Paper-Based Bipolar Electrode Electrochemiluminescence Platform Combined with Pencil-Drawing Trace for the Detection of M.SssI Methyltransferase

An ultra-sensitive CRISPR-Cas12a and aptamer-based biosensor utilizing Entropy-driven catalytic DNA networks for precise detection of DNA Methyltransferase 1

DNA Methyltransferase 1 (DNMT1) serves as a crucial biomarker associated with various diseases and is essential for evaluating DNA methylation levels, diagnosing diseases, and evaluating prognosis. As a result, a convenient, quantitative, and sensitive assay for detecting DNMT1 is in high demand. However, current techniques for DNMT1 detection struggle to balance accuracy, low cost, and high sensitivity, limiting their clinical usefulness. To address this challenge, we have developed a DNMT1 detection method (CAED), which combines aptamer-specific recognition with a highly programmable Entropy-driven catalysis DNA network and is further integrated with the CRISPR-Cas12a system. This innovative approach achieves a detection limit as low as 90.9 fmol/L. To demonstrate the clinical applicability and significance of our CAED method, we successfully measured DNMT1 levels in 10 plasma samples 10 cervical tissue samples. These results underscore the potential of our method as an accurate, affordable, and ultra-sensitive tool for evaluating DNMT1 levels. This innovative method offers a potent means for assessing DNMT1 levels and significantly advances disease diagnosis and health risk prediction. Plus, it establishes an innovative design framework for CRISPR-Cas12a-based biosensors, tailored explicitly for enzyme content quantification.

A separation-free paper-based hydrogel device for one-step reactive oxygen species determination by a smartphone

Paper-based analytical devices (PADs) are very convenient for determining biomarkers in point-of-care (POC) diagnosis while requiring sample pre-treatment or impurity separation. This study reports a novel hydrogel-coupled, paper-based analytical device (PAD) for separation-free H2O2 colorimetric detection in both aqueous solution and cell lysis with sample-to-answer analysis by directly loading into the sample test zone. By encapsulating an inorganic mimic enzyme and chromogenic substrate into the sodium alginate (SA) hydrogel, amplification of the color signal after catalyzing the substrate could be achieved. Taking advantage of the nanoscale porous structure of the hydrogel and the lateral flow channel of the PAD, large interference fragments or bio-macromolecules are prevented from diffusing into the chromogenic reaction, whereas the small target molecules enter the sensing region to trigger the catalytic reaction. This method demonstrated a rapid and accurate analysis with a limit of detection as low as 0.06 mM and detection selectivity. Our proposed device requires no enzyme and is separation-free, portable, easy-to-fabricate, and low-cost, and may offer a platform for quantitative or qualitative analysis of other analytes in body fluids for POC applications.

A spatial-potential resolved bipolar electrode electrochemiluminescence biosensor based on polarity conversion for dual-mode detection of miRNA-122 and CEA

In this work, a spatial-potential resolved bipolar electrode electrochemiluminescence (BPE-ECL) biosensor based on polarity conversion strategy and CuHCF electrocatalyst was constructed for dual-mode detection of miRNA-122 and carcinoembryonic antigen (CEA). ECL technology was firstly used to systematically study the polarity conversion of BPE. It was found that changing the polarity of the driving voltage would cause the polarity change of BPE, and led to the change of the luminescent position of Ru(bpy)32+. As a "proof-of-concept application", we developed a shielded dual-channel BPE-ECL biosensor for dual-mode detection of miRNA-122 and CEA. In order to further improve the detection sensitivity, a non-precious metal electrocatalyst CuHCF with outstanding electrocatalytic reduction activity of H2O2 was firstly introduced to the BPE-ECL biosensor for signal amplification, which could generate high faradaic current under the excitation of negative potential. Based on the charge neutrality principle of BPE, the enhancement of the faradaic current resulted in the ECL signal amplification of Ru(bpy)32+. The targets in the sensing grooves caused the introduction or fall off of CuHCF, which led to the ECL signal change of Ru(bpy)32+ in the signal grooves, and realized the dual-mode detection of miRNA-122 and CEA. This work provided a deeper understanding of the polarity change of BPE. Furthermore, the introduction of non-precious metal electrocatalyst had broadened the application range of BPE-ECL sensors.

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.

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.

