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The first DSC chip that features thin-film enclosures, very low-addenda heat capacity, low residual heat conduction, and rapid response for analyzing liquids.

Effective separation of small extracellular vesicles (EVs) especially exosomes from large EVs with a high recovery rate and purity based on electrokinetic principles in a microfluidic device featuring three-dimensional silicon microelectrodes.

Here, we introduce a microchip for differential measurements of aqueous samples in twin calorimetric arms with a sub-nL enclosed space. Each arm features a fluidic microchannel located in close proximity to a thin-film resistance thermometer and heater patterned on a low-stress SiN membrane held over a Si cavity with suspension beams. The chip exhibits a rapid response with a thermal time constant of less than 10 ms in atmosphere and a residual thermal conductance below $6{\mu }\text{W}{\cdot }\text{K}^{-1 }$ , one of the lowest reported and accounts for the excellent sensitivity registered in vacuum up to 11 $\text{V}{\cdot }\text{W}^{-1 }$ . These values are in good agreement with those ones predicted by modeling using finite element method, lumped-capacitance analysis, and calorimeter electrothermal circuit simulation together with the measurement system. Long suspension beams in each arm ensure uniform temperature maintained across its membrane as revealed by the fluorescence-based melting curve analysis. We share the specific heat capacity values of water, glycerin, and mineral oil accurately measured by the chip. Lastly, we demonstrate the chip calorimeter utility on the measurement of the photothermal transduction efficiency of plasmonic nanoparticles, which makes our study further unique in expanding the applications of chip calorimeters. [2021-0044]

We present ordered surface crack patterns discovered in microfluidic channels/chambers in polydimethylsiloxane (PDMS). The cracks are formed in situ under confinement due to compression applied following an oxygen plasma step in a soft lithography process. The crack patterns are noticeable only after fluorescent labeling and vary with fluidic layout as well as material compliance.

For studying protein-protein interactions (PPIs) in general, a powerful and commonly used technique is conventional coimmunoprecipitation (co-IP/pulldown) followed by western blotting. However, the technique does not provide precise information regarding the kinetics and stoichiometry of PPIs. Another drawback is that the sensitivity of conventional co-IP is not suitable for examining PPIs in rare cells such as sensory hair cells, circulating tumor cells, embryonic stem cells, and subsets of immune cells. The current single-molecule pulldown (SiMPull) assay can potentially be used for studying PPIs in rare cells but its wide application is hindered by the high technical barrier and time consumption. We report an innovative, agarose microbead-based approach for SiMPull. We used commercially available, pre-surface-functionalized agarose microbeads to capture the protein of interest together with its binding partners specifically from cell extracts and observed these interactions under a microscope at the single-molecule level. Relative to the original method, microbead-based SiMPull is considerably faster, easier to use, and more reproducible and yet provides similar sensitivity and signal-to-background ratio; specifically, with the new method, sample-preparation time is substantially decreased (from ∼10 to ∼3 h). These crucial features should facilitate wide application of the powerful and versatile SiMPull method in common biological and clinical laboratories. Notably, by exploiting the simplicity and ultrahigh sensitivity of microbead-based SiMPull, we used the method in the study of rare auditory hair cells and γδ T cells for the first time.

We demonstrate multifunctional silicon 3D viaduct microelectrodes for continuous-flow cell manipulation by railing and cell transfection under a modulated activation. The microelectrodes serve as tracks along which cells can rail under dielectrophoretic force and hydrodynamic drag. A modulated activation was introduced to achieve railing efficiency up to 80%. Furthermore, cell electroporation is realized through sinewave bursts applied with varying amplitude, duration and interval. Successful transfection is demonstrated by delivering 3 kDa dextran molecules into HEK293 cells with > 60% efficiency. The multifunctional 3D viaduct electrodes show great potential for continuous-flow rapid cell railing and sorting and efficient transfection.

