3D hydrodynamic focusing microfluidics for emerging sensing technologies

Drug eluting protein and polysaccharides-based biofunctionalized fabric textiles- pioneering a new frontier in tissue engineering: An extensive review

In the ever-evolving landscape of tissue engineering, medicated biotextiles have emerged as a game-changer. These remarkable textiles have garnered significant attention for their ability to craft tissue scaffolds that closely mimic the properties of natural tissues. This comprehensive review delves into the realm of medicated protein and polysaccharide-based biotextiles, exploring a diverse array of fabric materials. We unravel the intricate web of fabrication methods, ranging from weft/warp knitting to plain/stain weaving and braiding, each lending its unique touch to the world of biotextiles creation. Fibre production techniques, such as melt spinning, wet/gel spinning, and multicomponent spinning, are demystified to shed light on the magic behind these ground-breaking textiles. The biotextiles thus crafted exhibit exceptional physical and chemical properties that hold immense promise in the field of tissue engineering (TE). Our review underscores the myriad applications of drug-eluting protein and polysaccharide-based textiles, including TE, tissue repair, regeneration, and wound healing. Additionally, we delve into commercially available products that harness the potential of medicated biotextiles, paving the way for a brighter future in healthcare and regenerative medicine. Step into the world of innovation with medicated biotextiles-where science meets the art of healing.

Spiral Large-Dimension Microfluidic Channel for Flow-Rate- and Particle-Size-Insensitive Focusing by the Stabilization and Acceleration of Secondary Flow

Inertial microfluidics has demonstrated its ability to focus particles in a passive and straightforward manner. However, achieving flow-rate- and particle-size-insensitive focusing in large-dimension channels with a simple design remains challenging. In this study, we developed a spiral microfluidic with a large-dimension channel to achieve inertial focusing. By designing a unique "big buffering area" and a "small buffering area" in the spiral microchannel, we observed the stabilization and acceleration of secondary flow. Our optimized design allowed for efficient (>99.9%) focusing of 15 μm particles within a wide range of flow rates (0.5-4.5 mL/min) during a long operation duration (0-60 min). Additionally, we achieved effective (>95%) focusing of different-sized particles (7, 10, 15, and 30 μm) and three types of tumor cells (K562, HeLa, and MCF-7) near the inner wall of the 1 mm wide outlet when applying different flow rates (1-3 mL/min). Finally, successful 3D cell focusing was achieved within an optimized device, with the cells positioned at a distance of 50 μm from the wall. Our strategy of stabilizing and accelerating Dean-like secondary flow through the unique configuration of a "big buffering area" and a "small buffering area" proved to be highly effective in achieving inertial focusing that is insensitive to the flow rate and particle size, particularly in large-dimension channels. Consequently, it shows great potential for use in hand-operated microfluidic tools for flow cytometry.

Twisted fiber microfluidics: a cutting-edge approach to 3D spiral devices

The development of 3D spiral microfluidics has opened new avenues for leveraging inertial focusing to analyze small fluid volumes, thereby advancing research across chemical, physical, and biological disciplines. While traditional straight microchannels rely solely on inertial lift forces, the novel spiral geometry generates Dean drag forces, eliminating the necessity for external fields in fluid manipulation. Nevertheless, fabricating 3D spiral microfluidics remains a labor-intensive and costly endeavor, hindering its widespread adoption. Moreover, conventional lithographic methods primarily yield 2D planar devices, thereby limiting the selection of materials and geometrical configurations. To address these challenges, this work introduces a streamlined fabrication method for 3D spiral microfluidic devices, employing rotational force within a miniaturized thermal drawing process, termed as mini-rTDP. This innovation allows for rapid prototyping of twisted fiber-based microfluidics featuring versatility in material selection and heightened geometric intricacy. To validate the performance of these devices, we combined computational modeling with microtomographic particle image velocimetry (μTPIV) to comprehensively characterize the 3D flow dynamics. Our results corroborate the presence of a steady secondary flow, underscoring the effectiveness of our approach. Our 3D spiral microfluidics platform paves the way for exploring intricate microflow dynamics, with promising applications in areas such as drug delivery, diagnostics, and lab-on-a-chip systems.

