Faraday-Cage-Type Electrochemiluminescence Immunoassay: A Rise of Advanced Biosensing Strategy

Faraday cage-type photocurrent polarity switching photoelectrochemical sensing platform for highly selective and sensitive detection of Vibrio parahaemolyticus

Highly selective and sensitive detection of foodborne pathogens is crucial for ensuring food safety. In this work, a photoelectrochemical (PEC) aptasensing platform was developed for the selective and sensitive detection of Vibrio parahaemolyticus (VP), adopting Faraday cage-type construction mode. When VP was present in the sample, the aptamer for VP (Apt) assembled on the Apt/Bi2S3/ITO electrode captured VP, which bound GO@Cu2O-Apt to the electrode surface. The graphene oxide (GO) in GO@Cu2O-Apt has a large surface area and good conductivity, on the surface of which a large amount of Cu2O that can switch the polarity of the Bi2S3 photocurrent was loaded, resulting in a highly selective and sensitive detection of VP with a detection limit of 1.0 CFU/mL. By adjusting the Apt, the platform can be used for the detection of other foodborne pathogens, offering broad application potential in foodborne pathogen detection.

Electrochemiluminescence immunoassay using ionic-liquid submicron particles for prostate-specific antigen determination

In this study, ionic-liquid submicron particles (ILSPs) encapsulating the luminophore tris(2',2-bipyridyl)ruthenium (II) ([Ru(bpy)3]2+) were developed as a carrier for an electrochemiluminescence immunoassay (ECLIA). The ILSPs were applied to quantitative determination of the model analyte prostate-specific antigen (PSA). The electrochemiluminescence of [Ru(bpy)3]2+ was measured with 2-(dibutylamino)ethanol as a co-reactant in nine ionic liquids (ILs). The electrochemiluminescence intensity was higher in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([BMIM][TFSA]) and N-(2-methoxyethyl)-N-methyl pyrrolidinium bis(trifluoromethanesulfonyl)imide ([MEMP][TFSA]) than the other ILs. ILSPs were prepared using polyoxyethylene sorbitan monolaurate and sorbitan monooleate as surfactants and either [BMIM][TFSA] or [MEMP][TFSA]. The [BMIM][TFSA] ILSPs had a mean particle size of 244 nm and zeta potential of - 21.0 mV, and the [MEMP][TFSA] ILSPs had a mean particle size of 293 nm and zeta potential of - 17.9 mV. Microscope images showed that ILSPs were IL-in-water emulsions that completely encapsulated [Ru(bpy)3]2+. The ILSPs with [BMIM][TFSA] were more stable than those with [MEMP][TFSA], and [BMIM][TFSA] ILSPs was selected as a carrier in ECLIA for PSA determination. The calibration curve of PSA for ECLIA using the [BMIM][TFSA] ILSPs showed a good linear relationship (y = 0.29x + 4.02, r = 0.95) for the PSA concentration range of 100 pg/mL-100 μg/mL. The limit of detection and limit of quantification were 544 pg/mL and 35 ng/mL, respectively. Our results demonstrate that ECLIA using ILSPs can be used to easily determine the PSA concentration even with ILSPs in the particle state.

Emerging trends and recent advances in MXene/MXene-based nanocomposites toward electrochemiluminescence sensing and biosensing

Electrochemiluminescence (ECL) sensing systems have surged in popularity in recent years, making significant strides in sensing and biosensing applications. The realization of high-throughput ECL sensors hinges on the implementation of novel signal amplification strategies, propelling the field toward a new era of ultrasensitive analysis. A key strategy for developing advanced ECL sensors and biosensors involves utilizing novel structures with remarkable properties. The past few years have witnessed the emergence of MXenes as a captivating class of 2D materials, with their unique properties leading to exploitation in diverse applications. This review provides a comprehensive summary of the latest advancements in MXene-modified materials specifically engineered for ECL sensing and biosensing applications. We thoroughly analyze the structure, surface functionalization, and intrinsic properties of MXenes that render them exceptionally suitable candidates for the development of highly sensitive ECL sensors and biosensors. Furthermore, this study explores the broad spectrum of applications of MXenes in ECL sensing, detailing their multifaceted roles in enhancing the performance and sensitivity of ECL (bio)sensors. By providing a comprehensive overview, this review is expected to promote progress in related areas.

