Potential-resolved “in-electrode” type electrochemiluminescence immunoassay based on functionalized g-C 3 N 4 nanosheet and Ru-NH 2 for simultaneous determination of dual targets

A Novel Ratiometric Photoelectrochemical Biosensor Based on Front and Back Illumination for Sensitive and Accurate Glutathione Sensing

The ratiometric detection method has a strong attraction for photoelectrochemical bioanalysis due to its high reliability and real-time calibration. However, its implementation typically depends on the spatial resolution of equipment and the pairing of wavelength/potential with photoactive materials. In this paper, a novel ratiometric photoelectrochemical biosensor based on front and back illumination was prepared for the detection of glutathione (GSH). Unlike traditional ratio methods, this ratiometric biosensor does not require voltage and wavelength modulation, thereby avoiding potential crosstalk caused by voltage and wavelength modulation. Additionally, the formation of a heterojunction between mTiO2 and Ag2S is conducive to enhancing light absorption and promoting charge separation, thereby boosting the photocurrent signal. Apart from forming a heterojunction with TiO2, Ag2S also shows a specific affinity towards GSH, thus enhancing the selectivity of the mTiO2/Ag2S ratiometric photoelectrochemical biosensor. The results demonstrate that the ratiometric photoelectrochemical biosensor exhibits a good detection range and a low detection limit for GSH, while also possessing significant interference elimination capability. The GSH detection range is 0.01-10 mmol L-1 with a detection limit of 6.39 × 10-3 mmol·L-1. The relative standard deviation of 20 repeated detections is 0.664%. Impressively, the proposed novel ratiometric PEC biosensor demonstrates enviable universality, providing new insights for the design and construction of PEC ratiometric sensing platforms.

Potential-Resolved Ratiometric Aptasensor for Sensitive Acetamiprid Analysis Based on Coreactant-free Electrochemiluminescence Luminophores of Gd-MOF and "Light Switch" Molecule of [Ru(bpy)2dppz]2

For conventional potential-resolved ratiometric electrochemiluminescence (ECL) systems, the introduction of multiplex coreactants is imperative. However, the undesirable interactions between different coreactants inevitably affect analytical accuracy and sensitivity. Herein, through the coordination of aggregation-induced emission ligands with gadolinium cations, the self-luminescent metal-organic framework (Gd-MOF) is prepared and serves as a novel coreactant-free anodic ECL emitter. By the intercalation of [Ru(bpy)2dppz]2+ with light switch effect into DNA duplex, one high-efficiency cathodic ECL probe is obtained using K2S2O8 as a coreactant. In the presence of acetamiprid, the strong affinity between the target and its aptamer induces the release of [Ru(bpy)2dppz]2+, resulting in a decreasing cathode signal and an increasing anode signal owing to the ECL resonance energy transfer from Gd-MOF to [Ru(bpy)2dppz]2+. In this way, an efficient dual-signal ECL aptasensor is constructed for the ratiometric analysis of acetamiprid, exhibiting a remarkably low detection limit of 0.033 pM. Strikingly, by using only one exogenous coreactant, the cross interference from multiple coreactants can be eliminated, thus improving the detection accuracy. The developed high-performance ECL sensing platform is successfully applied to monitor the residual level of acetamiprid in real samples, demonstrating its potential application in the field of food security.

Potential-resolved electrochemiluminescence biosensor for simultaneous determination of multiplex miRNA

The multi-target simultaneous detection strategy based on potential-resolved electrochemiluminescence (ECL) has still been a research hotspot in analytical science, but the limited selection of ECL luminophores hinders the development of this field. Herein, polyethyleneimine functionalized perylene derivatives (PTC-PEI) and luminol functionalized gold nanoparticles (Lu-Au NPs) possessed significantly resolved emission potentials as ECL luminophore. The ternary ECL system was constructed with MoS2 nanoflowers and K2S2O8 as the coreaction accelerator and coreactant respectively, which significantly improved the cathode ECL emission of PTC-PEI. Simultaneously, the anode coreaction accelerator ZnO nanoflowers could promote the anode coreactant dissolved O2 reduction, and extremely enhanced the anode ECL emission of Lu-Au NPs. The proposed strategy addressed the major technical challenge of cross interference and competition of the coreactants for dual-biomarker detection, thus enabling accurate detection of miRNA-205 and miRNA-21 from 10 fM to 100 nM, with detection limits of 2.57 and 1.15 fM, respectively. In general, this work achieved a single-step synchronous detection of dual biomarkers, providing a new idea for the ECL detection of multiple biomarkers, and having potential value in the clinical diagnosis.