Simplified 3D hydrodynamic flow focusing for lab-on-chip single particle study

Accurately control of the position of a fluid and particle within lab-on-a-chip platform is a critical prerequisite for many downstream analysis processes, such as detection, trapping and separation, moving the sensing at the single-particle level. With the development of microfluidic fabrication technology, particle/cell focusing has shifted from two to three dimensions. 3D hydrodynamic focusing, which sorts and aligns the incoming cloud of particles so that they pass through the interrogation area one by one, enables new possibilities and breakthroughs in the single-cell analysis system. Despite the excellent results shown in literature, there is still a lack of a device that can simultaneously fulfilling the requirements of high throughput, compactness, high integrability, and ease of use operation to become a widely accepted work center for biomedical research and clinical applications. Here, we proposed a unique 3D flow focusing microfluidic device buried in fused silica substrate that potentially combines all this advantages. By designing a sample channel suspended inside a larger buffer channel, manufactured by exploiting the laser-assisted micromachine technique, a not size-dependent focusing capability is shown. A spatially and temporally stable central flow of a mixture of 15 μm and 6 μm PS particles to a 1 μm PS microsphere solution has been obtained with high accuracy. Finally, to test the achievable focusing resolution, the chip was tested for the detection of Escherichia Coli bacteria in water solution as proof of concept of biological application.

Processes for the 3D Printing of Hydrodynamic Flow-Focusing Devices

Flow focusing is an important hydrodynamic technique for cytometric analysis, enabling the rapid study of cellular samples to identify a variety of biological processes. To date, the majority of flow-focusing devices are fabricated using conventional photolithography or flame processing of glass capillaries. This article presents a suite of low-cost, millifluidic, flow-focusing devices that were fabricated using a desktop sterolithgraphy (SLA) 3D printer. The suite of SLA printing strategies consists of a monolithic SLA method and a hybrid molding process. In the monolithic SLA approach, 1.3 mm square millifluidic channels were printed as a single piece. The printed device does not require any post processing, such as bonding or surface polishing for optical access. The hybrid molding approach consists of printing a mold using the SLA 3D printer. The mold is treated to an extended UV exposure and oven baked before using PDMS as the molding material for the channel. To demonstrate the viability of these channels, we performed a series of experiments using several flow-rate ratios to show the range of focusing widths that can be achieved in these devices. The experiments are validated using a numerical model developed in ANSYS.

Backscattering-Based Discrimination of Microparticles Using an Optofluidic Multiangle Scattering Chip

In this research, we designed and fabricated an optofluidic chip for the detection and differentiation of single particles via the combination of backscattered (BSC) and forward-scattered (FSC) or side-scattered (SSC) light intensity. The high sensitivity of BSC light to the refractive index of the particles enabled an effective approach for the differentiation of individual particles based on the type of material. By recording BSC as well as FSC and SSC light intensities from single particles, transiting through the illumination zone in a microfluidic channel, the size and type of material could be detected simultaneously. The analysis of model samples of polystyrene (PS), as a primary microplastic particle, and silica microspheres showed substantially higher BSC signal values of PS because of a larger refractive index compared to the silica. The scatter plots correlating contributions of BSC (FSC-BSC and SSC-BSC) allowed a clear differentiation of PS and silica particles. To demonstrate the great potential of this methodology, two "real-life" samples containing different types of particles were tested as application examples. Commercial toothpaste and peeling gel products, as primary sources of microplastics into effluents, were analyzed via the optofluidic chip and compared to results from scanning electron microscopy. The scattering analysis of the complex samples enabled the detection and simultaneous differentiation of particles such as microplastics according to their differences in the refractive index via distinctive areas of high and low BSC signal values. Hence, the contribution of BSC light measurements in multiangle scattering of single particles realized in an optofluidic chip opens the way for the discrimination of single particles in a liquid medium in manifold fields of application ranging from environmental monitoring to cosmetics.

Hand-Powered Inertial Microfluidic Syringe-Tip Centrifuge

Conventional sample preparation techniques require bulky and expensive instruments and are not compatible with next-generation point-of-care diagnostic testing. Here, we report a manually operated syringe-tip inertial microfluidic centrifuge (named i-centrifuge) for high-flow-rate (up to 16 mL/min) cell concentration and experimentally demonstrate its working mechanism and performance. Low-cost polymer films and double-sided tape were used through a rapid nonclean-room process of laser cutting and lamination bonding to construct the key components of the i-centrifuge, which consists of a syringe-tip flow stabilizer and a four-channel paralleled inertial microfluidic concentrator. The unstable liquid flow generated by the manual syringe was regulated and stabilized with the flow stabilizer to power inertial focusing in a four-channel paralleled concentrator. Finally, we successfully used our i-centrifuge for manually operated cell concentration. This i-centrifuge offers the advantages of low device cost, simple hand-powered operation, high-flow-rate processing, and portable device volume. Therefore, it holds potential as a low-cost, portable sample preparation tool for point-of-care diagnostic testing.