Preparation and application of multiple particle binding-liposomes for electrochemiluminescent signal amplification in bioassays

In this study, multiple particle binding-liposomes (MPB-Lips), encapsulating the luminophore tris(2',2-bipyridyl)ruthenium (II) complex ([Ru(bpy)3]2+), were developed as an electrochemiluminescence (ECL) signal amplifier and were applied to detect the model analyte streptavidin (SA) using the indirect competitive ECL method. The MPB-Lips were prepared by mixing various ratios of two different liposomes-one containing a phospholipid with a primary amine group and a biotinyl group (BIO/NH2-Lip) and one containing a phospholipid with an N-hydroxysuccinimide group (NHS-Lip) to allow binding between particles via amide bonds. Quartz crystal microbalance analysis using SA-modified gold-coated quartz crystals showed that the frequency shift values of MPB-Lips gradually decreased in the order BIO/NH2-Lip:NHS-Lip = 1:0 < 1:1 < 1:3 < 1:5. This indicated that MPB-Lips were successfully formed. The indirect competitive ECL method using SA-modified gold electrodes showed that the 1:5-Lip system had greater sensitivity than the 1:0-Lip system-the limit of detection and quantification values for the systems were 1.84 and 6.30 μg mL-1 for 1:0-Lip, and 1.20 and 1.74 μg mL-1 for 1:5-Lip. Finally, the recovery of SA spiked in fetal bovine serum samples using the 1:5-Lip system showed good accuracy and precision with a recovery rate of 83-106% and relative standard deviation of 4-14%. Our study demonstrated that the MPB-Lips system was an effective and useful ECL amplifier and the ECL method using MPB-Lips could be applied to detect an analyte in a real sample.

A papain-based colorimetric catalytic sensing system for immunoassay detection of carcinoembryonic antigen

A colorimetric immunoassay was built for determination of carcinoembryonic antigen (CEA) based on papain-based colorimetric catalytic sensing system through the use of glucose oxidase (GOx). In the presence of GOx, glucose was catalytically oxidized to produce H2O2. Through the assistance of papain (as a peroxide mimetic enzyme), the signal came from the oxidative color development of 3,3',5,5'-tetramethylbenzidine (TMB, from colorless to blue) catalyzed by the generated H2O2. Herein, a sandwich-type immunoassay was built based on GOx as labels. As the concentration of CEA increased, more GOx-labeled antibodies specifically associate with target, which leaded to more H2O2 generation. Immediately following this, more TMB were oxidized with the addition of papain. Accordingly, the absorbance increased further. As a result, the concentration of CEA is positively correlated with the change in absorbance of the solution. Under optimal conditions, the CEA concentration was linear in the range of 0.05-20.0 ng/mL, and the limit of detection (LOD) reached 37 pg/mL. The papain-based colorimetric immunoassay also exhibited satisfactory repeatability, stability, and selectivity.

Tripedal DNA Walker as a Signal Amplifier Combined with a Potential-Resolved Multicolor Electrochemiluminescence Strategy for Ultrasensitive Detection of Prostate Cancer Staging Indicators

A multicolor electrochemiluminescence (ECL) biosensor based on a closed bipolar electrode (BPE) array was proposed for the rapid and intuitive analysis of three prostate cancer staging indicators. First, [Irpic-OMe], [Ir(ppy)2(acac)], and [Ru(bpy)3]2+ were applied as blue, green, and red ECL emitters, respectively, whose mixed ECL emission colors covered the whole visible region by varying the applied voltages. Afterward, we designed a simple Mg2+-dependent DNAzyme (MNAzyme)-driven tripedal DNA walker (TD walker) to release three output DNAs. Immediately after, three output DNAs were added to the cathodic reservoirs of the BPE for incubation. After that, we found that the emission colors from the anode of the BPE changed as a driving voltage of 8.0 V was applied, mainly due to changes in the interfacial potential and faradaic currents at the two poles of the BPE. Via optimization of the experimental parameters, cutoff values of such three indicators at different clinical stages could be identified instantly with the naked eye, and standard precision swatches with multiple indicators could be prepared. Finally, in order to precisely determine the prostate cancer stage, the multicolor ECL device was used for clinical analysis, and the resulting images were then compared with standard swatches, laying the way for accurate prostate cancer therapy.

An LF-NMR homogeneous immunoassay for Vibrio parahaemolyticus based on superparamagnetic 2D nanomaterials

In this work, a sensitive low field nuclear magnetic resonance (LF-NMR) homogeneous immunoassay, also called magnetic resonance switch (MRSw) sensor, for Vibrio parahaemolyticus (VP) was developed. Superparamagnetic 2D nanomaterial was designed and used as the magnetic probe of MRSw sensor. It was GO@SPIONs&Ab, a composite nanomaterial with many superparamagnetic Fe3O4 nanoparticles (SPIONs) providing a magnetic signal and VP antibody (Ab) specifically recognizing the target VP evenly distributed on the surface of GO. The presence of VP controllably changed the aggregation state of the probe, eliminating the uncertainty of MRSw sensor type, and thus then achieving a regular variation of transverse relaxation time T2 and ensuing quantitative detection of VP. Triple signal enhancement of the MRSw sensor was obtained due to the application of the designed 2D probe, by increasing the number of SPIONs, improving the magnetic intensity and susceptibility, and forming a synergistic effect. Under optimized experimental conditions, VP could be detected with satisfied sensitivity, selectivity, precision, accuracy, and stability, even in turbid real samples. LOQ for VP was 10 CFU/mL. This detection principle is widely applicable, providing an idea for the construction of highly sensitive MRSw sensors.