A dual-channel flow-through microcalorimeter device is presented along with a non-contact precision method of temperature calibration. A microfluidic channel with a volume of ≈550 pL in a spiral layout was fabricated from low-stress nitride suspended over a cavity in a silicon substrate. The thin-film heater and resistive temperature detector (RTD) on the channel were defined by a patterned Ti layer. The device exhibited a rapid thermal response with the following thermal characteristics: a time constant of ≈10.5 ms, a heat conductance of $\approx 152~\mu ~\text{W}\,\cdot ~{\mathrm {K}}^{-{1}} $ and a heat capacitance of $\approx 1.6~\mu \text{J}\,\cdot {\mathrm {K}}^{-{1}} $ on average based on the measurements of nine separate units fabricated on the same wafer. Further, the melting curve analysis (MCA) of a double-stranded DNA was proposed as a non-contact method of microcalorimeter RTD calibration. The method revealed that the measurement by the RTD underestimates the temperature of the channel interior by an amount of nearly 15%, at ≈ 9 mW. At this dissipated power level, the method also revealed a spatial nonuniformity of ≈ ± 0.8 °C across the microcalorimeter. [2020-0173]

We report on electrokinetic manipulation of submicron particles in a device with microfabricated Si electrodes featuring segmented sidewalls acting as tracks guiding particles under hydrodynamic drag. Electrohydrodynamic drag, both AC electroosmosis in low-conductive medium and electrothermal flow in high-conductive medium, gives rise to fluid rolls that deliver particles to tracks where they are held under the influence of dielectrophoretic forces. Particles are being railed along tracks under pressure-driven flow to a downstream junction where tracks act as bridges, keeping particles on course within the main channel causing their post-junction enrichment. This outcome, however, is strongly coupled to electrode sidewall contours as demonstrated here. We also report on particle oscillations under strong AC electroosmosis. Specifically, particles in deionized water can be seen bouncing off tracks or circulating with convective rolls in and out of space beneath tracks at an oscillation frequency and amplitude depending on the activation frequency. These results collectively draw attention to the functional use of electrode sidewall contours for continuous-flow manipulation of particles, which are rarely explored in microfluidics and yet could lead to more effective designs for particle separation and enrichment.

Continuous-flow electrokinetic enrichment/separation of nanoparticles is demonstrated in a device based on target nanoparticles railing along 3D microelectrode tracks. The device utilizes dielectrophoresis and electrohydrodynamic drag including electrothermal flow in high-conductive media and AC electroosmosis in low-conductive media. An enrichment efficiency of ~100% is noted for 500 nm and 1 μm polystyrene spheres in media at a conductivity of 0.2 and 0.01 S/m. Size-based separation of the two is also shown efficient in deionized water using a modified design.

We report on a unique microfluidic device that can enrich nanoparticles in a continuous flow by railing them along activated tracks (electrodes). This was achieved based on dielectrophoretic force and electrohydrodynamic drag (electrothermal rolls and AC electroosmosis) in both low and high conductive media. The results have implication for the isolation of high quality and pure nanoparticles such as exosomes from biofluids for applications in cancer diagnosis and prognosis.

SUMMARYThe recently developed single-molecule pulldown (SiMPull) assay by Jain and colleagues is a highly innovative technique but its wide application is hindered by the high technical barrier and time consumption. We report an innovative, agarose microbead-based approach for SiMPull. We used commercially available, pre-surface-functionalized agarose microbeads to capture the protein of interest together with its binding partners specifically from cell extracts and observed these interactions under a microscope at the single-molecule level. Relative to the original method, microbead-based SiMPull is considerably faster, easier to use, and more reproducible and yet provides similar sensitivity and signal-to-noise ratio; specifically, with the new method, sample-preparation time is substantially decreased (from ∼10 to ∼3 h). These crucial features should facilitate wide application of powerful and versatile SiMPull in common biological and clinical laboratories. Notably, by exploiting the simplicity and ultrahigh sensitivity of microbead-based SiMPull, we used this method in the study of rare auditory hair cells for the first time.

We introduce a compact MEMS-based microcalorimeter ( $\mu \mathrm{C}$ ) for rapid ultrasmall-volume sample analysis. The chip features a time constant of 4 ms, with the possibility of achieving high scanning rate and sensitivity without noticeably distorting the thermograms. We demonstrated the chip performance in differential scanning calorimeter (DSC) mode and measured the melting temperature ( $T_{\mathrm{m}}$ ) of bovine serum albumin (BSA) at 75 K·min−1, one of the fastest scan rate reported. The measured melting point of 77.4 °C is practically identical to that measured by a conventional MEMS-based DSC. Our system exhibits an unprecedented accuracy at such a high scanning rate having the capability of performing a flash DSC analysis for a liquid phase sample.

