Integrating bipolar electrochemistry and electrochemiluminescence imaging with microdroplets for chemical analysis

An electrochemiluminescence microsensor based on DNA-silver nanoclusters amplification for detecting cellular adenosine triphosphate

Adenosine triphosphate (ATP), as the primary energy source, plays vital roles in many cellular events. Developing an efficient assay is crucial to rapidly evaluate the level of cellular ATP. A portable and integrated electrochemiluminescence (ECL) microsensor array based on a closed bipolar electrode (BPE) was presented. In the BPE unit, the ECL chemicals and oxidation/reduction were separated from the sensing chamber. The ATP aptamer was assembled with single-stranded DNA (ssDNA) in the sensing chamber. ATP capture made the aptamer disassemble from the ssDNA and facilitated DNA-templated silver nanocluster (Ag NC) generation by the target-rolling circle amplification (RCA) reaction. The guanine-rich padlock sequence produced tandem periodic cytosine-rich sequences by the RCA, inducing Ag NC generation in the cytosine-rich region of the produced DNA strands through Ag+ reduction. The in situ Ag NC generation enhanced the circuit conductivity of the BPE and promoted the ECL reaction of [Ru(bpy)2dppz]2+/tripropylamine in the anodic reservoir. On this ECL microsensor, a good linear relationship of ATP was achieved ranging from 30 to 1000 nM. The ATP content in HepG2 cells was selectively and sensitively determined without complex pretreatment. The ATP amount of 25 cells could be successfully detected when a sub-microliter sample was loaded.

Newly Developed Electrochemiluminescence Based on Bipolar Electrochemistry for Multiplex Biosensing Applications: A Consolidated Review

Recently, there has been an upsurge in the extent to which electrochemiluminescence (ECL) working in synergy with bipolar electrochemistry (BPE) is being applied in simple biosensing devices, especially in a clinical setup. The key objective of this particular write-up is to present a consolidated review of ECL-BPE, providing a three-dimensional perspective incorporating its strengths, weaknesses, limitations, and potential applications as a biosensing technique. The review encapsulates critical insights into the latest and novel developments in the field of ECL-BPE, including innovative electrode designs and newly developed, novel luminophores and co-reactants employed in ECL-BPE systems, along with challenges, such as optimization of the interelectrode distance, electrode miniaturization and electrode surface modification for enhancing sensitivity and selectivity. Moreover, this consolidated review will provide an overview of the latest, novel applications and advances made in this field with a bias toward multiplex biosensing based on the past five years of research. The studies reviewed herein, indicate that the technology is rapidly advancing at an outstanding purse and has an immense potential to revolutionize the general field of biosensing. This perspective aims to stimulate innovative ideas and inspire researchers alike to incorporate some elements of ECL-BPE into their studies, thereby steering this field into previously unexplored domains that may lead to unexpected, interesting discoveries. For instance, the application of ECL-BPE in other challenging and complex sample matrices such as hair for bioanalytical purposes is currently an unexplored area. Of great significance, a substantial fraction of the content in this review article is based on content from research articles published between the years 2018 and 2023.

Bipolar Electrochemistry - A Powerful Tool for Micro/Nano-Electrochemistry

The understanding of areas for "classical" electrochemistry (including catalysis, electrolysis and sensing) and bio-electrochemistry at the micro/nanoscale are focus on the continued performance facilitations or the exploration of new features. In the recent 20 years, a different mode for driving electrochemistry has been proposed, which is called as bipolar electrochemistry (BPE). BPE has garnered attention owing to the interesting properties: (i) its wireless nature facilitates electrochemical sensing and high throughput analysis; (ii) the gradient potential distribution on the electrodes surface is a useful tool for preparing gradient surfaces and materials. These permit BPE to be used for modification and analytical applications on a micro/nanoscale surface. This review aims to introduce the principle and classification of BPE and BPE at micro/nanoscale; sort out its applications in electrocatalysis, electrosynthesis, electrophoresis, power supply and so on; explain the confined BPE and summarize its analytical application for single entities (single cells, single particles and single molecules), and discuss finally the important direction of micro/nanoscale BPE.