Reduced acoustic resonator dimensions improve focusing efficiency of bacteria and submicron particles

In this study, we demonstrate an acoustofluidic device that enables single-file focusing of submicron particles and bacteria using a two-dimensional (2D) acoustic standing wave. The device consists of a 100 μm × 100 μm square channel that supports 2D particle focusing in the channel center at an actuation frequency of 7.39 MHz. This higher actuation frequency compared with conventional bulk acoustic systems enables radiation-force-dominant motion of submicron particles and overcomes the classical size limitation (≈2 μm) of acoustic focusing. We present acoustic radiation force-based focusing of particles with diameters less than 0.5 μm at a flow rate of 12 μL min^-1, and 1.33 μm particles at flow rates up to 80 μL min^-1. The device focused 0.25 μm particles by the 2D acoustic radiation force while undergoing a channel cross-section centered, single-vortex acoustic streaming. A suspension of bacteria was also investigated to evaluate the biological relevance of the device, which demonstrated the alignment of bacteria in the channel at a flow rate of up to 20 μL min^-1. The developed acoustofluidic device can align submicron particles within a narrow flow stream in a highly robust manner, validating its use as a flow-through focusing chamber to perform high-throughput and accurate flow cytometry of submicron objects.

Low-cost polymer-film spiral inertial microfluidic device for label-free separation of malignant tumor cells

We developed a low-cost polymer-film spiral inertial microfluidic device for the effective size-dependent separation of malignant tumor cells. The device was fabricated in polymer films by rapid laser cutting and chemical bonding. After fabricating the prototype device, the separation performance of our device was evaluated using particles and cells. The effects of operational flow rate, cell diameter, and cell concentration on the separation performance were explored. Our device successfully separated tumor cells from polydisperse white blood cells according to their different migration modes and lateral positions. Then, the separation of rare cells was carried out using the high-concentration lysed blood spiked with 200 tumor cells. Experimental results showed that 83.90% of the tumor cells could be recovered, while 99.87% of white blood cells could be removed. We successfully employed our device for processing clinical pleural effusion samples from patients with advanced metastatic breast cancer. Malignant tumor cells with an average purity of 2.37% could be effectively enriched, improving downstream diagnostic accuracy. Our device offers the advantages of label-free operation, low cost, and fast fabrication, thus being a potential tool for effective cell separation.

Focusing of Particles in a Microchannel with Laser Engraved Groove Arrays

Continuous microfluidic focusing of particles, both synthetic and biological, is significant for a wide range of applications in industry, biology and biomedicine. In this study, we demonstrate the focusing of particles in a microchannel embedded with glass grooves engraved by femtosecond pulse (fs) laser. Results showed that the laser-engraved microstructures were capable of directing polystyrene particles and mouse myoblast cells (C2C12) towards the center of the microchannel at low Reynolds numbers (Re < 1). Numerical simulation revealed that localized side-to-center secondary flows induced by grooves at the channel bottom play an essential role in particle lateral displacement. Additionally, the focusing performance proved to be dependent on the angle of grooves and the middle open space between the grooves based on both experiments and simulation. Particle sedimentation rate was found to critically influence the focusing of particles of different sizes. Taking advantage of the size-dependent particle lateral displacement, selective focusing of micrometer particles was demonstrated. This study systematically investigated continuous particle focusing in a groove-embedded microchannel. We expect that this device will be used for further applications, such as cell sensing and nanoparticle separation in biological and biomedical areas.

Secondary-flow-aided single-train elastic-inertial focusing in low elasticity viscoelastic fluids

Elastic-inertial focusing has attracted increasing interest in recent years due to the three-dimensional (3D) single-train focusing ability it offers. However, multi-train focusing, instead of single-train focusing, was observed in viscoelastic fluids with low elasticity as a result of the competition between inertia effect and viscoelasticity effect. To address this issue, we employed the secondary flow to facilitate single-train elastic-inertial focusing in low elasticity viscoelastic fluids. A three-section contraction-expansion channel was designed to induce the secondary flow to pinch the multiplex focusing trains into a single one exactly at the channel centerline. After demonstrating the focusing process and mechanism in our device, we systematically explored and discussed the effects of particle diameter, operational flow rate, polymer concentration, and channel dimension on particle focusing performances. Our device enables single-train focusing of particles in viscoelastic fluids with low elasticity, and offers advantages of planar single-layer structure, and sheathless, external-field free operation.