Faraday cage-type ECL biosensor for the detection of circulating tumor cell MCF-7

Herein, a Faraday cage-type electrochemiluminescence biosensor was designed for the detection of human breast cancer cell MCF-7. Two kinds of nanomaterials, Fe₃O₄-APTs and GO@PTCA-APTs, were synthesized as capture unit and signal unit, respectively. In presence of the target MCF-7, the Faraday cage-type electrochemiluminescence biosensor was constructed by forming a complex "capture unit-MCF-7-signal unit". In this case, lots of electrochemiluminescence signal probes were assembled and could participate in the electrode reaction, achieving a significant increase in sensitivity. In addition, the double aptamer recognition strategy was adopted to improve the capture, enrichment efficiency and detection reliability. Under optimal experimental conditions, the limit of detection was 3 cells/mL. And, the sensor could afford the detection of actual human blood samples, which is the first report on the detection of intact circulating tumor cells by the Faraday cage-type electrochemiluminescence biosensor.

Nanostructured biosensing platforms for the detection of food- and water-borne pathogenic Escherichia coli

Pathogenic bacterial infection is one of the principal causes affecting human health and ecosystems. The accurate identification of bacteria in food and water samples is of significant interests to maintain safety and health for humans. Culture-based tests are practically tedious and may produce false-positive results, while viable but non-culturable microorganisms (NCMs) cannot be retrieved. Thus, it requires fast, reliable, and low-cost detection strategies for on-field analysis and point-of-care (POC) monitoring. The standard detection methods such as nucleic acid analysis (RT-PCR) and enzyme-linked immunosorbent assays (ELISA) are still challenging in POC practice due to their time-consuming (several hours to days) and expensive laboratory operations. The optical (surface plasmon resonance (SPR), fluorescence, and surface-enhanced Raman scattering (SERS)) and electrochemical-based detection of microbes (early stage of infective diseases) have been considered as alternative routes in the emerging world of nanostructured biosensing since they can attain a faster and concurrent screening of several pathogens in real samples. Moreover, optical and electrochemical detection strategies are opening a new route for the ability of detecting pathogens through the integration of cellphones, which is well fitted for POC analysis. This review article covers the current state of sensitive mechanistic approaches for the screening and detection of Escherichia coli O157:H7 (E. coli) pathogens in food and water samples, which can be potentially applied in clinical and environmental monitoring.

Cluster-bomb type magnetic biosensor for ultrasensitive detection of Vibrio parahaemolyticus based on low field nuclear magnetic resonance

Herein, a novel cluster-bomb type signal sensing and amplification strategy in low field nuclear magnetic resonance was proposed, and a magnetic biosensor for ultrasensitive homogeneous immunoassay of Vibrio parahaemolyticus (VP) was developed. The capture unit MGO@Ab was magnetic graphene oxide (MGO) immobilized by VP antibody (Ab) to capture VP. And, the signal unit PS@Gd-CQDs@Ab was polystyrene (PS) pellets covered by Ab to recognize VP and Gd-CQDs i.e. carbon quantum dots (CQDs) containing lots of magnetic signal labels Gd³⁺. In presence of VP, the immunocomplex signal unit-VP-capture unit could be formed and separated by magnetic force conveniently from the sample matrix. With the successive introduction of disulfide threitol and hydrochloric acid, signal units were cleaved and disintegrated, resulting in a homogeneous dispersion of Gd³⁺. Thus, cluster-bomb type dual signal amplification was achieved through increasing the amount and the dispersity of signal labels simultaneously. Under optimal experimental conditions, VP could be detected in the concentration range of 5-1.0 × 10⁶ CFU/mL, with a limit of quantitation (LOQ) 4 CFU/mL. In addition, satisfactory selectivity, stability and reliability could be obtained. Therefore, this cluster-bomb type signal sensing and amplification strategy is powerful in designing magnetic biosensor and detecting pathogenic bacteria.

Novel rapid coordination of ascorbic acid 2-phosphate and iron(III) as chromogenic substrate system based on Fe2O3 nanoparticle and application in immunoassay for the colorimetric detection of carcinoembryonic antigen

This work for the first time reports on a simple and rapid colorimetric immunoassay with rapid coordination of ascorbic acid 2-phosphate (AAP) and iron (III) for determination of carcinoembryonic antigen (CEA, used as a model) by using Fe₂O₃ nanoparticle based-chromogenic substrate system. The signal was produced rapidly (1 min) from the coordination of AAP and iron (III) with color development of colorless to brown. TD-DFT calculation methods were employed to simulate the UV-Vis spectra of AAP-Fe²⁺ and AAP-Fe³⁺ complexes. Moreover, Fe₂O₃ nanoparticle could be dissolved with the aid of acid, thereby releasing free iron (III). Herein, a sandwich-type immunoassay was established based on Fe₂O₃ nanoparticle as labels. As target CEA concentration increased, the number of Fe₂O₃ labelled-antibodies (bound specifically) increased, resulting in loading more Fe₂O₃ nanoparticle on platform. The absorbance increased as the number of free iron (III), derived from Fe₂O₃ nanoparticle, increased. So, the absorbance of reaction solution is positively correlated with antigen concentration. Under optimal conditions, the current results showed good performance for CEA detection in the range 0.02-10.0 ng/mL with a detection limit of 11 pg/mL. Moreover, the repeatability, stability, and selectivity of the colorimetric immunoassay were also acceptable.

