Interdigitated Electrode Array Research Articles

Scalable flexible and stretchable high performance UV photodetector based on MoS2-WO3/Ag composite on a PU substrate by utilizing LIG electrodes

The rapid advancements in photodetector device technologies have captivated the optoelectronic industry owing to their strong features, such as wearability, stretchability, energy efficiency, scalability and cost-effectiveness. However, there is still scope for enhancement in device performance, reliability, and scalable fabrication. In this research work, we have proposed a novel strategy for fabricating stretchable ultraviolet (UV) photodetector (PD) on a polyethylene glycol solution-processed synthesis of MoS2-WO3/Ag composite-based nanocrystals onto a polyurethane (PU) substrate. Moreover, laser induced graphene (LIG) interdigitated electrode arrays for swift photogenerated charge extraction due to their high conductivity. The device displays high photoresponsivity, external quantum efficiency, and specific detectivity, measured at 6.84 A/W, 143 %, and 2.87×1011 Jones, respectively. Additionally, the device demonstrates a quick response time of 80 ms when exposed to 360 nm light, indicating its high speed. These essential advantages have a great potential for applications in real life and mass production. The integration of advanced materials and LIG electrodes enhances the device capability for next-generation stretchable, flexible and wearable electronic devices.

Enhanced Performance of All‐Inorganic Lead Halide Perovskite/MoS2 Heterojunction Photodetectors by Achieving Interfacial Carrier Separation

A heterojunction interface engineering aimed at improving the performance of all‐inorganic lead halide perovskite photodetectors (PDs) is demonstrated by coupling the two‐dimensional (2D) MoS2 materials with CsPbBr3 used in the chemical vapor deposition method in situ‐grown. The MoS2 carrier extraction layer facilitates electron injection, while the large injection barrier of the CsPbBr3/MoS2 heterojunction depletion layer keeps holes in the perovskite layer, resulting in effective separation of photogenerated carriers at the heterojunction interface. Moreover, the photoluminescence quenching and lifetime shortening of the heterojunction further prove that there is a large amount of charge transfer between the CsPbBr3 and MoS2 interface. As a result, PDs based on the CsPbBr3/MoS2/interdigitated array electrodes (IDA) heterojunction exhibit remarkable performance, such as high photoresponsivity (23.4 A W−1), detectivity (1.48 × 1013 Jones), and switching ratio (1.35 × 105), all of which are an order of magnitude better than pure CsPbBr3 PDs. The heterojunction PD also presents a superior response time (0.07 ms).

Array of Interdigitated Bipolar Electrodes for Selective Capture and Analysis of Melanoma Cells

AbstractWe report a method for dielectrophoretic capture of melanoma cells and their electrochemical analysis for tumor‐specific markers, using a microfluidic device composed of microwells overlying an array of interdigitated bipolar electrodes (IDBPEs). In this device, cells are captured on each IDBPE by dielectrophoresis, and microfabricated wells allow for retention of the cells to enable their subsequent electrochemical analysis. This advancement is significant because it addresses a need for cancer diagnostics with few‐ to single‐cell resolution amenable to use in low‐resource settings. Specifically, this approach combines the selectivity of dielectrophoresis for cell phenotype, the low cost of electrochemical methods, and the ability of BPEs to be arrayed, with the sensitivity afforded by interdigitation. The IDBPE detects a redox‐active species produced by an enzyme‐linked antibody targeted to a cell surface antigen, and reports the current by electrochemiluminescence. In this work, we first characterize cell capture by dielectrophoresis at the IDBPE array. Second, the retention of cells in the microwells and their viability is demonstrated. Then, the sensitivity of the IDBPE for the redox‐active species is quantified. Finally, we demonstrate capture and analysis of melanoma cells at the IDBPE array, which underscores the ability of the IDBPE to achieve biologically relevant detection limits.

