An integrated bipolar electrode with shared cathode for dual-mode detection and imaging of CEA.

In this paper, we designed a novel shared cathode bipolar electrode chip based on Ohm 's law and successfully constructed a dual-mode dual-signal biosensor platform (DD-cBPE). The device integrates ELISA, ECL, and ECL imaging to achieve highly sensitive detection and visual imaging of carcinoembryonic antigen (CEA). The unique circuit structure of the device not only realizes the dual signal detection of the target, but also breaks the traditional signal amplification concept. The total resistance of the system is reduced by series-parallel connection of BPE, and the total current in the circuit is increased. In addition, Au@NiCo2O4@MnO2 nanozyme activity probe was introduced into the common cathode to enhance the conductivity of the material. At the same time, due to the excellent peroxidase (POD) activity of NiCo2O4@MnO2, the decomposition of H2O2 was accelerated, so that more electrons flowed to the BPE anode, and finally the dual amplification of the ECL signal was realized. The device affects the current in the circuit by regulating the concentration of the co-reactant TPrA, thereby affecting the resistance of the system. Finally, different luminescent reagents emit light at the same potential and the luminous efficiency is similar. In addition, the chip does not need external resistance regulation, which improves the sensitivity of the immunosensor and meets the needs of timely detection. It provides a new idea for the deviceization of bipolar electrodes and has broad application prospects in biosensors, clinical detection, and environmental monitoring.

Closed Bipolar Nanoelectrode Array for Ultra-Sensitive Detection of Alkaline Phosphatase and Two-Dimensional Imaging of Epidermal Growth Factor Receptors.

The combination of closed bipolar electrodes (cBPE) with electrochemiluminescence (ECL) imaging has demonstrated remarkable capabilities in the field of bioanalysis. Here, we established a cBPE-ECL platform for ultrasensitive detection of alkaline phosphatase (ALP) and two-dimensional imaging of epidermal growth factor receptor (EGFR). This cBPE-ECL system consists of a high-density gold nanowire array in anodic aluminum oxide (AAO) membrane as the cBPE coupled with ECL of highly luminescent cadmium selenide quantum dots (CdSe QDs) luminophores to achieve cathodic electro-optical conversion. When an enzyme-catalyzed amplification effect of ALP with 4-aminophenyl phosphate monosodium salt hydrate (p-APP) as the substrate and 4-aminophenol (p-AP) as the electroactive probe is introduced, a significant improvement of sensing sensitivity with a detection limit as low as 0.5 fM for ALP on the cBPE-ECL platform can be obtained. In addition, the cBPE-ECL sensing system can also be used to detect cancer cells with an impressive detection limit of 50 cells/mL by labeling ALP onto the EGFR protein on A431 human epidermal cancer cell membranes. Thus, two-dimensional (2D) imaging of the EGFR proteins on the cell surface can be achieved, demonstrating that the established cBPE-ECL sensing system is of high resolution for spatiotemporal cell imaging.

Bipolar Textile Composite Electrodes Enabling Flexible Tandem Solid-State Lithium Metal Batteries.

A majority of flexible and wearable electronics require high operational voltage that is conventionally achieved by serial connection of battery unit cells using external wires. However, this inevitably decreases the energy density of the battery module and may cause additional safety hazards. Herein, a bipolar textile composite electrode (BTCE) that enables internal tandem-stacking configuration to yield high-voltage (6 to 12 V class) solid-state lithium metal batteries (SSLMBs) is reported. BTCE is comprised of a nickel-coated poly(ethylene terephthalate) fabric (NiPET) core layer, a cathode coated on one side of the NiPET, and a Li metal anode coated on the other side of the NiPET. Stacking BTCEs with solid-state electrolytes alternatively leads to the extension of output voltage and decreased usage of inert package materials, which in turn significantly boosts the energy density of the battery. More importantly, the BTCE-based SSLMB possesses remarkable capacity retention per cycle of over 99.98% over cycling. The composite structure of BTCE also enables outstanding flexibility; the battery keeps stable charge/discharge characteristics over thousands of bending and folding. BTCE shows great promise for future safe, high-energy-density, and flexible SSLMBs for a wide range of flexible and wearable electronics.

