Large-Area Silicon Nitride Nanosieve for Enhanced Diffusion-Based Exosome Isolation.

Nanoporous membranes have a variety of applications, one of which is the size-selective separation of nanoparticles. In drug delivery, nanoporous membranes are becoming increasingly important for the isolation of exosomes, which are bio-nanoparticles. However, the low pore density and thickness of commercial membranes limit their efficiency. There have been many attempts to fabricate sub-micrometer thin membranes, but the limited surface area has restricted their practicality. In this study, large-area silicon nitride nanosieves for enhanced diffusion-based isolation of exosomes are presented. Notably, these nanosieves are scaled to sizes of up to 4-inch-wafers, a significant achievement in overcoming the fabrication challenges associated with such expansive areas. The method employs a 200 nm porous sieve (38.2% porosity) for exosome separation and a 50 nm sieve (10.7% porosity) for soluble protein removal. These 300 nm thick nanosieves outperform conventional polycarbonate membranes by being 50 times thinner, thereby increasing nanoparticle permeability. The method enables a 90% recovery rate of intact exosomes from human serum and a purity ratio of 3 × 107 particles/µg protein, 4.6 times higher than ultracentrifugation methods. The throughput of the method is up to 15 mL by increasing the size of the nanosieve, making it an ideal solution for large-scale exosome production for therapeutic purposes.

SERS detection of surface-adsorbent toxic substances of microplastics based on gold nanoparticles and surface acoustic waves.

Microplastics adsorb toxic substances and act as a transport medium. When microplastics adsorbed with toxic substances accumulate in the body, the microplastics and the adsorbed toxic substances can cause serious diseases, such as cancer. This work aimed to develop a surface-enhanced Raman spectroscopy (SERS) detection method for surface-adsorbent toxic substances by forming gold nanogaps on microplastics using surface acoustic waves (SAWs). Polystyrene microparticles (PSMPs; 1 µm) and polycyclic aromatic hydrocarbons (PAHs), including pyrene, anthracene, and fluorene, were selected as microplastics and toxic substances, respectively. Gold nanoparticles (AuNPs; 50 nm) were used as a SERS agent. The Raman characteristic peaks of the PAHs adsorbed on the surface of PSMPs were detected, and the SERS intensity and logarithm of the concentrations of pyrene, anthracene, and fluorene showed a linear relationship (R2 = 0.98), and the limits of detection were 95, 168, and 195 nM, respectively. Each PAH was detected on the surface of PSMPs, which were adsorbed with toxic substances in a mixture of three PAHs, indicating that the technique can be used to elucidate mixtures of toxic substances. The proposed SERS detection method based on SAWs could sense toxic substances that were surface-adsorbed on microplastics and can be utilized to monitor or track pollutants in aquatic environments.

Aggregation of Ag nanoparticle based on surface acoustic wave for surface-enhanced Raman spectroscopy detection of dopamine.

BACKGROUND: Dopamine (DA), a vital neurotransmitter, plays a critical role in the human brain and relates to neuropsychiatric disorders such as Parkinson's disease and schizophrenia. Numerous studies have explored detection of such biomarkers through surface-enhanced Raman spectroscopy (SERS). However, most of the studies focused on SERS detection face significant challenges with plasmonic nanostructure development. Such challenges often include time-consuming processes, complex fabrication, specialized chemical labeling, poor reproducibility, and random hotspot generation. Therefore, the need for simple and rapid nanostructure development is evident in SERS. RESULTS: We propose an innovative SERS-active sensing technique for 50 nm silver nanoparticle (AgNP) clustering based on surface acoustic wave (SAW). When a 1 µL droplet of AgNP colloid is dispensed onto the SAW-propagation zone, the AgNP cluster is deposited after the droplet completely evaporates, developing plasmonic nanogaps for SERS hotspot caused by spherical AgNP aggregation. By optimizing the SAW system through the hydrophobic treatment and modulation of the operational power, the SAW-induced AgNP clustering showed densely packed AgNP within a dot-like configuration (∼2200 AgNP µm-2), effectively preventing particle welding. The characterization of 4-mercaptobenzoic acid as a probe analyte revealed that concentrations as low as 1.14 pM was detected using our SAW-SERS system under 785 nm laser excitation. Moreover, DA was detected up to 4.28 nM with a determination of 0.99 (R2). SIGNIFICANCE: This technique for AgNP clustering induced by SAW provides a rapid, in situ, label-free SERS sensing method with outstanding sensitivity and linearity. A mere act of dropping can create extensive plasmonic hotspots featuring nanogap of ∼1.5 nm. The SAW-induced AgNP clustering can serve as an ultrasensitive SERS-active substrate for diverse molecular detections, including neurotransmitter detection.