Spatial-Potential-Color-Resolved Bipolar Electrode Electrochemiluminescence Biosensor Using a CuMoOx Electrocatalyst for the Simultaneous Detection and Imaging of Tetracycline and Lincomycin

A spatial-potential-color-resolved bipolar electrode electrochemiluminescence biosensor (BPE-ECL) using a CuMoOx electrocatalyst was constructed for the simultaneous detection and imaging of tetracycline (TET) and lincomycin (LIN). HOF-101 emitted peacock blue light under positive potential scanning, and CdSe quantum dots (QDs) emitted green light under negative potential scanning. CuMoOx could catalyze the electrochemical reduction of H2O2 to greatly increase the Faradic current of BPE and realize the ECL signal amplification. In channel 1, CuMoOx-Aptamer II (TET) probes were introduced into the BPE hole (left groove A) by the dual aptamer sandwich method of TET. During positive potential scanning, the polarity of BPE (left groove A) was negative, resulting in the electrochemical reduction of H2O2 catalyzed by CuMoOx, and the ECL signal of HOF-101 was enhanced for detecting TET. In channel 2, CuMoOx-Aptamer (LIN) probes were adsorbed on the MXene of the driving electrode (DVE) hole (left groove B) by hydrogen-bonding and metal-chelating interactions. LIN bound with its aptamers, causing CuMoOx to fall off. During negative potential scanning, the polarity of DVE (left groove B) was negative and the Faradic current decreased. The ECL signal of CdSe QDs was reduced for detecting LIN. Furthermore, a portable mobile phone imaging platform was built for the colorimetric (CL) detection of TET and LIN. Thus, the multiple mode-resolved detection of TET and LIN could be realized simultaneously with only one potential scan, which greatly improved detection accuracy and efficiency. This study opened a new technology of BPE-ECL sensor application and is expected to shine in microchips and point-of-care testing (POCT).

Importance of DNA nanotechnology for DNA methyltransferases in biosensing assays

DNA methylation is the process by which specific bases on a DNA sequence acquire methyl groups under the catalytic action of DNA methyltransferases (DNMT). Abnormal changes in the function of DNMT are important markers for cancers and other diseases; therefore, the detection of DNMT and the selection of its inhibitors are critical to biomedical research and clinical practice. DNA molecules can undergo intermolecular assembly to produce functional aggregates because of their inherently stable physical and chemical properties and unique structures. Conventional DNMT detection methods are cumbersome and complicated processes; therefore, it is necessary to develop biosensing technology based on the assembly of DNA nanostructures to achieve rapid analysis, simple operation, and high sensitivity. The design of the relevant program has been employed in life science, anticancer drug screening, and clinical diagnostics. In this review, we explore how DNA assembly, including 2D techniques like hybridization chain reaction (HCR), rolling circle amplification (RCA), catalytic hairpin assembly (CHA), and exponential isothermal amplified strand displacement reaction (EXPAR), as well as 3D structures such as DNA tetrahedra, G-quadruplexes, DNA hydrogels, and DNA origami, enhances DNMT detection. We highlight the benefits of these DNA nanostructure-based biosensing technologies for clinical use and critically examine the challenges of standardizing these methods. We aim to provide reference values for the application of these techniques in DNMT analysis and early cancer diagnosis and treatment, and to alert researchers to challenges in clinical application.

Self-powered photoelectrochemical immunosensing platform for sensitive CEA detection using dual-photoelectrode synergistic signal amplification

Self-powered photoelectrochemical (PEC) sensing, as an emerging sensing mode, can effectively solve the problems such as weak anti-interference ability and poor signal response of individual photoanode or photocathode sensing. In this work, an ITO/Co-CuInS2 photocathode and ITO/WO3@CdS photoanode based self-powered cathodic PEC immunosensor was developed, which integrated dual-photoelectrode to synergistic amplify the signal for highly sensitive and specific detection of carcinoembryonic antigen (CEA). The self-powered PEC sensor could drive electrons transfer through the difference in Fermi levels between the two photoelectrodes without an external bias voltage. The photoanode was introduced to amplify the photoelectric signal, and the photocathode was only designed for the construction of sensing interfaces. The proposed sensor quantitatively determined the target CEA with the detection limit of 0.23 pg/mL and a linear correlation confine of 0.1 pg/mL ∼100 ng/mL. The constructed immunosensing platform exhibited high sensitivity, satisfactory stability and great biological detection selectivity, providing a feasible and effective strategy for the manufacture of new self-powered sensors in high-performance PEC bioanalytical applications.

