Integrating Bio-Sensing Array with Blood Plasma Separation on a Centrifugal Platform.

Numerous immunoassays have been successfully integrated on disc-based centrifugal platforms (CDs) over the last 20 years. These CD devices can be used as portable point-of-care (POC) platforms with sample-to-answer capabilities where bodily fluids such as whole blood can be used as samples directly without pre-processing. In order to use whole blood as a sample on CDs, centrifugation is used to separate red blood cells from plasma on CDs. There are several techniques for using specific fluidic patterns in the centrifugal fluidic network, such as reciprocation, that enhances the sensitivity of the immunoassays, including those using microarray antigen membranes. Present work demonstrates, for the first time, simultaneous integration of blood plasma separation (BPS) and reciprocation on the CD platform. The integrated design allows plasma that is separated from the red blood cells in a sedimentation chamber to flow into the reciprocation chamber via a narrow connecting channel of 0.5 mm × 0.5 mm cross-section. Due to the small cross-section of the connecting channel, there is no inflow of the red blood cell into the reciprocation chamber during subsequent fluidic operations of the CD. While no inflow of the red blood cells into the reciprocation chamber was observed, the conditions of 20 g jerk acceleration were also simulated in ANSYS finite element analysis software, and it was found that the CD design that was used is capable of retaining red blood cells in the sedimentation chamber. Experimentally, the isolation of red blood cells in the sedimentation chamber was confirmed using the ImageJ image processor to detect the visible color-based separation of the plasma from the blood. A fluorescent analyte testing on the bio-sensing array of the presented novel integrated design and on the standard reciprocation design CD was conducted for 7 min of reciprocation in each case. The test analyte was Europium Streptavidin Polystyrene analyte (10-3 mg/mL) and the microarray consisted of Biotin bovine serum albumin (BSA) dots. The fluorescent signals for the standard and integrated designs were nearly identical (within the margin of error) for the first several minutes of reciprocation, but the fluorescent signal for the integrated design was significantly higher when the reciprocation time was increased to 7 min.

Microvalves for Applications in Centrifugal Microfluidics.

Centrifugal microfluidic platforms (CDs) have opened new possibilities for inexpensive point-of-care (POC) diagnostics. They are now widely used in applications requiring polymerase chain reaction steps, blood plasma separation, serial dilutions, and many other diagnostic processes. CD microfluidic devices allow a variety of complex processes to transfer onto the small disc platform that previously were carried out by individual expensive laboratory equipment requiring trained personnel. The portability, ease of operation, integration, and robustness of the CD fluidic platforms requires simple, reliable, and scalable designs to control the flow of fluids. Valves play a vital role in opening/closing of microfluidic channels to enable a precise control of the flow of fluids on a centrifugal platform. Valving systems are also critical in isolating chambers from the rest of a fluidic network at required times, in effectively directing the reagents to the target location, in serial dilutions, and in integration of multiple other processes on a single CD. In this paper, we review the various available fluidic valving systems, discuss their working principles, and evaluate their compatibility with CD fluidic platforms. We categorize the presented valving systems into either "active", "passive", or "hybrid"-based on their actuation mechanism that can be mechanical, thermal, hydrophobic/hydrophilic, solubility-based, phase-change, and others. Important topics such as their actuation mechanism, governing physics, variability of performance, necessary disc spin rate for valve actuation, valve response time, and other parameters are discussed. The applicability of some types of valves for specialized functions such as reagent storage, flow control, and other applications is summarized.

Fabrication of polymer and carbon polyhedra through controlled cross-linking and capillary deformations.

Fabrication of polymer polyhedral structures is achieved by first producing origami sheets with dissimilar stiffness levels at their folds and faces via multi-step photolithography. Subsequent capillary folding of the sheets towards permanently folded target shapes is realized by thermally controlling, simultaneously, the compliance of the sheets and the volume of the deposited droplets. This fabrication method allows us to create millimeter and sub-millimeter polyhedral structures with arbitrary levels of folding, to manufacture permanently folded polymer polyhedra using single-material monolayer sheets, and to produce carbon shapes from these carbon-rich polymer polyhedra through pyrolysis.