Low-Triggering-Potential Single-Color Electrochemiluminescence from Bovine Serum Albumin-Stabilized Unary Au Nanocrystals for Immunoassays

Herein, low-triggering-potential (LTP) electrochemiluminescence (ECL) with an onset around 0.0 V (vs Ag/AgCl) is proposed with bovine serum albumin (BSA)-stabilized Au nanocrystals (BSA-AuNCs) as a luminophore and hydrazine hydrate (N₂H₄) as a coreactant. The BSA-AuNCs/N₂H₄ system can exhibit efficient LTP-ECL around 0.37 V with the luminophore of both monodispersed and surface-confined states. The LTP-ECL of BSA-AuNCs/N₂H₄ is a kind of single-color emission with a maximum emission wavelength around 740 nm, which is obviously red-shifted for 80 nm from that of BSA-AuNCs PL, and indicates that the ECL is generated in a surface-defect-involved route instead of the band-gap-engineered route. Importantly, BSA-AuNCs can be utilized as ECL tags to perform sandwich-type immunoassays with acceptable sensitivity and selectivity, which exhibits a wide linear response for determining CA125 from 0.5 to 1000 mU/mL and a limit of detection of 0.05 mU/mL (S/N = 3).

Dual-potential electrochemiluminescence of single luminophore for detection of biomarker based on black phosphorus quantum dots as co-reactant

Simultaneous cathodic and anodic electrochemiluminescence (ECL) emissions of needle-like nanostructures of Ru(bpy)₃²⁺ (RuNDs) as the only luminophore are reported based on different co-reactants. Cathodic ECL was attained from RuNDs/K₂S₂O₈ system, while anodic ECL was achieved from RuNDs/black phosphorus quantum dots (BPQDs) system. Ferrocene attached to the hairpin DNA could quench the cathodic and anodic ECL simultaneously. Subsequently, the ECL signals recovered in the presence of tumor marker mucin 1 (MUC1), which made it possible to quantitatively detect MUC1. The variation of ECL signal was related linearly to the concentrations of MUC1 in the range 20 pg mL^-1 to 10 ng mL^-1, and the detection limits were calculated to 2.5 pg mL^-1 (anodic system, 3σ) and 6.2 pg mL^-1 (cathodic system, 3σ), respectively. The recoveries were 97.0%, 105%, and 95.2% obtained from three human serum samples, and the relative standard deviation (RSD) is 5.3%. As a proof of concept, this work realized simultaneous ECL emission of  a single luminophore, which initiates a new thought in biomarker ECL detection beyond the traditional ones. Simultaneous cathodic and anodic ECL emissions of RuNDs were reported based on different co-reactants. Ferrocene could quench the ECL emission in the cathode and the anode simultaneously. Thus, an aptasensor was constructed based on the variation of ECL intensity. As a proof of concept, this work realized simultaneous ECL emission of a single luminophore, which initiates a new thought in biomarker ECL detection beyond the traditional ones by avoiding the false positive signals.

Paper-Based Bipolar Electrode Electrochemiluminescence Platform for Detection of Multiple miRNAs