Deconvolution of Charge-Transfer, Mass Transfer, and Ohmic Resistances of Phosphonic Acid-Sulfonic Acid Ionomer Binders in Electrochemical Hydrogen Pumps

Ion-pair high-temperature polymer electrolyte membranes (HT-PEMs) paired with phosphonic acid ionomer electrode binders have substantially improved the performance of HT-PEM electrochemical hydrogen pumps (EHPs)1, 2 and fuel cells3. Recently, blending poly(pentafluorstyrene-co-tetrafluorostyrene phosphonic acid) (PTFSPA) with NafionTM improved ionomer conductivity under anhydrous conditions in the temperature range of 100 °C to 250 °C. Using the said polymer blend as an electrode binder resulted in a 2 W.cm-2 peak power density of fuel cells4 at 240 °C (a HT-PEM fuel cell record). However, much is still unknown about how phosphonic acid ionomers blended with perfluorosulfonic acid (PFSA) materials affect electrode kinetics and gas transport in porous electrodes. In this work, we studied the ionic conductivity, electrode kinetics, and gas transport resistance of 3 types of phosphonic acid ionomers, poly(vinyl phosphonic acid), poly(vinyl benzyl phosphonic acid) by themselves and when blended with Aquivion®. These studies were performed in the context of an EHP platform – both membrane electrode assemblies (MEAs) and interdigitated electrode arrays (IDAs) decorated with nanoscale platinum electrocatalysts with thin film ionomer electrolytes. For all phosphoric acid ionomer types, the addition of Aquivion® promoted ionic conductivity, hydrogen oxidation/evolution reaction kinetics (HOR/HER), and hydrogen gas permeability. Solid-state 31P NMR revealed that the addition of Aquivion® significantly reduced phosphate ester formation in phosphoric acid ionomers and this played a vital role in enhancing ionomer blend conductivity. Using the best blend variant, PTFSPA-Aquivion®, a remarkable EHP performance of 5.1 A.cm-2 at 0.4 V at T = 200 °C was attained. Density functional theory (DFT) simulations identified that phosphonic acids with electron-withdrawing moieties reduced the propensity of the phosphonic acid to adsorb to platinum electrocatalyst surfaces. All phosphonic acid ionomers are anticipated to have a greater affinity for adsorption on platinum when compared to sulphonic acid ionomers (PFSAs). The relative adsorption affiliation of the various phosphoric acid ionomers from DFT is consistent with an explanation that stronger anion-specific adsorption has a detrimental impact and is commensurate with experimentally obtained MEA charge-transfer kinetics. A machine learning-aided compositional model5 revealed that the addition of Aquivion® reduced activation and concentration overpotentials in EHP MEAs and improved exchange current density and diffusivity in EHP IDAs. Future work involves employing the EHPs in a real-world application for separating and compressing hydrogen from the natural gas mixture.References Venugopalan, G.; Bhattacharya, D.; Andrews, E.; Briceno-Mena, L.; Romagnoli, J.; Flake, J.; Arges, C. G., Electrochemical Pumping for Challenging Hydrogen Separations. ACS Energy Letters 2022, 7 (4), 1322-1329.Venugopalan, G.; Bhattacharya, D.; Kole, S.; Ysidron, C.; Angelopoulou, P. P.; Sakellariou, G.; Arges, C. G., Correlating high temperature thin film ionomer electrode binder properties to hydrogen pump polarization. Materials Advances 2021, 2 (13), 4228-4234.Atanasov, V.; Lee, A. S.; Park, E. J.; Maurya, S.; Baca, E. D.; Fujimoto, C.; Hibbs, M.; Matanovic, I.; Kerres, J.; Kim, Y. S., Synergistically integrated phosphonated poly(pentafluorostyrene) for fuel cells. Nat Mater 2021, 20 (3), 370-377.Lim, K. H.; Lee, A. S.; Atanasov, V.; Kerres, J.; Park, E. J.; Adhikari, S.; Maurya, S.; Manriquez, L. D.; Jung, J.; Fujimoto, C.; Matanovic, I.; Jankovic, J.; Hu, Z.; Jia, H.; Kim, Y. S., Protonated phosphonic acid electrodes for high power heavy-duty vehicle fuel cells. Nature Energy 2022, 7 (3), 248-259.Briceno-Mena, L. A.; Venugopalan, G.; Romagnoli, J. A.; Arges, C. G., Machine learning for guiding high-temperature PEM fuel cells with greater power density. Patterns 2021, 2 (2), 100187. Figure 1