Rapid Iodine Sensing on Mechanically Treated Carbon Nanofibers.

In this work, we report on a rapid, efficient electrochemical iodine sensor based on mechanically treated carbon nanofiber (MCNF) electrodes. The electrode’s highly graphitic content, unique microstructure, and the presence of nitrogen heteroatoms in its atomic lattice contribute to increased heterogeneous electron transfer and improved kinetics compared to conventional pyrolytic carbons. The electrode demonstrates selectivity for iodide ions in the presence of both interfering agents and high salt concentrations. The sensor exhibits clinically relevant limits of detection of 0.59 µM and 1.41 µM, in 1X PBS and synthetic urine, respectively, and a wide dynamic range between 5 µM and 700 µM. These results illustrate the advantages of the material’s unique electrochemical properties for iodide sensing, in addition to its simple, inexpensive fabrication. The reported iodine sensor eliminates the need for specimen processing, revealing its aptitude for applications in point-of-care diagnostics.

Nitrogen-Rich Polyacrylonitrile-Based Graphitic Carbons for Hydrogen Peroxide Sensing.

Catalytic substrate, which is devoid of expensive noble metals and enzymes for hydrogen peroxide (H2O2), reduction reactions can be obtained via nitrogen doping of graphite. Here, we report a facile fabrication method for obtaining such nitrogen doped graphitized carbon using polyacrylonitrile (PAN) mats and its use in H2O2 sensing. A high degree of graphitization was obtained with a mechanical treatment of the PAN fibers embedded with carbon nanotubes (CNT) prior to the pyrolysis step. The electrochemical testing showed a limit of detection (LOD) 0.609 µM and sensitivity of 2.54 µA cm-2 mM-1. The promising sensing performance of the developed carbon electrodes can be attributed to the presence of high content of pyridinic and graphitic nitrogens in the pyrolytic carbons, as confirmed by X-ray photoelectron spectroscopy. The reported results suggest that, despite their simple fabrication, the hydrogen peroxide sensors developed from pyrolytic carbon nanofibers are comparable with their sophisticated nitrogen-doped graphene counterparts.

Polymethacrylate Coated Electrospun PHB Fibers as a Functionalized Platform for Bio-Diagnostics: Confirmation Analysis on the Presence of Immobilized IgG Antibodies against Dengue Virus.

In this article, a combination of far field electrospinning (FFES) and free-radical polymerization has been used to create a unique platform for protein immobilization via the physical attachment of biomolecules to the surface of the fiber mats. The large specific surface area of the fibers with its tailored chemistry provides a desirable platform for effective analyte-surface interaction. The detailed analysis of protein immobilization on a newly developed bio-receptive surface plays a vital role to gauge its advantages in bio-diagnostic applications. We relied on scanning electron microscopy (SEM), diameter range analysis, and X-ray photoelectron spectroscopy (XPS), along with thermal gravimetric analysis (TGA), water-in-air contact angle analysis (WCA), Fourier transform infrared spectroscopy (FTIR), and atomic force microscopy (AFM) to study our developed platforms and to provide valuable information regarding the presence of biomolecular entities on the surface. Detailed analyses of the fiber mats before and after antibody immobilization have shown obvious changes on the surface of the bioreceptive surface including: (i) an additional peak corresponding to the presence of an antibody in TGA analysis; (ii) extra FTIR peaks corresponding to the presence of antibodies on the coated fiber platforms; and (iii) a clear alteration in surface roughness recorded by AFM analysis. Confirmation analyses on protein immobilization are of great importance as they underlay substantial grounds for various biosensing applications.

Development of a passive liquid valve (PLV) utilizing a pressure equilibrium phenomenon on the centrifugal microfluidic platform.

