Microfluidic Electrode Research Articles

Synergistic Effect of Electrical and Biochemical Stimulation on Human iPSC-Derived Neural Differentiation in a Microfluidic Electrode Array Chip.

Neural differentiation is crucial for advancing our understanding of the nervous system and developing treatments for neurological disorders. The advanced methods and the ability to manipulate the alignment, proliferation, and differentiation of stem cells are essential for studying neuronal development and synaptic interactions. However, the utilization of human induced pluripotent stem cells (iPSCs) for disease modeling of neurodegenerative conditions may be constrained by the prolonged duration and uncontrolled cell differentiation required for functional neural cell differentiation. Here, we developed a microfluidic chip to enhance the differentiation and maturation of specific neural lineages by placing aligned microelectrodes on the glass surface to regulate the neural differentiation of human iPSCs. The utilization of electrical stimulation (ES) in conjunction with neurotrophic factors (NF) significantly enhanced the efficiency in generating functional neurons from human iPSCs. We also observed that the simultaneous application of NF and ES to human iPSCs promoted their differentiation and maturation into functional neurons while increasing synaptic interactions. Our research demonstrated the effect of combining NF and ES on human iPSC-derived neural differentiation.

Stretchable, Self-Rolled, Microfluidic Electronics Enable Conformable Neural Interfaces of Brain and Vagus Neuromodulation.

Implantable neuroelectronic interfaces have gained significant importance in long-term brain-computer interfacing and neuroscience therapy. However, due to the mechanical and geometrical mismatches between the electrode-nerve interfaces, personalized and compatible neural interfaces remain serious issues for peripheral neuromodulation. This study introduces the stretchable and flexible electronics class as a self-rolled neural interface for neurological diagnosis and modulation. These stretchable electronics are made from liquid metal-polymer conductors with a high resolution of 30 μm using microfluidic printing technology. They exhibit high conformability and stretchability (over 600% strain) during body movements and have good biocompatibility during long-term implantation (over 8 weeks). These stretchable electronics offer real-time monitoring of epileptiform activities with excellent conformability to soft brain tissue. The study also develops self-rolled microfluidic electrodes that tightly wind the deforming nerves with minimal constraint (160 μm in diameter). The in vivo signal recording of the vagus and sciatic nerve demonstrates the potential of self-rolled cuff electrodes for sciatic and vagus neural modulation by recording action potential and reducing heart rate. The findings of this study suggest that the robust, easy-to-use self-rolled microfluidic electrodes may provide useful tools for compatible neuroelectronics and neural modulation.

Integrated microfluidic multiple electrode aggregometry for point-of-care platelet function analysis.

Point-of-care (POC) platelet function analysis can enable timely and precise management of bleeding and clotting in emergency rooms, operation rooms and intensive care units. However, POC platelet testing is currently not commonly performed, due to the complexity of sample preparation and limitations of existing technologies. Here, we report the development of an integrated microfluidic multiple electrode aggregometry (μMEA) sensor which uses multi-frequency impedance measurement of an embedded microelectrode array to perform platelet aggregometry directly from whole blood, sensing and measuring platelet activation in a label-free manner and without requiring any additional sample preparation. Additionally, the sensor incorporates blood flow during the assay to account for physiological flow and shear conditions. We show that the impedance signal from the sensor can be used to accurately detect and quantify platelet aggregation in a label-free manner, which was further validated by simultaneous fluorometric measurement and visualization of platelet aggregation. Further, we optimized the sensitivity and repeatability of the sensor using its frequency response and demonstrated that the sensor could be used to characterize drug dose-response in antiplatelet therapy with a frequency-tunable dynamic range. We also demonstrate that the sensor provides high sensitivity to perform platelet aggregometry under thrombocytopenic or low platelet count conditions. The μMEA sensor could thus enable POC platelet function analysis across several clinical applications.