Fluorogenic RNA Aptamer-Based Amplification and Transcription Strategy for Label-free Sensing of Methyltransferase Activity in Complex Matrixes

DNA methyltransferase is significant in cellular activities and gene expression, and its aberrant expression is closely linked to various cancers during initiation and progression. Currently, there is a great demand for reliable and label-free techniques for DNA methyltransferase evaluation in tumor diagnosis and cancer therapy. Herein, a low-background fluorescent RNA aptamer-based sensing approach for label-free quantification of cytosine-guanine (CpG) dinucleotides methyltransferase (M.SssI) is reported. The fluorogenic light-up RNA aptamers-based strategy exhibits high selectivity via restriction endonuclease, padlock-based recognition, and RNA transcription. By combining rolling circle amplification (RCA), and RNA transcription with fluorescence response of RNA aptamers of Spinach-dye compound, the proposed platform exhibited efficiently ultrahigh sensitivity toward M.SssI. Eventually, the detection can be achieved in a linear range of 0.02-100 U mL-1 with a detection limit of 1.6 × 10-3 U mL-1. Owing to these superior features, the method is further applied in serum samples spiked M.SssI, which delivers a recovery ranging from 92.0 to 107.0% and a relative standard deviation <7.0%, providing a promising and practical tool for determining M.SssI in complex biological matrices.

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.

Dual-Photoelectrode Fuel Cell Based Self-Powered Sensor for a Picomole Level Pollutant: Using an In Situ Molecularly Imprinted p-Type Organic Photocathode

Developing a dual-photoelectrode fuel cell based self-powered sensor (DPFC-SPS) with an ideal signal output capability and high sensitivity performance for the detection of environmental pollutant atrazine (ATZ) has an important value. In this work, the in situ molecularly imprinting functionalized p-type organic semiconductor polyterthiophene (MI-pTTh) is used as a photocathode to construct a DPFC-SPS toward the typical environmental pollutant ATZ for the first time. Due to its excellent photoactivity, higher stability, and superior oxygen reduction reaction activity, pTTh serves as the photocathode material for constructing a self-powered sensing platform with a stable signal output and high photoelectric activity. Based on the sensitive light-triggered large self-bias of the DPFC-SPS, the open circuit potential (EOCV) of the device reaches 1.21 V and the maximum power density (Pmax) reaches 121.5 μW·cm-2, which is much higher than most reported PFC-SPSs. Simultaneously, in situ molecularly imprinted (MI) functionization of pTTh can further endow it with specific recognition ability, helping the constructed SPS achieve high sensitivity, selectivity, and effective recognition of the important environmental pollutants ATZ in complex systems. It exhibits a broad linear relationship from 0.002 to 100 nM and a low detection limit (estimated by S/N > 3) of 0.21 pM toward ATZ. The mechanism of the binding kinetics of the MI-pTTh with the target ATZ is further studied via in situ infrared spectroscopy. This work provides theoretical guidance for sensing strategies using dual-photoelectrode devices and offers a rational device design for cost-effective electricity generation from renewable resources.

Label-free and sensitive detection of N6-methyladenosine demethylase activity in crude cell extracts and clinical cancer tissues based on demethylation-triggered exponential signal amplification

The m6A demethylase catalyzes the removal of m6A modification to establish proper RNA methylation patterns, and it has emerged as a promising disease biomarker and a therapeutic target. The reported m6A demethylase assays often suffer from tedious producers, expensive reagents, radioactive risk, limited sensitivity, and poor specificity. Herein, we develop a simple, selective, label-free, and highly sensitive fluorescent biosensor for m6A demethylase assay based on demethylation-triggered exponential signal amplification. In this biosensor, m6A demethylase-catalyzed demethylation can protect the circular DNA from the digestion by DpnI, subsequently triggering hyperbranched rolling circle amplification to achieve exponential signal amplification for producing abundant ssDNA and dsDNA products. The amplified DNA signal can be sensitively and simply detected by SYBR Gold in a label-free manner. This biosensor avoids any antibodies, washing/separation procedures, and fluorophore-/quencher-labeled probes, great simplifying the assay procedures and reducing the assay cost. Moreover, this biosensor achieves good specificity and excellent sensitivity with a detection limit of 1.2 fg/μL, which is superior to conventional ELISA (36.3 pg/μL). Especially, this biosensor enables direct monitoring of m6A demethylase activity in crude cell extracts with high accuracy, and it can be further applied for the screening of m6A demethylase inhibitor, measurement of m6A demethylase activity in different cell lines, and discrimination of m6A demethylase level in clinical cancer and healthy tissues, providing a facile and robust platform for RNA methylation-related biomedical research, disease diagnosis, and drug discovery.

