Co3O4/NiCo2O4 heterojunction as oxygen evolution reaction catalyst for efficient luminol anode electrochemiluminescence

Luminol has garnered significant attention from analysts as one of the most effective and commonly used electrochemiluminescence (ECL) reagents. However, the efficient luminescence of luminol anode is limited by the excitation of various reactive oxygen species (ROS). Typically, ROS are generated through co-reactive reagents and dissolved oxygen. Unfortunately, the former suffers from two drawbacks, namely biotoxicity and instability, while the latter cannot offer sufficient oxygen due to its limited solubility in aqueous solutions. Consequently, a low decomposition rate is usually obtained, leading to insufficient ROS. Therefore, there is an urgent need to develop efficient luminol anode systems. This study focuses on the use of zeolitic imidazolate framework-67 (ZIF-67) as a template, employing a controlled chemical etching method to create a ZIF-67/Ni-Co-layered double hydroxide (LDH). The intermediate composite is then annealed in air, resulting in the formation of a Co3O4/NiCo2O4 double-shelled nanobox (DSNB) heterostructure. Due to its structural advantages, the DSNB exhibits excellent electrocatalytic performance in the oxygen evolution reaction (OER). Furthermore, it was found that both the intermediates and products of OER can directly participate in the luminol chemiluminescence process, ultimately resulting in a 700-fold increase in the electrochemiluminescence (ECL) signal compared to an equal molar concentration of luminol solution. This work not only establishes the OER-mediated ECL system but also deepens the understanding of the relationship between ROS and luminol, providing a new pathway to study the luminol anodic ECL luminescence system.

Double-Amplified Electrochemiluminescence Immunoassay Sensor for Highly Sensitive Detection of CA19-9 Using a Ternary Semiconductor CdSSe

In this paper, an electrochemiluminescence (ECL) immunosensor for ultrasensitive detection of CA19-9 was constructed using ternary compound CdSSe nanoparticles as ECL emitter. The immunosensor employs Cu2S and gold-doped diindium trioxide (Au-In2O3) nanocubes as coreaction accelerators to achieve a double-amplification strategy. In general, a hexagonal maple leaf-shaped Cu2S with a large surface area was selected as the template, and the in situ growth of CdSSe on its surface was achieved using a hydrothermal method. The presence of Cu2S not only inhibited the aggregation of CdSSe nanoparticles to reduce their surface energy but also acted as an ECL cathode coreaction promoter, facilitating the generation of SO4•-. Consequently, the ECL intensity of CdSSe was significantly enhanced, and the reduction potential was significantly lower. In addition, the template method was employed to synthesize Au-In2O3 nanocubes, which offers the advantage of directly connecting materials with antibodies, resulting in a more stable construction of the immunosensor. Furthermore, In2O3 serves as a coreaction promoter, enabling the amplification strategy for ECL intensity of CdSSe, thus contributing to the enhanced sensitivity and performance of the immunosensor. The constructed immunosensor exhibited a wide linear range (100 μU mL-1 to 100 U mL-1) and a low detection limit of 80 μU mL-1, demonstrating its high potential and practical value for sensitive detection of CA19-9.

Nanozyme-assisted amplification-free CRISPR/Cas system realizes visual detection

The CRISPR (clustered regularly interspaced short palindromic repeats)/Cas (CRISPR associated) system has proven to be a powerful tool for nucleic acid detection due to its inherent advantages of effective nucleic acid identification and editing capabilities, and is therefore known as the next-generation of molecular diagnostic technology. However, the detection technologies based on CRISPR/Cas systems require preamplification of target analytes; that is, target gene amplification steps through isothermal amplification or PCR before detection to increase target analyte concentrations. This creates a number of testing limitations, such as extended testing time and the need for more sophisticated testing instruments. To overcome the above limitations, various amplification-free assay strategies based on CRISPR/Cas systems have been explored as alternatives, which omit the preamplification step to increase the concentrations of the target analytes. Nanozymes play a pivotal role in enhancing the sensitivity of CRISPR-based detection, enabling visual and rapid CRISPR assays. The utilization of nanozyme exceptional enzyme-like catalytic activity holds great promise for signal amplification in both electrochemical and optical domains, encompassing strategies for electrochemical signal sensors and colorimetric signal sensors. Rather than relying on converting a single detection target analyte into multiple analytes, these methods focus on signal amplification, the main mechanism of which involves the ability to form a large number of reporter molecules or to improve the performance of the sensor. This exploitation of nanozymes for signal amplification results in the heightened sensitivity and accuracy of detection outcomes. In addition to the strategies that improve sensor performance through the application of nanozymes, additional methods are needed to achieve visual signal amplification strategies without preamplification processes. Herein, we review the strategies for improving CRISPR/Cas systems that do not require preamplification, providing a simple, intuitive and preamplification-free CRISPR/Cas system detection platform by improving in-system one-step amplification programs, or enhancing nanozyme-mediated signal amplification strategies.