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.

Electrogenerated chemiluminescence of a Ru(bpy)32+/arginine system: a specific and sensitive detection of acetaminophen

Ru(bpy)₃Cl₂/TPrA is a prominent and widely used ECL system in analytical science. However, the co-reactant TPrA restricts the variety of applications because of its toxicity, volatility, and high cost. Here, we use arginine (Arg) as an alternative co-reactant for Ru(bpy)₃²⁺ by taking advantage of its low cost, non-toxicity, and biocompatibility. The mechanism of the Ru(bpy)₃²⁺/Arg system is that the deprotonated Arg can react with Ru(bpy)₃²⁺ to release emission. The similarity between the Ru(bpy)₃²⁺/Arg, Ru(bpy)₃²⁺/TPrA, and Ru(bpy)₃²⁺/DBAE systems demonstrates that Arg can be used as an alternative co-reactant for Ru(bpy)₃²⁺ ECL. As a proof of concept, we achieve an excellent performance for acetaminophen (Ace) detection based on the specificity of Arg and Ace, with excellent linearity, low detection limits, and good recoveries. This work is promising to expand the scope of the Ru(bpy)₃²⁺/Arg system and move forward their applications in bioassays.

We use arginine as an alternative co-reactant for Ru(bpy)₃²⁺ by taking advantage of its low cost, non-toxicity, and biocompatibility. It is promising to expand the scope of the Ru(bpy)₃²⁺/Arg system and move forward their applications in bioassays.

Bipolar Electrochemical Measurement of Enantiomeric Excess with Inherently Chiral Polymer Actuators

Straightforward enantioselective analytical methods are very important for drug safety, considering that in certain cases one of the two enantiomers of a chiral molecule might be harmful for humans. In this work, we propose a simple system for the direct and easy read-out of the enantiomeric excess of 3,4-dihydroxyphenylalanine (DOPA) as a model analyte. A conducting oligomer, i.e. oligo-(3,3'-dibenzothiophene), bearing inherently chiral features, is electrogenerated on a polypyrrole film. The resulting freestanding hybrid material is used as a wireless enantioselective actuator in a bipolar electrochemical cell. Combining in a single setup two individual actuators with opposite chiral features allows a direct visual read-out of enantiomeric excess, as the bending amplitude of each of the two actuators is directly correlated with the concentration of the corresponding stereoisomer of the analyte. Optimization of the experimental parameters results in efficient bending, giving access to the percentage values of the enantiomeric excess in mixtures containing different ratios of the antipodes, thus opening the way to potential applications for chiral in situ analysis.

Bipolar Electrochemiluminescence Imaging: A Way to Investigate the Passivation of Silicon Surfaces

This work depicts the original combination of electrochemiluminescence (ECL) and bipolar electrochemistry (BPE) to map in real-time the oxidation of silicon in microchannels. We fabricated model silicon-PDMS microfluidic chips, optionally containing a restriction, and monitored the evolution of the surface reactivity using ECL. BPE was used to remotely promote ECL at the silicon surface inside microfluidic channels. The effects of the fluidic design, the applied potential and the resistance of the channel (controlled by the fluidic configuration) on the silicon polarization and oxide formation were investigated. A potential difference down to 6 V was sufficient to induce ECL, which is two orders of magnitude less than in classical BPE configurations. Increasing the resistance of the channel led to an increase in the current passing through the silicon and boosted the intensity of ECL signals. Finally, the possibility of achieving electrochemical reactions at predetermined locations on the microfluidic chip was investigated using a patterning of the silicon oxide surface by etched micrometric squares. This ECL imaging approach opens exciting perspectives for the precise understanding and implementation of electrochemical functionalization on passivating materials. In addition, it may help the development and the design of fully integrated microfluidic biochips paving the way for development of original bioanalytical applications.

