Fluidic Cell Research Articles

Electroresponsive Structurally Colored Materials: A Combination of Structural and Electrochromic Effects.

Electroresponsive structurally colored materials composed of ordered arrays of polyaniline@poly(methyl methacrylate) (PANI@PMMA) core-shell nanoparticles have been successfully prepared. The core-shell nanoparticles were synthesized by deposition of PANI shells on the surfaces of the PMMA cores by the oxidative polymerization of anilinium chloride. Ordered arrays were then fabricated by using the fluidic cell method. Because the ordered arrays and the PANI shells generate structural and electrochromic colors, respectively, these core-shell colloidal crystals exhibited colors resulting from the combined effects of these materials. The crystal colors depended greatly on the size of PANI@PMMA particles and could also be varied by the application of a voltage. The electrochromic colors of these arrays were found to be quite different from those exhibited by pure PANI films prepared by electrochemical oxidation.

A microfluidic electrochemical biosensor based on multiwall carbon nanotube/ferrocene for genomic DNA detection of Mycobacterium tuberculosis in clinical isolates.

Herein we present a microfluidic-multiplexed platform that integrates electrochemical sensors based on carbon nanotubes associated with ferrocene as redox marker (carbon nanotube (CNT)/ferrocene) for direct detection of pathogenic viral DNA from Hepatitis C and genomic DNA from Mycobacterium tuberculosis in clinical isolates. By operating the fluidic device under high flow (150 μl/min), the formation of a very thin depletion layer at the sensor surface (δS = 230 nm) enhances the capture rate up to one DNA strand per second. By comparison, this capture rate is only 0.02 molecule/s in a static regime without flow. This fluidic protocol allows thus enhancing the limit of detection of the electrochemical biosensor from picomolar in bulk solution to femtomolar with a large dynamic range from 0.1 fM to 1 pM. Kinetics analysis also demonstrates an enhancement of the rate constant of electron transfer (kS) of the electrochemical process from 1 s(-1) up to 6 s(-1) thanks to the geometry of the miniaturized fluidic electrochemical cell. This microfluidic device working under high flow allows selective direct detection of a Mycobacterium tuberculosis (H37Rv) rpoB allele from clinical isolate extracted DNA. We envision that a microfluidic approach under high flow associated with a multiwall CNT/ferrocene sensor could find useful applications as the point-of-care for multi-target diagnostics of biomarkers in real samples.