An electrochemiluminescence resonance energy transfer biosensor based on CDs/PAMAM/rGO nanocomposites and Au@Ag2S nanoparticles for PML/RARα fusion gene detection

In recent years, electrochemiluminescence resonance energy transfer (ECL-RET) with low background signal and high specificity has attracted much attention among researchers. Herein, we established a novel ECL-RET biosensor for PML/RARα fusion gene detection. In this ECL-RET system, carbon dots (CDs) with low toxicity and prominent electrochemical activity were used as donor and Au@Ag2S core-shell nanoparticles (Au@Ag2S NPs) were employed as ECL acceptor. The Au@Ag2S NPs possessed a wide ultraviolet-visible (UV-vis) absorption spectrum between 500 nm and 700 nm, which completely overlapped with the ECL spectrum of CDs. Furthermore, the CDs-decorated poly-amidoamine/reduced graphene oxide (CDs/PAMAM/rGO) nanocomposites were prepared to improve the ECL signals and served as a substrate to stably load capture probe deoxyribonucleic acid (DNA). Based on the ECL-RET biosensing strategy, the Au@Ag2S NPs-labeled assistant probes and target DNA could pair with capture probes to form the sandwich-type DNA structure and the distance between donor and accepter was closed, leading to quenching of the ECL signal of CDs. The ECL-RET biosensor represented eminent analytical performance for PML/RARα fusion gene detection with a wide linear relationship from 5 fM to 500 pM and a low detection limit of 0.72 fM, which provided a novel technical means and theoretical basis for detection and diagnosis of acute promyelocytic leukemia.

Construction of an electrochemical-fluorescent dual-mode sensor with a dual-mode signal AgNC probe synthesized from cytosine-rich DNA for OTA detection

Herein, we have used DNA-silver nanocluster (DNA-AgNC) signal probes with both electrochemical and fluorescent signals for the first time to construct an electrochemical-fluorescent dual-mode sensor. The sensor has an easy-to-prepare dual-signal property combined with the magnetic separation technique for dual-mode detection of ochratoxin A (OTA). In the absence of OTA, the DNA strand used to synthesize AgNCs was not available in the system after magnetic separation. DNA-AgNCs probes could not be synthesized in the system, resulting in low fluorescence and electrochemical signals. In the presence of OTA, it led to the shedding of sulfhydryl-modified and cytosine-rich DNA (C-DNA). DNA-AgNCs probes with high fluorescence and electrochemical signals were formed by adding AgNO3 and NaBH4 to the supernatant after magnetic separation. Dual-mode detection of OTA was achieved by the signal response of fluorescence and electrochemistry. The detection ranges were 2.5 × 10-4-50 ng mL-1 and 2.5 × 10-4-25 ng mL-1 in the fluorescence mode and electrochemical mode with detection limits of 0.11 pg mL-1 and 0.025 pg mL-1, respectively. Meanwhile, the dual-mode sensor displayed better specificity, repeatability and reproducibility than conventional electrochemical and fluorescent single-mode sensors. The results of the spiked peanut and wheat flour detection showed that the fluorescence and electrochemical modes of the sensor exhibited satisfactory average recoveries.

A programmable DNA nanodevice for colorimetric detection of DNA methyltransferase activity using functionalized hemin/G-quadruplex DNAzyme

The measurement of DNA methyltransferase (MTase) activity and screening of DNA MTase inhibitors holds significant importance for the diagnosis and therapy of methylation-related illness. Herein, we developed a colorimetric biosensor (PER-FHGD nanodevice) to detect DNA MTase activity by integrating the primer exchange reaction (PER) amplification and functionalized hemin/G-quadruplex DNAzyme (FHGD). By replacing the native hemin cofactor into the functionalized cofactor mimics, FHGD has exhibited significantly improved catalytic efficiency, thereby enhancing the detection performance of the FHGD-based system. The proposed PER-FHGD system is capable of detecting Dam MTase with excellent sensitivity, exhibiting a limit of detection (LOD) as low as 0.3 U/mL. Additionally, this assay demonstrates remarkable selectivity and ability for Dam MTase inhibitors screening. Furthermore, using this assay, we successfully detect the Dam MTase activity both in serum and in E. coli cell extracts. Importantly, this system has the potential to serve as a universal strategy for FHGD-based diagnosis in point-of-care (POC) tests, by simply altering the recognition sequence of the substrate for other analytes.

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.

Photoelectrochemical sensors based on paper and their emerging applications in point-of-care testing

Point-of-care testing (POCT) technology is urgently required owing to the prevalence of the Internet of Things and portable electronics. In light of the attractive properties of low background and high sensitivity caused by the complete separation of excitation source and detection signal, the paper-based photoelectrochemical (PEC) sensors, featured with fast in analysis, disposable and environmental-friendly have become one of the most promising strategies in POCT. Therefore, in this review, the latest advances and principal issues in the design and fabrication of portable paper-based PEC sensors for POCT are systematically discussed. Primarily, the flexible electronic devices that can be constructed by paper and the reasons why they can be used in PEC sensors are expounded. Afterwards, the photosensitive materials involved in paper-based PEC sensor and the signal amplification strategies are emphatically introduced. Subsequently, the application of paper-based PEC sensors in medical diagnosis, environmental monitoring and food safety are further discussed. Finally, the main opportunities and challenges of paper-based PEC sensing platforms for POCT are briefly summarized. It provides a distinct perspective for researchers to construct paper-based PEC sensors with portable and cost-effective, hoping to enlighten the fast development of POCT soon after, as well as benefit human society.