This paper introduces a novel potential-resolved paper-based biosensor for simultaneous detection of multiple microRNAs (miRNAs) (taking miRNA-155 and miRNA-126 as examples) based on the bipolar electrode (BPE) electrochemiluminescence (ECL) strategy. The proposed multiple-channel paper-based sensing microfluidic platform was prepared by wax-printing technology, screen-printing method, and in situ Au nanoparticles (AuNPs) growth to form hydrophilic areas, hydrophobic boundaries, waterproof electronic bridge, driving electrode regions, and parallel bipolar electrode regions. CdTe quantum dots (QDs)-H2 and Au@g-C₃N₄ nanosheets (NSs)-DNA1 were used as dual electrochemiluminescence signal probes, and carboxylated Fe₃O₄ magnetic nanoparticles existed as carriers. CdTe QDs-H2/S₂O₈^2- and Au@g-C₃N₄ NSs-DNA1/S₂O₈^2- could exhibit two strong and stable ECL emissions at a drive voltage of 9 and 12 V, respectively, which can be used as effective potential-resolved signal tags. In addition, the proposed three-dimensional (3D) DNA nanomachine model and the target miRNA cycle strategy were used to achieve double amplification of electrochemiluminescence intensity. More importantly, the combination of the bipolar electrode system and the potential-resolved multitarget electrochemiluminescence method can greatly reduce the spatial interference between substances. The prepared ECL biosensor showed a favorable linear response for the detection of miRNA-155 and miRNA-126 with relatively low detection limits of 5.7 and 4.2 fM, respectively. With excellent sensitivity, the strategy may provide an efficient method for clinical application, especially in detection of trace multiple targets.

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

Electrochemiluminescence immunoassays are usually carried out through "on-electrode" strategy, i.e., sandwich-type immunoassay format, the sensitivity of which is restricted by two key bottlenecks: (1) the number of signal labels is limited and (2) only a part of signal labels could participate in the electrode reaction. In this Perspective, we discuss the development of an "in-electrode" Faraday-cage-type concept-based immunocomplex immobilization strategy. The biggest difference from the traditional sandwich-type one is that the designed "in-electrode" Faraday-cage-type immunoassay uses a conductive two-dimensional (2-D) nanomaterial simultaneously coated with signal labels and a recognition component as the detection unit, which could directly overlap on the electrode surface. In such a case, electrons could flow freely from the electrode to the detection unit, the outer Helmholtz plane (OHP) of the electrode is extended, and thousands of signal labels coated on the 2-D nanomaterial are all electrochemically "effective." Thus, then, the above-mentioned bottlenecks obstructing the improvement of the sensitivity in sandwich-type immunoassay are eliminated, and as a result a much higher sensitivity of the Faraday-cage-type immunoassay can be obtained. And, the applications of the proposed versatile "in-electrode" Faraday-cage-type immunoassay have been explored in the detection of target polypeptide, protein, pathogen, and microRNA, with the detection sensitivity improved tens to hundreds of times. Finally, the outlook and challenges in the field are summarized. The rise of Faraday-cage-type electrochemiluminescence immunoassay (FCT-ECLIA)-based biosensing strategies opens new horizons for a wide range of early clinical identification and diagnostic applications.

Ultrasensitive aptasensing of insulin based on hollow porous C3N4/S2O82-/AuPtAg ECL ternary system and DNA walker amplification

In this work, a high-efficiency electrochemiluminescence (ECL) ternary system was constructed for ultrasensitive assay of insulin based on hollow porous graphitic carbon nitride (HP-C₃N₄) as novel luminophore, S₂O₈^2- as coreactant and tri-metallic AuPtAg as coreaction accelerator. Specifically, in comparison with C₃N₄-based bulk nanomaterials, the as-prepared HP-C₃N₄ exhibits high luminous efficiency though decreased inner filter effect and minimized inactive ECL emitter. Noteworthy, tri-metallic AuPtAg, possessing the superiority of Au, Pt and Ag, was first used as coreaction accelerator to significantly enhance ECL intensity of HP-C₃N₄ and S₂O₈^2-. As a consequence, with the resultant ECL ternary (HP-C₃N₄/S₂O₈^2-/AuPtAg) system as aptasensing platform, a high-intense initial ECL signal was achieved. Subsequently, ferrocene-labeled quenching probe (Fc-HP2) as ECL quencher was used to quench the initial signal and achieve the low-background noise. Eventually, in the presence of insulin, the target-induced triple-helix molecular switch and Nb.BbvCI-assisted DNA walker amplification were executed to recover a strong ECL signal by releasing Fc-HP2 from the electrode surface. As expected, the constructed aptasensor presents an excellent sensitivity and selectivity for detecting insulin range from 0.05 pg mL^-1 to 100 ng mL^-1 with a detection limit of 17 fg mL^-1. This work provides a new avenue for developing highly efficient HP-C₃N₄ based ECL ternary system as well as ultrasensitive ECL aptasensors for bioanalysis.

