A low-cost, ultraflexible cloth-based microfluidic device for wireless electrochemiluminescence application

A dry chemistry-based self-enhanced electrochemiluminescence lateral flow immunoassay sensor for accurate sample-to-answer detection of luteinizing hormone

BACKGROUND

Colorimetric lateral flow immunoassay (LFIA) is a widely used point-of-care testing (POCT) technology, while it has entered a bottleneck period because of low detection sensitivity, expensive preparation materials, and incapable quantitative detection. Therefore, it is necessary to develop a novel POCT method that is ultrasensitive, simple, portable, and capable of accurately detecting biomarkers in biofluids daily, particularly for pregnancy preparation and early screening of diseases.

RESULT

In this work, a novel dry chemistry-based self-enhanced electrochemiluminescence (DC-SE-ECL) LFIA sensor is introduced for accurate POCT of luteinizing hormone (LH). The proposed DC-SE-ECL immunosensor significantly improves the detection sensitivity through the Poly-l-Lysine (PLL)-based SE-ECL probe and cathode modification of closed bipolar electrode (C-BPE). Additionally, a new type of C-BPE configuration is designed for easily performing the LFIA. And, two standalone absorbent pads are symmetrically arranged below the reporting channel of the electrode pad to decease useless residues on the detection pad, which further improves the detection performance. Under optimized conditions, the proposed LFIA sensor has a low limit of detection (9.274 μIU mL-1) and a wide linear dynamic range (0.01-100 mIU mL-1), together with good selectivity, repeatability and storage stability.

SIGNIFICANCE

These results indicate that the proposed DC-SE-ECL method has the potential as a new tool for detecting biomarkers in clinical samples.

Microfluidic sensors for the detection of emerging contaminants in water: A review

In recent years, numerous emerging contaminants have been identified in surface water, groundwater, and drinking water. Developing novel sensing methods for detecting diverse emerging pollutants in water is urgently needed, as even at low concentrations, these pollutants can pose a serious threat to human health and environmental safety. Traditional testing methods are based on laboratory equipment, which is highly sensitive but complex to operate, costly, and not suitable for on-site monitoring. Microfluidic sensors offer several benefits, including rapid evaluation, minimal sample usage, accurate liquid manipulation, compact size, automation, and in-situ detection capabilities. They provide promising and efficient analytical tools for high-performance sensing platforms in monitoring emerging contaminants in water. In this paper, recent research advances in microfluidic sensors for the detection of emerging contaminants in water are reviewed. Initially, a concise overview is provided about the various substrate materials, corresponding microfabrication techniques, different driving forces, and commonly used detection techniques for microfluidic devices. Subsequently, a comprehensive analysis is conducted on microfluidic detection methods for endocrine-disrupting chemicals, pharmaceuticals and personal care products, microplastics, and perfluorinated compounds. Finally, the prospects and future challenges of microfluidic sensors in this field are discussed.

Optimization and miniaturization of SE-ECL for potential-resolved, multi-color, multi-analyte detection

Electrochemiluminescence (ECL) is a bioanalytical technique with numerous advantages, including the potential for high temporal and spatial resolution, a high signal-to-noise ratio, a broad dynamic range, and rapid measurement capabilities. To reduce the complexity of a multi-electrode approach, we use a single-electrode electrochemiluminescence (SE-ECL) configuration to achieve the simultaneous emission and detection of multiple colors for applications that require multiplexed detection of several analytes. This method exploits intrinsic differences in the electric potential applied along single electrodes built into electrochemical cells, enabling the achievement of distinct colors through selective excitation of ECL luminophores. We present results on the optimization of SE-ECL intensity for different channel lengths and widths, with sum intensities being 5 times larger for 6 cm vs. 2 cm channels and linearly increasing with the width of the channels. Furthermore, we demonstrated for the first time that applying Alternating Current (AC) voltage within the single electrode setup for driving the ECL reactions has a dramatic effect on the emitted light intensity, with square waveforms resulting in higher intensities vs sine waveforms. Additionally, multiplexed multicolor SE-ECL on a 6.5 mm × 3.6 mm CMOS semiconductor image sensor was demonstrated for the first time, with the ability to simultaneously distinguish four different colors, leading to the ability to measure multiple analytes.