Fe-single-atom catalysts boosting electrochemiluminescence via bipolar electrode integrated with its peroxidase-like activity for bioanalysis.

Multifunctional single-atom catalysts (SACs) have been extensively investigated as outstanding signal amplifiers in bioanalysis field. Herein, a type of Fe single-atom catalysts with Fe-nitrogen coordination sites in nitrogen-doped carbon (Fe-N/C SACs) was synthesized and demonstrated to possess both catalase and peroxidase-like activity. Utilizing Fe-N/C SACs as dual signal amplifier, an efficient bipolar electrode (BPE)-based electrochemiluminescence (ECL) immunoassay was presented for determination of prostate-specific antigen (PSA). The cathode pole of the BPE-ECL platform modified with Fe-N/C SACs is served as the sensing side and luminol at the anode as signal output side. Fe-N/C SACs could catalyze decomposition of H2O2 via their high catalase-like activity and then increase the Faraday current, which can boost the ECL of luminol due to the electroneutrality in a closed BPE system. Meanwhile, in the presence of the target, glucose oxidase (GOx)-Au NPs-Ab2 was introduced through specific immunoreaction, which catalyzes the formation of H2O2. Subsequently, Fe-N/C SACs with peroxidase-like activity catalyze the reaction of H2O2 and 4-chloro-1-naphthol (4-CN) to generate insoluble precipitates, which hinders electron transfer and then inhibits the ECL at the anode. Thus, dual signal amplification of Fe-N/C SACs was achieved by increasing the initial ECL and inhibiting the ECL in the presence of target. The assay exhibits sensitive detection of PSA linearly from 1.0 pg/mL to 100 ng/mL with a detection limit of 0.62 pg/mL. The work demonstrated a new ECL enhancement strategy of SACs via BPE system and expands the application of SACs in bioanalysis field.

Dual "on-off" signal conversion strategy based on surface plasmon coupling and resonance energy transfer for visual electrochemiluminescence ratiometric analysis of MiRNA-141.

An electrochemiluminescence (ECL) biosensor with a pair of new ECL emitters and a novel sensing mechanism was designed for the high-sensitivity detection of microRNA-141 (miRNA-141). Sulfur-doped boron nitrogen quantum dots (S-BN QDs) were initially employed to modify the cathode of the bipolar electrode (BPE), while the anode reservoir was [Ir(dfppy)2(bpy)]PF6/TPrA system. The next step involved attaching H1-bound ultra-small WO3-x nanodots (WO3-x NDs) to the S-BN QDs-modified BPE cathode via DNA hybridization. A strong surface plasmon coupling (SPC) effect was observed between S-BN QDs and WO3-x NDs, which allowed for the enhancement of the red and visible ECL emission from S-BN QDs. After target-induced cyclic amplification to produce abundant Zn2+ and Au NPs-DNA3-Au NPs (Au NPs-S3-Au NPs), Zn2+ could cleave DNA at a nucleotide sequence-specific recognition site to release the WO3-x NDs, resulting in the first diminution of cathode ECL signal and the first enhancement of anode ECL signal. Moreover, the ECL signal at cathode decreased for the second time and the emission of [Ir(dfppy)2(bpy)]PF6 was continuously enhanced after the introduction of Au nanoparticles-S3-Au nanoparticles on the cathode surface. Our sensing mode with a dual "on-off" signal conversion strategy shows a good detection capability for miRNAs ranging from 10-17 to 10-10 M, with a limit of detection (LOD) as low as 10-17 M, which has great application potential in biomedical research and clinical diagnosis.

A triple read-out visible biosensing platform based on multifunctional nanozyme and bipolar electrode for multi-mode detection and imaging of CEA.