3D-Printed Microfluidic Nanoelectrospray Ionization Source Based on Hydrodynamic Focusing

Nanoelectrospray ionization (nESI) mass spectrometry (MS) is an ideal detection method for microfluidic chips, and its performances depend on nESI emitters. However, the fabrication of monolithic nESI emitters in chips was difficult. Herein, we propose a three-dimensional (3D) printing method to develop a microfluidic nanoelectrospray ionization source (NIS), composed of a nESI emitter and other components. Firstly, the NIS was compatible with a 50 - 500 nL min^-1 nanoflows by imposing 3D hydrodynamic focusing to compensate for the total flow rate, achieving a 7.2% best relative standard deviation in the total ion current (TIC) profiles. Additionally, it was applied to probe thirteen organic chemicals, insulin, and lysozyme with adequate signal-to-noise ratios and an accuracy of m/z between 9.02 × 10^-1 and 1.48 × 10³ ppm. Finally, the NIS achieved comparable limits of detection compared with its commercial counterpart. Considering the standardized preparation of NIS, it would be a potential option to develop 3D-printed customized Chip-MS platforms.

Super-resolution optofluidic scanning microscopy

Optofluidics enables visualizing diverse anatomical and functional traits of single-cell specimens with new degrees of imaging capabilities. However, the current optofluidic microscopy systems suffer from either low resolution to reveal subcellular details or incompatibility with general microfluidic devices or operations. Here, we report optofluidic scanning microscopy (OSM) for super-resolution, live-cell imaging. The system exploits multi-focal excitation using the innate fluidic motion of the specimens, allowing for minimal instrumental complexity and full compatibility with various microfluidic configurations. The results present effective resolution doubling, optical sectioning and contrast enhancement. We anticipate the OSM system to offer a promising super-resolution optofluidic paradigm for miniaturization and different levels of integration at the chip scale.

Automated Raman based cell sorting with 3D microfluidics

Raman activated cell sorting has emerged as a label-free technology that can link phenotypic function with genotypic properties of cells. However, its broad implementation is limited by challenges associated with throughput and the complexity of biological systems. Here, we describe a three-dimensional hydrodynamic focusing microfluidic system for a fully automated, continuous Raman activated cell sorting (3D-RACS). The system consists of a 3D printed detection chamber (1 mm3) that is integrated with a PDMS based sorting unit, optical sensors and an in-line collection module. It has the ability to precisely position cells in the detection chamber for Raman measurements, effectively eliminating spectroscopic interference from the device materials. This enables the sorting of a range of cell sizes (from 1 μm bacteria to 10's μm mammalian cells) with stable operation over >8 hours and high throughput. As a proof-of-concept demonstration, Raman-activated sorting of mixtures of Chlorella vulgaris and E. coli has demonstrated a purity level of 92.0% at a throughput of 310 cells per min. The platform employed in this demonstration features a simple "Raman window" detection system, enabling it to be built on a standard, inverted microscope. Together with its facile and robust operation, it provides a versatile tool for function-based flow cytometry and sorting applications in the fields of microbiology, biotechnology, life science and diagnostics.

Positional dependence of particles and cells in microfluidic electrical impedance flow cytometry: origin, challenges and opportunities

Microfluidic electrical impedance flow cytometry is now a well-known and established method for single-cell analysis. Given the richness of the information provided by impedance measurements, this non-invasive and label-free approach can be used in a wide field of applications ranging from simple cell counting to disease diagnostics. One of its major limitations is the variation of the impedance signal with the position of the cell in the sensing area. Indeed, identical particles traveling along different trajectories do not result in the same data. The positional dependence can be considered as a challenge for the accuracy of microfluidic impedance cytometers. On the other hand, it has recently been regarded by several groups as an opportunity to estimate the position of particles in the microchannel and thus take a further step in the logic of integrating sensors in so-called "Lab-on-a-chip" devices. This review provides a comprehensive overview of the physical grounds of the positional dependence of impedance measurements. Then, both the developed strategies to reduce position influence in impedance-based assays and the recent reported technologies exploiting that dependence for the integration of position detection in microfluidic devices are reviewed.