Mesoporous silica-mediated controllable electrochemiluminescence quenching for immunosensor with simplicity, sensitivity and tunable detection range

Straightforward and accurate measurement of medical biomarkers is of essential importance in clinical diagnostics and treatments. However, the major challenge is the diversity in dynamic range of different biomarkers ranging from pg mL^-1 to μg mL^-1 in various body fluids and tissues among patients. Here, we develop a mesoporous silica (MS)-mediated controllable electrochemiluminescence (ECL) quenching of immunosensor that allows accurate immunoassays with simplicity, sensitivity and tunable sensing range. MS is employed to enhance the sensitivity and tune ECL quenching to broaden the detection range just by altering luminophore (Ru(bpy)₃²⁺) and coreactant (DBAE) concentration without additional modifications. The immunoassay is followed: homogeneous sandwich immunoreaction, magnetic separation, and ECL quenching detection. As a proof-of-concept, simple and sensitive detection of IgG is achieved ranging from pg mL^-1 to μg mL^-1, and applications of the strategy are extended by the combination of ECL immunosensor with commercial ELISA kit. This study will not only be expected to serve as a new avenue for the assay of physiological and clinical implications of immunological biomarkers, but also benefit a wide range of applications that require a tunable detection range and ultrahigh sensitivity.

Mapping Solvent Entrapment in Multiphase Systems by Electrogenerated Chemiluminescence

The interfacial properties of multiphase systems are often difficult to quantify. We describe the observation and quantification of immiscible solvent entrapment on a carbonaceous electrode surface using microscopy-coupled electrogenerated chemiluminescence (ECL). As aqueous microdroplets suspended in 1,2-dichloroethane collide with a glassy carbon electrode surface, small volumes of the solvent become entrapped between the electrode and aqueous phase, resulting in an overestimation of the true microdroplet/electrode contact area. To quantify the contribution of solvent entrapment decreasing the microdroplet contact area, we drive an ECL reaction within the microdroplet phase using tris(bipyridine)ruthenium(II) chloride ([Ru(bpy)₃]Cl₂) as the ECL luminophore and sodium oxalate (Na₂C₂O₄) as the co-reactant. Importantly, the hydrophilicity of sodium oxalate ensures that the reaction proceeds in the aqueous phase, permitting a clear contrast between the aqueous and 1,2-dichloroethane present at the electrode interface. With the contrast provided by ECL imaging, we quantify the microdroplet radius, apparent microdroplet contact area (aqueous + entrapped 1,2-dichloroethane), entrapped solvent contact area, and the number of entrapped solvent pockets per droplet. These data permit the extraction of the true microdroplet/electrode contact area for a given droplet, as well as a statistical assessment regarding the probability of solvent entrapment based on microdroplet size.

Visualizing Phase Boundaries with Electrogenerated Chemiluminescence

Reactivity at phase boundaries is central to many areas of chemistry, from synthesis to heterogeneous catalysis. New tools are necessary to gain a more detailed understanding of processes occurring at these boundaries. We describe a series of experiments to visualize phase boundaries using electrogenerated chemiluminescence (ECL) on glassy carbon electrodes. By taking advantage of the solubilities of the ECL luminophore and the coreactant in different liquid phases, we demonstrate that the interface of various phases (i.e., the boundaries formed between a water microdroplet, 1,2-dichloroethane, and a glassy carbon electrode and the boundaries formed between an oxygen bubble, water, and a glassy carbon electrode) can be evaluated. We measured microdroplet contact radii, the three-phase boundary thickness, and growth dynamics of electrogenerated O₂ bubbles. These experimental tools and the fundamental knowledge they yield will find applications in biology, nanoscience, synthesis, and energy storage and conversion, where understanding phase boundary chemistry is essential.