In this paper, a proposal of closed bipolar electrode (BPE) and nanozyme based multi-mode biosensing platform is first presented. As a novel integrated chip, multi-mode-BPE (MMBPE) combines enzyme-linked immunoassay (ELISA), electrochemiluminescence (ECL), ECL imaging and light emitting diode (LED) imaging, enabling highly sensitive triple read-out visible detection of cancer embryonic antigen (CEA). The ECL probe Ab2@Au@Co3O4/CoFe2O4 hollow nanocubes (HNCs) with excellent peroxidase (POD) activity is introduced into the BPE cathode through immune adsorption. The Au@Co3O4/CoFe2O4 HNCs can increase the rate of hydrogen peroxide oxidation of TMB, thus promoting the reaction, and can be used for ELISA detection of CEA at different concentrations. The modification of the BPE sensing interface and reporting interface involved the introduction of the luminescent reagent Ru(bpy)32+ to the BPE anode. The decomposition rate of H2O2 increased under the catalytic action of Au@Co3O4/CoFe2O4 HNCs nanozyme, leading to an accelerated electron transfer rate in the MMBPE system and an enhanced ECL signal from Ru(bpy)32+. The LED imaging technology further provides a convenient and visible approach for CEA imaging in which no additional chemicals are needed. The integration of nanoenzymes as the catalytic core in MMBPE system provides impetus, while the combination of nanozymes with BPE expands the application of nanoenzymes in the field of biological analysis. The integration of intelligent chips with multiple modes of detection shows portable, miniaturized, and integrated excellent properties which meets the requirements of modern detection devices and thus offers a flexible approach for determination of nucleic acids, proteins, and cells.

A multichannel closed bipolar platform to visual electrochemiluminescence sensing of caffeic acid as a model: Potential for multiplex detection.

In this study, a fully-featured electrochemiluminescence (ECL) sensing platform based on a multichannel closed bipolar system (closed-BP, C-BP) for the determination of caffeic acid (CA) was successfully developed. The system comprises three individual reservoirs connected to each other by two pairs of gold rods as bipolar electrodes. Moreover, a single pair of gold rods functions as the driving electrodes. Due to configuration consisting of three channels and double-bipolar electrodes, the detection of CA was accomplished in two oxidation and reduction pathways within a single device. Firstly, through close observation of the reactions occurring within the device and utilizing a universal pH indicator and bipolar electrodes, a precise mechanism for the current bipolar systems was initially proposed. Then, the concentration of CA was monitored in the reporting chamber through the following ECL intensities resulting from luminol oxidation and H2O2. The monitoring process was performed using both a photomultiplier tube (PMT) and a digital camera. In the process of analyte oxidation, the PMT and visual (camera)-based detection exhibited a linear response from 5 µmol L-1 to 700 µmol L-1 (limit of detection (LOD) 1.2 µmol L-1) and 50 µmol L-1 to 600 µmol L-1 (LOD 14.8 µmol L-1), respectively. In the analyte reduction pathway, the respective values were 30 µmol L-1 to 450 µmol L-1 (LOD 8.6 µmol L-1) and 55 µmol L-1 to 400 µmol L-1 (LOD 21.2 µmol L-1), for the PMT and visual-based detection, respectively. Our experiments have demonstrated the practical application of the sensor array for efficient and high-performance analysis. This innovative design holds significant potential for diverse fields and paves the way for the development of a user-friendly device.

Investigation of lethal thresholds of nanosecond pulsed electric field in rabbit VX2 hepatic tumors through finite element analysis and verification with a single-needle bipolar electrode: A prospective strategy employing three-dimensional comparisons.