In this paper, we propose an easy-to-implement passive liquid valve (PLV) for the microfluidic compact-disc (CD). This valve can be implemented by introducing venting chambers to control the air flow of the source and destination chambers. The PLV mechanism is based on equalizing the main forces acting on the microfluidic CD (i.e., the centrifugal and capillary forces) to control the burst frequency of the source chamber liquid. For a better understanding of the physics behind the proposed PLV, an analytical model is described. Moreover, three parameters that control the effectiveness of the proposed valve, i.e., the liquid height, liquid density, and venting chamber position with respect to the CD center, are tested experimentally. To demonstrate the ability of the proposed PLV valve, microfluidic liquid switching and liquid metering are performed. In addition, a Bradford assay is performed to measure the protein concentration and evaluated in comparison to the benchtop procedure. The result shows that the proposed valve can be implemented in any microfluidic process that requires simplicity and accuracy. Moreover, the developed valve increases the flexibility of the centrifugal CD platform for passive control of the liquid flow without the need for an external force or trigger.

Three-dimensional carbon interdigitated electrode arrays for redox-amplification.

Three-dimensional (3D) carbon interdigitated electrode arrays (IDEAs) were fabricated using inexpensive, conventional, UV photolithography of SU-8 with modified exposure and post exposure bake settings followed by pyrolysis in an inert environment. The sensor performance was investigated as a function of both the IDEA digit width/gap ratio and digit height under flow and no flow conditions. We demonstrated a gradual increase in redox amplification with an increase in the IDEA digit width/gap ratio. The highest amplification of 37 was obtained for a width/gap ratio of 1.58 and for an electrode height of 1.1 µm. Redox amplification also increases significantly with an increase in the IDEA height, from a factor of 9 at a 0.22 µm digit height to a factor of 37 at a 1.1 µm height. The effect of potential sweep rates on redox amplification was also investigated. As the sweep rate was decreased from 50 mV/s to 5 mV/s, the collection efficiency increased from 0.92 to 0.97, whereas the amplification increased from 7 to 25. Under flow conditions, the amplification decreases substantially as the cycling of the redox species is impeded by convection, resulting in a drop in collection efficiency. The highest amplification of 37 dropped to 4 for the same electrode at a flow rate of 500 nL/s. Under flow, redox amplification increased with an increase in the IDEA height.

A roadmap to high-speed polymerase chain reaction (PCR): COVID-19 as a technology accelerator.

The limit of detection (LOD), speed, and cost of crucial COVID-19 diagnostic tools, including lateral flow assays (LFA), enzyme-linked immunosorbent assays (ELISA), and polymerase chain reactions (PCR), have all improved because of the financial and governmental support for the epidemic. The most notable improvement in overall efficiency among them has been seen with PCR. Its significance for human health increased during the COVID-19 pandemic, when it emerged as the commonly used approach for identifying the virus. However, because of problems with speed, complexity, and expense, PCR deployment in point-of-care settings continues to be difficult. Microfluidic platforms offer a promising solution by enabling the development of smaller, more affordable, and faster PCR systems. In this review, we delve into the engineering challenges associated with the advancement of high-speed microfluidic PCR equipment. We introduce criteria that facilitate the evaluation and comparison of factors such as speed, LOD, cycling efficiency, and multiplexing capacity, considering sample volume, fluidics, PCR reactor geometry and materials, as well as heating/cooling methods. We also provide a comprehensive list of commercially available PCR devices and conclude with projections and a discussion regarding the current obstacles that need to be addressed in order to progress further in this field.

Doxorubicin Conjugated γ-Globulin Functionalised Gold Nanoparticles: A pH-Responsive Bioinspired Nanoconjugate Approach for Advanced Chemotherapeutics.