Experimental and theoretical analysis of a Visible-Light photodetector based on cadmium sulfide fabricated on interdigitated electrodes

The wide range of applications for photodetectors, such as in space, industry, medical, and military, has garnered significant research attention in recent years. In this study, an n-type single-layer photodetector based on a Cu/CdS/Cu metal–semiconductor-metal structure with a micro interdigitated electrode array (IDE) was fabricated. The surface morphology and absorption properties of the CdS thin films were characterized using atomic force microscopy, scanning electron microscopy, and UV–Vis spectrometry. The photo response characteristics of the photodetector were recorded across wavelengths of 400–780 nm. The optoelectronic analyses of the structure revealed a maximum responsivity value of approximately 98.73 % at 405 nm incident light, with a high response time of about 0.12 s. Furthermore, the structure was theoretically studied and simulated, with the simulation results demonstrating good agreement with the measured experimental evidence. The above results indicate that the present CdS photodetector holds excellent potential for use in high-sensitivity optoelectronic integrated circuits.

Highly-sensitive wearable pressure sensor based on AgNWs/MXene/non-woven fabric

Nowadays, wearable medical devices are getting more and more public attention. As a continuous monitoring device in wearable medical devices, flexible pressure sensors have also attracted much attention in the field of wearable electronics. High sensitivity and long-term durability in a wide linear range are key requirements for making reliable and flexible wearable pressure sensors. Here, a comfortable, flexible, environmentally friendly and wearable non-woven fabric is proposed as a substrate for the pressure sensor. Conductive AgNWs/MXene/non-woven fabric is prepared by a simple dip-coating technique and then an overall sandwich structure is formed between two layers of polydimethylsiloxane (PDMS) film and an Interdigitated Array of Electrodes (IDE). The viscose fibres in nonwovens are rich in hydroxyl groups and their hydrophilicity is more conducive to the attachment of conductive MXene nanosheets to the entangled fibre network of nonwovens. The synergistic effect between Ti3C2Tx and AgNWs, and the unique intercalation structure can build a more effective conductive network. The pressure sensor based on AgNWs/MXene/non-woven fabric has a fibrous entanglement structure and a special sandwich structure of the sensor with high sensitivity (0.25–5 kPa pressure range: 14.28 kPa−1), and have a wide sensing range (0.25–400 kPa), rapid response and recovery times (60 ms/120 ms), excellent stability, and long term durability for use in human motion detection applications. In addition, the wearable pressure sensors was used to detect and discriminate between different signals related to human health, including monitoring human movement and breathing, and 4 × 4 arrays was used to detect stress distribution signals. These results suggest that the sensor can be potentially applied in mobile medical monitoring devices, showing broad potential in a new generation of wearable electronic devices.

Lithography-free interdigitated electrodes by trench-filling patterning on polymer substrate for Alzheimer's disease detection

Microelectrodes have played a crucial role in electrochemistry for the last few decades. However, the conventional lithographic processes, the key players in fabrication, are nonetheless technologically challenging, pricey, and lack reproducibility. In this work has developed a novel and low-cost patterned-replication fabrication technology for interdigitated electrode array (IDA) electrodes on the polymer substrate. Conventional UV-lithography has been utilized to fabricate the nickel IDA electrode pattern as a master mold on the stainless-steel substrate, which was replicated onto the polymer substrate by the hot-emboss technique. Then, gold was deposited on the replicated wafer by electron beam evaporation, and finally adhesive tape lift-off was used to obtain the gold IDA electrode. The fabricated IDA electrode was applied for electrochemical detection of various p-aminophenol (PAP) concentrations as a representative biomarker with a detection limit of 0.01 nM. Finally, different levels of amyloid beta 42 (Aß42) and amyloid beta aggregated (Aß Agg.), two Alzheimer's disease (AD) biomarkers, were measured using the developed IDA electrode via e-ELISA using enzyme by-products PAP. While quantified, the proposed IDA electrode successfully detects Aß42 and Aß Agg. with the lower detection limit (LOD) of 3.9 and 7.81 pg/ml, respectively.