Integrating Electrochemical and Colorimetric Sensors with a Webcam Readout for Multiple Gas Detection

Multisensor detectors have merits of low cost, compact size, and capability of supplying accurate and reliable information otherwise hard to obtain by any single sensors. They are therefore highly desired in various applications. Despite the advantages and needs, they face great challenges in technique especially when integrating sensors with different sensing principles. To bridge the gap between the demand and technique, we here demonstrated an integration of electrochemical and colorimetric sensors with a webcam readout for multiple gas detection. Designed with two parallel gas channels but independent sensor cells, the dual-sensor detector could simultaneously detect each gas from their gas mixture by analysis of the group photo of the two sensors. Using Ag electro-dissolution as reporter, the bipolar electrochemical sensor achieved quantitative analysis for the first time thanks to application of pulse voltage. The sacrificed Ag layer used in the bipolar electrochemical (EC) sensor was recycled from CD, which further decreased the sensor cost and supplied a new way of CD recycling. The EC O₂ sensor response, edge displacement of Ag layer due to electrochemical dissolution, has a linear relationship with O₂ concentration ranging from 0 to 30% and has good selectivity to common oxidative gases. The colorimetric NO₂ sensor linearly responded to NO₂ concentrations ranging from 0 to 230 ppb with low detection limit of 10 ppb, good selectivity, and humidity tolerance. This integration method could be extended to integrating other gas sensors.

Screen printed bipolar electrode for sensitive electrochemiluminescence detection of aflatoxin B1 in agricultural products

In order to avoid the occurrence of false positives and false negatives caused by improper pretreatment during the detection of aflatoxin B1 by enzyme linked immunosorbent assay (ELISA). In this paper, we developed a screen printed bipolar electrode (BPE) for sensitive electrochemiluminescence (ECL) detection of aflatoxin B1 in agricultural products. The sensor uses a cathode of closed BPE as a functional sensing interface and an anode as a signal collection interface. In this way, the analyte does not need to participate in the ECL reaction of the anode. It avoids direct contact of photoactive molecules with complex reaction systems and greatly broadens the range of applications for ECL. After mixing the test sample with a known fixed concentration of horseradish peroxidase-labeled AFB1 (HRP-AFB1), they compete for binding to monoclonal antibodies. HRP catalyzes the polymerization of aniline to form polyaniline (PANI). Thereby causing a change in the oxidation-reduction potential and the ECL intensity in the electrochemical system, and then achieve the purpose of detecting the AFB1 concentration in the sample. As a result, the sensor has a good analytical performance for AFB1 with a linear range of 0.1-100 ng mL^-1 and a detection limit of 0.033 ng mL^-1. The sensor avoids the direct contact between the reaction system and the signal measurement system. In recovery experiment for six grains, the results demonstrate that the recovery rate and accuracy of this sensor is better than that of ELISA. This method provides a new idea for the detection of other mycotoxins in grains.

Remotely Controlled in Situ Growth of Silver Microwires Forming Bioelectronic Interfaces

There is a pressing need to advance our ability to construct three-dimensional (3D) functional bioelectronic interfaces. Additionally, to ease the transition to building cellular electronic systems, a remote approach to merge electrical components with biology is desirable. By combining 3D digital inkjet printing with bipolar electrochemistry, we remotely control and fabricate conductive wires, forming a first of its kind contactless bionic manufacturing procedure. It enables controlled fabrication of conductive wires in a three-dimensional configuration. Moreover, we demonstrate that this technology could be used to grow and interface conductive conduits in situ with mammalian cells, offering a new strategy to engineering bioelectronic interfaces. This represents a step change in the production of functional complex circuitry and considerably increases the manufacturing capabilities of merging cells with electronics. This approach provides a platform to construct bioelectronics in situ offering a potential paradigm shift in the methods for building bioelectronics with potential applications in biosensing and bioelectronic medicine.

Closed bipolar electrochemistry in a four-electrode configuration

The thermodynamic theory underpinning closed bipolar electrochemistry in a 4-electrode configuration is presented; a technique applicable to spectro-electroanalysis, energy storage, electrocatalysis and electrodeposition.

