CuS as co-reaction accelerator in PTCA-K2S2O8 system for enhancing electrochemiluminescence behavior of PTCA and its application in detection of amyloid-β protein

Electrochemiluminescence biosensor for specific detection of pancreatic ductal carcinoma through dual targeting of MUC1 and miRNA-196a

Pancreatic ductal adenocarcinoma (PDAC) poses significant diagnostic challenges due to its asymptomatic nature in its early stages, low specificity of conventional in vitro assays, and limited efficacy of surgical interventions. However, clinical specificity of the current serum biomarkers is suboptimal, leading to diagnostic inaccuracies and oversights. Therefore, this study introduced a novel dual-target electrochemiluminescence (ECL) biosensor to address these critical issues. The ECL biosensor synergistically employs the serum biomarker MUC1 and microRNA-196a to detect early-stage PDAC precisely. While MUC1 is a differential marker between normal and cancerous pancreatic cells, its standalone diagnostic performance is limited. However, integrating miRNA-196a as a complementary marker substantially enhances the specificity of the assay. This biosensor exhibits distinct ECL signal modulation-"on-off" in the presence of MUC1 and "off-on" upon concurrent detection of MUC1 and miRNA-196a. The biosensor achieves remarkably low limits of detection (LODs) at 0.63 fg mL-1 and 4.57 aM for MUC1 and miRNA-196a, respectively. Thus, it facilitates the real-time differentiation between human normal pancreatic (hTERT-HPNE) and pancreatic cancer (PANC-1) cells in authentic biological matrices. This innovative approach heralds a significant advancement in the early and specific detection of PDAC, offering promising prospects for clinical translation and the broader landscape of cancer diagnostics.

Supersensitive detection of lincomycin with an ECL aptasensor based on the synergistic integration of gold-functionalized upconversion nanoparticles and thiolated 3,4,9,10-perylene tetracarboxylic acid

In this work, the supersensitive and selective determination of lincomycin (Lin) was achieved using a novel electroluminescent (ECL) aptasensor based on the synergistic integration of gold functionalized upconversion nanoparticles (UCNPs) and thiolated 3,4,9,10-perylene tetracarboxylic acid (PTCA). The integration of two luminophores of UCNPs and PTCA combined the merits of the cathodoluminescence stability of UCNPs and the high quantum yield of PTCA, which significantly promoted the ECL signal and analytical performance of the proposed sensor. The introduction of gold nanoparticles in UCNPs can not only improve the conductivity and ECL performance of UCNPs but also cause them to easily integrate with thiolated PTCA (t-PTCA) via an Au-S bond. The ECL signal of UCNPs@Au/t-PTCA/GCE was almost twice as strong as that of t-PTCA/GCE and tenfold higher than that of UCNPs@Au/GCE. Because of the non-conductive protein of the Lin aptamer, the ECL intensity of apt/UCNPs@Au/t-PTCA/GCE noticeably decreased. In the presence of Lin, the aptamer was pulled down from the sensing interface, resulting in the recovery of the ECL intensity of the sensor. Under optimal conditions, our proposed sensor can quantify the concentration of Lin in the range from 1.0 × 10-15 to 1.0 × 10-7 M with a low detection limit of 2.4 × 10-16 M (S/N = 3), exhibiting high sensitivity and specificity for the determination of Lin.

A novel "on-off-on" electrochemiluminescence strategy based on RNA cleavage propelled signal amplification and resonance energy transfer for Pb2+ detection

BACKGROUND

Lead (Pb) is one of the most toxic heavy-metal pollutants. Additionally, lead ions (Pb2+) can accumulate in the human body through the food chain, causing irreversible damage through organ damage and system disorders. In the past few years, the detection of Pb2+ has mainly relied on instrumental methods such as atomic absorption spectroscopy (AAS) and inductively coupled plasma mass spectrometry (ICP-MS). Nonetheless, these techniques are complicated in terms of equipment and procedures, along with being time-intensive and expensive in terms of detection. These drawbacks have limited their wide application. Hence, there is a pressing need to develop detection techniques for Pb2+ that are not only cost-efficient but also highly sensitive and specific.