NanoIEA: A Nanopatterned Interdigitated Electrode Array-Based Impedance Assay for Real-Time Measurement of Aligned Endothelial Cell Barrier Functions.

A nanopatterned interdigitated electrode array (nanoIEA)-based impedance assay is developed for quantitative real-time measurement of aligned endothelial cell (EC) barrier functions in vitro. A bioinspired poly(3,4-dihydroxy-L-phenylalanine) (poly (l-DOPA)) coating is applied to improve the human brain EC adhesion onto the Nafion nanopatterned surfaces. It is found that a poly (l-DOPA)-coated Nafion grooved nanopattern makes the human brain ECs orient along the nanopattern direction. Aligned human brain ECs on Nafion nanopatterns exhibit increased expression of genes encoding tight and adherens junction proteins. Aligned human brain ECs also have enhanced impedance and resistance versus unaligned ones. Treatment with a glycogen synthase kinase-3 inhibitor (GSK3i) further increases impedance and resistance, suggesting synergistic effects occur on the cell-cell tightness of in vitro human brain ECs via a combination of anisotropic matrix nanotopography and GSK3i treatment. It is found that this enhanced cell-cell tightness of the combined approach is accompanied by increased expression of claudin protein. These data demonstrate that the proposed nanoIEA assay integrated with poly (l-DOPA)-coated Nafion nanopatterns and interdigitated electrode arrays can make not only biomimetic aligned ECs, but also enable real-time measurement of the enhanced barrier functions of aligned ECs via tighter cell-cell junctions.

In situ detection with interdigitated array electrodes towards the platinum-catalyzed oxygen reduction reaction: Size effect and the reaction pathway

Platinum has long been recognized as a vital catalyst in energy conversion and utilization, particularly in oxygen reduction reaction (ORR), due to its exceptional catalytic activity. However, its exorbitant cost and scarcity have motivated researchers to explore the size-activity correlation of Pt catalysts in ORR, aiming to reduce Pt loading density while preserving high catalytic performance. In this work, we concentrate on the interdigitated-array(IDA)-electrodes-based precise detection of the influence of Pt cluster size on catalytic ability, focusing on (1) Direct synthesis of Pt catalyst onto electrodes surface, rather than offline preparation and pasting, to avoid interference from other chemicals and changes to the surface status of catalyst particles; (2) Use of IDA electrodes with largely improved sensitivity for in-situ detection of reaction intermediates (H2O2) and provide insight into the reaction pathway and electron transfer process. It indicates that the specific activity and mass activity are larger for the smaller-sized Pt cluster. Specifically, the proportion of different electron transfer pathways was analyzed with IDA results, and with the same amount of Pt catalyst loading, the smaller-sized Pt cluster produces a higher percent of H2O2; the smaller-sized Pt catalyzed ORR undergoes less proportion of 4-electron pathway than the larger-sized Pt catalyst (about 43% total catalytic current is contributed by the 4-electron pathway for the #6 Pt catalyst, and this number raises to 98% for the #1 Pt catalyst).

Steady-state currents of planar interdigitated electrode arrays in shallow cells

Analytical equations for the steady-state current at shallow electrochemical cells with embedded interdigitated electrode (IDE) arrays were found by solving the diffusion equation in steady state using conformal transformations. These equations consider the cases where the IDE is used with an external counter electrode (four-electrode configuration) and where one of its arrays is used as internal counter electrode (three- and two-electrode configuration). Since the expressions for the current depend on Jacobian elliptic functions, we found approximations which depend only on trigonometric and hyperbolic functions which can ease the calculations at the expense of an error below 5%. Additionally, we provide expressions for steady-state voltammograms for the case of Nernstian (reversible) electrode reactions. The obtained theoretical results agree with theoretical and simulation results from the literature and with our own experiments. These results can be useful as criteria for designing electrochemical cells based on IDEs, and as benchmarks for assessing their performance, especially for polymer- or paper-based microfluidics.