A visualization method for quickly detecting nitrite ions in breath condensate using a portable closed bipolar electrochemical sensor

A portable and non-invasive sensor presents an innovative way to measure inflammation biomarkers in exhaled breath condensate (EBC). This research is focused on developing a miniaturized bipolar electrochemical sensor that can be connected to a smartphone app. This device will be able to detect adding known amounts of nitrite (spikes) to a salt solution and small amounts of nitrite ions in collected real samples in EBC. The sensor was fabricated and tested for its rapid electron transfer capability and ability to detect nitrite ions even at very low concentrations and low real sample levels. In the proposed setup, when the required potential was applied by using a direct power supply, the nitrite ions were oxidized electrocatalytically at amine-functionalized graphene oxide (AGO) decorated with gold nanoparticles on a carbon paper anodic pole. On the other hand, the reduction reaction of Prussian blue occurred at the cathodic pole of the bipolar electrode simultaneously. This strategy led to a change in color from blue to white as a result of the reduction process and the color change is proportional to the concentration of nitrite ions in the analytical solution. The combination of smartphones with the colorimetric method has resulted in a platform for the detection of test strips that is more visual and convenient. The amperometry and voltammetric methods of nitrite detection showed a linear range of up to 1230 μM. The bipolar electrochemical sensor was able to detect the clinically relevant range of nitrite from 0.5 to 85 μM in a buffer with an ultralow detection limit (LOD) of 250 nM (S/N = 3), fast response and excellent selectivity. It was benchmarked by utilizing pre-characterized real EBC samples to differentiate patients with respiratory diseases from healthy volunteers. By tracking the results of nitrite measurements over time, it has become possible to detect trends and changes in an individual's nitrite ion concentration and to potentially identify lung inflammation earlier.

Ti3C2/Ni/Sm-based electrochemical glucose sensor for sweat analysis using bipolar electrochemistry

An innovative electrochemical sensor is introduced that utilizes bipolar electrochemistry on a paper substrate for detecting glucose in sweat. The sensor employs a three-dimensional porous nanocomposite (MXene/NiSm-LDH) formed by decorating nickel-samarium nanoparticles with double-layer MXene hydroxide. These specially designed electrodes exhibit exceptional electrocatalytic activity during glucose oxidation. The glucose sensing mechanism involves enzyme-free oxidation of the analyte within the sensor cell, achieved by applying an appropriate potential. This leads to the reduction of K3Fe(CN)6 in the reporter cell, and the resulting current serves as the response signal. By optimizing various parameters, the measurement platform enables the accurate determination of sweat glucose concentrations within a linear range of 10 to 200 µM. The limit of detection (LOD) for glucose is 3.6 µM (S/N = 3), indicating a sensitive and reliable detection capability. Real samples were analysed  to validate the sensor's efficiency, and the results obtained were both promising and encouraging.

Efficient Electrochemiluminescence Sensing in Microfluidic Biosensors: A Review

Microfluidic devices are capable of handling 10-9 L to 10-18 L of fluids by incorporating tiny channels with dimensions of ten to hundreds of micrometers, and they can be fabricated using a wide range of materials including glass, silicon, polymers, paper, and cloth for tailored sensing applications. Microfluidic biosensors integrated with detection methods such as electrochemiluminescence (ECL) can be used for the diagnosis and prognosis of diseases. Coupled with ECL, these tandem devices are capable of sensing biomarkers at nanomolar to picomolar concentrations, reproducibly. Measurement at this low level of concentration makes microfluidic electrochemiluminescence (MF-ECL) devices ideal for biomarker detection in the context of early warning systems for diseases such as myocardial infarction, cancer, and others. However, the technology relies on the nature and inherent characteristics of an efficient luminophore. The luminophore typically undergoes a redox process to generate excited species which emit energy in the form of light upon relaxation to lower energy states. Therefore, in biosensor design the efficiency of the luminophore is critical. This review is focused on the integration of microfluidic devices with biosensors and using electrochemiluminescence as a detection method. We highlight the dual role of carbon quantum dots as a luminophore and co-reactant in electrochemiluminescence analysis, drawing on their unique properties that include large specific surface area, easy functionalization, and unique luminescent properties.