RESULTS

A novel "on-off-on" electrochemiluminescence (ECL) sensor for detecting Pb2+ was developed based on the resonance energy transfer (RET) effect between AuNPs and boron nitride quantum dots (BN QDs) and the recognition of Pb2+ by DNAzyme along with the cleavage reaction of the substrate chain. Poly(6-carboxyindole)/stannic sulfide (P6ICA/SnS2) nanocomposite was employed as a co-reaction accelerator to consequently facilitate the production of intermediate SO4•-. This effective enhancement of the reaction led to an improved ECL intensity of BN QDs and enabled the sensor platform to exhibit a higher original ECL response. Benefiting from the combination of the DNAzyme signal amplification strategy with the "on-off-on" design, the ECL sensor showed satisfactory selectivity, good stability, and high sensitivity. This ECL sensor exhibited a linear detection range (LDR) of 10-12-10-5 M and a limit of detection (LOD) of 2.6 × 10-13 M.

SIGNIFICANCE

In the present work, an "on-off-on" ECL sensor is constructed based on RET effect for ultrasensitive detection of Pb2+. P6ICA/SnS2 was investigated as the co-reaction accelerator in this sensor. Moreover, this ECL sensor exhibited excellent analytical capability for detecting Pb2+ in actual water samples, providing a method for detecting other heavy metal ions as well.

Advances in targeted tracking and detection of soluble amyloid-β aggregates as a biomarker of Alzheimer's disease

Misfolding and aggregation of amyloid-β (Aβ) peptides are key hallmarks of Alzheimer's disease (AD). With accumulating evidence suggesting that different Aβ species have varied neurotoxicity and implications in AD development, the discovery of affinity ligands and analytical approaches to selective distinguish, detect, and monitor Aβ becomes an active research area. Remarkable advances have been achieved, which not only promote our understanding of the biophysical chemistry of the protein aggregation during neurodegeneration, but also provide promising tools for early detection of the disease. In view of this, we summarize the recent progress in selective and sensitive approaches for tracking and detection of Aβ species. Specific attentions are given to soluble Aβ oligomers, due to their crucial roles in AD development and occurrence at early stages. The design principle, performance of targeting units, and their cooperative effects with signal reporters for Aβ analysis are discussed. The applications of the novel targeting probes and sensing systems for dynamic monitoring oligomerization, measuring Aβ in biosamples and in vivo imaging in brain are summarized. Finally, the perspective and challenges are discussed regarding the future development of Aβ-targeting analytical tools to explore the unknown field to contribute to the early diagnosis and treatment of AD.

Aggregation-induced electrochemiluminescence enhancement of Ag-MOG for amyloid β 42 sensing

This study aimed to introduce an immunosensor for measuring amyloid β 42 (Aβ42) levels by aggregation-induced enhanced electrochemiluminescence (ECL). Metal-organic gels (MOGs) are novel soft materials with advantages such as high gel stability, good light-emitting properties, and easy preparation. This study used silver nanoparticle metal-organic gel (Ag-MOG) as a substrate to connect Aβ42-Ab2 and the cathodoluminescent probe. Potassium persulfate was used as a co-reactant that could emit a high ECL signal. CuS@Au had the benefits of a relatively large surface area with excellent carrier function; therefore, it was used as a substrate to load a large amount of Aβ42-Ab1, significantly improving the immunosensor sensitivity. The ECL intensity of Aβ42 was linear in the range of 0.01 pg/mL to 250 ng/mL with a detection limit of 2.2 fg/mL (S/N = 3) under optimized detection conditions. This ECL immunosensor has been successfully applied to detect Aβ42 in human serum with the advantages of excellent stability and high selectivity. This method not only expands the potential applications of ECL immunosensors based on biological testing and clinical diagnosis but also provides a viable approach to basic clinical testing.

Antenna effect of perylene-sensitized up-conversion luminescent material amplifies the signal of electrochemiluminescence biosensor platform for the ultra-sensitive detection of enrofloxacin