Disease diagnostics using hydrodynamic flow focusing in microfluidic devices: Beyond flow cytometry

The multi-disciplinary field of microfluidics has the potential to provide solutions to a diverse set of problems. It offers the advantages of high-throughput, continuous, rapid and expeditious analysis requiring minute quantities of sample. However, even as this field has yielded many mass-manufacturable and cost-efficient point-of-care devices, its direct and practical applications into the field of disease diagnostics still remain limited and largely overlooked by the industry. This review focuses on the phenomenon of hydrodynamic focusing and its potential to materialize solutions for appropriate diagnosis and prognosis. The study aims to look beyond its intended cytometric applications and focus on unambiguous disease detection, monitoring, drug delivery, studies conducted on DNA and highlight the instances in the scientific literature that have proposed such approach.

3D hydrodynamic focusing in microscale channels formed with two photoresist layers

3D hydrodynamic focusing was implemented with channel cross-section dimensions smaller than 10 μm. Microchannels were formed using sacrificial etching of two photoresist layers on a silicon wafer. The photoresist forms a plus-shaped prismatic focusing fluid junction which was coated with plasma-enhanced chemical-vapor-deposited oxide. Buffer fluid carried to the focusing junction envelopes an intersecting sample fluid, resulting in 3D focusing of the sample stream. The design requires four fluid ports and operates across a wide range of fluid velocities through pressure-driven flow. The focusing design was integrated with optical waveguides to interrogate fluorescing particles and confirm 3D focusing. Particle diffusion away from a focused stream was characterized.

Hierarchical fibers for water collection inspired by spider silk

Water scarcity plagues two-thirds of the global population. Interestingly, researchers have found that spider silk exhibits excellent water-collection ability owing to its unique structure and chemical components. Based on this characteristic, numerous bioinspired fibers have been fabricated for water collection. Herein, we review the water-collection process for spider silk and recent vital advances in bioinspired fibriform materials, focusing on the water-collection mechanisms of spindle-knot fibers, which exhibit directional droplet transport, hanging mechanism and hanging ability. Also, we evaluated their water-collection abilities on a micro- and macro-scale, which gave a better view for the design of bioinspired water-collection materials. These advances enable the significant use of bioinspired fibers in water collection, which may be applied in several other fields, such as directional transport, tissue engineering, oil-water separation and biosensors.

"Data characterizing microfabricated human blood vessels created via hydrodynamic focusing"

This data article provides further detailed information related to our research article titled “Microfabricated Blood Vessels Undergo Neovascularization” (DiVito et al., 2017) [1], in which we report fabrication of human blood vessels using hydrodynamic focusing (HDF). Hydrodynamic focusing with advection inducing chevrons were used in concert to encase one fluid stream within another, shaping the inner core fluid into ‘bullseye-like” cross-sections that were preserved through click photochemistry producing streams of cellularized hollow 3-dimensional assemblies, such as human blood vessels (Daniele et al., 2015a, 2015b, 2014, 2016; Roberts et al., 2016) [2], [3], [4], [5], [6]. Applications for fabricated blood vessels span general tissue engineering to organ-on-chip technologies, with specific utility in in vitro drug delivery and pharmacodynamics studies. Here, we report data regarding the construction of blood vessels including cellular composition and cell positioning within the engineered vascular construct as well as functional aspects of the tissues.

Printed microfluidic filter for heparinized blood

A simple lab-on-a-chip method for blood plasma separation was developed by combining stereolithographic 3D printing with inkjet printing, creating a completely sealed microfluidic device. In some approaches, one dilutes the blood sample before separation, reducing the concentration of a target analyte and increasing a contamination risk. In this work, a single drop (8 μl) of heparinized whole blood could be efficiently filtered using a capillary effect without any external driving forces and without dilution. The blood storage in heparin tubes during 24 h at 4 °C initiated the formation of small crystals that formed auto-filtration structures in the sample upon entering the 3D-printed device, with pores smaller than the red blood cells, separating plasma from the cellular content. The total filtration process took less than 10 s. The presented printed plasma filtration microfluidics fabricated with a rapid prototyping approach is a miniaturized, fast and easy-to-operate device that can be integrated into healthcare/portable systems for point-of-care diagnostics.