Modification-free pumpless laser-induced graphene multichannel open microfluidic electrode chip for simultaneous quantification of dual targets

Pumpless surface fluid transport technology has attracted concerns in the field of electroanalysis. However, the combination of surface wettability-controlled multichannel fluid transport and flexible three-electrode systems has been rarely reported for electrochemical detection. Here, we have developed a modification-free pumpless laser-induced graphene multichannel open microfluidic electrode chip (LIG-MOMEC) for simultaneous quantification of dual targets. The LIG-MOMEC enables rapid sample distribution to four addressable locations for multiple parallel tests on a single chip and simultaneous detection of dopamine (DA) and uric acid (UA) using differential pulsed voltammetry. The flexible polyimide templated by laser parameters supports a programmable electrochemical sensing surface with desired conductivity and optimal surface wettability without post-chemical modification, effectively avoiding the tedious multi-step processing and time-consuming surface modification of conventional modified electrodes. The LIG-MOMEC has a linear detection range of 0.91 ∼ 171.15 μM for DA and 0.83 ∼ 250.04 μM for UA with the LODs of 72 nM and 48 nM. Due to the advantages of superior selectivity, anti-interference and reliable stability, the LIG-MOMEC could be reversibly used 30 times with high reproducibility and attain satisfactory recovery in human serum samples. The LIG-MOMEC provides great potential for the rapid detection of biomolecules in clinical diagnostics and biochemical analysis.

µPED based electrode modified with nanocomposite for the detection of proline: An abiotic stress biomarker in plant

Plants when exposed to stressful conditions, accumulates array of metabolites. Among them proline plays significant and beneficial role as osmolyte, metal chelator and as anti-oxidative defense and regulator molecule. Thus the proline content is one of the potent bio-marker for the early detection of abiotic stress in plant. In this work a microfluidic paper-based electrochemical device (µPED) modified with copper oxide nanoparticles (CuO) decorated reduced graphene oxide (rGO) nanocomposite is utilized to develop disposable system for the detection of proline. Wax and screen printings were utilized to create microfluidic chambers and electrode pattern on paper device, respectively. Portable potentiostat was used for measuring the current in response from the addition of proline. The proposed sensor exhibits excellent electrochemical performance with broad linear responses over a proline concentration ranging from 0.1 mM to 7.5 mM (R2 =0.99) and showed lower detection limit of 0.05 mM at 0.4 V vs. pseudo Ag/AgCl. Excellent electrochemical performance may be attributed to presence of electroactive rGO and catalytic activity towards proline is due to the coordination between proline and copper (II) oxide nanoparticles. These results demonstrate that the proposed paper-based electrochemical sensor can be utilized in disposable and portable way to detect proline content in the abiotic-stressed plants and has potential to be applied in on-site application.

An addressable electrowetting valve for centrifugal microfluidics

Centrifugal microfluidic platforms aim to integrate and perform complex biological and chemical processes within disc-like substrates and valving through centrifugal forces and the Coriolis effect. Although the integration of active valves within such system can be used to enhance fluid control, the ability to fabricate and integrate addressable valves within centrifugal platforms remains a significant challenge. To address this issue, herein, we present and test an addressable electrowetting centrifugal (EWC) valve. The EWC valve comprises a hydrophobic burst valve, integrated side electrodes and a dielectric layer between the microfluidic channel and electrode structures. The burst valve is made from a hydrophobic material able hold a specified pressure. Specifically, application of an external electric field is used to alter the valve wettability, making the valve more hydrophilic, decreasing the threshold pressure and triggering the opening of the valve. To assess valve performance, we investigate the influence of electric properties and channel geometry on valve response and then demonstrate multiple operations on different fluid samples. Finally, and to highlight the utility of EWC valves, we demonstrate the detection and analysis of CD4 human immune cells.

Microfluidic electrode array chip for electrical stimulation-mediated axonal regeneration.