Additive Manufacturing and Electrochemistry

The Electrochemical Society Interface • Spring 2016 • www.electrochem.org 61 A lthough there has been tremendous growth in the capabilities of additive manufacturing in recent years, its roots go back hundreds of years. In many ways, some of the first electrochemists were also the first practitioners of additive manufacturing when they demonstrated that a low cost base metal could be coated with a premium finish in a conformal manner at room temperature in minutes. The first electrodeposition experiments date back over 200 years when Luigi Valentino Brugnatelli first electrodeposited gold upon silver, at first for academic experiments, and then for commercial application. Since that time, scaled commercial applications of electrodeposition have been critical to many aspects of science and engineering. More recently, the emergence of affordable, commercially-available 3D printers capable of depositing electrically insulating media via extrusion printing and additive photocuring methods have offered a wonderful complement to traditional electrodeposition, enabling both rapid prototyping and precise, high-throughput freeform manufacturing. In this issue of Interface we explore some of the benefits and opportunities that modern additive manufacturing methods offer for the practice of electrochemical analysis, engineering, and energy storage. In the first paper of this issue, Robert B. Channon, Maxim B. Joseph and Julie V. Macpherson, demonstrate the use of low cost additive manufacturing based on stereolithography, to create (micro) fluidic flow cells at scales that are either difficult or impossible to achieve with traditional methods. The ability to create high resolution, customized flow cells allows researchers to study fluid transport and electrochemical phenomena, as well as enabling highly accurate electroanalytical sensing with small analyte volumes and high throughput for a wide range of applications. With the methods described in this section, (micro)fluidic analysis systems can go from a sketch to a practical system within an afternoon, and that same device can be effortlessly replicated with slight variations in device geometry to create an array of parallel experiments. Trevor Braun and Dan Schwartz provide an article exploring the intersection of freeform patterning and electrodeposition with the use of software reconfigurable scanning electrodeposition cells. In traditional electrodeposition, the volume of the electrolyte is far larger than that of the deposited materials. This article shows that when the ratio is inverted, the small electrolyte volume can be used to direct growth and structure in exceptional ways without the limitations of traditional maskor stamp-based patterning techniques. Another exciting development that is discussed in this article is the use of bipolar electrochemistry to perform localized freeform electrodeposition without an electrical contact to the substrate, a development that greatly expands the utility and throughput of electrodeposition-based additive manufacturing. The final paper by Corrie Cobb and Christine Ho demonstrates how additive manufacturing and rapid prototyping methods can improve the performance and the range of applications of electrochemical energy storage. Given the particle/composite structure of most secondary storage devices, the materials selection available is largely the same as those for traditional batteries. A device designer, using the methods described here, can embed a battery optimized not only between power and energy density, but also between conformable, flexible, and stretchable factors. Critical to this new paradigm in product design is a deep level of interaction between the design of the battery, powertrain, and the device itself. With modern rapid prototyping methods, all three components can be iteratively edited and optimized with unprecedented speed. Beyond device integration, these new manufacturing methods for batteries may improve batteries for traditional applications: Rational integration of separator and electrode can allow for thicker electrodes at a given power density, improving cost per unit energy and energy density at a system level. Taken together, these three pieces provide an excellent overview of how recent advances in electrochemical engineering and electroanalytical tools can be merged with modern prototyping tools to create new opportunities for sensing, device production, and electrochemical energy storage. However, we believe that these examples are only the tip of the iceberg, and that the integration of electrochemical engineering and additive manufacturing will only accelerate in the years to come. While these articles are not meant to be comprehensive reviews of additive manufacturing, we hope that they inspire Interface readers to learn more about these powerful new tools and invent novel ways that additive manufacturing can advance electrochemistry, and that electrochemistry can advance additive manufacturing. Electrochemical engineering, the first in additive manufacturing and rapid prototyping, still has much to contribute to this growing field. In the spirit of access knowledge sharing, DS has recently created a website (echem.io) where users can share (via GitHub) 3D cad design files and other open source hardware and software tools that were generated as a part of electrochemistry-focused research and development efforts. We hope you check it out!

Fluidic origami with embedded pressure dependent multi-stability: a plant inspired innovation.

Inspired by the impulsive movements in plants, this research investigates the physics of a novel fluidic origami concept for its pressure-dependent multi-stability. In this innovation, fluid-filled tubular cells are synthesized by integrating different Miura-Ori sheets into a three-dimensional topological system, where the internal pressures are strategically controlled similar to the motor cells in plants. Fluidic origami incorporates two crucial physiological features observed in nature: one is distributed, pressurized cellular organization, and the other is embedded multi-stability. For a single fluidic origami cell, two stable folding configurations can coexist due to the nonlinear relationships among folding, crease material deformation and internal volume change. When multiple origami cells are integrated, additional multi-stability characteristics could occur via the interactions between pressurized cells. Changes in the fluid pressure can tailor the existence and shapes of these stable folding configurations. As a result, fluidic origami can switch between being mono-stable, bistable and multi-stable with pressure control, and provide a rapid 'snap-through' type of shape change based on the similar principles as in plants. The outcomes of this research could lead to the development of new adaptive materials or structures, and provide insights for future plant physiology studies at the cellular level.

Fluidic origami: a plant-inspired adaptive structure with shape morphing and stiffness tuning

Inspired by the physics behind the rapid plant movements and the rich topologies in origami folding, this research creates a unique class of multi-functional adaptive structure through exploring the innovation of fluidic origami. The idea is to connect multiple Miura folded sheets along their crease lines into a space-filling structure, and fill the tubular cells in-between with working fluids. The pressure and fluid flow in these cells can be strategically controlled much like in plants for nastic movements. The relationship between the internal fluid volume and the overall structure deformation is primarily determined by the kinematics of folding. This relationship can be exploited so that fluidic origami can achieve actuation/morphing by actively changing the internal fluid volume, and stiffness tuning by constraining the fluid volume. In order to characterize the working principles and performance potentials of these two adaptive functions, this research develops an equivalent truss frame model on a fluidic origami unit cell to analyze its fundamental elastic characteristics. Eigen-stiffness analysis based on this model reveals the primary modes of deformation and their relationships with initial folding configurations. Performances of the adaptive functions are correlated to the crease pattern design. In parallel to analytical studies, the feasibility of the morphing and stiffness tuning is also examined experimentally via a 3D printed multi-material prototype demonstrator. The research reported in this paper could lead to the synthesis of adaptive fluidic origami cellular metastructures or metamaterial systems for various engineering applications.