Developing successful nanomedicine hinges on regulating nanoparticle surface interactions within biological systems, particularly in intravenous nanotherapeutics. We harnessed the surface interactions of gold nanoparticles (AuNPs) with serum proteins, incorporating a γ-globulin (γG) hard surface corona and chemically conjugating Doxorubicin to create an innovative hybrid anticancer nanobioconjugate, Dox-γG-AuNPs. γG (with an isoelectric point of ~7.2) enhances cellular uptake and exhibits pH-sensitive behaviour, favouring targeted cancer cell drug delivery. In cell line studies, Dox-γG-AuNPs demonstrated a 10-fold higher cytotoxic potency compared to equivalent doxorubicin concentrations, with drug release favoured at pH 5.5 due to the γ-globulin corona's inherent pH sensitivity. This bioinspired approach presents a novel strategy for designing hybrid anticancer therapeutics. Our study also explored the intricacies of the p53-mediated ROS pathway's role in regulating cell fate, including apoptosis and necrosis, in response to these treatments. The pathway's delicate balance of ROS emerged as a critical determinant, warranting further investigation to elucidate its mechanisms and implications. Overall, leveraging the robust γ-globulin protein corona on AuNPs enhances biostability in harsh serum conditions, augments anticancer potential within pH-sensitive environments, and opens promising avenues for bioinspired drug delivery and the design of novel anticancer hybrids with precise targeting capabilities.

Rational PCR Reactor Design in Microfluidics.

Limit of detection (LOD), speed, and cost for some of the most important diagnostic tools, i.e., lateral flow assays (LFA), enzyme-linked immunosorbent assays (ELISA), and polymerase chain reaction (PCR), all benefited from both the financial and regulatory support brought about by the pandemic. From those three, PCR has gained the most in overall performance. However, implementing PCR in point of care (POC) settings remains challenging because of its stringent requirements for a low LOD, multiplexing, accuracy, selectivity, robustness, and cost. Moreover, from a clinical point of view, it has become very desirable to attain an overall sample-to-answer time (t) of 10 min or less. Based on those POC requirements, we introduce three parameters to guide the design towards the next generation of PCR reactors: the overall sample-to-answer time (t); lambda (λ), a measure that sets the minimum number of copies required per reactor volume; and gamma (γ), the system's thermal efficiency. These three parameters control the necessary sample volume, the number of reactors that are feasible (for multiplexing), the type of fluidics, the PCR reactor shape, the thermal conductivity, the diffusivity of the materials used, and the type of heating and cooling systems employed. Then, as an illustration, we carry out a numerical simulation of temperature changes in a PCR device, discuss the leading commercial and RT-qPCR contenders under development, and suggest approaches to achieve the PCR reactor for RT-qPCR of the future.

Fabrication of a three-dimensional micro/nanocarbon structure with sub-10 nm carbon fiber arrays based on the nanoforming and pyrolysis of polyacrylonitrile-based jet fibers.

To produce a three-dimensional micro/nanocarbon structure, a manufacturing design technique for sub-10 nm carbon fiber arrays on three-dimensional carbon micropillars has been developed; the method involves initiating electrostatic jetting, forming submicron-to-nanoscale PAN-based fibers, and maximizing the shrinkage from polyacrylonitrile (PAN)-based fibers to carbon fibers. Nanoforming and nanodepositing methods for polyacrylonitrile-based jet fibers as precursors of carbon fibers are proposed for the processing design of electrostatic jet initiation and for the forming design of submicron-to-nanoscale PAN-based fibers by establishing and analyzing mathematical models that include the diameter and tensile stress values of jet fibers and the electric field intensity values on the surfaces of carbon micropillars. In accordance with these methods, an array of jet fibers with diameters of ~80 nm is experimentally formed based on the thinning of the electrospinning fluid on top of a dispensing needle, the poking of drum into an electrospinning droplet, and the controlling of the needle-drum distance. When converting thin PAN-based jet fibers to carbon fibers, a pyrolysis method consisting of the suspension of jet nanofibers between carbon micropillars, the bond between the fibers and the surface of the carbon micropillar, and the control of micropillar spacing, stabilization temperature, and carbonation rate is presented to maximize the shrinkage from PAN-based fibers to carbon fibers and to form sub-10 nm carbon fiber arrays between three-dimensional carbon micropillars. The manufacturing design of a three-dimensional micro/nanocarbon structure can produce thin PAN-based jet nanofibers and nanofiber arrays aligned on micropillar surfaces, obtain shrinkage levels reaching 96% and incorporate sub-10 nm carbon fibers into three-dimensional carbon micropillars; these actions provide new research opportunities for correlated three-dimensional micro/nanocarbon structures that have not previously been technically possible.