High-Intensity Focused Ultrasound Combined with Ti3C2-TiO2 to Enhance Electrochemiluminescence of Luminol for the Sensitive Detection of Polynucleotide Kinase

Luminol is a classic electrochemiluminescence (ECL) luminophore. The luminol-O₂ ECL system suffers from a problem, that is, the conversion rate of dissolved O₂ into reactive oxygen species (ROS) is low. In this work, we used high-intensity focused ultrasound (HIFU) pretreatment combined with Ti₃C₂-TiO₂ to construct a highly sensitive luminol-O₂ ECL system for the specific detection of polynucleotide kinase (PNK) first. On the one hand, HIFU generated ROS in situ as a coreactant via the cavitation effect to boost the luminol emission. On the other hand, Ti₃C₂-TiO₂ was prepared in situ via Ti₃C₂ as a reducing agent, and it can aggregate and catalyze ROS generated in situ by HIFU. Moreover, the Ti on the Ti₃C₂-TiO₂ surface could bind to phosphate groups through chelation, thereby realizing highly specific detection of PNK. The sensor has a linear relationship range of 1.0 × 10^-5 to 10.0 U mL^-1, and the limit of detection is 1.48 × 10^-7 U mL^-1, which is superior to most existing methods. The sensor performance in HeLa cell lysate was measured with a satisfactory result. The designed ECL biosensor has potential applications in biological analysis and clinical diagnosis.

PEGylated Ni Single-Atom Catalysts as Ultrasensitive Electrochemiluminescent Probes with Favorable Aqueous Dispersibility for Assaying Drug-Resistant Pathogens

Ni single-atom catalysts (SACs) were synthesized by high-temperature calcination of nickel ions and 1,10-phenanthroline on carbon black as a carrier. Benefiting from the ultrahigh atom utilization efficiency, Ni SACs can significantly accelerate decay of dissolved oxygen to generate abundant reactive oxygen species through an oxygen reduction reaction occurring on cathodes. The generated reactive oxygen species can vastly enhance the electrochemiluminescent (ECL) signal of luminol without participation of exogenous co-reactants. To overcome the inherent unfavorable aqueous dispersibility of Ni SACs prepared by the calcination protocol, they were functionalized with highly hydrophilic PEG 2000. Thanks to the abundant carboxyl groups on PEG 2000, the PEGylated Ni SACs (Ni@PEG) can be used as ECL probes to tag biorecognition molecules. In this proof-of-principle work, an ECL biosensor for assaying methicillin-resistant Staphylococcus aureus was developed by using porcine IgG as capture molecule and phage cell-binding domain tagged with Ni@PEG as signal tracer. It shows a broad linear range of 73-7.3 × 10⁶ CFU/mL and a low detection limit of 25 CFU/mL. The recovery values for assaying spiked samples are between 80.8 and 119.2%. It was also utilized to assess MRSA susceptibility to four antibiotics, with results consistent with those obtained by the standard broth microdilution technique. To the best of our knowledge, it is the first time to utilize aqueous dispersible SACs as highly sensitive ECL probes for developing biosensors.

Nucleic acid isothermal amplification-based soft nanoarchitectonics as an emerging electrochemical biosensing platform

The emergence of nucleic acid isothermal amplification strategies based on soft nanoarchitectonics offers a new dimension to the traditional electrochemical technique, particularly because of its flexibility, high efficiency, and increased sensitivity for analytical applications. Various DNA/RNA isothermal amplification strategies have been developed for the design and fabrication of new electrochemical biosensors for efficient and important biomolecular detection. Herein, we provide an overview of recent efforts in this research field and the strategies for signal-amplified sensing systems, with their biological applications, current challenges and prospects in this promising new area.

Self-electrochemiluminescence biosensor based on CRISPR/Cas12a and PdCuBP@luminol nanoemitter for highly sensitive detection of cytochrome c oxidase subunit III gene of acute kidney injury

The cytochrome c oxidase subunit III (COX III) gene is a powerful biomarker for the early diagnosis of acute kidney injury. However, current methods for COX III gene detection are usually laborious and time-consuming, with limited sensitivity. Herein, we report a novel self-electrochemiluminescence (ECL) biosensor for highly sensitive detection of the COX III gene based on CRISPR/Cas12a and nanoemitters of luminol-loaded multicomponent metal-metalloid PdCuBP alloy mesoporous nanoclusters. The nanoemitter with excellent self-ECL in neutral media exhibited a high specific surface area for binding luminol and outstanding oxidase-like catalytic activity toward dissolved O₂. Meanwhile, the CRISPR/Cas12a system, as a target-trigger, was employed to specifically recognize the COX III gene and efficiently cleave the interfacial quencher of dopamine-labeled hairpin DNA. As a result, the ECL biosensor showed superior analytical performance for COX III gene detection without exogenous coreactant. Benefiting from the high-efficiency ECL emission of the nanoemitter and Cas12a-mediated interfacial cleavage of the quencher, the developed ECL biosensor exhibited high sensitivity to COX III with a low detection limit of 0.18 pM. The established ECL biosensing method possessed excellent practical performance in urine samples. Meaningfully, the proposed strategy presents promising prospects for nucleic acid detection in the field of clinical diagnostics.