Development of core-shell magnetic molecularly imprinted polymer-based electrochemical sensor for sensitive and selective detection of ezetimibe.

A sensitive electrochemical molecularly imprinted polymer (MIP) sensor was fabricated for detection of ezetimibe (Eze) as an effective cholesterol absorption inhibitor on the surface of a screen-printed carbon electrode based on a magnetic nanoparticle decorated with MIP (Fe3O4@MIP). Placing the magnetic nanoparticle inside the MIP increases the biocompatibility, surface-to-volume ratio, and sensitivity of the sensor. Methacrylic acid (MAA) was used as a monomer, ethylene glycol dimethacrylate (EGDMA) as a cross-linker, and Eze as a template. The fabricated Fe3O4@MIP was characterized using Fourier-transform infrared spectroscopy (FTIR), Transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Detection of Eze was achieved by differential pulse voltammetry. Using this sensor, Eze can be sensitively detected in the range of 1.0 nM-10 µM and detection limit of 0.7 nM. In addition, we have shown that the proposed sensor successfully detects different concentrations of Eze in human serum samples and thus proves its practical application.

Fast Reconfigurable Electrode Array Based on Titanium Oxide for Localized Stimulation of Cultured Neural Network.

Planar microelectrode arrays have become standard tools for in vitro neural-network analysis. However, these predefined micropatterned devices lack adaptability to target-specific cells within a cultured network. Herein, we fabricated a reconfigurable TiO2 electrode array with an anatase-brookite bicrystalline polymorphous mesoporous layer. Because of its selective absorption of ultraviolet (UV) light and corresponding photoconductivity, TiO2 electrode array was identified as a promising tool for high-resolution light-addressing. The TiO2 film was used as a semitransparent semiconductor with a high Roff/Ron ratio of 105 and a fast response time of 400 ms. In addition, the effect of UV radiation on the resistance of the TiO2 film over 30 d in an aqueous environment was analyzed, with the film exhibiting high stability. An arbitrary UV pattern was applied to a reconfigurable TiO2 electrode using a digital micromirror device (DMD), affording highly localized neural stimulation at the single-cell level. The reconfigurable TiO2 electrode with a patterned indium tin oxide (ITO) substrate enabled the independent connection of up to 60 points with external stimulators and signal recorders. We believe this technique would be helpful for electrophysiological research requiring the analysis of cell and neural-network features using a highly localized neural interface.

Permanent Anticoagulation Blood-Vessel by Mezzo-Sized Double Re-Entrant Structure.

Having a permanent omniphobicity on the inner surface of the tube can bring enormous advantages, such as reducing resistance and avoiding precipitation during mass transfer. For example, such a tube can prevent blood clotting when delivering blood composed of complex hydrophilic and lipophilic compounds. However, it is very challenging to fabricate micro and nanostructures inside a tube. To overcome these, a wearability and deformation-free structural omniphobic surface is fabricated. The omniphobic surface can repel liquids by its "air-spring" under the structure, regardless of surface tension. Furthermore, it is not lost an omniphobicity under physical deformation like curved or twisted. By using these properties, omniphobic structures on the inner wall of the tube by the "roll-up" method are fabricated. Fabricated omniphobic tubes still repels liquids, even complex liquids like blood. According to the ex vivo blood tests for medical usage, the tube can reduce thrombus formation by 99%, like the heparin-coated tube. So, the surface will soon replace typical coating-based medical surfaces or anticoagulation blood vessels.