Recently, up-conversion luminescent (UCL) materials have caught extensive sight on account of their excellent biocompatibility and weak automatic fluorescence background, but the low optical signal makes researchers shy away. Organic dye-sensitized UCL materials can improve the low optical signal drawback of UCL and rejuvenate it with adjustable optical properties and unique antenna effects. In this work, an efficient, simple and selective electrochemiluminescence (ECL) sensing platform was developed for determination of enrofloxacin (ENR). 3,4,9,10-perylene tetracarboxylic acid (PTCA) was successfully used as an "antenna" to improve the ECL performance of the UCL nanoparticles (PEI-NaYF4: Yb, Er) due to its appropriate excitation spectrum position and superior electron transfer rate. The specific recognition function of the aptamer enabled the sensor to eliminate the interference from conspecific impurity. In the presence of ENR, the specific combination of ENR with aptamer made the aptamer fall from surface of the electrode, thus we could see a considerable enhancement of signal. Under the most favourable conditions, the aptasensor based on antenna effect displayed a wide detection range (1.0 × 10-14∼1.0 × 10-6 M), low limit of detection (LOD = 3.0 × 10-15 M) and receivable recoveries (96.0%-102.4%) during water samples analysis. At this point, antenna effect provides a powerful strategy to expand the application of UCL in the field of ECL biosensing.

An In Situ Investigation of the Protein Corona Formation Kinetics of Single Nanomedicine Carriers by Self-Regulated Electrochemiluminescence Microscopy

Protein coronas are present extensively at the bio-nano interface due to the natural adsorption of proteins onto nanomaterials in biological fluids. Aside from the robust property of nanoparticles, the dynamics of the protein corona shell largely define their chemical identity by altering interface properties. However, the soft coronas are normally complex and rapidly changing. To real-time monitor the entire formation, we report here a self-regulated electrochemiluminescence (ECL) microscopy based on the interaction of the Ru(bpy)3 3+ with the nanoparticle surface. Thus, the heterogeneity of the protein corona is in situ observed in single nanoparticle "cores" before and after loading drugs in nanomedicine carriers. The label-free, optical stable and dynamic ECL microscopy minimize misinterpretations caused by the variation of nanoparticle size and polydispersity. Accordingly, the synergetic actions of proteins and nanoparticles properties are uncovered by chemically engineered protein corona. After comparing the protein corona formation kinetics in different complex systems and different nanomedicine carriers, the universality and accuracy of this technique were well demonstrated via the protein corona formation kinetics curves regulated by competitive adsorption of Ru(bpy)3 3+ and multiple proteins on surface of various carriers. The work is of great significance for studying bio-nano interface in drug delivery and targeted cancer treatment.

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.

AuNPs@MoSe2 heterostructure as a highly efficient coreaction accelerator of electrocheluminescence for amplified immunosensing of DNA methylation

Electrocheluminescence analysis amplified by coreaction accelerators has experienced breakthrough in ultrasensitive detection of biomarkers. Herein, a highly efficient coreaction accelerator, two-dimensional layered MoSe₂ nanosheets loaded with gold nanoparticles (AuNPs@MoSe₂ heterostructure), is proposed to enhance the ECL efficiency of Ru(bpy)₃²⁺/tripropylamine (TPrA) system. The presence of AuNPs avoids the aggregation of MoSe₂ nanosheets, and improves the electrical conductivity of modified surface. The AuNPs@MoSe₂ modified electrode also provides a large area for loading of abundant capture probe. MoSe₂ as an electroactive substrate can remarkably accelerate the generation of TPrA^•+ radicals to react with electrooxidized Ru(bpy)₃²⁺, which achieves about 3.4-fold stronger ECL intensity. Thus, an enhanced ECL immunoassay method can be achieved after Ru(bpy)₃²⁺-doped silica nanoparticle labeled antibody (Ab₂-Ru@SiO₂) is captured to the modified electrode via immunological recognition. Using methylated DNA as a target, the immunosensor was prepared by binding capture DNA on AuNPs@MoSe₂ modified electrode to successively capture the target, anti-5-methylcytosine antibody (anti-5mC) and Ab₂-Ru@SiO₂. The proposed strategy could detect 0.26 fM 5 mC (3σ) with a detectable concentration range of 1.0 fM - 10 nM at methylated DNA. This immunosensor showed excellent selectivity, good stability and reproducibility, and acceptable recovery, indicating the broad prospects of the novel coreaction accelerator in clinical diagnosis.