Theoretical analysis of immunochromatographic assay and consideration of its operating parameters for efficient designing of high-sensitivity cardiac troponin I (hs-cTnI) detection.

Troponin is the American College of Cardiology and American Heart Association preferred biomarker for diagnosing acute myocardial infarction (MI). We provide a modeling framework for high sensitivity cardiac Troponin I (hs-cTnI) detection in chromatographic immunoassays (flow displacement mode) with an analytical limit of detection, i.e., LOD < 10 ng/L. We show that each of the various control parameters exert a significant influence over the design requirements to reach the desired LOD. Additionally, the design implications in a multiplexed fluidic network, as in the case of Simple Plex™ Ella instrument, are significantly affected by the choice of the number of channels or partitions in the network. We also provide an upgrade on the existing LOD equation to evaluate the necessary minimum volume to detect a particular concentration by considering the effects of stochastics and directly incorporating the target number of copies in each of the partitions in case of multiplexed networks. Even though a special case of cTnI has been considered in this study, the model and analysis are analyte agnostic and may be applied to a wide class of chromatographic immunoassays. We believe that this contribution will lead to more efficient designing of the immunochromatographic assays.

Nitrogen-functionalized graphene quantum dot incorporated GelMA microgels as fluorescent 3D-tissue Constructs.

Biopolymer microgels present many opportunities in biomedicine and tissue engineering. To understand their in vivo behavior in therapeutic interventions, long-term monitoring is critical, which is usually achieved by incorporating fluorescent materials within the hydrogel matrix. Current research is limited due to issues concerning the biocompatibility and instability of the conventional fluorescent species, which also tend to adversely affect the bio-functionality of the hydrogels. Here, we introduce a microfluidic-based approach to generate nitrogen-functionalized graphene quantum dot (NGQD) incorporated gelatin methacryloyl (GelMA) hydrogel microspheres, capable of long-term monitoring while preserving or enhancing the other favorable features of 3D cell encapsulation. A multilayer droplet-based microfluidic device was designed and fabricated to make monodisperse NGQD-loaded GelMA hydrogel microspheres encapsulating skeletal muscle cells (C2C12). Control over the sizes of microspheres could be achieved by tuning the flow rates in the microfluidic device. Skeletal muscle cells encapsulated in these microgels exhibited high cell viability from day 1 (82.9 ± 6.50%) to day 10 (92.1 ± 3.90%). The NGQD-loaded GelMA microgels encapsulating the cells demonstrated higher metabolic activity compared to the GelMA microgels. Presence of sarcomeric α-actin was verified by immunofluorescence staining on day 10. A fluorescence signal was observed from the NGQD-loaded microgels during the entire period of the study. The investigation reveals the advantages of integrating NGQDs in microgels for non-invasive imaging and monitoring of cell-laden microspheres and presents new opportunities for future therapeutic applications.

Diffusion-free mediator based miniature biofuel cell anode fabricated on a carbon-MEMS electrode.