Improving the robustness of a catalyzed hairpin assembly with a three-arm nanostructure for nonenzymatic signal amplification.

Kinetically trapped hairpin DNA has great potential to dynamically build nanostructures, which can be initiated by sequence-specific nucleic acids. The branched junction, which has a multi-arm structure, is a representative nanostructure of DNA. In this study, we report a nonenzymatic and isothermal signal amplification accompanied by building a 3-arm structure based on a catalyzed hairpin DNA assembly (3-CHA). We improved the signal-to-background ratio of the 3-CHA by suppressing the leakage pathway of 3-CHA, thus eliminating unfavorable reaction sites exposed in the single-stranded region of hairpin DNAs. Background and amplified signals were analyzed with gel electrophoresis and real-time fluorescence monitoring. The limit of detection of the developed 3-CHA was estimated to be 29.3 pM for catalyst DNA at room temperature. Supported by the reduced leakage signal, the implemented 3-CHA showed great potential for detecting low concentrations of target DNA.

TAR RNA Mediated Folding of a Single-Arginine-Mutant HIV-1 Tat Protein within HeLa Cells Experiencing Intracellular Crowding.

The various effects of native protein folding on the stability and folding rate of intrinsically disordered proteins (IDPs) in crowded intracellular environments are important in biomedicine. Although most studies on protein folding have been conducted in vitro, providing valuable insights, studies on protein folding in crowded intracellular environments are scarce. This study aimed to explore the effects of intracellular molecular crowding on the folding of mutant transactivator HIV-1 Tat based on intracellular interactions, including TAR RNA, as proof of the previously reported chaperna-RNA concept. Considering that the Tat-TAR RNA motif binds RNA, we assessed the po tential function of TAR RNA as a chaperna for the refolding of R52Tat, a mutant in which the argi nine (R) residues at R52 have been replaced with alanine (A) by site-directed mutagenesis. We mon itored Tat-EGFP and Tat folding in HeLa cells via time-lapse fluorescence microscopy and biolayer interferometry using EGFP fusion as an indicator for folding status. These results show that the refolding of R52A Tat was stimulated well at a 0.3 µM TAR RNA concentration; wild-type Tat refolding was essentially abolished because of a reduction in the affinity for TAR RNA at that con centration. The folding and refolding of R52Tat were mainly promoted upon stimulation with TAR RNA. Our findings provide novel insights into the therapeutic potential of chaperna-mediated fold ing through the examination of as-yet-unexplored RNA-mediated protein folding as well as viral genetic variants that modulate viral evolutionary linkages for viral diseases inside a crowded intra cellular environment.

Diffusion-Based Separation of Extracellular Vesicles by Nanoporous Membrane Chip.

Extracellular vesicles (EVs) have emerged as novel biomarkers and therapeutic material. However, the small size (~200 nm) of EVs makes efficient separation challenging. Here, a physical/chemical stress-free separation of EVs based on diffusion through a nanoporous membrane chip is presented. A polycarbonate membrane with 200 nm pores, positioned between two chambers, functions as the size-selective filter. Using the chip, EVs from cell culture media and human serum were separated. The separated EVs were analyzed by nanoparticle tracking analysis (NTA), scanning electron microscopy, and immunoblotting. The experimental results proved the selective separation of EVs in cell culture media and human serum. Moreover, the diffusion-based separation showed a high yield of EVs in human serum compared to ultracentrifuge-based separation. The EV recovery rate analyzed from NTA data was 42% for cell culture media samples. We expect the developed method to be a potential tool for EV separation for diagnosis and therapy because it does not require complicated processes such as immune, chemical reaction, and external force and is scalable by increasing the nanoporous membrane size.

