Recent Advances in Electrochemiluminescence and Chemiluminescence of Metal Nanoclusters

EXPAR for biosensing: recent developments and applications

Emerging as a promising novel amplification technique, the exponential amplification reaction (EXPAR) offers significant advantages due to its potent exponential amplification capability, straightforward reaction design, rapid reaction kinetics, and isothermal operation. The past few years have witnessed swift advancements and refinements in EXPAR-based technologies, with numerous high-performance biosensing systems documented. A deeper understanding of the EXPAR mechanism has facilitated the proposal of novel strategies to overcome limitations inherent to traditional EXPAR. Furthermore, the synergistic integration of EXPAR with diverse amplification methodologies, including the use of a CRISPR/Cas system, metal nanoparticles, aptamers, alternative isothermal amplification techniques, and enzymes, has significantly bolstered analytical efficacy, aiming to enhance specificity, sensitivity, and amplification efficiency. This comprehensive review presents a detailed exposition of the EXPAR mechanism and analyzes its primary challenges. Additionally, we summarize the latest research advancements in the biomedical field concerning the integration of EXPAR with diverse amplification technologies for sensing strategies. Finally, we discuss the challenges and future prospects of EXPAR technology in the realms of biosensing and clinical applications.

Construction of self-enhanced luminescence probes based on Ti3C2 reducibility for ultrasensitive PNK analysis

Au nano-clusters (Au NCs) were promising electrochemiluminescence (ECL) nano-materials. However, the small size of Au NCs presented a challenge in terms of their immobilization during the construction of an ECL biosensing platform. This limitation significantly hindered the wider application of Au NCs in the ECL field. In this work, we successfully used the reducibility of Ti3C2 to fabricate in situ a self-enhanced nano-probe Ti3C2-TiO2-Au NCs. The strategy of in situ generation not only improved the immobilization of Au NCs on the probe but also eliminated the requirement of adding reducing agents during preparation. In addition, in situ generated TiO2 could serve as a co-reaction accelerator, shortening the electron transfer distance between S2O82- and Au NCs, thereby improving the utilization of intermediates and enhancing the ECL response of Au NCs. The constructed ECL sensing platform could achieve sensitive detection of polynucleotide kinase (PNK). At the same time, the 5'-end phosphate group of DNA phosphorylation could chelate with a large amount of Ti on the surface of Ti3C2, thereby achieving the goal of specific detection of PNK. The sensor based on self-enhanced ECL probes had a broad dynamic range spanning for PNK detection from 10.0 to 1.0 × 107 μU mL-1, with a limit of detection of 1.6 μU mL-1. Moreover, the ECL sensor showed satisfactory detection performance in HeLa cell lysate and serum. This study not only provided insights for addressing the issue of ECL luminescence efficiency in Au NCs but also presented novel concepts for ECL self-enhancement strategies.

Optical Bioassays Based on the Signal Amplification of Redox Cycling

Optical bioassays are challenged by the growing requirements of sensitivity and simplicity. Recent developments in the combination of redox cycling with different optical methods for signal amplification have proven to have tremendous potential for improving analytical performances. In this review, we summarized the advances in optical bioassays based on the signal amplification of redox cycling, including colorimetry, fluorescence, surface-enhanced Raman scattering, chemiluminescence, and electrochemiluminescence. Furthermore, this review highlighted the general principles to effectively couple redox cycling with optical bioassays, and particular attention was focused on current challenges and future opportunities.

Micelle-mediated chemiluminescence of 6-aza-2-thiothymine-protected gold nanoclusters for carbazochrome sodium sulfonate detection

Chemiluminescence (CL) intensity of luminol-H2O2 system was dramatically enhanced by cetyltrimethylammonium bromide (CTAB) micelle-mediated 6-aza-2-thiothymine-protected gold nanoclusters (ATT-AuNCs). It is proved that spherical micelles of CTAB in aqueous solution improved the dispersity of ATT-AuNCs, thus enhancing their catalytic activity, which brought in the increased CL intensity of luminol-H2O2 system. Carbazochrome sodium sulfonate (CSS) with a hemostatic containing tetrahydroindole structure broke the spherical micelles and notably quenched the CL intensity of luminol-H2O2-CTAB-ATT AuNCs system. Based on these results, a simple, fast, and sensitive CL method has been developed for the detection of CSS with a linear range of 0.25-25 μM and a detection limit of 0.11 μM. The method has also been successfully applied to the determination of CSS in serum with satisfied recoveries in the range of 89.6 % to 103.7 %. This study not only provides an effective approach for CSS detection but also paves the way for AuNCs-based CL applications.