Pulsed electric field has emerged as a promising modality for the solid tumor ablation with the advantage in treatment planning, however, the accurate prediction of the lesion margin requires the determination of the lethal electric field (E) thresholds. Herein we employ the highly repetitive nanosecond pulsed electric field (RnsPEF) to ablate the normal and VX2 tumor-bearing livers of rabbits. The ultrasound-guided surgery is operated using the conventional double- and newly devised single-needle bipolar electrodes. Finite element analysis is also introduced to simulate the E distribution in the practical treatments. Two- and three-dimensional investigations are performed on the image measurements and reconstructed calcification models on micro-CT, respectively. Specially, an algorithm considering the model surface, volume and shape is employed to compare the similarities between the simulative and experimental models. Blood vessel injury, temperature and synergistic efficacy with doxorubicin (DOX) are also investigated. According to the three-dimensional calculation, the overall E threshold is 4536.4 ± 618.2 V/cm and the single-needle bipolar electrode is verified to be effective in tissue ablation. Vessels are well preserved and the increment of temperature is limited. Synergy of RnsPEF and DOX shows increased apoptosis and improved long-term tumor survival. Our study presents a prospective strategy for the evaluation of the lethal E threshold, which can be considered to guide the future clinical treatment planning for RnsPEF.

Electrochemiluminescence sensing of HeLa cells labeled with biotinylated ruthenium complex using bipolar electrode based on microwell modified optical fiber.

Biotinylated ruthenium complexes exhibit improved photoluminescent (PL) properties when they bind with streptavidin, making them useful labels or probes in bio-related analysis. However, their ECL properties are still unknown to date. Herein, we reported the use of [Ru(bpy)2(biot-bpy)]2+ complexes as a new ECL luminophore, which was functionalized with biotin moiety and exhibited higher ECL efficiency after binding to streptavidin. Moreover, [Ru(bpy)2(biot-bpy)]2+ complexes could be attached to HeLa cells through the biotin-streptavidin binding. A microwell bipolar electrode (MBE) prepared at one end of an optical fiber bundle was applied to produce ECL of the labeled HeLa cells, which was remotely detected at the other end. The [Ru(bpy)2(biot-bpy)]2+-streptavidin binding effect together with the high surface/volume ratio of MBE promoted the ECL generation on HeLa cells, which was applied to sensitively detect HeLa cells with a linear range from 1.56 × 102 to 6.74 × 106 cells/mL and a detection limit of 83 cells/mL. Moreover, ECL images were successfully acquired to resolve the emission on each HeLa cell. Such cytosensor based on [Ru(bpy)2(biot-bpy)]2+ and MBE may extend the applications of ECL for cell detections.

Galvanic Bipolar Electrode Arrays with Self-Driven Optical Readouts.

In this work, we report a bipolar electrode (BPE) array system with self-driven optical readouts of the faradic current flowing through the BPEs. The BPE array system is based on the spontaneous redox reactions that are respectively occurring at opposite poles of the BPEs with appropriate electrocatalysts on the poles; this system is analogous to one consisting of galvanic electrochemical cells. The galvanic BPE array system operates in a self-powered mode that requires there to be neither a direct electrical connection nor external electrical polarization to each BPE. Importantly, the appropriate electrocatalysts on the poles play a critical role in the galvanic BPE array system to induce the spontaneous redox reactions occurring at the poles of BPEs. Moreover, the galvanic BPE array system provides self-driven optical readouts, including fluorometric and colorimetric ones, to report the faradaic current resulting from the spontaneous redox reactions on the BPE poles. Based on the unique benefits that the galvanic BPE array system has over conventional BPEs, we demonstrated the promising potential of galvanic BPE arrays for the simple yet rapid and quantitative screening of electrocatalysts for the oxygen reduction reaction as well as sensitive sensing of H2O2 in parallel.

Label free and high-throughput discrimination of cells at a bipolar electrode array using the AC electrodynamics.

BACKGROUND: Cell characterization and manipulation play an important role in biological and medical applications. Cell viability evaluation is of significant importance for cell toxicology assay, dose test of anticancer drugs, and other biochemical stimulations. The electrical properties of cells change when cells transform from healthy to a pathological state. Current methods for evaluating cell viability usually requires a complicated chip and the throughput is limited. RESULTS: In this paper, a bipolar electrode (BPE) array based microfluidic device for assessing cell viability is exploited using AC electrodynamics. The viability of various cells including yeast cells and K562 cells, can be evaluated by analyzing the electro-rotation (ROT) speed and direction of cells, as well as the dielectrophoresis (DEP) responses of cells. Firstly, the cell viability can be identified by the position of the cell captured on the BPE electrode in terms of DEP force. Besides, cell viability can also be evaluated based on both the cell rotation speed and direction using ROT. Under the action of travelling wave dielectric electrophoresis force, the cell viability can also be distinguished by the rotational motion of cells on bipolar electrode edges. SIGNIFICANCE: This study demonstrates the utility of BPEs to enable scalable and high-throughput AC electrodynamics platforms by imparting a flexibility in chip design that is unparalleled by using traditional electrodes. By using BPEs, our proposed new technique owns wide application for cell characterization and viability assessment in situ detection and analysis.