Confined Gold Single Atoms-MXene Heterostructure-Based Electrochemiluminescence Functional Material and Its Sensing Application

Herein, based on electronic metal-support interaction (EMSI), a gold single atom confined MXene (Au_SA/MXene) heterostructure was developed as the highly efficient electrochemiluminescence (ECL) functional material, which greatly improved the electrochemical properties and broadened the sensing application of MXenes. Gold single atoms were confined into the vacancy defects of Ti₃C₂T_x MXene, which could effectively avoid the masking of catalytic active sites. Meanwhile, electron transport could be accelerated with the assistance of titanium dioxide on the MXene nanosheets. Therefore, the Au_SA/MXene heterostructure had high catalytic activity and electrical activity to promote hydrogen peroxide to generate free radicals, which achieved high-efficiency ECL. Eventually, the Au_SA/MXene heterostructure was used to construct a Faraday cage-type ECL sensor with fluid nanoislands to detect miRNA-187 in triple-negative breast cancer tumor tissues.

Hemin-graphene oxide-gold nanoflower-assisted enhanced electrochemiluminescence immunosensor for determination of prostate-specific antigen

An ultrasensitive luminol electrochemiluminescence (ECL) immunosensor was constructed for the detection of prostate specific antigen (PSA) using glucose oxidase-decorated hemin-graphene oxide-gold nanoflowers ternary nanocomposites as probes. Graphene oxide was first modified with hemin and then with gold nanoflowers through an in situ growth method, which has significantly boosted the catalytic activity of this graphene oxide-based peroxidase mimetics. The biocatalytical activity of this ECL immunosensor was thoroughly investigated to achieve selective recognition of the analyte molecules (PSA) by specific binding between antigens and antibodies. The limit of detection was calculated to be 0.32 pg mL^-1 with a signal-to-noise ratio of 3. A broad linear range from 7.5 × 10^-4 to 2.5 ng mL^-1 was obtained. Such step-by-step assembled biosensor showed controlled nanostructure and exhibited promising application in analysis of human serum samples with a recovery range of 90.6-111.8% and a RSD range of 3.9-5.5%.

An Immunosensor Using Electroactive COF as Signal Probe for Electrochemical Detection of Carcinoembryonic Antigen

Two kinds of two-dimensional (2D) covalent-organic frameworks (COF) were used to construct a sandwich-type electrochemical immunosensor for a proof-of-concept study. Vinyl-functionalized COFTab-Dva could be linked with Ab1 by the thiol-ene "click" reaction. Electroactive COFTFPB-Thi was modified with gold nanoparticles (AuNPs) to ensure the successful connection with Ab2 through Au-S bond. Meanwhile, electroactive COFTFPB-Thi was used to as signal probe to realize both the detection of carcinoembryonic antigen (CEA) and the amplification of detection signal. In detection process of the sandwich-type electrochemical immunosensor, glassy carbon electrode (GCE) was modified with 2D COFTab-Dva first then connected with Ab1 by the thiol-ene "click" reaction, next quantitative CEA was captured, followed by specificially capturing signal probe of Ab2/AuNPs/COFTFPB-Thi where AuNPs acted as nanocarriers of Ab2 and COFTFPB-Thi served as the signal producers. As the amount of CEA was increased, the amount of signal probe captured to the electrode was also increased, and the peak signal intensity of the redox reaction of COFTFPB-Thi was enhanced accordingly. Thus, the quantitative detection of CEA could be realized according to the peak signal intensity of electroactive COFTFPB-Thi. The electrochemical immunosensor owned wide detection range of 0.11 ng/mL-80 ng/mL, low detection limit of 0.034 ng/mL and good practicability. This study opens up a new revelation for quantitative detection of CEA using electroactive COF as enhanced signal probe.

Biosensors and Point-of-Care Devices for Bacterial Detection: Rapid Diagnostics Informing Antibiotic Therapy

With an exponential rise in antimicrobial resistance and stagnant antibiotic development pipeline, there is, more than ever, a crucial need to optimize current infection therapy approaches. One of the most important stages in this process requires rapid and effective identification of pathogenic bacteria responsible for diseases. Current gold standard techniques of bacterial detection include culture methods, polymerase chain reactions, and immunoassays. However, their use is fraught with downsides with high turnaround time and low accuracy being the most prominent. This imposes great limitations on their eventual application as point-of-care devices. Over time, innovative detection techniques have been proposed and developed to curb these drawbacks. In this review, a systematic summary of a range of biosensing platforms is provided with a strong focus on technologies conferring high detection sensitivity and specificity. A thorough analysis is performed and the benefits and drawbacks of each type of biosensor are highlighted, the factors influencing their potential as point-of-care devices are discussed, and the authors' insights for their translation from proof-of-concept systems into commercial medical devices are provided.