Electrochemiluminescence nanoemitters for immunoassay of protein biomarkers

The family of electrochemiluminescent luminophores has witnessed quick development since the electrochemiluminescence (ECL) phenomenon of silicon nanoparticles was first reported in 2002. Moreover, these developed ECL nanoemitters have extensively been applied in sensitive detection of protein biomarker by combining with immunological recognition. This review firstly summarized the origin and development of various ECL nanoemitters including inorganic and organic nanomaterials, with an emphasis on metal-organic frameworks (MOFs)-based ECL nanoemitters. Several effective strategies to amplify the ECL response of nanoemitters and improve the sensitivity of immunosensing were discussed. The application of ECL nanoemitters in immunoassay of protein biomarkers for diagnosis of cancers and other diseases, especially lung cancer and heart diseases, was comprehensively presented. The recent development of ECL imaging with the nanoemitters as ECL tags for detection of multiplex protein biomarkers on single cell membrane also attracted attention. Finally, the future opportunities and challenges in the ECL biosensing field were highlighted.

Recent progress in assembly strategies of nanomaterials-based ultrasensitive electrochemiluminescence biosensors for food safety and disease diagnosis

The Electrochemiluminescence (ECL)-based biosensors have received considerable attention in food contaminants and disease diagnosis, due to their fascinating advantages such as low cost, fast analysis speed, wide linear range, high sensitivity, and excellent anti-interference ability. Meanwhile, with the vigorous development and improvement of nanotechnology, biosensor assembly strategies tend to diversify and be multifunctional. This review focuses on the representative ECL biosensors in food safety and disease diagnosis reported by our research group and other research groups based on nanomaterials assembly strategies in recent years. According to the different roles of nanomaterials played in the constitution of ECL biosensors, nanomaterials would be divided into the following two categories to be summarized: (1) Nanomaterials for signal amplification. (2) Nanomaterials as ECL emitters. Finally, this review prospects the perspectives on the future development direction of ECL biosensor in food safety and disease diagnosis.

A sensitive electrochemiluminescence immunosensor for the detection of CA15-3 based on CeO2/Pt/rGO as a novel co-reaction accelerator

In this work, we successfully constructed a label-free electrochemiluminescence (ECL) immunosensor for the detection of breast cancer marker antigen (CA15-3). In particular, 3,4,9,10-perylenetetracarboxylic acid (PTCA) is cleverly attached to the surface of silica spheres as a luminophore (NH₂-SiO₂-PTCA), which greatly alleviates the disadvantage of PTCA anti-induced aggregated luminescence and improves the ECL performance. Furthermore, Pt nanoparticles were used to dope CeO₂ and introducing reduced graphene oxide (rGO) to prepare CeO₂/Pt/rGO composites as a novel co-reaction accelerator. Among them, Pt nanoparticles were used to improve the electrical conductivity of CeO₂, and the use of rGO as a substrate allows for a more uniform dispersion of CeO₂ to increase the catalytic surface area, which effectively improves the performance of the co-reaction accelerator and thus increasing the ECL intensity of the PTCA/S₂O₈^2- system. Under the optimal conditions, the designed ECL immunosensor showed satisfactory results in the determination of CA15-3 with a linear range of 12.00 mU mL^-1 - 120.00 U mL^-1 and a low detection limit of 1.348 mU mL^-1. Importantly, the resulting biosensor has good stability, high sensitivity and reliable reproducibility, suggesting its potential application in clinical research.

Electrochemiluminescence resonance energy transfer of MnCO3 for ultrasensitive amyloid-β protein detection

A composite material MnCO₃/poly(diallyl dimethyl ammonium chloride) (PDDA)/Ag with excellent electrochemiluminescence (ECL) performance and high biocompatibility was prepared by adding MnCO₃ and PDDA to silver nanoparticles (AgNPs). MnCO₃/PDDA/Ag and Au@SiO₂NPs were used as ECL donors and acceptors, respectively. Thus, an effective ECL-resonance energy transfer (RET) sensing platform was established. In a potassium persulfate (K₂S₂O₈) medium, MnCO₃ exhibited ECL emission with an ECL band appearing at 500-600 nm. In addition, Au@SiO₂ nanoparticles showed a UV-visible absorption at 450-650 nm. The ECL emission spectra of MnCO₃ overlapped with the absorption spectra of Au@SiO₂NPs. The effective ECL quenching resulted in a good response to the concentration of Aβ₄₂ in serum samples. The linear range was 5 fg ⋅ mL^-1 to 100 ng ⋅ mL^-1, and the detection limit was 2 fg ⋅ mL^-1. The recovery ranged from 97.7% to 104%. The high-efficiency ECL-RET immunosensor has potential application in detecting human serum Aβ₄₂ and other biomarkers, and can be used for the early screening of diseases.