The determination of the physical properties of fluids—such as the thermal characteristics, which include heat transfer time (Δt)—is becoming more challenging as system sizes shrink to micro- and nanometer scales. Hence, knowledge of these properties is crucial for the operation of devices requiring precise temperature (T) control, such as polymerase chain reactions, melting curve analysis (MCA), and differential scanning fluorimetry. In this paper, we introduced a flow-through microfluidic system to analyze thermal properties such as Δt among samples and the sidewall of a silicon chip using microscopic image analysis. We performed a spatial MCA with double-stranded deoxyribonucleic acid (dsDNA) and EvaGreen intercalator, using a flow-through microfluidic chip, and achieved a T gradient of ≈ 2.23 K mm−1. We calculated the mean value of Δt as ≈ 33.9 ms from a melting temperature (TM) location shift along the microchannel for a variable flow rate. Our system had a T resolution of ≈ 1.2 mK pixel−1 to distinguish different dsDNA molecules—based on the TM location within the chip—providing an option to use it as a high-throughput device for rapid DNA or protein analysis.

Ion concentration polarization has received much interest in the past decade for lab-on-a-chip applications, primarily preconcentration of biomolecules and water desalination. Studying the basic phenomenon in microfluidics has also generated new knowledge, which could be pivotal in the design of novel devices. Many studies, however, have focused on designs featuring nanoslits/slots or surface-patterned ion-selective membranes whereas the characteristics of 1D nanochannels are still lacking. Here, we report on ion concentration polarization across highly ordered 1D nanochannels in isolation as well as in array formation. Intriguingly, the nanochannels in isolation exhibit a linear current-voltage characteristic at low salt concentrations despite the confirmed presence of ion-depletion zone, which is associated with the diffusion-limited transport and the consequent nonlinearity in the classical sense. The characteristic in array formation breaks away from the linearity with a peculiar dip in current for a critical salt concentration in the dilute limit. We describe these findings based on the interplay between the nanochannel conductance and the conductance of the neighboring microchannel walls (the so-called surface shunt). Also, the nanochannel transport is identified with the mobility of protons more closely than that of salt cations. We attribute fast transport to phosphorus-doped silicate glass, the nanochannel material known to have very fine pores likely to be populated with protons as a result of moisture and carbon dioxide adsorption from the air. The nanochannels possess a tubular profile 70 nm in nominal diameter and fabricated through thermal reflow of doped glass on silicon without using advanced lithography.

We introduce an integrated array of glass nanopores on a silicon microchip fabricated in a batch process through low-resolution photolithography and standard semiconductor processing tools. By functionalizing each nanopore against a distinct target, we further demonstrate ultrasensitive, label-free, multiplexed electrical detection of cancer-marker proteins in real time through charge-dependent ionic current rectification. As nanofluidic diode biosensors, the nanopores return rapid results, with a limit of detection reaching concentrations as low as attomolars in assay buffer and femtomolars in undiluted untreated human serum, a rare achievement for this class of nanosensors. Multiplexed detection capability has been demonstrated on proteins carcinoembryonic antigen, α-fetoprotein antigen, and human epidermal growth factor receptor-2, with the assay further scalable to a size that is limited by the readout electronics. The nanopores are also found with a considerably advanced detection limit as well as dynamic range in relation to the nanoslit counterparts, validated by the measurements on cardiac protein troponin T. This highly robust assay platform draws from rich nanopore physics and could provide further enhanced detection through concentration polarization, subsequent target enrichment, and serum desalting, all potentially induced by the nanopores presently redundant in the array. This integration would be crucial for removing major obstacles for the practical use of nanopore-based assays.

Mechanically deforming biological cells through microfluidic constrictions is a recently introduced technique for the intracellular delivery of macromolecules possibly through transient membrane pores induced in the process. The technique is attractive for research and clinical applications mainly because it is simple, fast, and effective while being free of adverse effects often associated with well-known techniques that rely on field- or vector-based delivery. In this nascent approach, an utmost and crucial role is played by the constriction, often in rectangular profile, and it squeezes cells only in one dimension. The results achieved suggest that the longer the constriction is the higher the delivery performance. Contrary to this view, we demonstrate here a unique constriction profile that is highly localized (point) and yet returns comparably effective delivery. Point constrictions are of a semiround geometry, forcing cells in both dimensions while introducing very little backpressure to the system, which is a silicon-glass platform wherein constrictions are arranged in series along an array of channels. The influence of the constriction size and count as well as treatment pressure on delivery performance is presented on the basis of the flow-cytometric analyses of HCT116 cells treated using dextran as model molecules. Delivery performance is also presented for common mammalian cell lines including NIH 3T3, HEK293, and MDCK. Moreover, the versatility of the platform is demonstrated in gene knockdown experiments using synthetic siRNA as well as on the delivery of proteins. Target proteins in some cells exhibit nondiffusive distribution profile raising the plausibility of mechanisms other than transient membrane pores.

