock proteins from single worms and from bulk samples. Provided is an extensive list of primers designed to amplify processed RNA for the majority of coding genes within the C. elegans genome.

Suspended Nanochannel Resonator Arrays with Piezoresistive Sensors for High-Throughput Weighing of Nanoparticles in Solution

As the use of nanoparticles is expanding in many industrial sectors, pharmaceuticals, cosmetics among others, flow-through characterization techniques are often required for in-line metrology. Among the parameters of interest, the concentration and mass of nanoparticles can be informative for yield, aggregates formation or even compliance with regulation. The Suspended Nanochannel Resonator (SNR) can offer mass resolution down to the attogram scale precision in a flow-through format. However, since the readout has been based on the optical lever, operating more than a single resonator at a time has been challenging. Here we present a new architecture of SNR devices with piezoresistive sensors that allows simultaneous readout from multiple resonators. To enable this architecture, we push the limits of nanofabrication to create implanted piezoresistors of nanoscale thickness (∼100 nm) and implement an algorithm for designing SNRs with dimensions optimized for maintaining attogram scale precision. Using 8-in. processing technology, we fabricate parallel array SNR devices which contain ten resonators. While maintaining a precision similar to that of the optical lever, we demonstrate a throughput of 40 000 particles per hour-an order of magnitude improvement over a single device with an analogous flow rate. Finally, we show the capability of the SNR array device for measuring polydisperse solutions of gold particles ranging from 20 to 80 nm in diameter. We envision that SNR array devices will open up new possibilities for nanoscale metrology by measuring not only synthetic but also biological nanoparticles such as exosomes and viruses.

Structural Stability of Optofluidic Nanostructures in Flow-Through Operation

Optofluidic sensors based on periodic arrays of subwavelength apertures that support surface plasmon resonance can be employed as both optical sensors and nanofluidic structures. In flow-through operation, the nanoapertures experience pressure differences across the substrate in which they are fabricated, which imposes the risk for structural failure. This work presents an investigation of the deflection and structural stability of nanohole array-based optofluidic sensors operating in flow-through mode. The analysis was approached using experiments, simulations via finite element method, and established theoretical models. The results depict that certain areas of the sensor deflect under pressure, with some regions suffering high mechanical stress. The offset in the deflection values between theoretical models and actual experimental values is overturned when only the effective area of the substrate, of 450 µm, is considered. Experimental, theoretical, and simulation results suggest that the periodic nanostructures can safely operate under trans-membrane pressures of up to 20 psi, which induce deflections of up to ~20 μm.

Robust Smartphone Assisted Biosensing Based on Asymmetric Nanofluidic Grating Interferometry

Point-of-care systems enable fast therapy decisions on site without the need of any healthcare infrastructure. In addition to the sensitive detection, stable measurement by inexperienced persons outside of laboratory facilities is indispensable. A particular challenge in field applications is to reduce interference from environmental factors, such as temperature, to acceptable levels without sacrificing simplicity. Here, we present a smartphone-based point-of-care sensor. The method uses an optofluidic grating composed of alternating detection and reference channels arranged as a reflective phase grating. Biomolecules adsorbing to the detection channel alter the optical path length, while the parallel reference channels enable a direct common mode rejection within a single measurement. The optical setup is integrated in a compact design of a mobile readout device and the usability is ensured by a smartphone application. Our results show that different ambient temperatures do not have any influence on the signal. In a proof-of concept experiment we measured the accumulation of specific molecules in functionalized detection channels in real-time and without the need of any labeling. Therefore, the channel walls have been modified with biotin as capture molecules and the specific binding of streptavidin was detected. A mobile, reliable and robust point-of-care device has been realized by combining an inherently differential measurement concept with a smartphone-based, mobile readout device.

Aqueous Stable Ti3C2 MXene Membrane with Fast and Photoswitchable Nanofluidic Transport

High, stable, and modulatable ionic conductivity is important for many nanofluidic applications of layered two-dimensional (2D) membranes. In this study, we demonstrate a proton and ionic conductivity of the Ti₃C₂T _x membrane that is orders of magnitude higher than that of bulk solution at low concentrations. Importantly, the membrane is highly stable in aqueous solution without any modification, due to the strong and attractive interlayer van der Waals interaction and weak electrostatic repulsive interaction. Furthermore, by exploiting the intrinsic photothermal property of MXene, we demonstrate that the ionic conductivity can be reversely, rapidly, and completely switched on or off with laser light. This study should prove MXene membrane as a suitable platform to study and utilize nanofluidic ion transport. It should also inspire future studies to manipulate the mass transport through 2D membranes using their inherent physicochemical properties.

A Direct Sensor to Measure Minute Liquid Flow Rates

Nanofluidics finds its root in the study of fluids and flows at the nanoscale. Flow rate is a quantity that is both central when dealing with flows and notoriously difficult to measure experimentally at the scale of an individual nanopore or nanochannel. We show in this letter that minute flow rate can be directly measured accumulating liquid over time within the compliant membrane of a commercial piezoresistive pressure sensor. Our flow rate sensor is versatile and can be operated independently of the nature of the liquid, flow profile, and type of nanochannel. We demonstrate this method by measuring the pressure-driven flow of silicon oil in a single nanochannel of average radius 200 nm. This approach gives reliable measurement of the flow rate up to 1 pL/min. Unlike other nanoscale flow measurements methods based, for instance, on particle tracking, our sensor delivers a direct voltage output suitable for nanoflow control applications.