A dual-readout sensing platform for the evaluation of cell viability integrating with optical and digital signals based on a closed bipolar electrode

Cell viability is essential for predicting drug toxicity and assessing drug effects in drug screening. However, the over/underestimation of cell viability measured by traditional tetrazolium colorimetric assays is inevitable in cell-based experiments. Hydrogen peroxide (H2O2) secreted by living cells may provide more comprehensive information about the cell state. Hence, it is significant to develop a simple and rapid approach for evaluating cell viability by measuring the excreted H2O2. In this work, we developed a dual-readout sensing platform based on optical and digital signals by integrating a light emitting diode (LED) and a light dependent resistor (LDR) into a closed split bipolar electrode (BPE), denoted as BP-LED-E-LDR, for evaluating cell viability by measuring the H2O2 secreted from living cells in drug screening. Additionally, the customized three-dimensional (3D) printed components were designed to adjust the distance and angle between the LED and LDR, achieving stable, reliable and highly efficient signal transformation. It only took 2 min to obtain response results. For measuring the exocytosis H2O2 from living cells, we observed a good linear relationship between the visual/digital signal and logarithmic function of MCF-7 cell counts. Furthermore, the fitted half inhibitory concentration curve of MCF-7 to doxorubicin hydrochloride obtained by the BP-LED-E-LDR device revealed a nearly identical tendency with the cell counting kit-8 assay, providing an attainable, reusable, and robust analytical strategy for evaluating cell viability in drug toxicology research.

Sample-to-answer sensing technologies for nucleic acid preparation and detection in the field

Efficient sample preparation and accurate disease diagnosis under field conditions are of great importance for the early intervention of diseases in humans, animals, and plants. However, in-field preparation of high-quality nucleic acids from various specimens for downstream analyses, such as amplification and sequencing, is challenging. Thus, developing and adapting sample lysis and nucleic acid extraction protocols suitable for portable formats have drawn significant attention. Similarly, various nucleic acid amplification techniques and detection methods have also been explored. Combining these functions in an integrated platform has resulted in emergent sample-to-answer sensing systems that allow effective disease detection and analyses outside a laboratory. Such devices have a vast potential to improve healthcare in resource-limited settings, low-cost and distributed surveillance of diseases in food and agriculture industries, environmental monitoring, and defense against biological warfare and terrorism. This paper reviews recent advances in portable sample preparation technologies and facile detection methods that have been / or could be adopted into novel sample-to-answer devices. In addition, recent developments and challenges of commercial kits and devices targeting on-site diagnosis of various plant diseases are discussed.

Comparison of Mobile Phone and CCD Cameras for Electrochemiluminescent Detection of Biogenic Amines

Biogenic amines are an important and widely studied class of molecules due to their link to the physiological processes of food-related illnesses and histamine poisoning. Electrochemiluminescent (ECL) detection offers an inexpensive and portable analytical method of detection for biogenic amines when coupled with recent advancements in low-cost carbon-based electrodes and a smartphone camera. In this work, a mobile phone camera was evaluated against a piece of conventional instrumentation, the charge-coupled device, for the detection of ECL from the reaction of biogenic amines with the luminescent compound tris(2,2'-bipyridyl)ruthenium(II). Assisted by a 3D-printed light-tight housing, the mobile phone achieved limits of detection of 127, 425 and 421 μM for spermidine, putrescine, and histamine, respectively. The mobile phone's analytical figures of merit were lesser than the CCD camera but were still within the range to detect contamination. In an exploration of real-world samples, the mobile phone was able to determine the contents of amines in skim milk on par with that of a CCD camera.

Shared-cathode closed bipolar electrochemiluminescence cloth-based chip for multiplex detection

Electrochemiluminescence (ECL) chips have been widely used in the field of medical diagnosis. However, most of these chips currently in use are costly and require high amounts of sample. In this work, we present, for the first time, a shared-cathode closed bipolar electrochemiluminescence (SC-CBP-ECL) cloth-based chip, which can be used for multiplex detection. The SC-CBP-ECL chips ($0.03-0.05 for each chip) are manufactured using carbon ink- and wax-based screen-printing techniques, without the need for expensive and complex fabrication equipment. Under optimised conditions, the SC-CBP-ECL chips were successfully used for coinstantaneous detection of glucose in double ECL systems (i.e., Ru(bpy)₃²⁺ and luminol), with corresponding linear ranges of 0.05-1 mM and 0.05-10 mM, and detection limits of 0.0382 mM and 0.0422 mM. To our knowledge, this is the first report on the application of fibre material-based closed bipolar electrodes (C-BPE) combined with double ECL systems. Furthermore, the SC-CBP-ECL chips exhibit an acceptable specificity and good reproducibility and stability and can be used for glucose detection in human serum samples with a good agreement compared with the clinical method. Finally, the SC-CBP-ECL chips could be successfully used for simultaneous detection of seven glucose samples and also show potential for simultaneous detection of three different targets (hydrogen peroxide [H₂O₂], glucose, and uric acid [UA]). Therefore, we believe that the chip described in this study has broad potential application in the field of cost-effective multiplex detection.