Disposable Plasmonics: Plastic Templated Plasmonic Metamaterials with Tunable Chirality.

Development of low-cost disposable plasmonic substrates is vital for the applicability of plasmonic sensing. Such devices can be made using injection-molded templates to create plasmonic films. The elements of these plasmonic films are hybrid nanostructures composed of inverse and solid structures. Tuning the modal coupling between the two allows optimization of the optical properties for nanophotonic applications.

Polyether Ether Ketone (PEEK) Fluidic Cell to Study Electrochemistry of Microelectrodes on Silicon Substrate

A robust fixture is designed as a fluidic cell, for studying electrochemistry of planar nano/microelectrodes and electrolyte interface. The microelectrode is fabricated using standard silicon micromachining processes on a silicon wafer. The fluidic cell is built using polyether ether ketone (PEEK). The PEEK structure is machined with alignment pins and the silicon wafer is fabricated with complementary alignment fields. This ensures that the electrodes on the silicon wafer are precisely aligned to the fluidic channel and there is minimal parasitic capacitance due to the overlap of the electrode with the conducting electrolyte in the system. The set-up was used to measure current flow across the electrode-electrolyte interface. Using the set-up gold-thiol interface of area with an opening of diameter 1 μm was characterized. © 2015 The Electrochemical Society. [DOI: 10.1149/2.0021510ssl] All rights reserved.

Label-Free Detection of Tumor Angiogenesis Biomarker Angiopoietin 2 Using Bloch Surface Waves on One Dimensional Photonic Crystals

We describe the design and fabrication of biochips based on 1-D photonic crystals supporting Bloch surface waves for label-free optical biosensing. The optical properties of Bloch surface waves are studied in relation to the geometry of the photonic crystals and on the properties of the dielectric materials used for the fabrication. The planar stacks of the biochips are composed of silica, tantala, and titania that were deposited using plasma-ion-assisted evaporation under high-vacuum conditions. The biochip surfaces were functionalized by silanization, and appropriate fluidic cells were designed to operate in an automated platform. An angularly resolved ellipsometric optical sensing apparatus was assembled to carry out the sensing studies. The angular operation is obtained by a focused laser beam at a fixed wavelength and detection of the angular reflectance spectrum by means of an array detector. The results of the experimental characterization of the physical properties of the fabricated biochips show that their characteristics, in terms of sensitivity and figure of merit, match those expected from the numerical simulations. Practical application of the sensor was demonstrated by detecting a specific glycoprotein, Angio-poietin 2, that is involved in angiogenesis and inflammation processes. The protocol used for the label-free detection of Angiopoietin 2 is described, and the results of an exemplary assay, carried out at a relatively high concentration of 1 μg/ml, are given and confirm that an efficient detection can be achieved. The limit of detection of the biochips for Angiopoietin 2, based on the protocol used, is 1.5 pg/mm2 in buffer solution. The efficiency of the label-free assay is confirmed by independent measurements carried out by means of confocal fluorescence microscopy.

Multi-cellular 3D human primary liver cell culture elevates metabolic activity under fluidic flow.