The precise manipulation of the neural stem cell (NSC)-derived neural differentiation is still challenging, and there is a technological barrier to regulate the axonal regeneration in a controlled manner. Here, we developed a microfluidic chip integrated with a microelectrode array as an axonal guidance platform. The microfluidic electrode array chip consisted of two compartments and a bridge microchannel that could isolate and guide the axons. We demonstrated that the NSCs were largely differentiated into neural cells as the electric field was applied to the microfluidic electrode array chip. We also confirmed the synergistic effects of the electrical stimulation (ES) and neurotrophic factor (NF) on axonal outgrowth. This microfluidic electrode array chip can serve as a central nervous system (CNS) model for axonal injury and regeneration. Therefore, it could be a potentially powerful tool for an in vitro model of the axonal regeneration.

Design and 3D modeling investigation of a microfluidic electrode array for electrical impedance measurement of single yeast cells.

High-resolution microscopic imaging may cause intensive image processing and potential impact of light irradiation on yeast replicative lifespan (RLS). Electrical impedance spectroscopy (EIS) could be alternatively used to perform high-throughput and label-free yeast RLS assays. Prior to fabricating EIS-integrated microfluidic devices for yeast RLS determination, systematic modeling and theoretical investigation are crucial for device design and optimization. Here, we report three-dimensional (3D) finite-element modeling and simulations of EIS measurement in a microfluidic single yeast in situ impedance array (SYIIA), which is designed by patterning an electrode matrix underneath a cell-trapping array. SYIIA was instantiated and modeled as a 5×5 sensing array comprising 25 units for cell immobilization, culturing, and time-lapse EIS recording. Simulations of yeast growing and budding in a sensing unit demonstrated that EIS signals enable the characterization of cell growth and daughter-cell dissections. In the 5×5 sensing array, simulation results indicated that when monitoring a target cell, daughter dissections in its surrounding traps may induce variations of the recorded EIS signals, which could cause mistakes in identifying target daughter-cell dissections. To eliminate the mis-identifications, electrode array pitch was optimized. Therefore, the results could conduct the design and optimization of microfluidic electrode-array-integrated devices for high-throughput and accurate yeast RLS assays.

Microfluidic thread-based electrochemical aptasensor for rapid detection of Vibrio parahaemolyticus

Vibrio parahaemolyticus is one of the foodborne bacteria that widely present in seafood as well as the leading cause of seafood-associated bacterial gastroenteritis. Traditional identification of such pathogens mainly relies on culturing methods, ELISA or PCR. These methods are usually laborious, time-consuming with poor diagnosis competences, or require costly and bulky equipment though of high sensitivity. In this study, a thread-based microfluidic electrochemical aptasensor was designed, fabricated and tested by using label-free aptamer immunosensing technology for rapid and highly sensitive detection of Vibrio parahaemolyticus in seafood. Both the microfluidic channels and electrodes were simply fabricated on threads. Molybdenum disulfide (MoS2) nanosheets were used to obtain enhanced sensitivity of the electrochemical measurement. When used in detecting Vibrio parahaemolyticus, the proposed aptasensor has a dynamic detection range of 10–106 CFU mL−1 with a detection limit of 5.74 CFU mL−1. Compared with traditional plate counting method, the proposed aptasensor has higher detection sensitivity and less assay time (30 min), while high specificity and accuracy are kept. The proposed microfluidic thread-based electrochemical aptasensor grabs the potential to detect other pathogens by simply functionalizing the threaded electrodes with aptamers for targeted biological substances.

Point-of-care biosensors in medicine: a brief overview of our achievements in this field based on the conducted research in EMRI (endocrinology and metabolism research Institute of Tehran University of medical sciences) over the past fourteen years.

The growing demand of diagnostic tools with enhanced analytical characteristics in term of sensitivity, selectivity, and low response time has encouraged researches to conduct their research towards development of point-of-care (POC) biosensors. POC diagnostic devices are powerful tools for detection, diagnosis, and monitoring of diseases at its initial stage. The above characteristics encouraged us to conduct active multidisciplinary and collaborative research oriented towards the design and development of POC sensing systems. Here, we present a brief overview of our recent achievement in the field of biomedical POC devices implemented in paper based microfluidic and screen printing electrodes and discuss the critical limitations that need to be surmounted to facilitate their translation into clinical practice in the future.