Development of Rapid Dispense-Printed Flexible Interdigitated Electrode Modified with rGO-TiO2 Nanohybrid for Glucose Detection

A rapid and facile method in developing a printed electrochemical glucose sensor constructed using flexible interdigitated electrode (IDE) employed with reduced graphene oxide (rGO)-Titanium dioxide (TiO2) is demonstrated. A 2 × 3 silver (Ag)-based IDE array based on a simulated IDE model, was fabricated via a single-step dispense-printing within less than 5 min, while a rGO-TiO2 nanohybrid and glucose oxidase (GOx) enzyme was coated on the IDE surface simply via drop-casting method. Exceptional reproducibility and repeatability of the printed IDE functionalized with rGO-TiO2/GOx in terms of electrical and mechanical performance were observed. The stability of the sensor was investigated over a week period, in which 6%–7% performance degradation was recorded based on resistance measurement in flat state, whereas no further significant loss was noted over the same period in bending state. The IDE sensor was tested using chronoamperometry with varied glucose concentrations up to 30 mM, resulted in a stabilized current after 5 s. The sensitivity plot attained depicted a best linear fit of 0.988 obtained at response time of 60 s, whilst covering lowest detection at 0.05 mM and selective detection from ascorbic acid and uric acid. The application of this sensor could contribute as an alternative method to develop a reliable and economical glucose sensing wearable for independent monitoring.

Enhanced adhesion of functional layers by controlled electrografting of ethylenediamine on ITO for electrochemical immunoassay in microfluidic channel.

Two-electrode (2E) system of the interdigitated electrode array (IDA), which operates neither reference nor counter electrodes, has great potential to miniaturize multiplex immunoassay in a microfluidic chip for point-of-care testing. However, it is necessary to firmly immobilize the mediator layer on IDA made of indium tin oxide (ITO) which is chemically inert. It is important because the mediator determines the electrochemical potential in the 2E system, but the layer is easy to be detached during the washing processes of immunoassay. Here, we controlled the concentration of ethylenediamine (EDA) to generate a permeable and robust film to adhere to mediators on the ITO IDA chip. Electrooxidation of EDA yielded thin oligomeric ethyleneimine (OEI) film and it provided amine groups for immobilizing the mediator, poly(toluidine blue) (pTB), via common conjugation reaction. Despite repeated flows in the microchannel, which are essential for sensitive immunoassay, the pTB/OEI layer was hardly washed and still remained on the ITO IDA. Myoglobin was measured down to∼pg/mL level. Therefore, the ITO IDA modified with the OEI film in the 2E system constituted a stable platform that withstands washing steps for sensitive electrochemical detection in the miniaturized immunoassay.

Simple and sensitive electrochemical detection of aminopeptidase N using monolayer-modified Au interdigitated array electrodes with moderate electrocatalytic activities

Electrochemical–electrochemical (EE) redox cycling using interdigitated array (IDA) electrodes is a simple and efficient approach for signal amplification. However, IDA electrodes with high or low electrocatalytic activities are inappropriate for obtaining high signal-to-background ratios in serum containing various interfering redox-active species. Accordingly, herein, Au IDA electrodes are modified with a monolayer of 6-mercapto-1-hexanol (MCH) to achieve moderate electrocatalytic activities, and the modified electrodes are applied to the simple and sensitive electrochemical detection of aminopeptidase N (APN) in human serum. APN liberates redox-active species (namely, 4-amino-1-naphthol, AN) via proteolytic cleavage of AN-conjugated substrates, and the released AN participates in the EE redox cycling. Among facilely synthesized five possible AN-conjugated substrates, AN-conjugated alanine is most rapidly cleaved by APN. MCH modification significantly decreases capacitive currents and the occurrences of unwanted faradaic reactions. The detection limit for APN in a 10-fold diluted human serum in the case of EE redox cycling without a washing step (3.8 ng/mL) is 40 times lower than that obtained without EE redox cycling (150 ng/mL). The proposed detection method exhibits high selectivity toward APN regardless of the presence of other proteases. This simple and selective method is practically promising for APN analysis in human serum.