PEGylation Improved Electrochemiluminescence Supramolecular Assembly of Iridium(III) Complexes in Apoferritin for Immunoassays Using 2D/2D MXene/TiO2 Hybrids as Signal Amplifiers

Dynamic self-assembly of iridium complexes in water-soluble nanocontainers is an important bottom-up process for fabricating electrochemiluminescence (ECL) bioprobes. PEGylated apoferritin (PEG-apoHSF) as the host offers a confined space to alter and modify the self-assembly of trans-bis(2-phenylpyridine)(acetylacetonate)iridium(III) [Ir(ppy)₂(acac)] based on a pH-dependent depolymerization/reassembly pathway, allowing the formation of ECL-active iridium cores in PEG-apoHSF cavities (Ir@PEG-apoHSF). With an improved encapsulation ratio in PEG-apoHSF, the coreactant ECL behavior of the fabricated Ir@PEG-apoHSF nanodots with tri-n-propylamine (TPrA) was further demonstrated, exhibiting maximum ECL emission at 530 nm that was theoretically dominated by the band gap transition. The application of Ir@PEG-apoHSF as a bioprobe in a "signal-on" ECL immunosensing system was developed based on electroactive Ti₃C₂T_x MXenes/TiO₂ nanosheet (Ti₃C₂T_x/TiO₂) hybrids. Combining with the efficiently catalyzed electro-oxidation of TPrA and Ir(ppy)₂(acac) by Ti₃C₂T_x/TiO₂ hybrids, the developed immunosensor showed dramatically amplified ECL responses toward the target analyte of neuron-specific enolase (NSE). Under experimental conditions, linear quantification of NSE from 100 fg/mL to 50 ng/mL was well established by this assay, achieving a limit of detection (LOD) of 35 fg/mL. The results showcased the capability of PEGylated apoHSF to host and stabilize water-insoluble iridium complexes as ECL emitters for aqueous biosensing and immunoassays.

A High-Throughput Platform for the Rapid Quantification of Phosphorylated Histone H2AX in Cell Lysates Based on Microplate Electrochemiluminescence Immunosensor Array

Sensitive detection of phosphorylated histone H2AX (γH2AX) in cells as a biomarker of DNA double-strand breaks has great significance in the field of molecular toxicology and life science research. However, current γH2AX detection methods require labor- and time-consuming steps. Here, for the first time, we designed a simple electrochemiluminescence (ECL) immunoassay integrated with a microplate-based sensor array to realize sensitive and high-throughput detection of γH2AX in cell lysates. Under the optimized conditions, this ECL immunosensor array could linearly respond to γH2AX concentrations in the range from 2 × 10² to 1 × 10⁵ pg/mL. In addition, our approach possessed excellent specificity and satisfactory reproducibility, and its practicality was verified in real cell lysates. The whole process including instrumental and manual operation was completed in no more than 3 h. This study provides a convenient and rapid alternative method for the sensitive quantification of γH2AX, which shows promising application in high-throughput screening of genotoxic chemicals and drug candidates.

Electrochemiluminescence Immunoassay Platform with Immunoglobulin G-Encapsulated Gold Nanoclusters as a "Two-In-One" Probe

Biomolecule-functionalized Au nanoclusters (AuNCs) have drawn great interest in the electrochemiluminescence (ECL) field due to their unique optical/electrical properties, biocompatibility, and versatile bioapplication potentials. Herein, we proposed a two-in-one ECL probe of immunoglobulin G-encapsulated AuNCs (IgG-AuNCs) for the development of a high-performance ECL immunoassay (ECLIA) platform. The IgG-AuNCs were not only used as an ECL probe due to their excellent anodic ECL performance with triethylamine (TEA) as a coreactant but also used as the biorecognition element because of their well-retained bioactivity of the IgG. As a proof of concept, a new type of competitive immunosensing platform has been applied to detect IgG representing several merits of facile preparation, rapid detection, sample saving, and good analytical performance. The sensing platform exhibited a linear range of 0.5-50,000 ng/mL with a limit of detection of 0.06 ng/mL for IgG detection with high selectivity. In addition, this convenient ECLIA platform also performed well in real serum sample detection. Notably, our work not only proved the "two-in-one" immuno-AuNC probe-based ECLIA strategy but also developed a rational framework for study of ECL bioassay platforms based on multifunctional AuNCs and other related nanomaterials.