Multilayered and heterogeneous hydrogel construct printing system with crosslinking aerosol.

Microextrusion bioprinting has been used to recreate the complex architecture and composition of a physiological system through the quick and accurate handling of various biomaterials. However, existing techniques are limited in precisely fabricating complex constructs, including multilayers and heterogeneous patterns with distinct regions, because the extruded bioink spreads rapidly upon contact with the substrate and is partially mixed with subsequently printed bioinks. This issue leads to difficulties in accurately and stably constructing multi-material structures with clear interfaces for prolonged printing before gelation. To fabricate multilayered and heterogeneous constructs, a bioprinting system should be able to continuously extrude various biomaterials and simultaneously crosslink the extruded bioink to stabilize the printed construct. In this study, a multiple-bioink printing system was developed by integrating a multibarrel nozzle for extruding multiple bioinks with a nebulizer for simultaneous crosslinking. The crosslinking aerosol sprayed from the nebulizer was able to gelate the various hydrogel bioinks as they were extruded through the multibarrel nozzle. Such aerosol-based crosslinking improved printing resolution and stability. The developed bioprinting system showed the possibility of recapitulating the physiological complex architecture such as a cancer microenvironment with well-defined interfaces between regions of different mechanical properties and cellular compositions. Using the integrated bioprinting system, a multilayered and heterogeneous construct was printed with four bioinks, including three types of cells (breast cancer cells, stromal cells, and vascular endothelial cells). The printed biological model was characterized by analyzing cancer cell migration and vascular network formation. The developed multiple-bioink printing system is expected to be highly efficient in recapitulating complex tissues and their environments with compartmentalized regions.

Photon-directed multiplexed enzymatic DNA synthesis for molecular digital data storage.

New storage technologies are needed to keep up with the global demands of data generation. DNA is an ideal storage medium due to its stability, information density and ease-of-readout with advanced sequencing techniques. However, progress in writing DNA is stifled by the continued reliance on chemical synthesis methods. The enzymatic synthesis of DNA is a promising alternative, but thus far has not been well demonstrated in a parallelized manner. Here, we report a multiplexed enzymatic DNA synthesis method using maskless photolithography. Rapid uncaging of Co2+ ions by patterned UV light activates Terminal deoxynucleotidyl Transferase (TdT) for spatially-selective synthesis on an array surface. Spontaneous quenching of reactions by the diffusion of excess caging molecules confines synthesis to light patterns and controls the extension length. We show that our multiplexed synthesis method can be used to store digital data by encoding 12 unique DNA oligonucleotide sequences with video game music, which is equivalent to 84 trits or 110 bits of data.

Single-cell analysis of a mutant library generated using CRISPR-guided deaminase in human melanoma cells.

CRISPR-based screening methods using single-cell RNA sequencing (scRNA-seq) technology enable comprehensive profiling of gene perturbations from knock-out mutations. However, evaluating substitution mutations using scRNA-seq is currently limited. We combined CRISPR RNA-guided deaminase and scRNA-seq technology to develop a platform for introducing mutations in multiple genes and assessing the mutation-associated signatures. Using this platform, we generated a library consisting of 420 sgRNAs, performed sgRNA tracking analysis, and assessed the effect size of the response to vemurafenib in the human melanoma cell line, which has been well-studied via knockout-based drop-out screens. However, a substitution mutation library screen has not been applied and transcriptional information for mechanisms of action was not assessed. Our platform permits discrimination of several candidate mutations that function differently from other mutations by integrating sgRNA candidates and gene expression readout. We anticipate that our platform will enable high-throughput analyses of the mechanisms related to a variety of biological events.

Flexible and Stable Omniphobic Surfaces Based on Biomimetic Repulsive Air-Spring Structures.