The analysis of dissolved inorganic carbon in liquid using a microfluidic conductivity sensor with membrane separation of CO2

Autonomous continuous analysis of oceanic dissolved inorganic carbon (DIC) concentration with depth is of great significance with regard to ocean acidification and climate change. However, miniaturisation of in situ analysis systems is hampered by the size, cost and power requirements of traditional optical instrumentation. Here, we report a low-cost microfluidic alternative based on CO2 separation and conductance measurements that could lead to integrated lab-on-chip systems for ocean float deployment, or for moored or autonomous surface vehicle applications. Conductimetric determination of concentration, in the seawater range of 1000–3000 µmol kg−1, has been achieved using a microfluidic thin-film electrode conductivity cell and a membrane-based gas exchange cell. Sample acidification released CO2 through the membrane, reacting in a NaOH carrier, later drawn through a sub-µL conductivity cell, for impedance versus time measurements. Precision values (relative standard deviations) were ~ 0.2% for peak height measurements at 2000 µmol kg−1. Comparable precision values of ~ 0.25% were obtained using a C4D electrophoresis headstage with similar measurement volume. The required total sample and reagent volumes were ~ 500 µL for the low volume planar membrane gas exchange cell. In contrast, previous conductivity-based DIC analysis systems required total volumes between 5000 and 10,000 µL. Long membrane tubes and macroscopic wire electrodes were avoided by incorporating a planar membrane (PDMS) in the gas exchange cell, and by sputter deposition of Ti/Au electrodes directly onto a thermoplastic (PMMA) manifold. Future performance improvements will address membrane chemical and mechanical stability, further volume reduction, and component integration into a single manifold.

An on-chip microfluidic-based electrochemical magneto-immunoassay for the determination of procalcitonin in plasma obtained from sepsis diagnosed preterm neonates.

A novel on-chip electrochemical magneto-immunoassay for the determination of procalcitonin (PCT) has been proposed. The strategy involved the on-line performing of the biorecognition event and detection on the thin-film microfluidic gold electrode chamber operating at E = -0.20 V (vs. Au). The complete assay was performed in less than 15 minutes using only 25 μL of the sample, covering the entire range of clinically relevant PCT concentrations in sepsis diagnosis with a limit of detection and quantification of 0.02 ng mL-1 and 0.05 ng mL-1, respectively (the sepsis diagnosis threshold: 0.5 ng mL-1). The on-chip electrochemical magneto-immunoassay provided excellent results in the analysis of very unique samples obtained from preterm neonates admitted with suspected sepsis, in which the sample volume is hardly available. These characteristics fulfill the POCT requirements for PCT determination in the whole clinically relevant concentration range. Because of the high clinical relevance and the important role of PCT in sepsis, this approach opens new perspectives for sepsis diagnosis and therapy guidance using low volume samples.

Rapid and inexpensive microfluidic electrode integration with conductive ink.

Electrode integration significantly increases the versatility of droplet microfluidics, enabling label-free sensing and manipulation at a single-droplet (single-cell) resolution. However, common fabrication techniques for integrating electronics into microfluidics are expensive, time-consuming, and can require cleanroom facilities. Here, we present a simple and cost-effective method for integrating electrodes into thermoplastic microfluidic chips using an off-the-shelf conductive ink. The developed conductive ink electrodes cost less than $10 for an entire chip, have been shown here in channel geometries as small as 75 μm by 50 μm, and can go from fabrication to testing within a day without a cleanroom. The geometric fabrication limits of this technique were explored over time, and proof-of-concept microfluidic devices for capacitance sensing, droplet merging, and droplet sorting were developed. This novel method complements existing rapid prototyping systems for microfluidics such as micromilling, laser cutting, and 3D printing, enabling their wider use and application.