Induced-charge membrane capacitive deionization enables high-efficient desalination with polarized porous electrodes.

Exposure of a conducting porous material to an electric field in electrolytes induces an electric dipole, which results in capacitive charging of cations and anions at opposite poles. In this letter, we investigate a novel desalination method using this induced-charge capacitive deionization (ICCDI). To do this, we devise a microscale ICCDI platform that can visualize in situ ion concentrations, pH shifts, and fluid flows, and study ion transport dynamics and desalination performances compared to conventional CDI with unipolar / bipolar connections. Similar ion concentration and fluid flow characteristics were observed in Ohmic, limiting, and over-limiting regimes, but variations in desalination performance trends were noted based on the number of stacks. In a single cell, ICCDI generates a higher electric field at the opposite poles of porous electrodes than simple conducted electrodes in CDIs with unipolar/bipolar connections, leading to superior salt removal and/or lower ionic current at a given applied voltage. This marks a clear contrast from CDI with bipolar connection, which lacks any advantage over CDI with unipolar connection in a single cell. These metrics of ICCDI however deteriorated as the stack number increased, likely due to short-circuiting between the dipoles. As a result, ICCDI in current form shows higher desalination efficient than conventional CDIs with low stack numbers (< 6), so we offer the scale-up module by repeating 4-stack ICCDI units. Our study enhances comprehension of ion transport dynamics and desalination performance in ICCDI, and the results could aid in the development of ICCDI for energy/cost-efficient desalination.

Rapid screening of electrochemically active bacteria based on a biocathode-functional bipolar electrode-electrochemiluminescence platform.

A functional bipolar electrode-electrochemiluminescence (BPE-ECL) platform based on biocathode reducing oxygen was constructed for detecting electrochemically active bacteria (EAB) in this paper. Firstly, thiolated trimethylated chitosan quaternary ammonium salt (TMC-SH) layer was assembled on the gold-plated cathode of BPE. TMC-SH contains quaternary ammonium salt branch chain, which can inhibit the growth of microorganisms on the surface or in the surrounding environment while absorbing bacteria. Then, the peristaltic pump was used to flow all of the samples through the cathode, and the EAB was electrostatically adsorbed on the electrode surface. Finally, applying a constant potential to the BPE, bacteria can catalyze electrochemical reduction of O2, and decrease the overpotential of O2 reduction at the cathode, which in turn generates an ECL reporting intensity change at the anode. In this way, live and dead bacteria can be distinguished, and the influence of complex food substrates on detection can be greatly reduced.

Microarray-Based Electrochemical Biosensing.

Microarrays are widely utilized in bioanalysis. Electrochemical biosensing techniques are often applied in microarray-based assays because of their simplicity, low cost, and high sensitivity. In such systems, the electrodes and sensing elements are arranged in arrays, and the target analytes are detected electrochemically. These sensors can be utilized for high-throughput bioanalysis and the electrochemical imaging of biosamples, including proteins, oligonucleotides, and cells. In this chapter, we summarize recent progress on these topics. We categorize electrochemical biosensing techniques for array detection into four groups: scanning electrochemical microscopy, electrode arrays, electrochemiluminescence, and bipolar electrodes. For each technique, we summarize the key principles and discuss the advantages, disadvantages, and bioanalysis applications. Finally, we present conclusions and perspectives about future directions in this field.

Paper-based bipolar electrode electrochemiluminescence sensors for point-of-care testing.