A Portable Microfluidic-Based Electrochemiluminescence Sensor for Trace Detection of Trenbolone in Natural Water

In this study, a portable electrochemiluminescence sensor chip was designed for trenbolone (TBE) trace detection in environmental water. First, a stable ECL signal was obtained with low-toxicity 3,4,9,10-perylenetetracarboxylic acid (PTCA) as a luminophore and persulfate (S₂O₈^2-) as a coreactant. Second, hollow-structured Cu₂MoS₄ was introduced as a coreaction accelerator to catalyze S₂O₈^2- reduction. The reversible conversion of the mixed-valence transition metal ions in Cu₂MoS₄ (Cu⁺/Cu²⁺ and Mo⁴⁺/Mo⁶⁺) greatly promoted the generation of the sulfate radical (SO₄^•-). Meanwhile, the special porous structure of Cu₂MoS₄ possessed a large specific surface area, thus enhancing its catalytic performance. Based on these enhancement mechanisms, a strong ECL signal was acquired, which improved the detection sensitivity of the constructed sensor. Importantly, a microfluidic chip was introduced for sensing detection, thereby improving the practicality of the sensor. The developed sensor chip was miniature and portable, exhibiting high sensitivity for TBE detection with a wide linear range (10 fg/mL-100 ng/mL) and lower detection limit (3.32 fg/mL). This was of great significance for timely and rapid analysis of steroid pollutants in natural water.

A double reaction system induced electrochemiluminescence enhancement based on SnS2 QDs@MIL-101 for ultrasensitive detection of CA242

At present, the development of electrochemiluminescence (ECL) immunosensor with excellent performance is still the research focus of immunoassay and detection. Herein, SnS₂ quantum dots (SnS₂ QDs) and metal-organic framework (MIL-101 (Cr)) are effectively combined to achieve synergistic signal amplification based on K₂S₂O₈ co-reactant, thereby constructing SnS₂ QDs/SO₄^•- and SO₄^•-/O₂ ECL double reaction luminous systems. SnS₂ QDs and singlet oxygen (¹(O₂)₂*) produced from the system as light-emitting devices jointly enhance the ECL response and significantly improve the sensitivity of the ECL immunosensor. Dissolved oxygen and SnS₂ QDs respectively generate HOO^• and SnS₂ QDs^•- under negative potential, and react with transient SO₄^•- to emit strong light respectively, so as to jointly enhance the ECL response. MIL-101 catalyzes the oxygen cathode reduction reaction to promote the conversion of dissolved oxygen into HOO^•, which greatly improves the ECL response of ¹(O₂)₂*. CuS with spherical nanoflower-like form as a co-reaction promoter of K₂S₂O₈ generate more SO₄^•- active substances, which further enhance the ECL response of the immunosensor. The constructed ECL immunosensor has the advantages of low detection limit, high sensitivity and better stability. Under the optimal conditions, the detection range is 0.1 mU/mL∼100 U/mL, and the detection limit is 0.015 mU/mL. The results show that the constructed ECL immunosensor can detect human CA242 samples and have a broad application prospect in biological analysis and early diagnosis of diseases.

Single-step microwave synthesis of a novel ternary nanocomposite as an efficient luminophore and boron nitride quantum dots as a new coreactant for a cathodic ECL monitoring of chlorpyrifos

In this study, a novel and innovative enzyme-free electrochemiluminescence (ECL) pesticide probe based on a ternary nanocomposite, CuS/CQDs/g-C₃N₄NS, was demonstrated for the accurate monitoring of chlorpyrifos. Boron nitride quantum dots were introduced as a new and effective coreactant in comparison with other coreactants, such as hydrogen peroxide, peroxydisulfate, and tripropylamine, in the negative potential range for the first time. The nanocomposite as a promoted luminophore was synthesized by a one-pot microwave route. Carbon quantum dots and copper sulfide nanostructures were truly incorporated on the porous graphitized carbon nitride, which displayed a good cooperative effect on the signal improvement. CuS as a co-reaction accelerator and CQDs with a superior luminescence effect produced more radical species, and thus, the ECL signal was amplified. Upon increasing the appropriate concentration of this coreactant in electrolyte media, the signal intensity of the nanocomposite increases. A low detection limit of 3.0 × 10^-16 M and a wide range from 2.0 × 10^-15 to 7.0 × 10^-9 M were gained. Also, the fabricated pesticide sensor presented excellent repeatability for 20 consecutive optical signals, with a RSD of about 1.4%. Owing to its high proficiency, the developed sensor was applied as a new probe for chlorpyrifos analysis in water and fruit samples.