Transport effects in biochip sensors with redox cycling amplification

We report a study of transport effects on a microfluidic sensor-chip in which electrochemical sensing is amplified by redox cycling using an interdigitated electrode array (IDA). A full three-dimensional simulation-based model and a simple one-dimensional model for the transition velocity between the two regimes is presented. These models indicate that there exist two dominant regimes: one which is limited by redox cycling diffusion—a unique feature of IDAs— and another which is limited by convection and has dominant flow effects. The transition velocity between the two sensing regimes was found to be vflow[mmsec]=0.335L[μm]+0.04 which is similar to the prediction of vflow∝1L, obtained from the one-dimensional model.

Ultramicro Interdigitated Array Electrode Chip with Optimized Construction for Detection of Ammonia Nitrogen in Water

Ammonia nitrogen is a common contaminant in water and its determination is important for environmental protection. In this paper, an electrochemical sensor based on an ultramicro interdigitated array electrode (UIAE) chip with optimized construction was fabricated with Micro-Electro-Mechanical System (MEMS) technology and developed to realize the detection of ammonia nitrogen in water. The effects of spacing-to-width ratio and width of the working electrode on UIAE's electrochemical characteristics and its ammonia nitrogen detection performance were studied by finite element simulation and experiment. The results demonstrated that the smaller the spacing-to-width ratio, the stronger generation-collection effect, and the smaller the electrode width, the stronger the edge effect, which led to an easier steady-state reach, a higher response current, and better ammonia nitrogen determination performance. The fabricated UIAE chip with optimized construction showed the linear detection range of 0.15 mg/L~2.0 mg/L (calculated as N), the sensitivity of 0.4181 μA·L·mg-1, and good anti-interference performance, as well as a long lifetime. UIAE based on bare Pt was successfully applied to ammonia nitrogen detection in water by optimizing structure, which might broaden the methods of ammonia nitrogen detection in water.

Active THz beam shaping using a one-dimensional array of photoconductive emitters

The spatial profile of a beam of pulsed terahertz (THz) radiation is controlled electrically using a multi-pixel photoconductive emitter, which consists of an array of interdigitated electrodes fabricated on semi-insulating GaAs. Activating individual pixels allows the transverse position of the THz beam's focus to be varied off-axis, as verified by spatial beam profiles. Enabling multiple pixels simultaneously permits non-Gaussian beam shapes to be created. The diffraction-limited performance of the system is established by comparison with the Abbé and Sparrow criteria, and a condition for effective beam steering using this design is derived. The spatial resolution of the approach is linked to the frequency of the THz radiation and the f-number of the collection optic.

Highly Sensitive Electrochemical Endotoxin Sensor Based on Redox Cycling Using an Interdigitated Array Electrode Device

The Limulus amebocyte lysate (LAL) reaction-based assay, the most commonly used endotoxin detection method, requires a skilled technician. In this study, to develop an easy-to-use and highly sensitive endotoxin sensor, we created an electrochemical endotoxin sensor by using an interdigitated array electrode (IDAE) device with advantages of amplifiable signals via redox cycling and portability. We added Boc-Leu-Gly-Arg-p-aminophenol (LGR-pAP) as an electrochemical substrate for an LAL reaction and detected p-aminophenol (pAP) released from LGR-pAP as a product of an endotoxin-induced LAL reaction via an IDAE device. The IDAE device showed a great redox cycling efficiency of 79.8%, and a 4.79-fold signal amplification rate. Then, we confirmed that pAP was detectable in the presence of LGR-pAP through chronoamperometry with the potential of the anode stepped from -0.3 to 0.5 V vs. Ag/AgCl while the cathode was biased at -0.3 V vs. Ag/AgCl. Then, we performed an endotoxin assay by using the IDAE device. Our endotoxin sensor detected as low as 0.7 and 1.0 endotoxin unit/L after the LAL reaction for 1 h and 45 min, respectively, and these data were within the cut-off value for ultrapure dialysis fluid. Therefore, our highly sensitive endotoxin sensor is useful for ensuring medical safety.