We have developed a low-cost liver cell culture device that creates fluidic flow over a 3D primary liver cell culture that consists of multiple liver cell types, including hepatocytes and non-parenchymal cells (fibroblasts, stellate cells, and Kupffer cells). We tested the performance of the cell culture under fluidic flow for 14 days, finding that hepatocytes produced albumin and urea at elevated levels compared to static cultures. Hepatocytes also responded with induction of P450 (CYP1A1 and CYP3A4) enzyme activity when challenged with P450 inducers, although we did not find significant differences between static and fluidic cultures. Non-parenchymal cells were similarly responsive, producing interleukin 8 (IL-8) when challenged with 10 μM bacterial lipoprotein (LPS). To create the fluidic flow in an inexpensive manner, we used a rocking platform that tilts the cell culture devices at angles between ±12°, resulting in a periodically changing hydrostatic pressure drop between reservoirs and the accompanying periodically changing fluidic flow (average flow rate of 650 μL min(-1), and a maximum shear stress of 0.64 dyne cm(-2)). The increase in metabolic activity is consistent with the hypothesis that, similar to unidirectional fluidic flow, primary liver cell cultures increase their metabolic activity in response to fluidic flow periodically changes direction. Since fluidic flow that changes direction periodically drastically changes the behavior of other cells types that are shear sensitive, our findings support the theory that the increase in hepatic metabolic activity associated with fluidic flow is either activated by mechanisms other than shear sensing (for example increased opportunities for gas and metabolite exchange), or that it follows a shear sensing mechanism that does not depend on the direction of shear. Our mode of device operation allows us to evaluate drugs under fluidic cell culture conditions and at low device manufacturing and operation costs.

High performance magnesium anode in paper-based microfluidic battery, powering on-chip fluorescence assay.

A high power density and long-lasting stable/disposable magnesium battery anode was explored for a paper-based fluidic battery to power on-chip functions of various Point of Care (POC) devices. The single galvanic cell with magnesium foil anode and silver foil cathode in Origami cellulose chip provided open circuit potential, 2.2 V, and power density, 3.0 mW/cm(2). A paper-based fluidic galvanic cell was operated with one drop of water (80 μl) and continued to run until it was dry. To prove the concept about powering on-chip POC devices, two-serial galvanic cells are developed and incorporated with a UV-light emitting diode (λ = 365 nm) and fluorescence assay for alkaline phosphatase reaction. Further, detection using smart phones was performed for quantitative measurement of fluorescent density. To conclude, a magnesium-based fluidic battery paper chip was extremely low-cost, required minute sample volumes, was easy to dispose of, light weight, easy to stack, store and transport, easy to fabricate, scalable, and has faster analysis times.

Positionable vertical microfluidic cell based on electromigration in a theta pipet.

A microscale vertical fluidic cell system has been implemented, based on a simple theta pipet pulled to a sharp point (ca. 10-20 μm diameter for the studies herein) and positioned with a high degree of control on a surface. The dual channel arrangement allows an electric field to be generated between an electrode in each compartment of the pipet that can be used to control the electromigration of charged species between the two compartments, across a thin liquid meniscus in contact with the substrate of interest. By visualizing the interfacial region using laser scanning confocal microscopy, the adsorption of fluorescently-labeled materials on surfaces is monitored quantitatively in real time, exemplified through studies of the adsorption of anionic microparticles (1.1 μm diameter) on positively and negatively charged substrate surfaces of poly-L-lysine (PLL) and poly-L-glutamic acid (PGA), respectively, on glass. These studies highlight significant electrostatic effects on adsorption rates and also that the adsorption of these particles is dominated by the three phase meniscus/solid/air boundary. The technique is easily modified to the case of a submerged substrate, resulting in a much larger deposition area. Finite element method modeling is used to calculate local electric field strengths that are used to understand surface deposition patterns. To demonstrate the applicability of the technique to live biological substrates, the delivery of fluorescent particles directly to the surface of a single root hair cell of Zea mays is demonstrated. The mobile pipet allows deposition to be directed to specific regions of the cell, allowing discrete sites to be labeled with particles. Finally, the technique is used to study the uptake of fluorescent polymer molecules to single root hair cells, with quantitative analysis of the adsorption rates of vinyl-sulfonic acid copolymers, with varying rhodamine B content.

Creation of a transient vapor nanogap between two fluidic reservoirs for single molecule manipulation.

We introduce a new experimental technique for manipulating a segment of a charged macromolecule inside a transient nanogap between two fluidic reservoirs. This technique uses an FPGA-driven nanopositioner to control the coupling of a nanopipette with the liquid surface of a fluidic cell. We present results on creating a transient nanogap, triggered by a translocation of double-stranded DNA between a nanopipette and a fluidic cell, and measure the probability to find the molecule near the tip of the nanopipette after closing the gap. The developed platform will enable testing of our recent theoretical predictions for the behavior of charged macromolecule in a nanogap between two fluidic reservoirs.