In artificial biological circulation systems such as extracorporeal membrane oxygenation, surface wettability is a critical factor in blood clotting problems. Therefore, to prevent blood from clotting, omniphobic surfaces are required to repel both hydrophilic and oleophilic liquids and reduce surface friction. However, most omniphobic surfaces have been fabricated by combining chemical reagent coating and physical structures and/or using rigid materials such as silicon and metal. It is almost impossible for chemicals to be used in the omniphobic surface for biomedical devices due to durability and toxicity. Moreover, a flexible and stable omniphobic surface is difficult to be fabricated by using conventional rigid materials. This study demonstrates a flexible and stable omniphobic surface by mimicking the re-entrant structure of springtail's skin. Our surface consists of a thin nanohole membrane on supporting microstructures. This structure traps air under the membrane, which can repel the liquid on the surface like a spring and increase the contact angle regardless of liquid type. By theoretical wetting model and simulation, we confirm that the omniphobic property is derived from air trapped in the structure. Also, our surface well maintains the omniphobicity under a highly pressurized condition. As a proof of our concept and one of the real-life applications, blood experiments are performed with our flat and curved surfaces and the results including contact angle, advancing/receding angles, and residuals show significant omniphobicity. We hope that our omniphobic surface has a significant impact on blood-contacting biomedical applications.

Electropreconcentration, gate injection, and capillary electrophoresis separation on a microchip.

The nanochannel-based electropreconcentration is not compatible with successive capillary zone electrophoresis (CZE). In this study, the incompatibility is theoretically discussed and experimentally proven, and then, the development of a monolithic glass microfluidic chip for performing integrated electropreconcentration and CZE separation is described. The sample is electropreconcentrated at the interface of a micro- and nanochannel where electric double layer overlap conditions exist. Because an ion-depletion region develops at the leading front of the preconcentrated plug, a field-enhanced sample stacking effect occurs which limits the separation efficiency unless compensated for. The ion-depletion region was confirmed by monitoring the solution conductivity at discrete points in the microchannel during the preconcentration step. The solution conductivity decreased >20-fold during the preconcentration step. To overcome the effects of this region, a cross-intersection was used to shunt the ion-depleted buffer away from the analysis channel while reintroducing the running buffer. When the preconcentrated sample plug arrives at the cross-intersection, it is gate injected into the analysis channel so that fresh running buffer surrounds the plug. Under these conditions, three-peptide mixture was preconcentrated ∼200-fold in 60 s and the preconcentrated plug was successfully resolved with better than 1% relative standard deviations in migration times.

Development of a low flow-resistive charged nanoporous membrane in a microchip for fast electropreconcentration.

A nanoporous poly-(styrene sulfonate) (poly-SS) membrane was developed for fast and selective ion transport in a microfluidic chip. The poly-SS membrane can be photopolymerized in-situ at arbitrary location of a microchannel, enabling integrated fluidics design in the microfluidic chip. The membrane is characterized by a low hydraulic resistance and a high surface charge to maximize the electroosmotic flow and charge selectivity. The membrane characteristics were investigated by charge-selective electropreconcentration method. Experimental results show membranes with various percentages of poly-SS are able to concentrate anions (fluorescein and TRITC-labeled BSA). The anion-selective electropreconcentration process is stable and 26-times faster than previously reported poly-AMPS (2-acrylamido-2-methyl-1-propanesulfonic acid) based system. The electropreconcentration was also demonstrated to depend on the sample valency and buffer concentration.

Integration of electropreconcentration and electrospray ionization in a microchip.

A microfluidic glass chip for performing sensitive mass spectrometry (MS) is developed by integrating nanochannel-based electropreconcentration with electrospray ionization (ESI). Cation analytes in acidic buffer conditions (∼pH 3) were preconcentrated at a micro-nano-microchannel junction where a positively charged polymer, polyE-323, is coated to reverse the electroosmotic flows (anodic EOF) and prevent sample adsorption. The preconcentrated cation analytes were delivered to a monolithic spray tip using an integrated field-free electrokinetic pump, enabling a stable positive ESI with negligible dead volume. The sample preconcentration-ESI-MS achieved one order of magnitude signal enhancement in MS signal with a peptide mixture.