Direct Observation of Oxidation Reaction via Closed Bipolar Electrode-Anodic Electrochemiluminescence Protocol: Structural Property and Sensing Applications

In this work, we developed an innovative closed bipolar electrode (BPE)-electrochemiluminescence (ECL) sensing strategy with generality for target detection. Based on charge balance and 100% current efficiency between the closed BPE poles and the driving electrodes, one of the driving electrodes in one cell of the closed BPE system was employed as ECL sensing surface to reflect the target on the BPE pole in the opposite cell. Compared with traditional BPE-ECL sensing method, which in general adopted the anodic ECL reagents such as Ru(bpy)₃²⁺ and its coreactant on one pole (anode) to reflect the target (occurring reduction reaction) on the other pole (cathode), the difference was that the targets occurring oxidation reaction could be detected by the anodic ECL reagents based on this strategy. To verify the feasibility of this strategy, the detection principle was stated first, and Fe(CN)₆^4- as model target at anodic BPE pole were detected by anodic ECL reagents (Ru(bpy)₃²⁺ and TprA) on the driving electrode first. The ECL signals showed good performance for target detection. By changing the size and the material of the BPE pole where the targets were located, the detection of l-ascorbic acid (AA), uric acid (UA), and dopamine (DA) as other model targets with higher detection limit were accomplished. Visual and high-throughput detection of AA, UA, and DA were also successfully realized by an array of the closed BPE system. This closed BPE (array) system is an effective supplement of traditional BPE-ECL sensing and could greatly expand the scope of the detection target.

Wireless Electromechanical Readout of Chemical Information

Collecting electrochemical information concerning the presence of molecules in a solution is usually achieved by measuring current, potential, resistance, or impedance via connection to a power supply. Here, we suggest wireless electromechanical actuation as a straightforward readout of chemical information. This can be achieved based on the concept of bipolar electrochemistry, which allows measuring the presence of different model species in a quantitative way. We validate the concept by using a free-standing polypyrrole film. Its positively polarized extremity participates in an oxidation of the analyte and delivers electrons to the opposite extremity for the reduction of the polymer. This reduction is accompanied by the insertion of counterions and thus leads to partial swelling of the film, inducing its bending. The resulting actuation is found to be a linear function of the analyte concentration, and also a Michaelis-Menten type correlation is obtained for biochemical analytes. This electromechanical transduction allows an easy optical readout and opens up very interesting perspectives not only in the field of sensing but also far beyond, such as for the elaboration of self-regulating biomimetic systems.

Ultrasensitive electrochemiluminescence determination of trace Ag ions based on the signal amplification caused by its catalytic effect on Mn(II) oxidation using graphite catheter as electrode

In this work, an ultrasensitive electrochemiluminescence (ECL) method was established for the detection of trace amount of Ag ions (Ag⁺). In sulfuric acid medium, Ag(II), the electro-oxidized product of Ag(I), oxidizes manganese ions (Mn²⁺) to produce permanganate (MnO₄^-) by using a pair of graphite catheters as electrodes. While permanganate and luminol can produce strong chemiluminescence, based on the catalytic effect of Ag(II) on Mn²⁺ oxidation, there is a good linear relationship between the concentration of Ag⁺ and luminescence intensity. Under optimized conditions, the linear range of this method for Ag⁺ is from 0.2 to 150 nM with a detection limit of 0.06 nM. The method was applied for determination of Ag⁺ in various water samples with satisfactory results.