Enhancing K2S2O8 electrochemiluminescence based on silver nanoparticles and zinc metal–organic framework composite (AgNPs@ZnMOF) for the determination of l-cysteine

A silver nanoparticle-doped Zn(ii) metal–organic framework composite (AgNPs@ZnMOF) was investigated as an electrochemiluminescence (ECL) signal enhancer for potassium persulfate. First, ZnMOF was prepared by a one-step hydrothermal method, and then AgNPs@ZnMOF composite was obtained by depositing AgNPs on the surface and interior of ZnMOF. After the AgNPs@ZnMOF composite was modified on the glass carbon electrode (GCE), the cathode luminescence of potassium persulfate on bare GCE was enhanced by 8 times. A dual amplification mechanism provided by Zn(ii) and Ag nanoparticles in the AgNPs@ZnMOF composite has been validated by ECL spectra, fluorescence spectra, and electrochemical methods. The interaction between the sulfhydryl groups in l-cysteine (l-Cys) and AgNPs significantly affects the catalytic luminescence of the AgNPs@ZnMOF composite. Thus, a sensitive ECL method for the determination of l-Cys was developed based on the inhibition effect of l-Cys on the ECL signal within the linear range from 5.0 nM to 1.0 μM and the limit of detection was found to be 2 nM (S/N = 3). The established method has been successfully applied to the determination of l-Cys in human urine.

A silver nanoparticle-doped Zn(ii) metal–organic framework composite (AgNPs@ZnMOF) was investigated as an electrochemiluminescence (ECL) signal enhancer for potassium persulfate.

Copper-Doped Terbium Luminescent Metal Organic Framework as an Emitter and a Co-reaction Promoter for Amplified Electrochemiluminescence Immunoassay

This work designed a signal amplification strategy for construction of a highly sensitive electrochemiluminescence (ECL) biosensor by doping Cu²⁺ in a terbium luminescent metal organic framework (Cu:Tb-MOF) to act as a co-reaction promoter, which enhanced the generation of SO₄^•- radical during the cathodic process in the presence of K₂S₂O₈ as a co-reactant. The porous and hollow morphology and the size of Cu:Tb-MOF could be efficiently tuned via changing the molar ratio of Cu²⁺ and Tb³⁺ and the reaction time, which were related to the specific surface area, pore diameter, and the ECL intensity of the MOF structure. To further improve the sensitivity of the ECL biosensor, H₂O₂ was introduced into the ECL system to act as another co-reaction promoter, leading to a new ECL mechanism involving dual co-reaction promoters. In view of the low electron transfer resistance of Cu:Tb-MOF, a label-free ECL immunosensor was conveniently constructed by co-immobilizing Cu:Tb-MOF and the capture antibody on the electrode surface. Using pro-gastrin-releasing peptide (ProGRP, a biomarker of small-cell lung cancer) as the model target, the proposed immunosensor exhibited excellent performance with a detection range of 1.0 pg·mL^-1 to 50 ng·mL^-1 and a limit of detection down to 0.68 pg·mL^-1 (3σ). This work demonstrated a strategy to use the MOF structures as both an emitter and a co-reaction promoter for amplified ECL emission and proposed an innovative route to extend the application of lanthanide MOFs.

Ultrasensitive ECL aptasensing of kanamycin based on synergistic promotion strategy using 3,4,9,10-perylenetetracar-boxylic-l-cysteine/Au@HKUST-1

Herein, a sensitive and selective electrochemiluminescence (ECL) aptasensor was designed using Au@HKUST-1 as accelerator towards the perylene derivative (PTC-Cys)/peroxydisulfate (S₂O₈^2-) system for kanamycin (KAN) assay. Firstly, the PTC-Cys was prepared by covalently binding l-cysteine to 3,4,9,10-perylenete-tracarboxylic acid, which was acted as the luminophore. Then Au@HKUST-1could play the part of effective catalyst to accelerate the electrochemical reduction process of S₂O₈^2-to produce more sulfate radical anions (SO₄^•-), thus the ECL signal of the compound was noticeably raised by 2.4 times in comparison with that in which only luminophore and S₂O₈^2- are present, achieving signal amplification of the ECL system. In the presence of KAN, aptamer was pulled down from the sensing interface, achieving a considerable enhancement of ECL intensity in S₂O₈^2- solution. Upon the optimal condition, our proposed strategy can quantify the concentration of KAN from 1.0 × 10^-13 to 1.0 × 10^-8 M with low limit of detection of 4.2 × 10^-14 M (S/N = 3).Besides, our proposed ECL aptasensor exhibited excellent sensitivity, stability and specificity, and could be successfully applied to detect KAN in practical samples, which proved its potential to detect other antibiotics in food security.