We report on the functionalization of a micropatterned carbon electrode fabricated using the carbon-MEMS process for its use as a miniature diffusion-free glucose oxidase anode. Carbon-MEMS based electrodes offer precise manufacturing control on both the micro- and nanoscale and possess higher electron conductivity than redox hydrogels. However, the process involves pyrolysis in a reducing environment that renders the electrode surface less reactive and introduction of a high density of functional groups becomes challenging. Our functionalization strategy involves the electrochemical oxidation of amine linkers onto the electrode. This strategy works well with both aliphatic and aryl linkers and uses stable compounds. The anode is designed to operate through mediated electron transfer between 2,5-dihydroxybenzaldehyde (DHB) based redox mediator and glucose oxidase enzyme. The electrode was first functionalized with ethylene diamine (EDA) to serve as a linker for the redox mediator. The redox mediator was then grafted through reductive amination, and attachment was confirmed through cyclic voltammetry. The enzyme immobilization was carried out through either adsorption or attachment, and their efficiency was compared. For enzyme attachment, the DHB attached electrode was functionalized again through electro-oxidation of aminobenzoic acid (ABA) linker. The ABA functionalization resulted in reduction of the DHB redox current, perhaps due to increased steric hindrance on the electrode surface, but the mediator function was preserved. Enzyme attachment was then carried out through a coupling reaction between the free carboxyl group on the ABA linker and the amine side chains on the enzyme. The enzyme incubation for both adsorption and attachment was done either through a dry spotting method or wet spotting method. The dry spotting method calls for the evaporation of enzyme droplet to form a thin film before sealing the electrode environment, to increase the effective concentration of the enzyme on the electrode surface during incubation. The electrodes were finally protected with a gelatin based hydrogel film. The anode half-cell was tested using cyclic voltammetry in deoxygenated phosphate buffer saline solution pH 7.4 to minimize oxygen interference and to simulate the pH environment of the body. The electrodes that yielded the highest anodic current were prepared by enzyme attachment method with dry spotting incubation. A polarization response was generated for this anodic half-cell and exhibits operation close to maximum efficiency that is limited by the mass transport of glucose to the electrode.

Controlled continuous patterning of polymeric nanofibers on three-dimensional substrates using low-voltage near-field electrospinning.

We report on a continuous method for controlled electrospinning of polymeric nanofibers on two-dimensional (2D) and three dimensional (3D) substrates using low voltage near-field electrospinning (LV NFES). The method overcomes some of the drawbacks in more conventional near-field electrospinning by using a superelastic polymer ink formulation. The viscoelastic nature of our polymer ink enables continuous electrospinning at a very low voltage of 200 V, almost an order of magnitude lower than conventional NFES, thereby reducing bending instabilities and increasing control of the resulting polymer jet. In one application, polymeric nanofibers are freely suspended between microstructures of 3D carbon on Si substrates to illustrate wiring together 3D components in any desired pattern.

Elastic membrane enabled inward pumping for liquid manipulation on a centrifugal microfluidic platform.

Nowadays, centrifugal microfluidic platforms are finding wider acceptance for implementing point-of-care assays due to the simplicity of the controls, the versatility of the fluidic operations, and the ability to create a self-enclosed system, thus minimizing the risk of contamination for either the sample or surroundings. Despite these advantages, one of the inherent weaknesses of CD microfluidics is that all the sequential fluidic chambers and channels must be positioned radially since the centrifugal force acts from the center of the disk outward. Implementation of schemes where the liquid can be rerouted from the disk periphery to the disk center would significantly increase the utility of CD platforms and increase the rational utilization of the real estate on the disk. The present study outlines a novel utilization of elastic membranes covering fluidic chambers to implement inward pumping whereby the fluid is returned from the disk periphery to the center of the disk. When the disk revolves at an angular velocity of 3600 rpm, liquid enters the chamber covered by the elastic membrane. This membrane is deflected upward by liquid, storing energy like a compressed spring. When the angular velocity of the disk is reduced to 180 rpm and thus the centrifugal force is diminished, the elastic membrane pushes the liquid from the chamber inward, closer to the center of the disk. There are two channels leading from the elastic membrane-covered reservoir-one channel has a higher fluidic resistance and the other (wider) has a lower fluidic resistance. The geometry of these two channels determines the fluidic path inward (toward the center of the disk). Most of the liquid travels through the recirculating channel with lower resistance. We demonstrated an inward pumping efficiency in the range of 78%-89%. Elastic membrane-driven inward pumping was demonstrated for the application of enhanced fluid mixing. Additionally, to demonstrate the utility of the proposed pumping mechanism for multi-step assays on the disk, we implemented and tested a disk design that combines plasma separation and inward pumping.