Low-voltage driven portable paper bipolar electrode-supported electrochemical sensing device

Aiming to overcome the obstacles of power supply requirement and chip usefulness in practice, a low-cost and convenient portable electrochemical sensing device is introduced for the first time, featuring bipolar electrode system, LED read-out, laminated paper-based devices, and low-voltage button cells. The electric circuits of this practical device are constructed on laminating films with copper and conductive carbon tapes, and the reservoirs facilitating chemical reactions are made with chromatography paper. The device is sensitive to electrochemical responses, validated by the demonstrative hydrogen peroxide and enzyme-assisted glucose detection. The business-card-size chip achieves sensitive analyte detection by naked eyes as well as further image processing in both laboratory samples and human serum samples testing, featuring detection limit as low as 1.79 μM and a dynamic range from 10 μM to 10 mM. This new practical design of point-of-care sensing chip entails the properties of facile fabrication, simple usage, high robustness, low power consumption, and accurate sensing showing the attainability of fabricating a useful and portable analytical device.

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.

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

The rising need for low-cost diagnostic devices has led to the search for inexpensive matrices that allow performing alternative analytical assays. Cloth is a viable material for the development of analytical devices due to its low material and manufacture costs, ability to wick assay fluids by capillary forces, and potential for patterning multiplexed channel geometries. In this paper, we describe the construction of low-cost, ultraflexible microfluidic cloth-based analytical devices (μCADs) for wireless electrochemiluminescence based on closed bipolar electrodes (C-WL-ECL), employing extremely cheap materials and a manufacturing process. The C-WL-ECL μCADs are built with wax-screen-printed cloth channels and carbon ink screen-printed electrodes, and the estimated cost per device is only $0.015. To demonstrate the performance of C-WL-ECL μCADs, the two most commonly used ECL systems - tris(2,2'-bipyridyl)ruthenium(ii)/tri-n-propylamine (Ru(bpy)3(2+)/TPA) and 3-aminophthalhydrazide/hydrogen peroxide (luminol/H2O2) - are applied. Under optimized conditions, the C-WL-ECL method has successfully fulfilled the quantitative determination of TPA with a detection limit of 0.085 mM. In addition, on the bent μCADs (bending angle (θ) = 180°), the luminol/H2O2-based ECL system can detect H2O2 as low as 0.024 mM. Based on such an ECL system, the bent μCADs are further used for determination of glucose in a phosphate buffer solution (PBS), with the detection limit of 0.195 mM. Finally, the applicability and validity, anti-interference ability, and storage stability of the C-WL-ECL μCADs are investigated. The results indicate that the proposed device has shown potential to extend the use of microfluidic analytical devices, due to its simplicity, low cost, ultraflexibility, and acceptable analytical performance.

Electrogenerated Chemiluminescence Reporting on Closed Bipolar Microelectrodes and the Influence of Electrode Size

We report a fundamental study of the use of Ru(bpy)32+-based electrogenerated chemiluminescence (ECL) as an optical reporting system for the detection of redox-active analyte on closed bipolar microelectrodes, focused on gaining an in-depth understanding of the correlation between ECL emission intensity and electrochemical current. We demonstrate the significant effect that the size of the anodic and cathodic poles has on the resulting ECL signal and show how this influences the quantitative detection of analyte on a closed bipolar electrode. By carefully designing the geometry of the bipolar electrode, the detection performance of the system can be tuned to different analyte concentration ranges. We show that through a simple voltammetric study of the individual reactions, one can understand the coupled bipolar behavior and accurately predict the ECL signal response to a range of analyte concentrations, enabling the accurate prediction of calibration curves.

Closed bipolar electrode-enabled dual-cell electrochromic detectors for chemical sensing

Battery operation of a closed-BPE dual cell with colorimetric readout by smartphone camera yields a simple, inexpensive, field-deployable electrochemical sensor.

Double remote electrochemical addressing and optical readout of electrochemiluminescence at the tip of an optical fiber

A double remote strategy based on wireless addressing and remote readout of electrochemiluminescence at the tip of an optical fiber is reported.

A bipolar electrochemiluminescence sensing platform based on pencil core and paper reservoirs

A very simple, portable and disposable BPE-ECL sensing platform has been investigated using commercial pencil core and paper cells.