In the past few years, point-of-care testing (POCT) technology has crossed the boundaries of laboratory determination and entered the stage of practical applications. Herein, the latest advances and principal issues in the design and fabrication of paper-based bipolar electrode electrochemiluminescence (BPE-ECL) sensors, which are widely used in the POCT field, are highlighted. After introducing the attractive physical and chemical properties of cellulose paper, various approaches aimed at enhancing the functions of the paper, and their underlying principles are described. The materials typically employed for fabricating paper-based BPE are also discussed in detail. Subsequently, the universal method of enhancing BPE-ECL signal and improving detection accuracy is put forward, and the ECL detector widely used is introduced. Furthermore, the application of paper-based BPE-ECL sensors in biomedical, food, environmental and other fields are displayed. Finally, future opportunities and the remaining challenges are analyzed. It is expected that more design concepts and working principles for paper-based BPE-ECL sensors will be developed in the near future, paving the way for the development and application of paper-based BPE-ECL sensors in the POCT field and providing certain guarantee for the development of human health.

Robust electrolysis system divided by bipolar electrode and non-conductive membrane for energy-efficient calcium hardness removal.

In this study, an energy-efficient divided bipolar electrolysis system was developed for water softening, where two PTFE membranes were used as the separating materials and a bipolar electrode was employed to enhance the H2O-splitting reactions. As compared with other two operation modes, the optimum calcium harness removal efficiencies of 85% and 57% could be reached in the induction cathode effluent and terminal effluent, respectively, at 8 mA cm-2 in the mode A. Increasing the current density from 5 to 20 mA cm-2 evidently promoted the removal of calcium hardness from 33% to 65% in the terminal effluent and the CaCO3 precipitation rate from 743 to 1462 gCaCO3 h-1 m-2 with the increased energy consumption from 0.53 to 2.2 kWh kg-1CaCO3. The optimized Ca2+/HCO3- molar ratio was 1:1.2 for the calcium hardness removal. In addition, increasing the flow rate into each cathode chamber from 10 to 40 mL min-1 gradually decreased from 67% to 35%. The calcium hardness was mainly removed in the forms of vaterite and calcite in the alkaline effluents and was marginally precipitated as aragonite and calcite on the cathodes surface. Generally, present energy-efficient electrochemical water softening system showed great potential for application in industrial processes.

Versatile FeMoOv nanozyme bipolar electrode electrochemiluminescence biosensing and imaging platform for detection of H2O2 and PSA.

In this work, a unique FeMoOv nanozyme-bipolar electrode (NM-BPE) electrochemiluminescence (ECL) biosensing and imaging platform was proposed for the first time to realize sensitive detection of target hydrogen peroxide (H2O2) and prostate specific antigen (PSA). Considering the advantage that the cathode and anode poles of the bipolar electrode (BPE) can be modified respectively, this work was carried out using anode equipped with ECL reagent bipyridine ruthenium (Ru(bpy)32+), and cathode equipped with the Fe-doped molybdenum oxide/Au nanoparticles (FeMoOv/AuNPs) with excellent peroxidase (POD) and catalase (CAT)-like activity. Because FeMoOv/AuNPs show efficient enzyme catalysis effect and can greatly promote the decomposition of H2O2, thus the electron transfer rate in the NM-BPE system would be much accelerated to enhance the ECL signal of Ru(bpy)32+. Based on this principle, this work not only realized sensitive detection of H2O2, but also ingeniously designed an sandwich immunosensor using FeMoOv/AuNPs as recognition probe to mediate the ECL response on the anode, achieving highly sensitive detection of PSA. Furthermore, a unique mobile phone ECL imaging system was developed for assay of PSA at different concentrations, which opened a new portable imaging sensing device for bioassays. This work was the first time to combine nanozymes with bipolar electrodes for ECL analysis and imaging, which not only broadened the applications of nanozymes, but also pioneered the new joint ECL research technique of bipolar electrode and ECL imaging in bioassays, showing great application prospect for multiple detection of proteins, nucleic acids and cancer cells.

Novel electrochemiluminescence biosensor of fumonisin B1 detection using MWCNTs-PDMS flexible bipolar electrode.