Fabrication of crystalline submicro-to-nano carbon wire for achieving high current density and ultrastable current.

Crystalline carbon nanowire arrays were fabricated taking advantage of near-field electrospinning and stress decyanation. A novel fabrication method for carbon nanowires with radii ranging from ~2.15 µm down to ~25 nm was developed based on implementing nitrogen pretreatment on the silica surface and then aligning polymer nanofibers during near-field electrospinning at an ultralow voltage. Stress decyanation was implemented by subsequently pyrolyzing a polymer nanofiber array on the silica surface at 1000 °C for 1 h in an N2 atmosphere, thus obtaining a crystalline carbon nanowire array with a nanostructured surface. Various crystalline nanostructures were fabricated on the nanowire surface, and their electrochemical performance was evaluated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Crystalline carbon wires with diameters ranging from micrometers to submicrometers displayed carbon nanoelectrode-like behavior with their CV curve having a sigmoidal shape. A highly crystalline carbon nanowire array showed distinct behavior, having a monotonically increasing straight line as its CV curve and a semicircular EIS spectrum; these results demonstrated its ultrastable current, as determined by electron transfer. Furthermore, nanocrystalline-structured carbon wires with diameters of ~305 nm displayed at least a fourfold higher peak current density during CV (4000 mA/m2) than highly crystalline carbon nanowires with diameters of ~100 nm and porous microwires with diameters of ~4.3 µm.

Micro and Nano Interdigitated Electrode Array (IDEA)-Based MEMS/NEMS as Electrochemical Transducers: A Review.

Micro and nano interdigitated electrode array (µ/n-IDEA) configurations are prominent working electrodes in the fabrication of electrochemical sensors/biosensors, as their design benefits sensor achievement. This paper reviews µ/n-IDEA as working electrodes in four-electrode electrochemical sensors in terms of two-dimensional (2D) planar IDEA and three-dimensional (3D) IDEA configurations using carbon or metal as the starting materials. In this regard, the enhancement of IDEAs-based biosensors focuses on controlling the width and gap measurements between the adjacent fingers and increases the IDEA's height. Several distinctive methods used to expand the surface area of 3D IDEAs, such as a unique 3D IDEA design, integration of mesh, microchannel, vertically aligned carbon nanotubes (VACNT), and nanoparticles, are demonstrated and discussed. More notably, the conventional four-electrode system, consisting of reference and counter electrodes will be compared to the highly novel two-electrode system that adopts IDEA's shape. Compared to the 2D planar IDEA, the expansion of the surface area in 3D IDEAs demonstrated significant changes in the performance of electrochemical sensors. Furthermore, the challenges faced by current IDEAs-based electrochemical biosensors and their potential solutions for future directions are presented herein.

Characterization of Fluidic-Barrier-Based Particle Generation in Centrifugal Microfluidics.

The fluidic barrier in centrifugal microfluidic platforms is a newly introduced concept for making multiple emulsions and microparticles. In this study, we focused on particle generation application to better characterize this method. Because the phenomenon is too fast to be captured experimentally, we employ theoretical models to show how liquid polymeric droplets pass a fluidic barrier before crosslinking. We explain how secondary flows evolve and mix the fluids within the droplets. From an experimental point of view, the effect of different parameters, such as the barrier length, source channel width, and rotational speed, on the particles' size and aspect ratio are investigated. It is demonstrated that the barrier length does not affect the particle's ultimate velocity. Unlike conventional air gaps, the barrier length does not significantly affect the aspect ratio of the produced microparticles. Eventually, we broaden this concept to two source fluids and study the importance of source channel geometry, barrier length, and rotational speed in generating two-fluid droplets.