This study demonstrates hydrodynamic chromatography of DNA fragments in a microchip. The microchip contains a highly regular array of nanofluidic channels (nanocapillaries) that are essential for resolving DNA in this chromatography mode. The nanocapillaries are self-enclosed robust structures built inside a doped glass layer on silicon using low-resolution photolithography and standard semiconductor processing techniques. Additionally, the unique nanocapillaries feature a cylindrical inner radius of 600 nm maintained over a length scale of 5 cm. The microchip with bare open nanocapillaries is shown to rapidly separate a digest of lambda DNA in free solution (

Most organs contain interconnected tubular tissues that are one-cell-thick, polarized epithelial monolayers enclosing a fluid-filled lumen. Such tissue organization plays crucial roles in developmental and normal physiology, and the proper functioning of these tissues depends on their regulation by complex biochemical perturbations and equally important, but poorly understood, mechanical perturbations. In this study, by combining micropatterning techniques and atomic force microscopy, we developed a simple in vitro experimental platform for characterizing the mechanical properties of the MDCK II cyst, the simplest model of lumen-enclosing epithelial monolayers. By using this platform, we estimated the elasticity of the cyst monolayer and showed that the presence of a luminal space influences cyst mechanics substantially, which could be attributed to polarization and tissue-level coordination. More interestingly, the results from force-relaxation experiments showed that the cysts also displayed tissue-level poroelastic characteristics that differed slightly from those of single cells. Our study provides the first quantitative findings, to our knowledge, on the tissue-level mechanics of well-polarized epithelial cysts and offers new insights into the interplay between cyst mechanics and cyst physiology. Moreover, our simple platform is a potentially useful tool for enhancing the current understanding of cyst mechanics in health and disease.

Optofluidic devices combining optics and microfluidics have recently attracted attention for biomolecular analysis due to their high detection sensitivity. Here, we show a silicon chip with tubular microchannels buried inside the substrate featuring temperature gradient (∇T) along the microchannel. We set up an optical fluorescence system consisting of a power-modulated laser light source of 470 nm coupled to the microchannel serving as a light guide via optical fiber. Fluorescence was detected on the other side of the microchannel using a photomultiplier tube connected to an optical fiber via a fluorescein isothiocyanate filter. The PMT output was connected to a lock-in amplifier for signal processing. We performed a melting curve analysis of a short dsDNA – SYBR Green I complex with a known melting temperature (TM) in a flow-through configuration without gradient to verify the functionality of the proposed detection system. We then used the segmented flow configuration and measured the fluorescence amplitude of a droplet exposed to ∇T of ≈ 2.31 °C mm−1, determining the heat transfer time as ≈ 554 ms. The proposed platform can be used as a fast and cost-effective system for performing either MCA of dsDNAs or for measuring protein unfolding for drug-screening applications.

This paper reports the very first nanofluidic memristor based on the principle of ion concentration polarization (ICP). ICP is induced through highly-ordered cylindrical nanochannels. These so-called nanocapillaries are formed within a glass layer on silicon through a thermal reflow process and low-resolution lithography. The current–voltage plots exhibit characteristic pinched-hysteresis loops and the concurrent tracking of fluorescent charged particles correlates the memristive behaviour to the ICP. The ICP-based nanofluidic memristor could have implications in emerging areas such as integrated fluid-based logic circuits.

Highly localized (point) constrictions featuring a round geometry with ultra-sharp edges in silicon have been demonstrated for the reagent-free continuous-flow rapid mechanical lysis of mammalian cells on a single-cell basis. Silicon point constrictions, robust structures formed by a single-step dry etching process, are arranged in a cascade along microfluidic channels and can effectively rupture cells delivered in a pressure-driven flow. The influence of the constriction size and count on the lysis performance is presented for fibroblasts in reference to total protein, DNA, and intact nuclei levels in the lysates evaluated by biochemical and fluoremetric assays and flow-cytometric analyses. Protein and DNA levels obtained from an eight-constriction treatment match or surpass those from a chemical method. More importantly, many intact nuclei are found in the lysates with a relatively high nuclei-isolation efficiency from a four-constriction treatment. Point constrictions and their role in rapid reagent-free disruption of the plasma membrane could have implications for integrated sample preparation in future lab-on-a-chip systems.