Focusing particles by induced charge electrokinetic flow in a microchannel

A novel method of sheathless particle focusing by induced charge electrokinetic flow in a microchannel is presented in this paper. By placing a pair of metal plates on the opposite walls of the channel and applying an electrical field, particle focusing is achieved due to the two pairs of vortex that constrain the flow of the particle solution. As an example, the trajectories of particles under different electrical fields with only one metal plate on one side channel wall were numerically simulated and experimentally validated. Other flow focusing effects, such as the focused width ratio (focused width/channel width) and length ratio (focused length/half-length of metal plate) of the sample solution, were also numerically studied. The results show that the particle firstly passes through the gaps between the upstream vortices and the channel walls. Afterwards, the particle is focused to pass through the gap between the two downstream vortices that determine the focused particle position. Numerical simulations show that the focused particle stream becomes thin with the increases in the applied electrical field and the length of the metal plates. As regards to the focused length ratio of the focused stream, however, it slightly increases with the increase in the applied electrical field and almost keeps constant with the increase in the length of the metal plate. The size of the focused sample solution, therefore, can be easily adjusted by controlling the applied electrical field and the sizes of the metal plates.

Microfluidic Hydrodynamic Focusing for Synthesis of Nanomaterials

Microfluidics expands the synthetic space such as heat transfer, mass transport, and reagent consumption to conditions not easily achievable in conventional batch processes. Hydrodynamic focusing in particular enables the generation and study of complex engineered nanostructures and new materials systems. In this review, we present an overview of recent progress in the synthesis of nanostructures and microfibers using microfluidic hydrodynamic focusing techniques. Emphasis is placed on distinct designs of flow focusing methods and their associated mechanisms, as well as their applications in material synthesis, determination of reaction kinetics, and study of synthetic mechanisms.

Sulfur and Its Role In Modern Materials Science

Although well-known and studied for centuries, sulfur continues to be at the center of an extensive array of scientific research topics. As one of the most abundant elements in the Universe, a major by-product of oil refinery processes, and as a common reaction site within biological systems, research involving sulfur is both broad in scope and incredibly important to our daily lives. Indeed, there has been renewed interest in sulfur-based reactions in just the past ten years. Sulfur research spans the spectrum of topics within the physical sciences including research on improving energy efficiency, environmentally friendly uses for oil refinery waste products, development of polymers with unique optical and mechanical properties, and materials produced for biological applications. This Review focuses on some of the latest exciting ways in which sulfur and sulfur-based reactions are being utilized to produce materials for application in energy, environmental, and other practical areas.

Textile Technologies and Tissue Engineering: A Path Toward Organ Weaving

Textile technologies have recently attracted great attention as potential biofabrication tools for engineering tissue constructs. Using current textile technologies, fibrous structures can be designed and engineered to attain the required properties that are demanded by different tissue engineering applications. Several key parameters such as physiochemical characteristics of fibers, microarchitecture, and mechanical properties of the fabrics play important roles in the effective use of textile technologies in tissue engineering. This review summarizes the current advances in the manufacturing of biofunctional fibers. Different textile methods such as knitting, weaving, and braiding are discussed and their current applications in tissue engineering are highlighted.

Three-dimensional hydrodynamic focusing microfluidic emitter: a strategy to inhibit sample ion expansion in nanoelectrospray ionization

A proposed 3D HFNE was used to generate a wrapped electrospray to achieve the inhibition of sample ion expansion, thus restraining injection loss in electrospray ionization.

Mechanical and physical properties of poly(vinyl alcohol) microfibers fabricated by a microfluidic approach

A microfluidic platform was used to fabricate polyvinyl alcohol microfibers with various morphology and mechanical properties.

Sheath-flow microfluidic approach for combined surface enhanced Raman scattering and electrochemical detection

The combination of hydrodynamic focusing with embedded capillaries in a microfluidic device is shown to enable both surface enhanced Raman scattering (SERS) and electrochemical characterization of analytes at nanomolar concentrations in flow. The approach utilizes a versatile polystyrene device that contains an encapsulated microelectrode and fluidic tubing, which is shown to enable straightforward hydrodynamic focusing onto the electrode surface to improve detection. A polydimethyslsiloxane (PDMS) microchannel positioned over both the embedded tubing and SERS active electrode (aligned ∼200 μm from each other) generates a sheath flow that confines the analyte molecules eluting from the embedded tubing over the SERS electrode, increasing the interaction between the Riboflavin (vitamin B2) and the SERS active electrode. The microfluidic device was characterized using finite element simulations, amperometry, and Raman experiments. This device shows a SERS and amperometric detection limit near 1 and 100 nM, respectively. This combination of SERS and amperometry in a single device provides an improved method to identify and quantify electroactive analytes over either technique independently.

Microfluidic fabrication of chitosan microfibers with controllable internals from tubular to peapod-like structures

Chitosan microfibers with controllable internals from tubular to peapod-like structures are fabricated from microfluidics for microfluid transport and synergistic encapsulation.