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.

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.

Dry Chemistry-Based Bipolar Electrochemiluminescence Immunoassay Device for Point-of-Care Testing of Alzheimer-Associated Neuronal Thread Protein

In this study, we developed, for the first time, a novel dry chemistry-based bipolar electrochemiluminescence (ECL) immunoassay device for point-of-care testing (POCT) of Alzheimer-associated neuronal thread protein (AD7c-NTP), where the ECL signals were automatically collected and analyzed after the sample and buffer solutions were manually added onto the immunosensor. The proposed immunoassay device contains an automatic ECL analyzer and a dry chemistry-based ECL immunosensor fabricated with a screen-printed fiber material-based chip and a three-dimensional (3D)-printed shell. Each pad of the fiber material-based chip was premodified with certain reagents for immunoreaction and then assembled to form the ECL immunosensor. The self-enhanced ECL of the Ru(II)-poly-l-lysine complex and the lateral flow fiber material-based chip make the addition of coreactants and repeated flushing unnecessary. Only the sample and buffer solutions are added to the ECL immunosensor, and the process of ECL detection can be completed in about 6 min using the proposed automatic ECL analyzer. Under optimized conditions, the linear detection range for AD7c-NTP was 1 to 10⁴ pg/mL, and the detection limit was 0.15 pg/mL. The proposed ECL immunoassay device had acceptable selectivity, stability, and reproducibility and had been successfully applied to detect AD7c-NTP levels in human urine. In addition, the accurate detection of AD7c-NTP and duplex detection of AD7c-NTP and apolipoprotein E ε4 gene were also validated. It is believed that the proposed ECL immunoassay device may be a candidate for future POCT applications.

Visual/Photoelectrochemical Off-On Sensor Based on Cu/Mn Double-Doped CeO2 and Branched Sheet Embedded Cu2O/CuO Nanocubes

An integrated dual-signal bioassay was devised to fulfil thrombin (TB) ultrasensitive detection by integrating visualization with the photoelectrochemical technique based on G-quadruplex/hemin. During the process, branched sheet embedded copper-based oxides prepared with illumination and alkaline condition play a vital role in obtaining the desirable photocurrent. The switchover of photoelectrochemical signal was realized by the adjustable distance between electron acceptor G-quadruplex/hemin and interface materials due to dissociation of the Cu/Mn double-doped cerium dioxide (CuMn@CeO₂)/DNA caused by the addition of TB. Then, CuMn@CeO₂ transferred onto visual zones triggered catalytic reactions under the existence of 3,3',5,5'-tetramethylbenzidine and hydrogen peroxide, making a variation in color recognized by the naked eye and providing visual prediction. Under optimized conditions, this bioassay protocol demonstrated wide linear ranges (0.0001-50 nM), high selectivity, stability, and reproducibility. More importantly, the proposed visual/photoelectrochemical transduction mechanism platform exhibits a lower background signal and more reliable detection results, which also offers an effective way for detecting other proteins and nucleic acids.

A novel PCR-free and label-free cloth-based DNA sensor for sensitive and rapid detection of Escherichia coli

BACKGROUND

As is known to all, pathogenic bacteria have a serious impact on human health. The development of sensitive, simple, rapid and low-cost bacterial detection method is necessary. Nowadays, some conventional methods (such as plate count, polymerase chain reaction (PCR) and immunological techniques) can not meet the above needs. This work was aimed at providing a new method for addressing these unmet needs.

RESULT

This study proposed a novel PCR-free and label-free DNA sensor based on multiple linear hybridization chain reaction (ML-HCR) and cloth-based closed bipolar electrochemiluminescence for sensitive and rapid detection of Escherichia coli (E. coli). The target DNA can be obtained from the E. coli genomic DNA by using the restriction enzyme instead of PCR. The auxiliary probe-triggered ML-HCR is carried out with continuous hybridization of two hairpin DNA, and as a result the double stranded DNA is formed to provide a large number of binding sites for Ru(bpy)₃²⁺. The whole detection is PCR-free and label-free, and thus the detection procedure is easier and faster. Under optimized conditions, the linear detection range was from 10² to 10⁷ CFU/mL, and the detection limit was low to 38 CFU/mL. In addition, the proposed DNA sensor has an acceptable selectivity, stability and reproducibility, and is successfully applied to detect E. coli in milk samples with the recoveries from 96.24% to 105.98%.