Peptide-Based Electrochemiluminescence Biosensors Using Silver Nanoclusters as Signal Probes and Pd-Cu2O Hybrid Nanoconcaves as Coreactant Promoters for Immunoassays

Metal nanoclusters (NCs) possess high light stability and biocompatibility because of their unique quantum size effect, which has gradually become a new type of electrochemiluminescence (ECL) nanomaterial for immunoassays. However, the luminescence efficiency of metal NCs is too low to meet the needs of trace analysis, which limits its application. Herein, Ag NCs served as signal probes and Pd-Cu₂O hybrid nanoconcaves served as coreaction promoters, developing a highly efficient peptide-based biosensor for neuron-specific enolase (NSE) detection. Utilizing the reversible cycle of Cu⁺/Cu²⁺ and the reduction characteristics of Pd NPs, Pd-Cu₂O greatly accelerates the reduction of S₂O₈^2-. Meanwhile, Pd-Cu₂O has good hydrogen evolution activity, which promotes the generation of oxygen by improving the redox efficiency of the overall reaction, thus increasing the yield of active intermediates (OH^•) to promote the reduction of S₂O₈^2-. Specially, this is an effective attempt to use the hydrogen evolution reaction (HER) to accelerate the ECL emission of the S₂O₈^2- system. In addition, a short peptide ligand (NARKFYKGC, NFC) was developed to implement the targeted immobilization of antibodies, which can specifically bind to the Fc fragment of antibodies, thereby avoiding the occupation of the antigen binding site (Fab fragment). The introduction of NFC not only improves the binding efficiency of antibodies but also protects its bioactivity, thus significantly improving the sensitivity of the biosensor. Based on these strategies, the proposed biosensor provides a new perspective for the applications of metal NCs in ECL systems.

Peptide-Based Biosensor with a Luminescent Copper-Based Metal-Organic Framework as an Electrochemiluminescence Emitter for Trypsin Assay

A copper-based metal-organic framework (JUC-1000) has emerged as a promising electrochemiluminescence (ECL) emitter in the domains of bioanalysis and immunoassay. Herein, a highly efficient signal "on-off" peptide-based biosensor was constructed for trypsin (TPN) assay. JUC-1000 synthesized using an organic ligand of H₄BDPO was functionalized as the ECL emitter, whose cathodic ECL behavior in aqueous media was first investigated using potassium persulfate (K₂S₂O₈) as the coreactant. To further amplify the ECL signal, highly catalytic Ag@CeO₂ nanoparticles were fabricated as both a substrate and an coreaction accelerator, which can efficiently catalyze the reduction of S₂O₈^2- to generate more sulfate anion radicals (SO₄^•-) for ECL enhancement, thereby generating strong and stable ECL signals in a "signal on" state. The functionalized JUC-1000 emitter was connected to the Ag@CeO₂ sensing layer though a heptapeptide (HWRGWVC, HGC), and TPN as the target can specifically cleave the carboxyl side of arginine residues in HGC, leading to the release of emitters in a "signal off" state. Based on the efficient signal-switching, the biosensor exhibited linear ECL responses to the added TPN concentration, realizing sensitive detection of TPN in 10 fg/mL to 100 ng/mL with a limit of detection of 3.46 fg/mL. This work proposed an attractive orientation for the fundamental research of applying transition metal-organic frameworks as ECL emitters in bioanalysis and immunoassay.