A glucose/O2 biofuel cell integrated with an exonuclease-powered DNA walker for self-powered sensing of microRNA

With the aid of an exonuclease-powered DNA walker, the amount of glucose oxidase immobilized on the bioanode can be facilely tailored by varying the concentration of microRNA-141, so a glucose/O₂ biofuel cell is employed as a self-powered sensor for sensitive and selective detection of microRNA-141.

Plasmon-Boosted Cu-Doped TiO2 Oxygen Vacancy-Rich Luminol Electrochemiluminescence for Highly Sensitive Detection of Alkaline Phosphatase

In this study, an effective oxygen vacancy (O_v)-involved luminol-dissolved oxygen (O₂) electrochemiluminescence (luminol-DO ECL) system was developed and exploited for ECL sensing applications through significant plasmon enhancement of the O_v-involved weak luminol-DO ECL signals by the combined use of Cu-doped TiO₂ oxygen vacancy and a Au@SiO₂ nanomembrane. The results disclosed that the ECL response of the corresponding system could be synergistically boosted, and the plausible underlying mechanism has been discussed. Furthermore, for the first time, the developed system has been successfully applied for the highly sensitive detection of alkaline phosphatase with a low limit of detection of 0.005 U/L, with an excellent linear range from 0.005 to 10 U/L, as well as good stability and reproducibility.

The electrochemiluminescence coreactant accelerator of metal-organic frameworks grafted with N-(aminobutyl)-N-(ethylisoluminol) for the ultrasensitive detection of chloramphenicol

In this work, metal-organic frameworks (MOFs) are utilized as effective ECL coreactant accelerator to enhance the ECL responses of N-(aminobutyl)-N-(ethylisoluminol) (ABEI). Zn-based MOFs (MOF-Zn-1) were prepared by chelating Zn ions with melamine and thiophenedicarboxylic acid (TPDA), which observably accelerated the electrocatalytic oxidation of tripropylamine (TPA). Then, ABEI-MOF-Zn-1 as a high-performance ECL emitter was synthesized via an amide reaction between ABEI and mercaptopropionic acid (MPA) modified MOF-Zn-1. Strikingly, the ABEI-MOF-Zn-1 showed the 18-fold increase in the ECL signals relative to pure ABEI by using TPA as a coreactant. Moreover, ferrocene (Fc) as a quencher was first linked with capture DNA (cDNA), and then used to modify the ABEI-MOF-Zn-1, thereby constructing a label-free ECL biosensor. After the linkage between chloramphenicol (CAP) and aptamer DNA (aptDNA), the ECL response was definitely recovered by releasing L-DNA from double-stranded DNA (dsDNA, hybridization of aptDNA and L-DNA). The resultant sensor showed a wide linear range of 1.00 nM-0.10 mM (R² = 0.99) and a low limit of detection (LOD) down to 0.11 nM for detecting CAP. This work developed a novel pattern to design an efficient ECL enhanced emitter, coupled by expanding its potential applications in clinical diagnosis.

Ternary Electrochemiluminescence Biosensor Based on DNA Walkers and AuPd Nanomaterials as a Coreaction Accelerator for the Detection of miRNA-141

In this study, a ternary electrochemiluminescence (ECL) sensing platform coupled with a multiple signal amplification strategy was proposed for ultrasensitive detection of miRNA-141. The initial signal amplification was achieved via three-dimensional reduced graphene oxide (3D-rGO)@Au nanoparticles (NPs) to form an excellent conductive layer. Then, AuPd NPs as a coreaction accelerator was introduced into the N-(4-aminobutyl)-N-(ethylisoluminol) (ABEI)-H₂O₂ system to facilitate the transformation from H₂O₂ to excess superoxide anion radicals (O₂^•-), which further amplified the ECL emission of ABEI, leading to a significant increase of the ECL signal. Meanwhile, in the presence of miRNA-141 and T7 Exonuclease (T7 Exo), the self-assembled DNA swing arm can be driven to walk autonomously. The DNA walker reaction could result in the release of numerous labeled luminophores, which could react to achieve an extremely weak ECL signal. Surprisingly, the established ECL sensor platform for the detection of miRNA-141 demonstrated excellent sensitivity with a low detection limit of 31.9 aM in the concentration range from 100 aM to 1 nM. Consequently, the designed strategy greatly improves the luminous efficiency of the ternary ECL system and provides a special approach for the detection of nucleic acids and biomarkers in clinical and biochemical analysis.