Photothermal-Induced Electrochemical Interfacial Region Regulation Enables Signal Amplification for Dual-Mode Detection of Ovarian Cancer Biomarkers

Detection sensitivity of an electrochemical immunosensor mainly depends on the accessible distance toward the sensing interface; regulating the electrochemical interfacial region thereon is an effective strategy for signal amplification. Herein, a photothermal-regulated sensing interface was designed based on a near-infrared (NIR)-responsive hydrogel probe for ultrasensitive detection of human epididymis protein 4 (HE4). Silver nanoparticle-deposited graphene oxide nanosheet (AgNPs@GO) hybrids as electrochemical signal tags and a photothermal transducer, which were encapsulated in the poly(N-isopropylacrylamide) (pNIPAM) hydrogel, were used to develop the NIR-responsive GO@AgNPs-pNIPAM hydrogel probe. Under NIR light irradiation, the excellent photothermal effect of AgNPs@GO hybrids not only rapidly converted NIR light into heat for temperature readout but also triggered the shrinkage behavior of the hydrogel for electrochemical signal amplification. Compared with the conventional sandwich immunoassay, the shrinkage behavior of the hydrogel signal probe endowed itself with interface regulation capability to improve the electrochemical reaction efficiency; on the basis of ensuring the extended outer Helmholtz plane (OHP) region, the proposed photothermal-induced interface regulation also shortened the OHP, leading to higher sensitivity. Moreover, the obtained dual-mode signals provided satisfactory accuracy for the detection of tumor markers. Therefore, this detection scheme provided an opportunity for the broad applications of the photothermal effect in clinical diagnosis.

DNA walker-mediated biosensor for target-triggered triple-mode detection of Vibrio parahaemolyticus

Herein, we have constructed a target-triggered and DNA walker-mediated biosensor with triple signal (BTS) outputs mode for sensitive and reliable detection of pathogenic bacteria. Vibrio parahaemolyticus (VP) being the detection target model, the aptamer conformational changes induced by VP have been designed to activate the DNA walk on the modifiable and conductive surface of Fe3O4 nanoparticles to generate triple signal outputs, including electrochemiluminescence (ECL), fast scan cyclic voltammetry (FSCV) and fluorescent pixel counting (FLPC). Limits of quantification (LOQ) of VP were as low as 1 CFU⋅mL-1 by ECL with a linear range of 1-106 CFU⋅mL-1, 1 CFU⋅mL-1 by FSCV with a linear range of 1-106 CFU⋅mL-1, and 10 CFU⋅mL-1 by FLPC with a linear range of 10-107 CFU⋅mL-1 respectively, all squared correlation coefficients R2 being > 0.99. In addition, optical and electrochemical results, signal-on and signal-off results, electrode phase and solution phase results could be mutually verified by integrating of multiple detection techniques in one biosensor, greatly improving the accuracy and reliability. Therefore, the designed BTS has provided a powerful strategy for pathogenic bacteria detection considering its high detection sensitivity and accuracy, exhibiting great potential in food safety, water quality and biological contamination.

Electrochemiluminescent immunoassay for the determination of CA15-3 and CA72-4 using graphene oxide nanocomposite modified with CdSe quantum dots and Ru(bpy)3 complex

A novel immunoassay is introduced based on co-reactant enhancing strategy for the electrochemiluminescent (ECL) determination of CA15-3 and CA72-4 tumor markers in real samples. For the preparation of the signaling probe, CA15-3 and CA72-4 antibodies first were labeled using Ru(bpy)₃²⁺-N-hydroxysuccinimide ester (Ru(bpy)₃²⁺-NHS) and conjugated with L-cysteine capped cadmium selenide (CdSe) quantum dots. Finally, it was cross-linked with chitosan-grafted graphene oxide (GO@CS) nanocomposite. The capture probe was constructed by deposition of multi-walled carbon nanotubes (MWCNT) at the surface of dual-working gold screen-printed electrodes (MWCNT-dwSPE) and covalent attachment of capture CA15-3 and CA72-4 antibodies to MWCNT-dwSPE. ECL signals were recorded by applying cyclic potential ranging from 0.3 to 1.1 V (vs. pseudo-reference Ag/AgCl) at the scan rate of 100 mV.s^-1. This immunoassay was used for determination of CA15-3 and CA72-4 in real samples the detection limits of 9.2 μU.ml^-1 and 89 μU.ml^-1 within linear ranges of 10 μU.ml^-1-500 U.ml^-1 and 100 μU.ml^-1-150 U.ml^-1, respectively. This immunoassay also showed acceptable accuracy with recoveries in the range 96.5-108 % and high reproducibility with RSD of 3.1 and 4.9.

A sandwich-configuration electrochemiluminescence immunoassay based on Cu2O@OMC-Ru nanocrystals and OMC-MoS2 nanocomposites for determination of alpha-fetoprotein

A sandwich-format electrochemiluminescence (ECL) immunosensor has been developed for alpha-fetoprotein (AFP) detection based on the use of ordered mesoporous carbon-molybdenum disulfide (OMC-MoS₂) as a sensor platform and cuprous oxide @ ordered mesoporous carbon-Ru(bpy)₃²⁺ (Cu₂O@OMC-Ru) composites as signal tags. OMC alongside MoS₂ plays a synergistic role in improving the electrochemical performance of the electrode in the electron transfer process. The uniform cubic-shaped Cu₂O@OMC-Ru nanocrystals display excellent luminous efficiency, with a signal amplification strategy of OMC-MoS₂ synergistic enhancement and Cu₂O@OMC which is capable of immobilizing more Ru(bpy)₃²⁺ serving as a tracing tag to label antibodies. A detectable ECL emission at a Cu₂O@OMC-Ru nanocrystals modified electrode is initiated at an applied voltage of +1.15 V (scanning range: 0-1.2 V), in the presence of the tripropylamine (TPA) as coreactant. With the increase in AFP concentration, the loading of Cu₂O@OMC-Ru at the electrode increases. Afterward, the ECL detection of AFP shows a wide linear range from 0.1 pg/mL to 10 ng/mL with a correlation coefficient of 0.9964 and a detection limit of 0.011 pg/mL (S/N = 3) under the optimal experimental conditions. The recoveries were in the range 91.2-97.1% with RSD varying from 4.8 to 8.5%. Overall, the novel immunosensor has been successfully applied to the analysis of human serum samples, indicating a great potential for application in clinical diagnostics.