A microfluidic cloth-based photoelectrochemical analytical device for the detection of glucose in saliva

Photoelectrochemical (PEC) detection is a widely used detection method that uses light to stimulate and photocurrent signals to detect the target. Due to the disengagement of the excitation unit and the detection unit, the PEC background signal is reduced, and the detection sensitivity is improved. In this work, we report the first demonstration of PEC detection for microfluidic cloth-based analytical devices (μCADs). Using PEC μCADs integrated with cadmium sulfide quantum dots (CdS QDs) and multiwalled carbon nanotubes (MWCNTs), the nonenzymatic, sensitive and rapid measurement of glucose in saliva has been achieved. For the cloth-based device, the PEC reaction zone and cloth-based electrodes can be fabricated by inexpensive wax-based and carbon ink-based screen-printing, respectively. By the layer-by-layer method, the as-prepared poly (dimethyl diadly ammonium chloride-functionalized) MWCNTs (PDDA-MWCNTs) and CdS QDs are successively adsorbed onto the working electrode surface of the cloth-based device. In the presence of an excitation source and glucose, the CdS QDs generate a strong oxidizing electron hole that can then continuously oxidize glucose to produce an electrical signal for glucose detection. Under optimized conditions, a linear dependence is obtained between the PEC signal and glucose concentrations in the range of 0.05-1000 μM with a detection limit of 15.99 nM. In the detection range, the cloth-based device also shows acceptable selectivity, reproducibility, and long-term stability. Moreover, the method has been implemented for the detection of glucose in real saliva samples, suggesting good potential for biochemical applications.

IoT Enabled PMT and Smartphone based Electrochemiluminescence Platform to Detect Choline and Dopamine Using 3D-Printed Closed Bipolar Electrodes

There is a growing demand to realize low-cost miniaturized point-of-care testing diagnostic devices capable of performing many analytical assays. To fabricate such devices, three-dimensional printing (3DP) based fabrication technique provides a turnkey approach with remarkable precision and accuracy. Herein, 3DP fabrication technique was successfully utilized to fabricate closed bipolar electrode-based Electrochemiluminescence devices using conductive graphene filament. Further, using these ECL devices, Ru (bpy)₃ ²⁺ /TPrA and Luminol/H₂ O₂ based electrochemistry was leveraged to sense dopamine and choline respectively. For ECL signal capturing, two distinct approaches were used, first a smartphone-based miniaturized platform and the second with a photomultiplier tube (PMT) embedded with the Internet of Things technology. Choline sensing led to a linear range 5 μM to 700 μM and 30 μM to 700 μM with limit of detection (LOD) of 1.25 μM (R² = 0.98, N = 3) and 3.27 μM (R² = 0.97, N = 3). Further, dopamine sensing was achieved in a linear range of 0.5 μM to 100 μM with LOD = 2 μM (R² = 0.99, N = 3) and LOD = 0.33 μM (R² = 0.98, N = 3). Overall, the fabricated devices have the potential to be utilized effectively in real-time applications such as point-of-care testing.

A novel cloth-based supersandwich electrochemical aptasensor for direct, sensitive detection of pathogens