SIGNIFICANCE

The proposed DNA sensor has broad application prospects in the fields of bacterial detection and gene diagnose. Further, this method has potential to be extended for establishing miniaturized, integrated, and automated detection system.

PEC/Colorimetric Dual-Mode Lab-on-Paper Device via BiVO4/FeOOH Nanocomposite In Situ Modification on Paper Fibers for Sensitive CEA Detection

A dual-mode lab-on-paper device based on BiVO₄/FeOOH nanocomposites as an efficient generating photoelectrochemical (PEC)/colorimetric signal reporter has been successfully constructed by integration of the lab-on-paper sensing platform and PEC/colorimetric detection technologies for sensitive detection of carcinoembryonic antigen (CEA). Concretely, the BiVO₄/FeOOH nanocomposites were in situ synthesized onto the paper-working electrode (PWE) through hydrothermal synthesis of the BiVO₄ layer on cellulose fibers (paper-based BiVO₄) which were initially modified by Au nanoparticles for improving the conductivity of three dimensional PWE, and then the photo-electrodeposition of FeOOH onto the paper-based BiVO₄ to construct the paper-based BiVO₄/FeOOH for the portable dual-mode lab-on-paper device. The obtained nanocomposites with an FeOOH needle-like structure deposited on the BiVO₄ layer exhibits enhanced PEC response activity due to its effective separation of the electron-hole pair which could further accelerate the PEC conversion efficiency during the sensing process. With the introduction of CEA targets onto the surface of nanocomposite-modified PWE assisted by the interaction with the CEA antibody from a specific recognition property, a signal-off PEC signal state with a remarkable photocurrent response decreasing trend can be achieved, realizing the quantitative detection of CEA with the PEC signal readout mode. By means of a smart origami paper folding, the colorimetric signal readout is achieved by catalyzing 3,3',5,5'-tetramethylbenzidine (TMB) to generate blue oxidized TMB in the presence of H₂O₂ due to the satisfied enzyme-like catalytic activity of the needle-like structure, FeOOH, thereby achieving the dual-mode signal readout system for the proposed lab-on-paper device. Under the optimal conditions, the PEC and colorimetric signals measurement were effectively carried out, and the corresponding linear ranges were 0.001-200 ng·mL^-1 and 0.5-100 ng·mL^-1 separately, with the limit of detection of 0.0008 and 0.013 ng·mL^-1 for each dual-mode. The prepared lab-on-paper device also presented a successful application in serum samples for the detection of CEA, providing a potential pathway for the sensitive detection of target biomarkers in clinical application.

Nanomaterials-based portable electrochemical sensing and biosensing systems for clinical and biomedical applications

Miniaturized electrochemical sensing systems are employed in day-to-day uses in the several area from public health to scientific applications. A variety of electrochemical sensor and biosensor systems may not be effectively employed in real-world diagnostic laboratories and biomedical industries due to their limitation of portability, cost, analytical period, and need of skilled trainer for operating devices. The design of smart and portable sensors with high sensitivity, good selectivity, rapid measurement, and reusable platforms is the driving strength for sensing glucose, lactate, hydrogen peroxide, nitric oxide, mRNA, etc. The enhancement of sensing abilities of such sensor devices through the incorporation of both novel sensitive nanomaterials and design of sensor strategies are evidenced. Miniaturization, cost and energy efficient, online and quantitative detection and multiple sensing ability are the beneficial of the nanostructured-material-based electrochemical sensor and biosensor systems. Owing to the discriminating catalytic action, solidity and biocompatibility for designing sensing system, nanoscale materials empowered electrochemical detection systems are accomplished of being entrenched into/combined with portable or miniaturized devices for specific applications. In this review, the advance development of portable and smart sensing/biosensing systems derived from nanoscale materials for clinical and biomedical applications is described.

Graphical Abstract

Framework and Spherical Nucleic Acids Synergistically Enhanced Electrochemiluminescence Nanosensors for Rapidly Diagnosing Acute Myocardial Infarction Based on Circulating MicroRNA Levels

Acute myocardial infarction (AMI)-related microRNAs (miRNAs) in circulating blood have been proved as promising biomarkers for AMI diagnosis. The detection of these miRNAs at ultralow levels usually requires nucleic acid amplification strategies to improve the sensitivity at the cost of time. Given that the first hour after an AMI attack is the golden time for saving AMI patients' lives, shortening the time of ultrasensitive miRNA analysis is of great significance for clinical AMI diagnosis. Toward this goal, here we present a direct electrochemiluminescence (ECL) sensing strategy for fast and ultrasensitive miRNA detection, circumventing the time-consuming signal amplification steps. Target miRNAs are directly hybridized with two probe strands that are attached to a covalently hemin-modified spherical nucleic acid enzyme (SNAzyme) and a truncated triangular pyramid DNA nanoplatform on the electrode, respectively. Both of them improve the ECL signal and meanwhile reduce the background, thereby remarkably promoting the detection sensitivity of target miRNAs. It enables the rapid detection of an AMI-related miRNA (miR-499) at 10 aM in human serum within 30 min using the SNAzyme-catalyzed luminol-H₂O₂ ECL reaction. This sensing strategy is then utilized for AMI diagnosis via probing endogenous miR-499 in patients' circulating blood with endogenous miR-16 as an intrinsic reference, showing a significant difference (P < 0.001) between the miR-499 levels of patients and the healthy.