Electropreconcentration-induced local pH change.

Ion-permselective nanochannel-based sample preconcentration or electropreconcentration has been demonstrated as an effective technique for concentrating charged analytes at the interface between a micro- and nanochannel. The anion-selective electropreconcentration involves extraction of hydroxide in the preconcentrated sample plug, resulting in pH decrease. We investigated the pH change in a microchannel using charged pH indicators with different conditions including running buffer pH, sample channel electric field, and salt concentration. The anion-selective preconcentration showed pH decrease from 11 to under 7 in the preconcentrated sample plug. Therefore, careful design and interpretation are required with pH-dependent experiments such as analyzing enzyme or antibody characteristics. The pH change could be mitigated by reducing the sample channel electric field and/or increasing salt concentration in the buffer.

Separation of extracellular nanovesicles and apoptotic bodies from cancer cell culture broth using tunable microfluidic systems.

Extracellular vesicles (EVs) are the cell-secreted nano- and micro-sized particles consisted of lipid bilayer containing nucleic acids and proteins for diagnosis and therapeutic applications. The inherent complexity of EVs is a source of heterogeneity in various potential applications of the biological nanovesicles including analysis. To diminish heterogeneity, EV should be isolated and separated according to their sizes and cargos. However, current technologies do not meet the requirements. We showed noninvasive and precise separation of EVs based on their sizes without any recognizable damages. We separated atto-liter volumes of biological nanoparticles through operation of the present system showing relatively large volume of sample treatment to milliliters within an hour. We observed distinct size and morphological differences of 30 to 100 nm of exosomes and apoptotic bodies through TEM analysis. Indeed, we confirmed the biological moiety variations through immunoblotting with noninvasively separated EVs opening new windows in study and application of the biological nanoparticles.

Development of a conductivity-based photothermal absorbance detection microchip using polyelectrolytic gel electrodes.

The development and application of polyelectrolytic gel electrodes (PGEs) for a microfluidic photothermal absorbance detection system is described. The PGEs are used to measure changes in conductivity based on heat generation by analytes absorbing light and changing the solution viscosity. The PGEs are suitable for direct contact conductivity measurements since they do not degrade with exposure to high electric fields. Both a 2-electrode system with DC voltages and a 3-electrode system with AC voltages were investigated. Experimental factors including excitation voltage, excitation frequency, laser modulation frequency, laser power, and path length were tested. The limits of detection for the 3-electrode and 2-electrode systems are 500nM and 0.55nM for DABSYL-tagged glucosamine, respectively. In addition, an electrokinetic separation of a potassium, DABSYL-tagged glucosamine, Rhodamine 6G, and Rhodamine B mixture was demonstrated.

Electroosmotic Effects on Sample Concentration at the Interface of a Micro/Nanochannel.

Electroosmotic effect on electropreconcentration of analytes was investigated at the micro/nanochannel interface for a series of 1-D glass nanochannels with depths of 72, 54, 29, and 9 nm. The electric double layer approaches overlap conditions as the nanochannel depth decreases, suppressing the electroosmotic flow. The nanochannels' electroosmotic flows (µeonano) were determined and compared to the analyte's (fluorescein) electrophoretic mobility (µep). For the instances where µeonano > µep, the analytes were concentrated on the anodic side of the nanochannel (72, 54, and 29 nm deep channels), whereas when µeonano < µep, the analyte was concentrated on the cathodic side of the nanochannel (9 nm deep channel). In order to maintain a stable concentrated sample plug, a "drain" channel was incorporated for increasing the nanochannel electroosmotic flow while decreasing the sample channel electroosmotic flow. A sample preconcentration rate of over 20-fold per second was achieved. Finally, fundamental limits of the nanochannel-based preconcentration are discussed and experimentally demonstrated.