Traditional detection methods for food-borne pathogens are usually expensive and laborious, so there is an urgent need for an economical, facile and sensitive method. In this work, a novel cloth-based supersandwich electrochemical aptasensor (CSEA) is firstly developed for direct detection of pathogens. Carbon ink- and wax-based screen-printing is used to make cloth-based electrodes and hydrophilic/hydrophobic regions respectively to fabricate the sensing devices. Two well-designed, specific single-stranded DNA sequences arise a cascade hybridization reaction to form the DNA supersandwich (DSS) whose grooves can be inserted by methylene blue (MB), which effectively amplifies the current signal to greatly improve the detection sensitivity. Taking the detection of Salmonella typhimurium (S. typhimurium) as an example, the aptamers bind to S. typhimurium to form the target-aptamers complex, which can simultaneously bind to the capture probe and DSS, resulting in detection of S. typhimurium. Moreover, the addition of tail sequences of aptamer makes the proposed CSEA versatile. Under optimized conditions, the electrochemical signal increases linearly with the logarithm of S. typhimurium concentration over the range from 10² to 10⁸ CFU mL^-1, with a limit of detection of 16 CFU mL^-1. Additionally, the CSEA efficiently determined the levels of S. typhimurium in milk samples. Experimental results illustrate that the fabricated CSEA is sensitive, specific, reproducible and stable. Moreover, when Ru(bpy)₃²⁺ replaces MB, the electrochemiluminescence (ECL) can be performed. Thus, for the proposed sensing strategy, the dual-mode detection of electrochemistry and ECL is easily realized.

3D microfluidic cloth-based analytical devices on a single piece of cloth by one-step laser hydrophilicity modification

In this work, we report for the first time a simple and robust method for constructing a 3D microfluidic analytical device on a single piece of hydrophobic cotton cloth. Specifically, laser scanning technology was applied to process hydrophilic regions at the top and bottom of a single piece of hydrophobic cloth. Symmetrical hydrophilic regions at the bottom and top constituted vertical microfluidic channels, and asymmetrical hydrophilic regions constituted transverse flow channels. Liquid flow velocity in 3D cloth-based microchannels can be adjusted flexibly by modifying laser parameters, and programmable laser scanning can be utilized to process 3D microfluidic devices with various patterns. Single-piece 3D cloth-based microfluidic devices formed via this method can be used in many fields such as information encryption and anti-counterfeiting, multi-liquid printing and liquid mixing dilution. Compared to traditional processing methods of 3D cloth-based microfluidic devices, the laser scanning method eliminates multiple complex and repetitive assembly processes, which is a significant advance in this research area. This processing method provides a new option for fast and large-scale manufacturing of 3D cloth-based microfluidic analysis devices for point-of-care testing application in undeveloped regions/countries.

Microfluidic devices based on textile threads for analytical applications: state of the art and prospects

Microfluidic devices based on textile threads have interesting advantages when compared to systems made with traditional materials, such as polymers and inorganic substrates (especially silicon and glass). One of these significant advantages is the device fabrication process, made more cheap and simple, with little or no microfabrication apparatus. This review describes the fundamentals, applications, challenges, and prospects of microfluidic devices fabricated with textile threads. A wide range of applications is discussed, integrated with several analysis methods, such as electrochemical, colorimetric, electrophoretic, chromatographic, and fluorescence. Additionally, the integration of these devices with different substrates (e.g., 3D printed components or fabrics), other devices (e.g., smartphones), and microelectronics is described. These combinations have allowed the construction of fully portable devices and consequently the development of point-of-care and wearable analytical systems.

Bipolar (Bio)electroanalysis

This contribution reviews a selection of the most recent studies on the use of bipolar electrochemistry in the framework of analytical chemistry. Despite the fact that the concept is not new, with several important studies dating back to the middle of the last century, completely novel and very original approaches have emerged over the last decade. This current revival illustrates that scientists still (re)discover some exciting virtues of this approach, which are useful in many different areas, especially for tackling analytical challenges in an unconventional way. In several cases, this "wireless" electrochemistry strategy enables carrying out measurements that are simply not possible with classic electrochemical approaches. This review will hopefully stimulate new ideas and trigger scientists to integrate some aspects of bipolar electrochemistry in their work in order to drive the topic into yet unexplored and eventually completely unexpected directions.

Miniaturized Electrochemiluminescence Platform With Laser-Induced Graphene Electrodes for Multiple Biosensing

The present work demonstrates a miniaturized 3D printed Electrochemiluminescence (ECL) sensing platform with Laser-Induced Graphene (LIG) based Open Bipolar Electrodes (OBEs). To fabricate OBEs, polyimide (PI) substrate has been used as it provides properties like low-cost fabrication, high selectivity, great stability, easy reproducibility, cost-effectiveness and rapid prototyping. Moreover, graphene can be created on PI in a single step during the ablation of the CO₂ laser. Android smartphone was efficiently used to sense ECL signals as well as to drive the required voltage to the OBEs. With the optimized parameters, the imaging system was successfully used to detect Hydrogen Peroxide (H₂ O₂) with a linear range of 1 [Formula: see text] to [Formula: see text] and detection of limit (LOD) [Formula: see text] (R² = 0.9449, n = 3). In addition, the detection of glucose has been carried out with a linear range of [Formula: see text] to [Formula: see text] and detection of limit (LOD) [Formula: see text] (R² = 0.9875, n = 3). Further, real samples were tested to manifest the workability of the platform for random samples. Overall, the developed low-cost, rapidly realized and the miniaturized system can be used in many biomedical applications, environmental monitoring and point-of-care testings.