Reduced graphene oxide‐based sensing platform for electric cell–substrate impedance sensing

Graphene, with its unique electrical properties and biocompatibility, has become a material of choice for the development of biosensor platforms. In this study, a microelectrode array based on reduced graphene oxide (rGO) was constructed and used as a platform for electrical monitoring of cell–substrate adhesion. The rGO‐based sensor arrays were designed in order to facilitate sensor pads comparable to the size of individual cells. The sensor chips were fabricated in a scalable manner via site‐specific immobilization of graphene oxide flakes onto microelectrode pairs followed by reduction to rGO. The sensor chips were mounted on a measurement platform equipped with a fluidic cell. Electrical characteristics were recorded and field‐effect behavior was confirmed. Sensors reacted to changes of pH value in the solution. Finally, as a proof‐of‐concept, the graphene oxide‐based sensing platform was used for electrical cell–substrate impedance sensing of individual HEK293 cells in culture. Schematic view of the rGO‐based sensor chip for electrical cell–substrate adhesion assays.

Design and fabrication of a multiple-thickness electrochemical cantilever sensor

This paper presents a new design and fabrication process of a multiple-thickness electrochemical cantilever sensor, in order to assess the role of the cantilever’s thickness on the chemically-induced mechanical effects. Each cantilever can act not only as a functionalized cantilever, but also as an independent working electrode (WE) for electrochemical measurement. The different thicknesses of the silicon nitride layer are achieved by successive masking and reactive ion etching of partially overlapping openings at a low etch rate (10.8nm/min, 15.8nm/min, 20.1nm/min, or 26.5nm/min). A small-scale thickness difference (<30nm) is successfully obtained. One advantage of this fabrication process is that the thickness distribution of cantilevers can be altered and broadened by combination of different RIE recipes or modification of the etching time. In addition, the integration of the cantilever chip with a fluidic cell, a printed circuit board (PCB) and a temperature-controlled plate to form a hybrid system is also addressed.

Photoelectron spectroscopy of wet and gaseous samples through graphene membranes.

Photoelectron spectroscopy (PES) and microscopy are highly important for exploring morphologically and chemically complex liquid-gas, solid-liquid and solid-gas interfaces under realistic conditions, but the very small electron mean free path inside dense media imposes serious experimental challenges. Currently, near ambient pressure PES is conducted using dexterously designed electron energy analyzers coupled with differentially pumped electron lenses which make it possible to conduct PES measurements at a few hPa. This report proposes an alternative ambient pressure approach that can be applied to a broad class of samples and be implemented in conventional PES instruments. It uses ultrathin electron transparent but molecular impermeable membranes to isolate the high pressure sample environment from the high vacuum PES detection system. We demonstrate that the separating graphene membrane windows are both mechanically robust and sufficiently transparent for electrons in a wide energy range to allow soft X-ray PES of liquid and gaseous water. The performed proof-of-principle experiments confirm the possibility to probe vacuum-incompatible toxic or reactive samples placed inside such hermetic, gas flow or fluidic environmental cells.

A lab-on-chip cell-based biosensor for label-free sensing of water toxicants

This paper presents a lab-on-chip biosensor containing an enclosed fluidic cell culturing well seeded with live cells for rapid screening of toxicants in drinking water. The sensor is based on the innovative placement of the working electrode for the electrical cell-substrate impedance sensing (ECIS) technique as the top electrode of a quartz crystal microbalance (QCM) resonator. Cell damage induced by toxic water will cause a decrease in impedance, as well as an increase in the resonant frequency. For water toxicity tests, the biosensor's unique capabilities of performing two complementary measurements simultaneously (impedance and mass-sensing) will increase the accuracy of detection while decreasing the false-positive rate. Bovine aortic endothelial cells (BAECs) were used as toxicity sensing cells. The effects of the toxicants, ammonia, nicotine and aldicarb, on cells were monitored with both the QCM and the ECIS technique. The lab-on-chip was demonstrated to be sensitive to low concentrations of toxicants. The responses of BAECs to toxic samples occurred during the initial 5 to 20 minutes depending on the type of chemical and concentrations. Testing the multiparameter biosensor with aldicarb also demonstrated the hypothesis that using two different sensors to monitor the same cell monolayer provides cross validation and increases the accuracy of detection. For low concentrations of aldicarb, the variations in impedance measurements are insignificant in comparison with the shifts of resonant frequency monitored using the QCM resonator. A highly linear correlation between signal shifts and chemical concentrations was demonstrated for each toxicant.