Rapid fabrication of interdigitated electrodes by laser ablation with application to electrokinetically enhanced surface plasmon resonance imaging

SignificanceDielectrophoresis, electro-osmosis, and other electrokinetic effects are frequently used in a variety of applications but necessitate patterning of electrodes on sensor surfaces. This typically requires a cleanroom and time-consuming, expensive, and arcane lithography and etching procedures. AimTo demonstrate the applicability of commercial laser direct writing equipment for rapid patterning of electrodes into gold layers on glass substrates, particularly with application to producing electrokinetically active plasmonic sensors. ApproachA commercial printed circuit board prototyper was used to pattern interdigitated electrode (IDE) arrays into the surface of gold-coated slides and off-the-shelf surface plasmon resonance (SPR) prisms. The electrode geometries resulting from different patterning parameters were characterized by profilometry and electron microscopy. The patterned surfaces were then employed for trapping and electro-kinetic manipulation of bacteria, and finally for sensing of bacteria by SPR imaging. ResultsFabrication of an IDE array can be completed in as little as 12 s, with longer fabrication times permitting superior geometry and minimum feature size of 15 µm. The patterned IDEs were capable of concentrating bacteria and controlling their position on the sensor surface as a function of applied frequencies. SPR was demonstrated to detect specific interactions between bacteria and immobilized antimicrobial peptides. ConclusionsLaser direct writing is demonstrated as a feasible, cleanroom-free alternative to more lengthy lithography methods, permitting very rapid fabrication and prototyping of IDEs, which are compatible with active plasmonic sensing and bacterial detection.

A Review on Microfluidics-Based Impedance Biosensors

Electrical impedance biosensors are powerful and continuously being developed for various biological sensing applications. In this line, the sensitivity of impedance biosensors embedded with microfluidic technologies, such as sheath flow focusing, dielectrophoretic focusing, and interdigitated electrode arrays, can still be greatly improved. In particular, reagent consumption reduction and analysis time-shortening features can highly increase the analytical capabilities of such biosensors. Moreover, the reliability and efficiency of analyses are benefited by microfluidics-enabled automation. Through the use of mature microfluidic technology, complicated biological processes can be shrunk and integrated into a single microfluidic system (e.g., lab-on-a-chip or micro-total analysis systems). By incorporating electrical impedance biosensors, hand-held and bench-top microfluidic systems can be easily developed and operated by personnel without professional training. Furthermore, the impedance spectrum provides broad information regarding cell size, membrane capacitance, cytoplasmic conductivity, and cytoplasmic permittivity without the need for fluorescent labeling, magnetic modifications, or other cellular treatments. In this review article, a comprehensive summary of microfluidics-based impedance biosensors is presented. The structure of this article is based on the different substrate material categorizations. Moreover, the development trend of microfluidics-based impedance biosensors is discussed, along with difficulties and challenges that may be encountered in the future.

Development of a simultaneous electrorotation device with microwells for monitoring the rotation rates of multiple single cells upon chemical stimulation.

Here, we described a unique simultaneous electrorotation (ROT) device for monitoring the rotation rate of Jurkat cells via chemical stimulation without fluorescent labeling and an algorithm for estimating cell rotation rates. The device comprised two pairs of interdigitated array electrodes that were stacked orthogonally through a 20 μm-thick insulating layer with rectangular microwells. Four microelectrodes (two were patterned on the bottom of the microwells and the other two on the insulating layer) were arranged on each side of the rectangular microwells. The cells, which were trapped in the microwells, underwent ROT when AC voltages were applied to the four microelectrodes to generate a rotating electric field. These microwells maintained the cells even in fluid flows. Thereafter, the ROT rates of the trapped cells were estimated and monitored during the stimulation. We demonstrated the feasibility of estimating the chemical efficiency of cells by monitoring the ROT rates of the cells. After introducing a Jurkat cell suspension into the device, the cells were subjected to ROT by applying an AC signal. Further, the rotating cells were chemically stimulated by adding an ionomycin (a calcium ionophore)-containing aliquot. The ROT rate of the ionomycin-stimulated cells decreased gradually to 90% of the initial rate after 30 s. The ROT rate was reduced by an increase in membrane capacitance. Thus, our device enabled the simultaneous chemical stimulation-induced monitoring of the alterations in the membrane capacitances of many cells without fluorescent labeling.