Microfluidic cloth-based analytical devices: Emerging technologies and applications

Cloth (or fabric) is an omnipresent material that has various applications in everyday life, and has become one of the things people are most familiar with. It has some attractive properties such as low cost, ability to transport fluid by capillary force, high tensile strength and durability, good wet strength, and great biocompatibility and biodegradability. Hence, cloth is an ideal material for the development of economical and user-friendly diagnostic devices for many applications including food detection, environmental monitoring, disease diagnosis and public health. Microfluidic cloth-based analytical devices (μCADs) (or microfluidic fabric-based analytical devices (μFADs)) first emerged in 2011 as a low-cost alternative to conventional laboratory testing, with the goal of improving point of care testing and disease screening in the developing world. In this review, we examine the advances in the development of μCADs from 2011 to 2020, especially highlighting emerging technologies and applications related to the μCADs. First, different fabrication methods for μCADs are introduced and compared. Second, a series of cloth-based microfluidic functional components are discussed, including microvalves, fluid velocity control elements, micromixers, and microfilters. Then, electroanalytical μCADs are described, especially focusing on the use of cloth-based electrodes. Next, various detection methods for μCADs, together with their corresponding applications, are compared and categorized. In addition, the current development of wearable μCADs is also demonstrated. Finally, the future outlook and trends in this field are discussed.

Recent advances in thread-based microfluidics for diagnostic applications

Over the past decades, researchers have been seeking attractive substrate materials to keep microfluidics improving to outbalance the drawbacks and issues. Cellulose substrates, including thread, paper and hydrogels are alternatives due to their distinct structural and mechanical properties for a number of applications. Thread have gained considerable attention and become promising powerful tool due to its advantages over paper-based systems thus finds numerous applications in the development of diagnostic systems, smart bandages and tissue engineering. To the best of our knowledge, no comprehensive review articles on the topic of thread-based microfluidics have been published and it is of significance for many scientific communities working on Microfluidics, Biosensors and Lab-on-Chip. This review gives an overview of the advances of thread-based microfluidic diagnostic devices in a variety of applications. It begins with an overall introduction of the fabrication followed by an in-depth review on the detection techniques in such devices and various applications with respect to effort and performance to date. A few perspective directions of thread-based microfluidics in its development are also discussed. Thread-based microfluidics are still at an early development stage and further improvements in terms of fabrication, analytical strategies, and function to become low-cost, low-volume and easy-to-use point-of-care (POC) diagnostic devices that can be adapted or commercialized for real world applications.

Microscale and Nanoscale Electrophotonic Diagnostic Devices

Detecting and identifying infectious agents and potential pathogens in complex environments and characterizing their mode of action is a critical need. Traditional diagnostics have targeted a single characteristic (e.g., spectral response, surface receptor, mass, intrinsic conductivity, etc.). However, advances in detection technologies have identified emerging approaches in which multiple modes of action are combined to obtain enhanced performance characteristics. Particularly appealing in this regard, electrophotonic devices capable of coupling light to electron translocation have experienced rapid recent growth and offer significant advantages for diagnostics. In this review, we explore three specific promising approaches that combine electronics and photonics: (1) assays based on closed bipolar electrochemistry coupling electron transfer to color or fluorescence, (2) sensors based on localized surface plasmon resonances, and (3) emerging nanophotonics approaches, such as those based on zero-mode waveguides and metamaterials.