Here, we present an experimental demonstration of slowing DNA translocation across a nanochannel by modulating the channel surface charge through an externally applied gate bias. The experiments were performed on a nanofluidic field-effect transistor, which is a monolithic integrated platform featuring a 50 nm-diameter in-plane alumina nanocapillary whose entire length is surrounded by a gate electrode. The field-effect transistor behavior was validated on the gating of ionic conductance and protein transport. The gating of DNA translocation was subsequently studied by measuring discrete current dips associated with single λ-DNA translocation events under a source-to-drain bias of 1 V. The translocation speeds under various gate bias conditions were extracted by fitting event histograms of the measured translocation time to the first passage time distributions obtained from a simple 1D biased diffusion model. A positive gate bias was observed to slow the translocation of single λ-DNA chains markedly; the translocation speed was reduced by an order of magnitude from 18.4 mm/s obtained under a floating gate down to 1.33 mm/s under a positive gate bias of 9 V. Therefore, a dynamic and flexible regulation of the DNA translocation speed, which is vital for single-molecule sequencing, can be achieved on this device by simply tuning the gate bias. The device is realized in a conventional semiconductor microfabrication process without the requirement of advanced lithography, and can be potentially further developed into a compact electronic single-molecule sequencer.

Microfluidic devices typically require complex shapes such as funnels, spirals, splitters, channels with different widths, or customized objects of arbitrary complexity with a smooth transition between these elements. Device layouts are generally designed by software developed for the design of integrated circuits or by general computer-aided design drawing tools. Both methods have their limitations, making these tasks time consuming. Here, a script-based, time-effective method to generate the layout of various microfluidic chips with complex geometries is presented. The present work uses the nanolithography toolbox (NT), a platform-independent software package, which employs parameterized fundamental blocks (cells) to create microscale and nanoscale structures. In order to demonstrate the functionality and efficiency of the NT, a few classical microfluidic devices were designed using the NT and then fabricated in glass/silicon using standard microfabrication techniques and in poly(dimethylsiloxane) using soft lithography as well as more complex techniques used for flow-through calorimetry. In addition, the functionality of a few of the fabricated devices was tested. The powerful method proposed allows the creation of microfluidic devices with complex layouts in an easy way, simplifying the design process and improving design efficiency. Thus, it holds great potential for broad applications in microfluidic device design.

Infectious diseases, such as the most recent case of COVID-19, have brought the prospect of point-of-care (POC) diagnostic tests into the spotlight. A rapid, accurate, low-cost, and easy-to-use test in the field could stop epidemics before they develop into full-blown pandemics. Unfortunately, despite all the advances, it still does not exist. Here, we critically review the limited number of prototypes demonstrated to date that is based on a polymerase chain reaction (PCR) and has come close to fulfilling this vision. We summarize the requirements for the POC-PCR tests and then go on to discuss the PCR product-detection methods, the integration of their functional components, the potential applications, and other practical issues related to the implementation of lab-on-a-chip technologies. We conclude our review with a discussion of the latest findings on nucleic acid-based diagnosis., Highlights • Recently there is a boom in development of portable microfluidic based system for SARS-CoV-2 molecular diagnostics. • Most of those techniques approved by US FDA is based on a reverse transcription polymerase chain reaction (RT-PCR). • Drawback of the RT-PCR methods such as sample preparation to remove PCR inhibitors and perform sample preconcentration.

We demonstrate a unique microfluidic device for continuous-flow cell sorting by railing target cells along physical tracks (electrode sidewalls) based on the combined effect of dielectrophoresis and hydrodynamic drag. The tracks are the raised digits of comb-like structures made of conducting bulk silicon as the electrodes. Unlike other volumetric electrodes, the structures feature a segmented sidewall profile with linear and concave segments forming the tracks and supporting columns, respectively. The interdigitated bulk electrodes lead to a built-in flow chamber in which the digits (tracks) extend downstream at a characteristic angle with respect to the flow, which runs through the passages between the columns. Target cells leaving the passages are levitated and docked against the tracks under positive dielectrophoresis and railed under hydrodynamic drag. Railing efficiency, as high as >95%, is reported against the activation voltage and flow rate for the designs 7°, 16°, and 26° as the track angles. A collection efficiency of about 86% is noted for both target (HCT116) and non-target cells (K562) in the 16° design at a sample flow rate of 8.3 μL min−1 and an activation voltage of 12.5 Vp at 200 kHz. This performance is comparable if not better than those obtained with thin-film surface microelectrodes and yet achieved here at an order of magnitude higher sample flow rate. This enhancement mainly arises from a considerably low drag along the tracks in relation to the chamber top or bottom surface where the thin-film electrodes would be typically placed.