A novel portable and disposable bipolar electrode (BPE)-electrochemiluminescence (ECL) device was fabricated for fumonisin B1 (FB1) detection. BPE was fabricated by using MWCNTs and polydimethylsiloxane (PDMS) due to their excellent electrical conductivity and good mechanical stiffness. After the deposition of Au NPs on the cathode of BPE, the ECL signal could be improved 89-fold. Then a specific aptamer-based sensing strategy was constructed by grafting capture DNA on Au surface, followed by hybridizing with aptamer. Meanwhile, an excellent catalyst, Ag NPs was labeled on aptamer to activate oxygen reduction reaction, leading to a 13.8-fold enhancement in ECL signal at the anode of BPE. Under the optimal conditions, the biosensor exhibited a wide linear range of 0.10 pg/mL to 10 ng/mL for FB1 detection. Meanwhile, it demonstrated satisfactory recoveries for real sample detection with good selectivity, making it to be a convenient and sensitive device for mycotoxin assay.

Insights into the Mechanism of Bipolar Electrodeposition of Au Films and Its Application in Visual Detection of Prostate Specific Antigens.

Au particles are commonly used for deposition on the surface of a bipolar electrode (BPE) in order to amplify electrochemical and electrochemiluminescence (ECL) signal because of their excellent conductivity, biocompatibility, and large surface area. In this work, a closed BPE device was fabricated and Au particles were deposited on the two poles of a BPE via bipolar deposition. Results indicated that the electrochemical stability of Au film on the anode part of the BPE and the reduction of AuCl4- to Au on the cathode part of the BPE depended on the conductivity of the solution. The prepared Au-Au BPE exhibited a remarkable amplification effect on the ECL signal. Then, a specific sensing interface was constructed on one pole of the BPE for the visual detection of prostate-specific antigens (PSA) based on sandwich-type immunoreactions between primary PSA antibodies (Ab1) on the electrode surface, PSA, and SiO2 nanoparticles labeled secondary PSA antibodies (SiO2-Ab2). The designed biosensor exhibited a good linear relationship for the ECL detection of PSA in the range of 1 × 10-6 to 1 × 10-10 g/mL with a correlation coefficient of 0.9866; the limit of detection (LOD) was 1.5 × 10-11 g/mL. Additionally, the biosensor can realize the electrochemical imaging of PSA by regulating the electrochemical oxidation of the Au anode with the immunoreactions on the cathode part of BPE. Therefore, the small, portable and highly sensitive biosensors have great potential for on-site detection.

Ultrasensitive multicolor electrochromic sensor built on closed bipolar electrode: Application in the visual detection of Pseudomonas aeruginosa.

Pseudomonas aeruginosa (P. aeruginosa) is an opportunistic infection-causing pathogen that threatens human health. Accordingly, a rapid and ultrasensitive analytical method is required urgently. Herein, an ultrasensitive multicolor electrochromic sensing platform was established on the basis of a closed bipolar electrode (BPE). Prussian blue (PB), the blue spot that can be easily electrodeposited, was selected as an electrochromic indicator at the closed BPE cathode. Integrating with the anodic emitter, Ru(bpy)32+, which emitted optical red light, visualized multicolor electrochromism was achieved on closed BPE. Particularly, physical separation between the positive and negative poles of the closed BPE greatly prevented mutual interference between Ru(bpy)32+ and PB. Consequently, the sensitivity and accuracy of the proposed biosensor considerably improved. Notably, owing to magnetic-separation technology, the closed BPE surface required no modification. Without any complex pretreatment, the entire experiment time could be greatly shortened because the PA@MBs completely captured P. aeruginosa in food matrix within only 20 min. By comparing the visual electrochromic colors, ultrasensitive screening of P. aeruginosa was accomplished within 1-108 CFU mL-1. Combining the merits of closed BPE, electrochemiluminescence (ECL), and electrochromic, this strategy provided an accurate and intrinsic way for visual detection of P. aeruginosa, as well as great potential in measuring other pathogens.