Life-Saving Threads: Advances in Textile-Based Analytical Devices

Novel approaches that incorporate electrofluidic and microfluidic technologies are reviewed to illustrate the translation of traditional enclosed structures into open and accessible textile based platforms. Through the utilization of on-fiber and on-textile microfluidics, it is possible to invert the typical enclosed capillary column or microfluidic "chip" platform, to achieve surface accessible efficient separations and fluid handling, while maintaining a microfluidic environment. The open fiber/textile based fluidics approach immediately provides new possibilities to interrogate, manipulate, redirect, extract, characterize, and quantify solutes and target species at any point in time during such processes as on-fiber electrodriven separations. This approach is revolutionary in its simplicity and provides many potential advantages not otherwise afforded by the more traditional enclosed platforms.

Sensitivity enhancement of cloth-based closed bipolar electrochemiluminescence glucose sensor via electrode decoration with chitosan/multi-walled carbon nanotubes/graphene quantum dots-gold nanoparticles

In this work, a novel facile closed bipolar electrochemiluminescence (C-BP-ECL) sensor has been developed for highly sensitive detection of glucose based on the integration of chitosan (CS), poly(diallyldimethylammonium chloride)-functioned multi-walled carbon nanotubes (PDDA-MWCNTs) and graphene quantum dots-gold nanoparticles (GQDs-AuNPs) on the wax/carbon ink-screen-printed cloth-based device. When CS, PDDA-MWCNTs and GQDs-AuNPs are successively decorated onto the cathode of closed bipolar electrode (C-BPE), the C-BPE anode can emit much stronger C-BP-ECL signals. Moreover, the cathodic decoration of the C-BPE can generate a stronger ECL signal in comparison with its anodic decoration. Under optimized conditions, glucose can be detected in the range of 0.1-5000 μM, and the limit of detection is estimated to be 64 nM, which is about three orders of magnitude lower than that in case of the bare C-BPE cathode (31 μM). It has been shown that the proposed sensor has high detection sensitivity, wide dynamic range, and as well acceptable reproducibility, selectivity and stability. Finally, the applicability and validity of the C-BP-ECL sensor are demonstrated for the detection of glucose in human serum samples. We believe that this novel highly-sensitive sensor will have potential applications in various areas such as clinical diagnosis, food analysis and environmental monitoring.

Paper-based electrochemiluminescence sensor for highly sensitive detection of amyloid-β oligomerization: Toward potential diagnosis of Alzheimer's disease

Development of a rapid and sensitive method for Aβ(1-42) aggregation detection is of great importance to overcome the limitations of conventional techniques. In this study, we developed a label-free paper-based electrochemiluminescence sensor for amyloid-β aggregation detection toward potential diagnosis of Alzheimer's disease (AD). The paper-based chip used in the system serves as a low-cost and disposable detection method. In this detection platform, the bonding of [Ru(phen)2dppz]2+ to Aβ(1-42) aggregates results in enhanced electrochemiluminescence due to the change in the polarity of the microenvironment when [Ru(phen)2dppz]2+ intercalated into the β-sheets during oligomerization. The oligomerization process of Aβ(1-42) can be monitored in real time by the novel method, and as low as 100 pM equivalent monomer concentration of Aβ(1-42) could be detected simultaneously. In addition, the cerebrospinal fluid of transgenic AD model mice was tested by this method, which is highly consistent with genetic identification. In addition, we demonstrated that this detection platform could be a potential new method for the screening of Aβ(1-42) aggregation inhibitors, highlighting the practical application capacity of this platform. The platform is label free, low cost and sensitive. Therefore, the proposed platform holds great promise for the diagnosis of AD.

Bipolar Electrodes with 100% Current Efficiency for Sensors

A bipolar electrode (BPE) is an electron conductor that is embedded in the electrolyte solution without the direct connection with the external power source (driving electrode). When the sufficient voltage was provided, the two poles of BPE promote different oxidation and reduction reactions. During the past few years, BPEs with wireless feature and easy integration showed great promise in the various fields including asymmetric modification/synthesis, motion control, targets enrichment/separation, and chemical sensing/biosensing combined with the quantitative relationship between two poles of BPE. In this perspective paper, we first describe the concept and history of the BPE for analytical chemistry and then review the recent developments in the application of BPEs for sensing with ultrahigh current efficiency (η_c = i_BPE/i_channel) including the open and closed bipolar system. Finally, we offer the guide for possible challenge faced and solution in the future.

Facile and sensitive chemiluminescence detection of H2O2 and glucose by a gravity/capillary flow and cloth-based low-cost platform

A gravity/capillary flow and cloth-based low-cost platform is proposed for the facile and sensitive chemiluminescence detection of H₂O₂ and glucose.