We present 3D microelectrodes featuring castellated blocks for dielectrophoretically isolating cells. These electrodes provide a more effective dielectrophoretic force field than thin-film surface electrodes and yet immobilize cells near stagnation points across a parabolic flow profile for enhanced cell viability and separation efficiency. Unlike known volumetric electrodes with linear profiles, the electrodes with structural variations introduced along their depth scale are versatile for constructing monolithic structures with readily integrated fluidic paths. This is exemplified here in the design of an interdigitated comb array wherein electrodes with castellated surfaces serve as building blocks and form digits with an array of fluidic pores. Activation of the design with low-voltage oscillations (±5 Vp, 400 kHz) is found adequate for retaining most viable cells (90.2% ± 3.5%) while removing nonviable cells (88.5% ± 5%) at an increased throughput (5 × 10(5) cells h(-1)). The electrodes, despite their intricate profile, are structured into single-crystal silicon through a self-aligned etching process without a precision layer-by-layer assembly.

Continuous-flow electrophoresis of macromolecules is demonstrated using an integrated capillary-well sieve arranged into a two-dimensional anisotropic array on silicon. The periodic array features thousands of entropic barriers, each resulting from an abrupt interface between a 2 μm deep well (channel) and a 70 nm capillary. These entropic barriers owing to two-dimensional confinement within the capillaries are vastly steep in relation to those arising from slits featuring one-dimensional confinement. Thus, the sieving mechanisms can sustain relatively large electric field strengths over a relatively small array area. The sieve rapidly sorts anionic macromolecules, including DNA chains and proteins in native or denatured states, into distinct trajectories according to size or charge under electric field vectors orthogonally applied. The baseline separation is achieved in less than 1 min within a horizontal migration length of ∼1.5 mm. The capillaries are self-enclosed conduits in cylindrical profile featuring a uniform diameter and realized through an approach that avoids advanced patterning techniques. The approach exploits a thermal reflow of a layer of doped glass for shape transformation into cylindrical capillaries and for controllably shrinking the capillary diameter. Lastly, atomic layer deposition of alumina is introduced for the first time to fine-tune the capillary diameter as well as to neutralize the surface charge, thereby suppressing undesired electroosmotic flows.

This paper presents an integrated nanofluidic diode biosensor based on a single asymmetric nanoslit with a nominal width of 30 nm. The nanoslit dimension is fine-tuned by the highly conformal atomic layer deposition (ALD) of Al 2 O 3 . The surface of the nanoslit is further modified with an ultra-thin layer of SiO 2 that is placed onto the Al 2 O 3 layer for improved sensing performance. The device has been demonstrated for electrical label-free detection of human cardiac troponin biomarker at clinically relevant concentrations across a range over four orders of magnitudes. The precise control of the slit dimension and its robust sensing performance could pave the way for the single-slit nanofluidic diode biosensor as a promising diagnostic tool for acute myocardial infarction.

A silicon chip featuring self-enclosed integrated glass nanocapillaries at a length scale of 5 cm is demonstrated for the hydrodynamic chromatography of DNA. The integrated nanocapillaries offer exceptional performance, delivering a fast separation (3 min) at a high plate number (162 000 plates/m). These advantages are ascribed to the cylindrical geometry that exhibits less axial dispersions unlike of the rectangular profile, and a smooth surface finish by a thermal reflow process unlike of a typical etch. It should be noted that the nanocapillaries are achieved highly uniform in radius (600 nm) over a great length scale (5 cm) using a batch-fabricated process that relies on a low-resolution high-throughput lithography.

A two-dimensional (2D) capillary-well (CW) motif is a novel structure featuring thousands of cylindrical glass capillaries in diameter 100 and 600 nm and integrated through low-resolution photolithography (∼2 μm) and standard silicon processing techniques. Owing to high entropic energy barriers imposed at capillary openings, this design offers a rapid high-performance sieving of biomolecules under intense electric fields as demonstrated here for continuous-flow DNA or protein electrophoresis.