Electrochemical-Signal-Amplification Strategy for an Electrochemiluminescence Immunoassay with g-C3N4 as Tags

Signal amplification for electrochemiluminescence (ECL) has conventionally been achieved by employing effective matrixes that can accelerate the electrochemical redox processes or carry more electrochemiluminophores. Herein, a convenient signal-amplification strategy was proposed for an ECL immunoassay with carboxylated g-C₃N₄ nanosheets (NSs) as tags and carcinoembryonic antigen (CEA) as the model target via electrochemically pretreating the substrate: a glassy-carbon electrode (GCE) modified with a polymerized 2-aminoterephthalic acid (ATA) film (GCE/ATA). Bioconjugates of g-C₃N₄ NSs and the signal CEA antibody (Ab₂) (i.e., g-C₃N₄ NS-Ab₂) were immobilized on GCE/ATA via a sandwich immunoreaction to form GCE/ATA-Ab₁-Ag-Ab₂-NSs. Electrochemical-impedance spectroscopy and potential-resolved ECL characterization proved that GCE/ATA plays an important role in the electron-transfer resistance ( R_et) of the GCE/ATA-Ab₁-Ag-Ab₂-NSs for ECL and that successively scanning GCE/ATA-Ab₁-Ag-Ab₂-NSs from 0 to -1.6 V in K₂S₂O₈- and H₂O₂-containing medium could reduce the R_et and bring out 3.3-times-enhanced ECL at the 10th scan cycle compared with that of the 1st scan cycle, which was about 10.2 times the ECL of the GCE/ATA-Ab₁-Ag-Ab₂-NSs in medium containing merely K₂S₂O₈. Inspired by this, direct and successive scanning of GCE/ATA in K₂S₂O₈- and H₂O₂-containing medium was employed during fabrication, which dramatically reduced the R_et of GCE/ATA-Ab₁-Ag-Ab₂-NSs and brought out obviously enhanced ECL responses for selectively determining CEA from 0.1 pg/mL to 1 ng/mL, with a detection limit of 3 fg/mL.

A label-free aptasensor for ultrasensitive Pb2+ detection based on electrochemiluminescence resonance energy transfer between carbon nitride nanofibers and Ru(phen)32

A label-free aptasensor was developed for ultrasensitive detection of Pb²⁺ based on electrochemiluminescence resonance energy transfer (ECL-RET) from graphitic carbon nitride nanofibers (CNNFs) to Ru(phen)₃²⁺. The CNNFs synthesized via a facile two-step hydrolysis-electrolysis strategy showed intense and stable ECL signal by taking advantages of amplifying and stabilizing effect of carbon nanotubes and Au nanoparticles. After the specific hybridation between capture DNA and Pb²⁺ specific aptamer, Ru(phen)₃²⁺ could be captured onto CNNFs modified electrode by effectively intercalating into the grooves of double-strand DNA, thus triggering the ECL-RET and leading to highly enhanced ECL intensity. The presence of Pb²⁺ would result in the detachment of Ru(phen)₃²⁺ and then the inhibition of ECL-RET. Then Pb²⁺ concentration could be quantified based on ECL change before and after introduction of Pb²⁺. The target recycling based on exonuclease I (Exo I) mediated digestion of Pb²⁺-aptamer complex was implemented to further improve the sensitivity. These synergistic amplification strategies enabled the aptasensor to be ultrasensitive for Pb²⁺ determination with a detection limit of 0.04 pM. The proposed probe was utilized to analyze environmental samples with satisfactory results.

Graphitic-phase carbon nitride-based electrochemiluminescence sensing analyses: recent advances and perspectives

This review describes the current trends in synthesis methods, signaling strategies, and sensing applications of g-C₃N₄-based ECL emitters.