A Paper-Based Photoelectrochemical Sensing Platform Based on In Situ Grown ZnO/ZnIn2S4 Heterojunctions onto Paper Fibers for Sensitively Detecting AFP

Nowadays, developing a cost-effective, easy-to-operate, and efficient signal amplification platform is of important to microfluidic paper-based analytical devices (μPAD) for end-use markets of point-of-care (POC) assay applications. Herein, an ultrasensitive, paper-based photoelectrochemical (PEC) bioassay platform is constructed by in situ grown ZnO/ZnIn₂S₄ heterojunctions onto paper fibers, which acted as photoactive signal amplification probes for enhancing the sensitivity of antibodies-based diagnostic assays, for the sensitive detection of alpha-fetoprotein (AFP) targets. The crystalline flake-like ZnIn₂S₄ composited with hexagonal nanorods (NRs) morphology of ZnO is an in situ grown, at the first time, onto cellulose fibers surface supported with Au nanoparticle (Au NP) modification to improve conductivity of the device working zone. The obtained composites on paper fibers are implemented as a flexible paper-based photoelectrode to realize remarkable performance of the fabricated μPAD, resulting from the enhanced PEC activity of heterojunctions with effective electron-hole pair separation for accelerating photoelectric conversion efficiency of the sensing process under light irradiation. Once the target AFP was introduced into the biosensing interface assistant, with a specific recognition interaction of AFP antibody, a drastically photocurrent response was generated, in view of the apparent steric effects. With the concentration increase of AFP targets, more immune conjugates could be confined onto the biosensing interface, eventually leading to the quantitative decrease of photocurrent intensity. Combined with an ingenious origami design and permitting the hydrophobic/hydrophilic conversion procedure in the bioassay process, the ultrasensitive PEC detection of AFP targets was realized. Under the optimized conditions, the level of AFP could be sensitively tracked by the prepared μPAD with a liner range from 0.1 to 100 ng mL^-1 and limit of detection of 0.03 ng mL^-1. This work provides a great potential application for highly selective and sensitive POC testing of AFP, and finally, developments for clinical disease diagnosis.

Photothermal-Reagent-Triggered Visual Thermoresponsive and Quantized Photoelectrochemical Dual-Signal Assay

In vitro biosensing chips are urgently needed for early-stage diagnosis and real-time surveillance of epidemic diseases. Herein, a versatile zone with photothermal effects is implanted in the miniature space of a collapsible lab-on-paper photoelectrochemical biosensor for on-site detection of microRNA-141 in body fluids, which can flexibly interconnect the traditional photocurrent signal with functional temperature response. The visualized thermoresponsive results are enhanced by the exciton energy conversion between Fe₃O₄ nanoparticles (Fe₃O₄ NPs) and formed Prussian blue nanoparticles under near-infrared irradiation, which not only presents heat energy gradient variations but also generates color changes. Significantly, the controlled release of Fe₃O₄ NPs is actuated by a target-triggered enzyme assist strand displacement cycle strategy to efficiently improve the accuracy of target temperature signal prediction, which can concurrently mediate photoelectric signal attenuation via promoting the rapid recombination of photoexcited charge carriers on the CuInS₂/CoIn₂S₄ electrode surface, affording dependable ultrasensitive detection results. Benefitting from the ingenious design of the versatile thermoresponsive-photoelectric sensing platform, the preliminary screening and ultrasensitive quantitative analysis can be simultaneously achieved in a single-drop sample. As a consequence, speedy prediction results and satisfied monitoring data are acquired in the ranges of 0.5 pM to 2 nM and 0.001 pM to 5 nM by measuring the temperature change and photocurrent intensity. By right of these advantages, such research paves a prospective paradigm for the manufacture of a visual, rapid, broad-spectrum, and reliable real-time surveillance platform, which allows it to be a promising candidate for epidemic disease home diagnosis and intelligent diagnosis.