Using tungsten oxide quantum-dot enhanced electrochemiluminescence to measure thrombin activity and screen its inhibitors

A thrombin-activity-based electrochemiluminescence (ECL) biosensor was successfully constructed using tungsten oxide quantum dots (WO3-x QDS) as the co-reactant and thrombin-cleavable peptides as the recognizer. Specifically, Ru(bpy)32+ were doped on silica nanoparticles (Ru@SiO2), which greatly enhanced the ECL potential. AuNPs@WO3-x QDs composite was then prepared to accelerate electron transfer and improve the ECL signal by 219 times. Under ideal conditions, the limit of detection for thrombin in serum was determined to be 0.28 μU/mL with a linear range from 1 μU/mL to 1 U/mL. In addition, the developed ECL biosensor was used to screen for thrombin inhibitors from 12 compounds in Artemisiae Argyi Folium. Among the compounds tested, it was observed that 100 μmol/L luteolin exhibited a significantly higher inhibition rate (exceeding 80%) compared to apigenin, isorhamnetin, naringin, or eriodictyol. In an in-vitro anticoagulation experiment, luteolin (100 μmol/L) prolonged APTT by 49%, and the molecular docking assay indicated that luteolin had binding sites of Gly219 and Asp189 in the active pockets of thrombin. This may have been the main reason underpinning luteolin's anticoagulation effects. Overall, the Ru@WO3-x QDS ECL biosensor provided a reliable strategy for thrombin activity assay and screening of anticoagulant agents.

Nucleic acid aptamer-based biosensors and their application in thrombin analysis

Thrombin is a multifunctional serine protease that plays an important role in coagulation and anticoagulation processes. Aptamers have been widely applied in biosensors due to their high specificity, low cost and good biocompatibility. This review summarizes recent advances in thrombin quantification using aptamer-based biosensors. The primary focus is optical sensors and electrochemical sensors, along with their applications in thrombin analysis and disease diagnosis.

Recent advances in optical aptasensors for biomarkers in early diagnosis and prognosis monitoring of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) accounts for approximately 90% of all primary liver cancers and is one of the main malignant tumor types globally. It is essential to develop rapid, ultrasensitive, and accurate strategies for the diagnosis and surveillance of HCC. In recent years, aptasensors have attracted particular attention owing to their high sensitivity, excellent selectivity, and low production costs. Optical analysis, as a potential analytical tool, offers the advantages of a wide range of targets, rapid response, and simple instrumentation. In this review, recent progress in several types of optical aptasensors for biomarkers in early diagnosis and prognosis monitoring of HCC is summarized. Furthermore, we evaluate the strengths and limitations of these sensors and discuss the challenges and future perspectives for their use in HCC diagnosis and surveillance.

From M6 to M12, M19 and M38 molecular alloy Pt-Ni carbonyl nanoclusters: selective growth of atomically precise heterometallic nanoclusters