Rational Fabrication of a Smart Electrochemiluminescent Sensor: Synergistic Effect of a Self-Luminous Faraday Cage and Biomimetic Magnetic Vesicles

A smart electrochemiluminescent (ECL) sensor has been designed in this work. The sensing system consisted of Ag NPs-Ti₃AlC₂ nanosheets (Ag-TACS) as the self-luminous Faraday cage and biomimetic magnetic vesicles as the functional substrate. By engineering the structure and properties of Ti₃AlC₂ nanosheets to induce the Faraday-cage effect, the outer Helmholtz plane (OHP) was extended to contribute to ECL enhancement. Compared with the Faraday cage that further incorporated luminous materials, the self-luminous Faraday cage in the "direct label" model kept all the luminous materials on the OHP. Meanwhile, biomimetic magneticvesicles with highly efficient fluidity were used to improve the sensing efficiency and obtain a perfect Faraday-cage structure to enhance the ECL signals. The highest ECL enhancement (ca. 25 times) has been achieved by the synergistic effect of the Faraday cage and biomimetic magnetic vesicles. This sensing system was used to detect the wild-type K-ras gene in the colorectal tumor tissue. It provides not only an important guide for the novel ECL sensing concept but also a smart modulation system of the electromagnetic field.

Advances in electrochemiluminescence co-reaction accelerator and its analytical applications

Electrochemiluminescence (ECL) can be produced through two main routes: annihilation route and coreactant route. The vast majority of applications of ECL are based on coreactant ECL which can be generated in aqueous media at relatively low potentials compared with organic solvents. However, the development of more efficient ECL systems remains a compelling goal. Co-reaction accelerator (CRA) can significantly enhance the ECL signal through promoting more production of the coreactant intermediate. Compared with other ECL enhancement strategies, the CRA protocol is distinctive owing to its diverse, simple, and highly effective features. Various species such as inorganic compound, organic compound, and nanomaterials (NMs) have been developed as CRA and NM CRA has gained particular attention owing to their unique properties of excellent catalytic behavior and large surface area. By integration with the inherent advantages of ECL, bioanalysis based on CRA-enhanced ECL showed excellent performance such as ultrahigh sensitivity, wide dynamic range, low cost, simple instrumentation, and measurements in complex media. It has been extensively applied in various fields including clinical diagnosis, environmental monitoring, and food safety. Therefore, it is of great interest to present a systematic and critical review on the advances in ECL CRA. Herein, the recent progress on CRA and its applications in ECL bioanalysis are summarized by illustrating some representative work and a discussion of the future development trends of CRA ECL is offered.

Switching the Photoluminescence and Electrochemiluminescence of Liposoluble Porphyrin in Aqueous Phase by Molecular Regulation

By a facile peripheral decoration of 5-(4-aminophenyl)-10,15,20-triphenylporphyrin (ATPP) with inherent aggregation-induced emission (AIE) active tetraphenylethene (TPE), a versatile AIEgenic porphyrin derivative (ATPP-TPE) was obtained, which greatly abolishes the detrimental π-π stacking and thus surmounts the notorious aggregation-caused quenching (ACQ) effect of ATPP in aqueous phase. The photoluminescence of ATPP-TPE is 4.5-fold stronger than ATPP at aggregation state. Moreover, an unequivocal aggregation induced electrochemiluminescence (AIECL) of ATPP-TPE was found to be seriously dependent on its aggregation property in aqueous solution with efficiency of 34 %, which is 6 times higher than pure ATPP. The versatility of this molecular structure modulation strategy along with the ACQ-to-AIE transformation in this work provides direction to guide for applying liposoluble porphyrins in aqueous phase by designs of synthetic porphyrin AIEgens.