Ordinary microfluidic electrodes combined with bulk nanoprobe produce multidimensional electric double-layer capacitances towards metal ion recognition

While multidimensional sensors are powerful platforms towards multitarget analyses, the successive synthesis/fabrication of multiple probes and measurements to each one of these units still damage the device miniaturization, scalability, cost, consumption of samples, operational simplicity, precision, and analysis time. Herein, we describe an electrochemical sensing array that affords the discrimination of metal ions from a single ready-to-use probe and experiment. The sensing probe consisted of commercial stainless-steel capillaries, which defined a microfluidic circuit and acted as electric double-layer parallel capacitors into devices prototyped by a fast, cleanroom-free, and green technique. The probes assured differential responses due to heterogeneous interactions with samples and multichannel capacitance outputs. In addition, we address an effective strategy to further improve the repeatability and recognition ability of the sensor by using oxidized multi-walled carbon nanotubes as a single bulk probe. The nanotubes provided differential electrostatic adsorptions of ions, then increasing the variance of the capacitance responses. The approach was successfully applied in the identification of samples of mineral water, lake, and petroleum according to the presence of metal ions. Using supervised machine learning tasks, the sensor assured reproducible, sensitive, and accurate classification of dozens of lake samples spiked with multiple heavy metals in accordance with their safe limits. Remarkably, simultaneous quantification of the individual concentration of these ions was also possible from universal impedimetric assays by treating the data through multi-output regression. The sensor will be of significance for advanced discriminations from a single ordinary probe and measurement in a direct mode using scalable chips.

Electrochemical POC device for fast malaria quantitative diagnosis in whole blood by using magnetic beads, Poly-HRP and microfluidic paper electrodes

Malaria, a parasitic infection caused by Plasmodium parasites and transmitted through the bite of infected female Anopheles mosquitos, is one of the main causes of mortality in many developing countries. Over 200 million new infections and nearly half a million deaths are reported each year, and more than three billion people are at risk of acquiring malaria worldwide. Nevertheless, most malaria cases could be cured if detected early. Malaria eradication is a top priority of the World Health Organisation. However, achieving this goal will require mass population screening and treatment, which will be hard to accomplish with current diagnostic tools.We report an electrochemical point-of-care device for the fast, simple and quantitative detection of Plasmodiumfalciparum lactate dehydrogenase (PfLDH) in whole blood samples. Sample analysis includes 5-min lysis to release intracellular parasites, and stirring for 5 more min with immuno-modified magnetic beads (MB) along with an immuno-modified signal amplifier. The rest of the magneto-immunoassay, including sample filtration, MB washing and electrochemical detection, is performed at a disposable paper electrode microfluidic device. The sensor provides PfLDH quantitation down to 2.47 ng mL−1 in spiked samples and for 0.006–1.5% parasitemias in Plasmodium-infected cultured red blood cells, and discrimination between healthy individuals and malaria patients presenting parasitemias >0.3%. Quantitative malaria diagnosis is attained with little user intervention, which is not achieved by other diagnostic methods.

A novel 3D paper-based microfluidic electrochemical glucose biosensor based on rGO-TEPA/PB sensitive film

A novel 3D paper-based microfluidic screen-printed electrode (SPE) composed of two layers was constructed by photolithography and screen-printing technology. Aldehyde functionalized hydrophilic zone of the counter and reference electrodes layer was prepared for glucose oxidase immobilization. Highly conductive prussian blue deposited reduced graphene oxide-tetraethylene pentamine (rGO-TEPA/PB) modified paper working electrode layer can be used as an electrochemical sensitive membrane for quantitative detection of hydrogen peroxide (H2O2), which was the enzyme-catalyzed reaction product. Therefore, this 3D paper-based microfluidic electrochemical biosensor can be used for quantitative detection of glucose. Under optimum conditions, the proposed biosensor can be used for quantitative determination of glucose over a wide linear range of 0.1 mM–25 mM with detection limit of 25 μM. Finally, the 3D paper-based microfluidic electrochemical biosensor was applied to determine glucose in human sweat and blood, and the obtained results were in good consistency with values measured by Roche’s blood glucose meter. In addition, the proposed 3D paper-based electrochemical device showed good repeatability, stability, and anti-interference, which would be of great potential to monitor glucose in complex biological fluids.