Heterometallic Chini-type clusters [Pt_6-xNi_x(CO)₁₂]^2- (x = 0-6) were obtained by reactions of [Pt₆(CO)₁₂]^2- with Ni-clusters such as [Ni₆(CO)₁₂]^2-, [Ni₉(CO)₁₈]^2- and [H₂Ni₁₂(CO)₂₁]^2-, or from [Pt₉(CO)₁₈]^2- and [Ni₆(CO)₁₂]^2-. The Pt/Ni composition of [Pt_6-xNi_x(CO)₁₂]^2- (x = 0-6) depended on the nature of the reagents employed and their stoichiometry. Reactions of [Pt₉(CO)₁₈]^2- with [Ni₉(CO)₁₈]^2- and [H₂Ni₁₂(CO)₂₁]^2-, as well as reactions of [Pt₁₂(CO)₂₄]^2- with [Ni₆(CO)₁₂]^2-, [Ni₉(CO)₁₈]^2- and [H₂Ni₁₂(CO)₂₁]^2-, afforded [Pt_9-xNi_x(CO)₁₈]^2- (x = 0-9) species. [Pt_6-xNi_x(CO)₁₂]^2- (x = 1-5) were converted into [Pt_12-xNi_x(CO)₂₁]^4- (x = 2-10) upon heating in CH₃CN at 80 °C, with almost complete retention of the Pt/Ni composition. Reaction of [Pt_12-xNi_x(CO)₂₁]^4- (x ≈ 8) with HBF₄·Et₂O afforded the [HPt_14+xNi_24-x(CO)₄₄]^5- (x ≈ 0.7) nanocluster. Finally, [Pt_19-xNi_x(CO)₂₂]^4- (x = 2-6) could be obtained by heating [Pt_9-xNi_x(CO)₁₈]^2- (x = 1-3) in CH₃CN at 80 °C, or [Pt_6-xNi_x(CO)₁₂]^2- (2-4) in DMSO at 130 °C. The molecular structures of these new alloy nanoclusters have been determined by single crystal X-ray diffraction. The site preference of Pt and Ni within their metal cages has been computationally investigated. The electrochemical and IR spectroelectrochemical behavior of [Pt_19-xNi_x(CO)₂₂]^4- (x = 3.11) has been studied and compared to the isostructural homometallic nanocluster [Pt₁₉(CO)₂₂]^4-.

Cucurbituril Enhanced Electrochemiluminescence of Gold Nanoclusters via Host-Guest Recognition for Sensitive D-Dimer Sensing

Gold nanoclusters (AuNCs) are promising electrochemiluminescence (ECL) signal probes for their outstanding biocompatibility, unusual molecule-like structures, and versatile optical and electrochemical properties. Nevertheless, their relatively low ECL efficiency and poor stability in aqueous solutions hindered their application in the ECL sensing field. Herein, a facile host-guest recognition strategy was proposed to enhance the ECL efficiency and stability of Au NCs by rigidifying the surface of ligand-stabilized AuNCs via supramolecular self-assembly between cucurbiturils[7] (CB[7]) and l-phenylalanine (l-Phe). Meanwhile, mercaptopropionic acid (MPA) was introduced as a ligand in order to cooperatively enhance the performance of the AuNCs and facilitate the link between AuNCs and bioactive substances. The prepared CB[7]/l-Phe/MPA-AuNCs had a higher ECL emission efficiency, achieving about 2-fold stronger ECL intensity than that of l-Phe/MPA-AuNCs. In addition, after non-covalent modification with CB[7], the finite stability of the papered AuNCs was significantly improved. The prepared CB[7]/l-Phe/MPA-AuNCs showed excellent D-dimer sensing results, exhibiting a linear range from 50.00 fg/mL to 100.0 ng/mL and a detection limit of 29.20 fg/mL (S/N = 3). Our work demonstrated that the host-guest self-assembly strategy provided a universal approach for strengthening the ECL efficiency and stability of nanostructures on an ultra-small scale.

Strategies for Enhancing the Sensitivity of Electrochemiluminescence Biosensors

Electrochemiluminescence (ECL) has received considerable attention as a powerful analytical technique for the sensitive and accurate detection of biological analytes owing to its high sensitivity and selectivity and wide dynamic range. To satisfy the growing demand for ultrasensitive analysis techniques with high efficiency and accuracy in complex real sample matrices, considerable efforts have been dedicated to developing ECL strategies to improve the sensitivity of bioanalysis. As one of the most effective approaches, diverse signal amplification strategies have been integrated with ECL biosensors to achieve desirable analytical performance. This review summarizes the recent advances in ECL biosensing based on various signal amplification strategies, including DNA-assisted amplification strategies, efficient ECL luminophores, surface-enhanced electrochemiluminescence, and ratiometric strategies. Sensitivity-enhancing strategies and bio-related applications are discussed in detail. Moreover, the future trends and challenges of ECL biosensors are discussed.