One-step electrodeposition preparation of polyaniline/f-MWCNTs as electrochemical sensors for detection of 10-hydroxycamptothecine

In our work, one-step electro-deposition method was adopted to produce polyaniline (PANI) and functional multiwalled carbon nanotubes (f-MWCNTs) films on glass carbon electrodes, and the modified electrodes were applied as an electrochemical sensor for determination of 10-hydroxycamptothecine (10-HCPT). The f-MWCNTs were handled by ultrasound processing in concentrated oxidizing acid solution, which can obtain a wonderful dissolution in water and attach new functional groups, such as -COOH and -OH. Then, aniline monomer could polymerize on the surface easily. The surface characterization was investigated using various techniques including scanning electron microscope, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction, and electro-catalytic properties were characterized by cyclic voltammetry and electrochemical impedance spectroscopy. Under optimal conditions, the resulting of PANI/f-MWCNTs sensor showed a wide linear range (3 × 10^-9 to 7 × 10^-7 mol L^-1 ) and a low detection limit (1 × 10^-9 mol L^-1 ), which is attributing to its large special surface area and good conductivity. Moreover, the modified electrodes are convenient to fabricate, which can be used to detect 10-HCPT in urine samples successfully.

Electrochemiluminescence Biosensors Using Screen-Printed Electrodes

Electrogenerated chemiluminescence (also called electrochemiluminescence (ECL)) has become a great focus of attention in different fields of analysis, mainly as a consequence of the potential remarkably high sensitivity and wide dynamic range. In the particular case of sensing applications, ECL biosensor unites the benefits of the high selectivity of biological recognition elements and the high sensitivity of ECL analysis methods. Hence, it is a powerful analytical device for sensitive detection of different analytes of interest in medical prognosis and diagnosis, food control and environment. These wide range of applications are increased by the introduction of screen-printed electrodes (SPEs). Disposable SPE-based biosensors cover the need to perform in-situ measurements with portable devices quickly and accurately. In this review, we sum up the latest biosensing applications and current progress on ECL bioanalysis combined with disposable SPEs in the field of bio affinity ECL sensors including immunosensors, DNA analysis and catalytic ECL sensors. Furthermore, the integration of nanomaterials with particular physical and chemical properties in the ECL biosensing systems has improved tremendously their sensitivity and overall performance, being one of the most appropriates research fields for the development of highly sensitive ECL biosensor devices.

Macroscopic Au@PANI Core/Shell Nanoparticle Superlattice Monolayer Film with Dual-Responsive Plasmonic Switches

The self-assembled gold nanoparticle (NP) superlattice displays unusual but distinctive features such as high mechanical and free-standing performance, electrical conductivity, and plasmonic properties, which are widely employed in various applications especially in biological diagnostics and optoelectronic devices. For a two-dimensional (2D) superlattice monolayer film composed of a given metal nanostructure, it is rather challenging to tune either its plasmonic properties or its optical properties in a reversible way, and it has not been reported. It is therefore of significant value to construct a free-standing 2D superlattice monolayer film of gold nanoparticles with an intelligent response and desired functions. Herein, we developed an easy and efficient approach to construct a gold nanoparticle superlattice film with a dual-responsive plasmonic switch. In this system, gold nanoparticles were coated by polyaniline (PANI) and then interracially self-assembled into a monolayer film at the air-liquid interface. The PANI shell plays two important roles in the superlattice monolayer film. First, the PANI shell acts as a physical spacer to provide a steric hindrance to counteract the van der Waals (vdW) attraction between densely packed nanoparticles (NPs), resulting in the formation of a superlattice by adjusting the thickness of the PANI shell. Second, the PANI shells provide the superlattice film with multiple stimuli such as electrical potential and pH change, leading to reversible optical and plasmonic responsiveness. The superlattice monolayer film can show a vivid color change from olive green to pink, or from olive green to violet by the change of the corresponding stimuli. Also, the localized surface plasmonic resonance (LSPR) of the superlattice monolayer film can be reversibly modulated by both by changing the local pH and applying an electric potential. Notably, a significant plasmonic shift of 157 nm can be achieved in the superlattice monolayer film when the PANI shell with a thickness of 35 nm and gold nanorods as a core were used. The superlattice monolayer film with dual-responsive plasmonic switches is promising for a range of potential applications in optoelectronic devices, plasmonic and colorimetric sensors, and surface-enhanced Raman scattering (SERS).

Core-shell gold-nickel nanostructures as highly selective and stable nonenzymatic glucose sensor for fermentation process

Non-enzymatic electrodes based on noble metals have excellent selectivity and high sensitivity in glucose detection but no such shortcomings as easy to be affected by pH, temperature, and toxic chemicals. Herein, spherical gold-nickel nanoparticles with a core-shell construction (Au@Ni) are prepared by oleylamine reduction of their metal precursors. At an appropriate Au/Ni ratio, the core-shell Au@Ni nanoparticles as a sensor for glucose detection combine the high electrocatalytic activity, good selectivity and biological compatibility of Au with the remarkable tolerance of Ni for chlorine ions (Cl-) and poisoning intermediates in catalytic oxidation of glucose. This electrode exhibits a low operating voltage of 0.10 V vs. SCE for glucose oxidation, leading to higher selectivity compared with other Au- and Ni-based sensors. The linear range for the glucose detection is from 0.5 mmol L-1 to 10 mmol L-1 with a rapid response time of ca. 3 s, good stability, sensitivity estimated to be 23.17 μA cm-2 mM-1, and a detection limit of 0.0157 mM. The sensor displays high anti-toxicity, and is not easily poisoned by the adsorption of Cl- in solution.