Conformal Graphene-Decorated Nanofluidic Sensors Based on Surface Plasmons at Infrared Frequencies

An all-in-one prism-free infrared sensor based on graphene surface plasmons is proposed for nanofluidic analysis. A conformal graphene-decorated nanofluidic sensor is employed to mimic the functions of a prism, sensing plate, and fluidic channel in the tradition setup. Simulation results show that the redshift of the resonant wavelength results in the improvement of sensitivity up to 4525 nm/RIU. To reshape the broadened spectral lines induced by the redshift of the resonant wavelength to be narrower and deeper, a reflection-type configuration is further introduced. By tuning the distance between the graphene and reflective layers, the figure of merit (FOM) of the device can be significantly improved and reaches a maximum value of 37.69 RIU⁻¹, which is 2.6 times that of the former transmission-type configuration. Furthermore, the optimized sensor exhibits superior angle-insensitive property. Such a conformal graphene-decorated nanofluidic sensor offers a novel approach for graphene-based on-chip fluidic biosensing.

The Nanolithography Toolbox

This article introduces in archival form the Nanolithography Toolbox, a platform-independent software package for scripted lithography pattern layout generation. The Center for Nanoscale Science and Technology (CNST) at the National Institute of Standards and Technology (NIST) developed the Nanolithography Toolbox to help users of the CNST NanoFab design devices with complex curves and aggressive critical dimensions. Using parameterized shapes as building blocks, the Nanolithography Toolbox allows users to rapidly design and layout nanoscale devices of arbitrary complexity through scripting and programming. The Toolbox offers many parameterized shapes, including structure libraries for micro- and nanoelectromechanical systems (MEMS and NEMS) and nanophotonic devices. Furthermore, the Toolbox allows users to precisely define the number of vertices for each shape or create vectorized shapes using Bezier curves. Parameterized control allows users to design smooth curves with complex shapes. The Toolbox is applicable to a broad range of design tasks in the fabrication of microscale and nanoscale devices.

Rapid Prototyping of Nanofluidic Slits in a Silicone Bilayer

This article reports a process for rapidly prototyping nanofluidic devices, particularly those comprising slits with microscale widths and nanoscale depths, in silicone. This process consists of designing a nanofluidic device, fabricating a photomask, fabricating a device mold in epoxy photoresist, molding a device in silicone, cutting and punching a molded silicone device, bonding a silicone device to a glass substrate, and filling the device with aqueous solution. By using a bilayer of hard and soft silicone, we have formed and filled nanofluidic slits with depths of less than 400 nm and aspect ratios of width to depth exceeding 250 without collapse of the slits. An important attribute of this article is that the description of this rapid prototyping process is very comprehensive, presenting context and details which are highly relevant to the rational implementation and reliable repetition of the process. Moreover, this process makes use of equipment commonly found in nanofabrication facilities and research laboratories, facilitating the broad adaptation and application of the process. Therefore, while this article specifically informs users of the Center for Nanoscale Science and Technology (CNST) at the National Institute of Standards and Technology (NIST), we anticipate that this information will be generally useful for the nanofabrication and nanofluidics research communities at large, and particularly useful for neophyte nanofabricators and nanofluidicists.

Enhanced discrimination of DNA molecules in nanofluidic channels through multiple measurements

Nanofluidic sensing elements have been the focus of recent experiments for numerous applications ranging from nucleic acid fragment sizing to single-molecule DNA sequencing. These applications critically rely on high measurement fidelity, and methods to increase resolution are required. Herein, we describe fabrication and testing of a nanochannel device that enhances measurement resolution by performing multiple measurements (>100) on single DNA molecules. The enhanced measurement resolution enabled length discrimination between a mixture of λ-DNA (48.5 kbp) and T7 DNA (39.9 kbp) molecules, which were detected as transient current changes during translocation of the molecules through the nanochannel. As long DNA molecules are difficult to resolve quickly and with high fidelity with conventional electrophoresis, this approach may yield potentially portable, direct electrical sizing of DNA fragments with high sensitivity and resolution.

Concentration-enhanced rapid detection of human chorionic gonadotropin (hCG) on a Au surface using a nanofluidic preconcentrator

Here, we report a new method of concentration-enhanced binding kinetics for a rapid immunoassay screening test on a gold surface in a poly(dimethylsiloxane) (PDMS) microfluidic chip format. The use of alkylthiolate self-assembled monolayers on gold surfaces of a PDMS-glass microchip resulted in accelerated binding kinetics of Human chorionic gonadotropin (hCG) at an electrokinetic trapping zone. We used a PBS solution (buffer concentration ~ 150 mM), not a dibasic buffer system (~10 mM), for the dynamic preconcentrating operation and the preconcentration of cy3 labeled streptavidin onto biotinylated Au surface revealed that the binding kinetics of the protein were linearly proportional to the concentration profile of the preconcentration plug. We showed rapid detection of hCG in the clinical range with a shorten assay time of 10 min. Also, we demonstrated that the amount of sample needed were detection was decreased from ~4 mL to ~25 μL in the standard serum tests. The enhanced binding kinetics between hcG Ag-Ab via preconcentration showed good feasibility for use in a rapid immunoassay screening test.