The role of doping strategy in nanoparticle-based electrochemiluminescence biosensing

Doping plays a crucial role in electrochemiluminescence (ECL) due to the followings: (1) Modulation of electronic structure, alteration of the surface state of nanoparticles (NPs), providing effective protection from the surrounding environment, thereby leading to ECL emitters with exceptional properties including tunable spectra, high luminescence efficiency, low excitation potential, and good stability. (2) Employment of doped NPs as promising coreactant alternatives due to the presence of functional groups such as amines induced by NP doping. (3) Serving as novel co-reaction accelerators (CRAs) for ECL through doping induced high catalytic properties. (4) Behaving as excellent carriers to load ECL emitters, recognition elements, and catalysts due to doping-induced larger surface area, higher conductivity and better biocompatibility of NPs. As a consequence, doped NPs have aroused broad interest and found wide applications in various ECL sensing platforms. In this review, the current promising improvements, concepts, and excellent applications of doped NPs for ECL biosensing are addressed. We aim to bring to light the physicochemical characteristics of various doped NPs that endow them with appealing ECL performance, leading to diverse applications in biosensing.

Supramolecular Self-Assembly of Atomically Precise Silver Nanoclusters with Chiral Peptide for Temperature Sensing and Detection of Arginine

Metal nanoclusters (NCs) as a new type of fluorescent material have attracted great interest due to their good biocompatibilities and outstanding optical properties. However, most of the studies on metal NCs focus on the synthesis, atomic or molecular assembly, whereas metal NCs ability to self-assemble to higher-level hierarchical nanomaterials through supramolecular interactions has rarely been reported. Herein, we investigate atomic precise silver NCs (Ag₉-NCs, [Ag₉(mba)₉], where H₂mba = 2-mercaptobenzoic acid) and peptide DD-5 were used to induce self-assembly, which can trigger an aggregation-induced luminescence (AIE) effect of Ag₉-NCs through non-covalent forces (H-bond, π–π stacking) and argentophilic interactions [Ag(I)–Ag(I)]. The large Stokes shift (~140 nm) and the microsecond fluorescence lifetime (6.1 μs) indicate that Ag₉-NCs/DD-5 hydrogel is phosphor. At the same time, the chirality of the peptide was successfully transferred to the achiral Ag₉-NCs because of the supramolecular self-assembly, and the Ag₉-NCs/DD-5 hydrogel also has good circularly polarized luminescence (CPL) properties. In addition, Ag₉-NCs/DD-5 luminescent hydrogel is selective and sensitive to the detection of small biological molecule arginine. This work shows that DD-5 successfully induces the self-assembly of Ag₉-NCs to obtain high luminescent gel, which maybe become a candidate material in the fields of sensors and biological sciences.

An Electrochemiluminescence Biosensor for the Detection of Alzheimer's Tau Protein Based on Gold Nanostar Decorated Carbon Nitride Nanosheets

Human Tau protein is the most reliable biomarker for the prediction of Alzheimer's disease (AD). However, the assay to detect low concentrations of tau protein in serum is a great challenge for the early diagnosis of AD. This paper reports an electrochemiluminescence (ECL) immunosensor for Tau protein in serum samples. Gold nanostars (AuNSs) decorated on carbon nitride nanosheets (AuNS@g-CN nanostructure) show highly strong and stable ECL activity compared to pristine CN nanosheets due to the electrocatalytic and surface plasmon effects of AuNSs. As a result of the strong electromagnetic field at branches, AuNSs showed a better ECL enhancement effect than their spherical counterpart. For the fabrication of a specific immunosensor, immobilized AuNSs were functionalized with a monoclonal antibody specific for Tau protein. In the presence of Tau protein, the ECL intensity of the immunosensor decreased considerably. Under the optimal conditions, this ECL based immunosensor exhibits a dynamic linear range from 0.1 to 100 ng mL-1 with a low limit of detection of 0.034 ng mL-1. The LOD is less than the Tau level in human serum; thus, this study provides a useful method for the determination of Tau. The fabricated ECL immunosensor was successfully applied to the detection of Tau, the biomarker in serum samples. Therefore, the present approach is very promising for application in diagnosing AD within the early stages of the disease.

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.