This work presents an innovative design for a flow-through dielectrophoretic cell sorting based on silicon bulk microelectrodes featuring sidewall undercuts. The microelectrodes are configured into an interdigitated array with digits extending across the flow chamber at an oblique angle against the flow stream. Target cells under dielectrophoretic forces and hydrodynamic drag can slide along the digits to a dedicated outlet. The design has been showcased for continuous-flow sorting of viable and non-viable mammalian cells, achieving a throughput of 16,600 cells/min, an order of magnitude higher than those reported for existing continuous-flow cell sorting designs using thin-film or volumetric microelectrodes.

Here, we report on a micropump that generates hydraulic pressure owing to a mismatch in EOF rates of microchannels and submicrometer cylindrical glass capillaries integrated on silicon. The electrical conductance of such capillaries in the dilute limit departs from bulk linear behavior as well as from the surface-charge-governed saturation in nanoslits that is well described by the assumption of a constant surface charge density. The capillaries show rather a gradual decrease in conduction at low salt concentrations, which can be explained more aptly by a variable surface charge density that accounts for chemical equilibrium of the surface. The micropump uses a traditional cross-junction structure with ten identical capillaries integrated in parallel on a side arm and each with a 750 nm diameter and 3 mm length. For an applied voltage of 700 V, a hydraulic pressure up to 5 kPa is generated with a corresponding flow velocity nearly 3 mm/s in a straight field-free branch 20 μm wide, 10 μm deep, and 10 mm long. The micropump utility has been demonstrated in an open tubular LC of three fluorescently labeled amino acids in just less than 20 s with minimal plate height values between 3 and 7 μm. The submicrometer capillaries are self-enclosed and produced through a unique process that does not require high-resolution advanced lithography or wafer-bonding techniques to define their highly controlled precise structures.

Here, we report on DNA electrophoresis through a novel artificial sieving matrix based on the highly regular submicrometer cylindrical glass capillary segments alternatingly arranged with wells. Such round capillaries pose a higher-order confinement resulting in a lower partition coefficient and greater entropic energy barrier while limiting the driving field strength to a small fraction of the applied electric field. In return, the separation can be performed at high average field strengths (up to 1.6 kV/cm) without encountering the field-dependent loss of resolving power. This leads to fast DNA sieving as demonstrated here on the capillaries of 750 nm in diameter. The 600 bp to 21 kbp long chains are shown to resolve within 4 min after having undergone a fairly limited number of entropic barriers (128 in total). The capillary matrix also exhibits a critical field threshold below which DNA bands fail to launch, and this occurs at a considerably greater magnitude than in other matrixes. The submicrometer capillaries are batch-fabricated on silicon through a fabrication process that does not require high-resolution advanced lithography or well-controlled wafer bonding techniques to define their critical dimension.

Surface-enhanced Raman scattering (SERS) encountered in interstitial gaps between closely positioned metal nanostructures, hot spots, offers tremendous potential for molecular analysis at the trace or single-molecule level. SERS-active sites, hot spots, can be achieved at a higher density when metal nanostructures are configured on a three-dimensional (3D) platform than on a planar two-dimensional (2D) substrate. Yet, 3D platforms demonstrated thus far such as anodized alumina and microstructured fibers offer capillaries/pores either too narrow for the sample to be infused or may not be compatible with microfluidic integration due to their non-planar feature. Here, we introduce a 3D SERS-active platform based on a planar component that is readily available and presents densely packed highly aligned precision microchannels, the so-called microchannel plate (MCP). The microchannels, owing to their alignment biased at a small but precise angle (7°) with respect to the plate surface normal and their reasonably large diameter (~6 μm) can be functionalized with Ag nanorods through shadowing-based deposition that requires no other template or lithography. The plate functionalized with Ag nanorods delivers an enhancement factor with values in the range of 10 6 –10 8 as verified with probing molecules 4-mercatobenzoic acid (4-MBA) and rhodamine-6G.