A Multichannel Electroosmotic Flow Pump Using Liquid Metal Electrodes

Injecting a room-temperature liquid metal into microchannels offers a simple, rapid, and low-cost method of fabricating microfluidic electrodes. In this work, these electrodes are used to develop a multichannel electroosmotic flow pump for high-flow-rate microfluidic bio analysis applications. In this pump, two identical square-wave shaped liquid metal electrodes were located at both ends of pumping channels on the same horizontal level, and were separated by polydimethylsiloxane gaps from the pumping channels. To test the pumping performance, fluorescent particles were diluted with deionized water and injected into the pumping channels to measure the flow velocity. The results show that the pump with five parallel pumping channels can drive water at a speed of 4.63–45.76 μm/s with applied voltage of 300–1000 V, when the pumping channels are 30 μm high, and 250 μm long with 30-μm polydimethylsiloxane gaps. It can reach its highest possible flow rate of 325 nl/min when the applied voltage reaches its limit 3900V (150 μm long pumping channels, 150 μm long nonpumping channels and 30 μm PDMS gap with 10 parallel pumping channels). This EOF pump should be potential in many high-flow-rate microfluidic applications.

Epilepsy-on-a-Chip System for Antiepileptic Drug Discovery.

Hippocampal slice cultures spontaneously develop chronic epilepsy several days after slicing and are used as an in vitro model of post-traumatic epilepsy. Here, we describe a hybrid microfluidic-microelectrode array (μflow-MEA) technology that incorporates a microfluidic perfusion network and electrodes into a miniaturized device for hippocampal slice culture based antiepileptic drug discovery. Field potential simulation was conducted to help optimize the electrode design to detect a seizure-like population activity. Epilepsy-on-a-chip model was validated by chronic electrical recording, neuronal survival quantification, and anticonvulsant test. To demonstrate the application ofμflow-MEA in drug discovery, we utilized a two-stage screening platform to identify potential targets for antiepileptic drugs. In Stage I, lactate and lactate dehydrogenase biomarker assays were performed to identify potential drug candidates. In Stage II, candidate compounds were retested withμflow-MEA-based chronic electrical assay to provide electrophysiological confirmation of biomarker results. We screened 12 receptor tyrosine kinases inhibitors, and EGFR/ErbB-2 and cFMS inhibitors were identified as novel antiepileptic compounds. This epilepsy-on-a-chip system provides the means for rapid dissection of complex signaling pathways in epileptogenesis, paving the way for high-throughput antiepileptic drug discovery.