In Situ Imaging of Endogenous Hydrogen Peroxide Efflux from Living Cells via Bipolar Gold Nanoelectrode Array and Electrochemiluminescence Technology

The integration of a closed bipolar electrode (c-BPE) array and electrochemiluminescence (ECL) detection received a boost in applications in the detection of cell adhesion and disease-related biomarkers. This work proposed a gold nanorod array based c-BPE-ECL system to realize an in situ image of endogenous hydrogen peroxide (H₂O₂) efflux from living cells and parallel analysis of endogenous H₂O₂ released from multiple cells by converting electrochemical signals into optical signals. The gold nanorod array with high density was prepared by a repeating chronopotentiometry procedure with anodic aluminum oxide (AAO) membrane as a template. The c-BPE array was fabricated by assembling poly(dimethylsiloxane) (PDMS) chips on both sides of the gold nanorod array. When an appropriate driving potential is applied, H₂O₂ generated from living cells at the sensing pole was reduced on the gold nanorod, triggering the oxidation of the ECL reagent at the reporting pole, which allowed the detection of H₂O₂ released from living cells. Under phorbol myristate acetate (PMA) stimulation, H₂O₂ released from living HeLa, HepG2, MCF-7, and LO2 cells was determined to be 47, 32.4, 25.7, and 6.3 μM, respectively. This indicated that the amount of H₂O₂ released from PMA-stimulated cancer cells was significantly higher than that from the stimulated normal cells. This work presented a new approach for in situ imaging of H₂O₂ released from living cells and could also be used to detect other electrochemically active or non-electrochemically active molecules through simple cell surface modification, which may have potential applications in cell apoptosis study and disease diagnosis.

Simple immunosensor for ultrasensitive electrochemical determination of biomarker of the bone metabolism in human serum

Ultrasensitive and selective determination of biomarkers of the bone metabolism in serum is crucial for early screening, timely treatment, and monitoring of the curative effect of osteoporosis, which is a silent disease with serious health threats. Immunoassay with a simple sensing interface and ultrahigh sensitivity is highly desirable. Herein, a simple electrochemical immunosensor is demonstrated based on gold nanoparticles (AuNPs) electrodeposited on chitosan-reduced graphene oxide (CS-G) composite modified electrode, which can achieve sensitive determination of the important biomarker of bone metabolism, bone gamma-carboxyglutamate protein (BGP). To overcome the agglomeration of graphene and introduce a biocompatible matrix with functional amino groups, CS-G is prepared and modified on the supporting glassy carbon electrode (GCE). Then, AuNPs are electrodeposited on CS-G through their interaction between amine groups of CS. The immobilized AuNPs provide numerous binding sites to immobilize anti-BGP antibodies (Ab_BGP). The specific recognition between BGP and Ab_BGP results in a reduction in the mass transfer of the electrochemical probe (Fe(CN)₆^3-/4-) in solution, leading to a reduced electrochemical signal. Based on this mechanism, fast and ultrasensitive electrochemical detection of BGP is achieved when the concentration of BGP ranges from 100 ag ml⁻¹ to 10 μg mL⁻¹ with a limit of detection (LOD) of 20 ag ml⁻¹ (S/N = 3). The determination of BGP in human serum is also realized with high reliability.

A reagentless electrochemical immunosensor for sensitive detection of carcinoembryonic antigen based on the interface with redox probe-modified electron transfer wires and effectively immobilized antibody

Convenient and sensitive detection of tumors marked in serum samples is of great significance for the early diagnosis of cancers. Facile fabrication of reagentless electrochemical immunosensor with efficient sensing interface and high sensitivity is still a challenge. Herein, an electrochemical immunosensor was easily fabricated based on the easy fabrication of immunoassay interface with electron transfer wires, confined redox probes, and conveniently immobilized antibodies, which can achieve sensitive and reagentless determination of the tumor marker, carcinoembryonic antigen (CEA). Carboxyl multi-walled carbon nanotubes (MWCNTs) were firstly modified with an electrochemical redox probe, methylene blue (MB), which has redox potentials distinguished from those of redox molecules commonly existing in biological samples (for example, ascorbic acid and uric acid). After the as-prepared MB-modified MWCNT (MWCNT-MB) was coated on the supporting glassy carbon electrode (GCE), the MWCNT-MB/GCE exhibited improved active area and electron transfer property. Polydopamine (PDA) was then in situ synthesized through simple self-polymerization of dopamine, which acts as the bio-linker to covalently immobilize the anti-CEA antibody (Ab). The developed immunosensor could be applied for electrochemical detection of CEA based on the decrease in the redox signal of MB after specific binding of CEA and immobilized Ab. The fabricated immunosensor can achieve sensitive determination of CEA ranging from 10 pg/ml to 100 ng/ml with a limit of detection (LOD) of 0.6 pg/ml. Determination of CEA in human serum samples was also realized with high accuracy.