This paper describes the design, the fabrication, and the characterization of an interdigitated 3-D silicon (Si) ring microelectrodes for dielectrophoretic (DEP) manipulation of particles. The 3-D microelectrodes are derived from a high-aspect-ratio comb structure etched in a doped single crystal Si on an insulating dielectric (silicon-on-insulator). Fingers of the comb are evolved into ring microelectrodes once perforated with a linear array of well-defined round lateral constrictions. This is achieved by the segmented finger layout and the Si dry release strategy borrowed from inertial microelectromechanical systems. The fingers and their interspaces are sealed with a cover layer forming a microfluidic flow chamber surrounded by 3-D microelectrodes and accessible via single inlet/outlet. The functionality of the device has been verified on 2- and 10-μm polystyrene microspheres in pressure-driven flow through the ring microelectrodes at 3.3 μL/min effectively focusing them into streams or trapping them around the fingers at moderate voltage levels (20-40 Vpp).

We present a novel plasmapheresis device designed for a fully integrated point-of-care blood analysis microsystem. In the device, fluidic microchannels exhibit a characteristic cross-sectional profile arising from distinct three-dimensional (3D) microelectrodes featuring sidewall undercuts readily integrated through a single-mask process. The structure leverages mainly electrothermal convective rolls that efficiently manifest themselves in physiological fluids and yet have received inadequate attention for the application of plasmapheresis due to concerns over Joule heating. Using this device, we show that such convective rolls not only lead to plasma extraction at a high yield and purity but also deliver plasma at an acceptable quality with no evidence of hemolytic stress or protein denaturation. Specifically, plasma from 1.5 μL of whole blood diluted to 4% hematocrit in a high-conductivity buffer (1.5 S/m) is extracted in a continuous flow at a fraction of 70% by using a peak voltage of ±10 Vp applied at 650 kHz; the extracted plasma is nearly 99% pure, as shown by a rigorous assessment using flow cytometry. The plasmas obtained using this device and using conventional centrifugation and sedimentation are of comparable quality as revealed by absorbance and circular dichroism spectra despite thermal gradients; however, these gradients effectively drive electrothermal bulk flows, as assessed using the microparticle image velocity technique. The device achieves high target molecule recovery efficiency, delivering about 97% of the proteins detected in the plasma obtained using sedimentation. The utility of the extracted plasma is further validated based on the detection of prostate-specific antigen at clinically relevant levels.

We demonstrate a silicon chip featuring self-enclosed integrated glass microcapillaries for pressure-driven liquid chromatography. The microcapillaries offer exceptional performance (740,000 plates/m) owing to their unique features, which set them apart from conventional fluidic channels and could pave the way to more effective bioanalytical microsystems. These include a cylindrical capillary lumen as opposed to the rectangular geometry typical of fluidic channels and a smooth surface finish imparted by thermal reflow of phosphosilicate glass (PSG) as opposed to the rough surface finish inherited from subtractive techniques (e.g. etch). All these are achieved using standard fabrication processes and shown here using 1-cm-long capillaries in 1-μm diameter that can be further scaled down via extended glass reflow.

This is the first account of a single-cell impedance flow cytometry microsystem based on 3D silicon microelectrodes. Such microelectrodes emerge being readily aligned during lithographic patterning of silicon and thus relieve the burden of alignment that comes with planar microelectrodes and their opposing arrangement for a maximum sensitivity. The opposing arrangement of the microelectrodes generate homogeneous electric field and thus maintain maximum sensitivity while individual cells passing by. The microsystem has been showcased here for the flow impedance measurement of polystyrene microspheres and cells at 10 MHz. Successful classification of human colorectal cancer cells and red blood cells has also been demonstrated using this device.

Dielectrophoresis (DEP) induced by activating a patterned two-dimensional electron gas (2DEG) at the interface of compound semiconductor AlGaN/GaN heterojunction has been demonstrated for the first time in our previous work. Briefly, with a peak voltage of ±10 V and a frequency from 100 kHz to 1 MHz, characteristics of both positive and negative DEP have been observed successfully manipulating 2 µm polystyrene microspheres in a drop of deionized (DI) water (pH ∼ 7 and conductivity 1 × 10−4 S m−1) over castellated 2DEG electrodes separated by critical dimensions 50 and 150 µm. This study reports a peculiar observation encountered when performing the DEP experiments under ultraviolet (UV) radiation: The microspheres have been repelled from the 2DEG electrodes yet remained on the surface during pDEP and then levitated upon switching to nDEP. This behavior is not observed in DEP with conventional microelectrodes and explained here by the UV-induced electron–hole generation and the subsequent charge redistribution in the AlGaN/GaN heterostructure.