Synthesizing fluidic flexible matrix composite–based multicellular adaptive structure for prescribed spectral data

A cellular adaptive structure concept based on fluidic flexible matrix composite is investigated for its potential of achieving multifunctionalities simultaneously. This structure consists of a string of fluidic-connected fluidic flexible matrix composite cells with different properties. When under dynamic loading, the structure exhibits distinct poles and zeros (spectral data). These spectral data can be assigned, by tailoring fluidic flexible matrix composite design, so that the structure can perform dynamic functions such as vibration absorption or actuation with enhanced authority. To fully explore the potential of the fluidic flexible matrix composite–based cellular structure, this article carries out two progressive tasks. The first task is to develop a dynamic model for the multicellular structure. This model incorporates the concept of constitutive parameters to describe the performance of individual fluidic flexible matrix composite cell. The second task is to develop a synthesis procedure to assign these constitutive parameters so that the structure can achieve the prescribed spectral data. This procedure combines genetic algorithm with discrete variables and Jacobi inverse eigenvalue problem. Case studies show that the proposed procedure is successful for synthesizing structures with three cells. The range of the achievable spectral data is found through a numerical survey, and for each set of achievable spectral data, multiple designs can be synthesized efficiently.

A Fluidic Cell Embedded Electromagnetic Wave Sensor for Online Indication of Neurological Impairment during Surgical Procedures

Lactate is known to be an indicator of neurological impairment during aortic aneurysm surgery. It is suggested that cerebrospinal fluid removed during such surgery could provide useful information in this regard. Medical professionals find the prospect of online detection of such analytes exciting, as current practice is time consuming and leads to multiple invasive procedures. Advancing from the current laboratory based analysis techniques to online methods could provide the basis for improved treatment regimes, better quality of care, and enhanced resource efficiency within hospitals. Accordingly, this article considers the use of a low power fluidic system with embedded electromagnetic wave sensor to detect varying lactate concentrations. Results are promising over the physiological range of 0 − 20 mmol/L with a calibration curve demonstrating an R2 value > 0.98.

Real-Time Monitoring of Pseudomonas Aeruginosa Concentration Using a Novel Electromagnetic Sensors Microfluidic Cell Structure

This study demonstrates an electromagnetic wave-based sensor embedded within a fluidic cell for the purposes of quantifying Pseudomonas aeruginosa in real time, which implies it could be applied for provision of point-of-care diagnostics. The sensors operates through the interaction of the electromagnetic field with the analyte flowing through the fluidic system, and via the sensor head which has a specifically designed planar pattern to maximize the sensor sensitivity for the given bacteria type. The sensor is demonstrated to respond linearly (R(2) = 0.9942) to OD(550) 25 × 10(-3) - 1.0 bacteria concentration through changing resonant frequency and peak quality factor. This innovative approach is expected to contribute to better provision of healthcare services, minimizing the need for hospital visits through real-time point-of-care diagnostics as opposed to lengthy laboratory assays.

A Fluorescent One-Dimensional Photonic Crystal for Label-Free Biosensing Based on Bloch Surface Waves

A one-dimensional photonic crystal (1DPC) based on a planar stack of dielectric layers is used as an optical transducer for biosensing, upon the coupling of TE-polarized Bloch Surface Waves (BSW). The structure is tailored with a polymeric layer providing a chemical functionality facilitating the covalent binding of orienting proteins needed for a subsequent grafting of antibodies in an immunoassay detection scheme. The polymeric layer is impregnated with Cy3 dye, in such a way that the photonic structure can exhibit an emissive behavior. The BSW-coupled fluorescence shift is used as a means for detecting refractive index variations occurring at the 1DPC surface, according to a label-free concept. The proposed working principle is successfully demonstrated in real-time tracking of protein G covalent binding on the 1DPC surface within a fluidic cell.