Single-Step 3D Printing Monolithic Electrochemical Microfluidic Devices

Microfluidic devices are advantageous for a wide variety of chemical and biological applications because they offer a way to manipulate small sample volumes, thus decreasing cost of potentially expensive reagents and enabling high throughput by harnessing the unique properties of fluids on the microscale.1 3D printing of microfluidic chips has sparked tremendous interest because commercial bench-top printers are becoming commonplace at reasonably low cost and devices can be made outside of a cleanroom, thus opening the field for more widespread development.2 3D printing has a distinct advantage over photolithography when fabricating chips with complex channel geometries and internal voids, because these types of devices can be fabricated in a single-step due to bottom-up, layer-by-layer nature of the technique.3 One of the challenges for microfluidics is the integration between the microfluidic fluid handling with a suitable analysis technique that can be performed “on chip”. For this reason, many analysis techniques used in microfluidics employ optical-based detection schemes using colorimetric or fluorescent labels, because light can easily pass through the microfluidic substrate. In addition, there are no additional fabrication steps required in order to make chips that can perform on chip analyses using these techniques. However, when coupling capillary electrophoresis or electrochemistry on chip, integrating the detection with the fluid handling can be a challenge. In order to integrate electrodes into microfluidic devices, one of the following approaches are typically utilized: epoxying metal wires or mesh into a flow channel,4 potting metallic wires in microfluidic fittings that are interfaced using screws and ferrules,5 or by evaporation of metal films (or carbon bands) onto flat wafers followed by bonding with the PDMS chip.6,7 Here we present the single-step fabrication of monolithic microfluidic devices with embedded composite-carbon electrodes suitable for electrochemical detection of a variety of chemical species prepared by 3D printing. In this approach, we employ a dual-extrusion fused deposition modeling printer is used in order to simultaneously print the microfluidic body and electrodes, which eliminates multiple steps in the fabrication and greatly simplifies device manufacturing. We demonstrate the utility of this approach using two exemplar microfluidic systems for hydrodynamic electrochemistry: in a simple channel flow configuration and for the detection of water-in-oil droplets. We show that the carbon electrodes employed here may be modified for different applications by electrodepositing metals such as platinum or gold on the carbon electrode surface in situ. We envision these devices to have broad applications for chemical and biological sensing. References (1) Whitesides, G. M. The Origins and the Future of Microfluidics. Nature 2006, 442, 368–373. (2) Gross, B. C.; Lockwood, S. Y.; Spence, D. M. Recent Advances in Analytical Chemistry by 3D Printing. Anal. Chem. 2017, 89, 57–70. (3) Channon, R. B.; Joseph, M. B.; Macpherson, J. V. Additive Manufacturing for Electrochemical (Micro)Fluidic Platforms. Electrochem. Soc. Interface 2016, 25, 63–68. (4) O’Neil, G. D.; Christian, C. D.; Brown, D. E.; Esposito, D. V. Hydrogen Production with a Simple and Scalable Membraneless Electrolyzer. J. Electrochem. Soc. 2016, 163, F3012–F3019. (5) Bishop, G. W.; Satterwhite-warden, J. E.; Bist, I.; Chen, E.; Rusling, J. F. Electrochemiluminescence at Bare and DNA-Coated Graphite Electrodes in 3D-Printed Fluidic Devices. ACS Sensors 2016, 1, 197–202. (6) Anderson, M. J.; Crooks, R. M. Microfluidic Surface Titrations of Electroactive Thin Films. Langmuir 2017, 10.1021/acs.langmuir.7b01542. (7) Channon, R. B.; Joseph, M. B.; Bitziou, E.; Bristow, A. W. T.; Ray, A. D.; Macpherson, J. V. Electrochemical Flow Injection Analysis of Hydrazine in an Excess of an Active Pharmaceutical Ingredient: Achieving Pharmaceutical Detection Limits Electrochemically. Anal. Chem. 2015, 87 (19), 10064–10071.

Liquid-phase alloy as a microfluidic electrode for micro-electro-discharge patterning

This study reports on the first patterning method based on micro-electro-discharge machining (μEDM) that uses microfluidic electrodes in a liquid form. This novel method is developed to address a variety of problems associated with electrode wear, which is one of the most fundamental issues with μEDM technology. During the machining process, a liquid electrode is continuously supplied to a metallic micro capillary nozzle to eliminate the impact of its “wear” or liquid consumption on the removal process. Experiments show that Galinstan, a non-toxic liquid alloy, can be used as the electrode material to create discharge pulses and perform microscale removal on the samples. Controlled discharge generation and scanning-mode arbitrary patterning are experimentally demonstrated using the microfluidic Galinstan electrodes. The process is evaluated with varying discharge conditions to reveal the dependence of the patterned geometry on the parameters. It is also shown that a Parylene C coating is effective for protecting the nozzle from discharging. The elemental analysis of the processed samples indicates that the process does not cause detectable Galinstan contamination on the patterned surfaces.