Rare Self-Luminous Mixed-Valence Eu-MOF with a Self-Enhanced Characteristic as a Near-Infrared Fluorescent ECL Probe for Nondestructive Immunodetection

Steady and efficient sensitized emission of Eu²⁺ to Eu³⁺ can be achieved through a rare mixed-valence Eu-MOF (L₄Eu^III₂Eu^II). Compared with the sensitization of other substances, the similar ion radius and configuration of the extranuclear electron between Eu²⁺ and Eu³⁺ make sensitization easier and more efficient. The sensitization of Eu²⁺ to Eu³⁺ is of great assistance for the self-enhanced luminescence of L₄Eu^III₂Eu^II, the longer luminous time, and the more stable electrochemiluminescence (ECL) signal. Simultaneously, L₄Eu^III₂Eu^II possesses near-infrared (NIR) fluorescence of around 900 nm and a mighty self-luminous characteristic, which render it useful as a NIR fluorescent probe and as a luminophore to establish a NIR ECL biosensor. This NIR biosensor can greatly reduce the damage to the detected samples and even achieve a nondestructive test and improve the detection sensitivity by virtue of strong susceptibility and environmental suitability of NIR. In addition, the CeO₂@Co₃O₄ triple-shelled microspheres further enhanced the ECL intensity due to two redox pairs of Ce³⁺/Ce⁴⁺ and Co²⁺/Co³⁺. The NIR ECL biosensor based on these strategies owns an ultrasensitive detection ability of CYFRA 21-1 with a low limit of detection of 1.70 fg/mL and also provides a novel idea for the construction of a highly effective nondestructive immunodetection biosensor.

Ultrasensitive near-infrared electrochemiluminescence biosensor derived from Eu-MOF with antenna effect and high efficiency catalysis of specific CoS2 hollow triple shelled nanoboxes for procalcitonin

In this paper, we report a novel multiple amplification strategy for ultrasensitive near-infrared electrochemiluminescence (ECL) immunoassay in K₂S₂O₈ solution. The realization of this strategy is based on the antenna effect of Eu-MOF (EuBTC) and a high efficiency catalysis of CoS₂ hollow triple shelled nanoboxes (TSNBs). The H₃BTC ligand in the antenna effect first undergoes π-π* absorption and a singlet-singlet electronic transition. Its energy passes through the intersystem to the triplet state, next transfers from the lowest excited triplet state to the vibrational energy level of the rare earth ion, finally realizing sensitizing center ion luminescence. Moreover, ionic reaction and structural advantages endow CoS₂ TSNBs a dual signal enhancement effect. This sandwich-type ECL biosensor has a near-infrared luminescence in 800-900 nm, thus avoiding damage to the sample in the meantime. In practical diagnosis, the normal critical value of procalcitonin (PCT) (<0.5 ng/mL) is much higher than the detection limit (3.65 fg/mL) and is in the detection range (10 fg/mL-100 ng/mL), which means that the ECL biosensor has a high sensitivity in the detection of PCT and meet the requirement for diagnosis of disease completely. Therefore, the strategy provides a feasible method for efficient and stable analysis of systemic inflammatory response such as fearful bacterial infection, hepatitis B, and peritonitis.

Enhanced electrochemiluminescence of CdS quantum dots capped with mercaptopropionic acid activated by EDC for Zika virus detection

Enhanced electrochemiluminescence (ECL) signals of CdS quantum dots capped with 3-mercaptopropionic acid (MPA@CdS QDs) have been observed after using N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC) to activate the carboxyl groups. The generated ECL signals are strong enough that their images can be captured using a Huawei mobile phone. A possible mechanism for the generation of enhanced ECL signals has been proposed. Then, a sandwich immunosensor platform for detecting Zika virus (ZIKV) was fabricated with silica microspheres as the carrier and MPA@CdS QDs as ECL signal labels. Due to the dual signal amplification of EDC activation and microsphere enrichment, good linearity from 1.0 fg mL-1 to 1.0 ng mL-1 was exhibited by the QD-based ECL immunosensor for ZIKV detection. The detection limit was 0.3 fg mL-1.

A novel electrochemiluminescence sensor based on resonance energy transfer from MoS2QDs@g-C3N4 to NH2-SiO2@PTCA for glutathione assay

In this work, a solid-state electrochemiluminescence (ECL) sensor based on resonance energy transfer (RET) was proposed using MoS2QDs@g-C3N4 as a donor and NH2-SiO2@PTCA as an acceptor. Herein, MoS2QDs could significantly facilitate the stability and efficiency of the ECL of g-C3N4. PTCA provided a large platform to anchor NH2-SiO2 nanoparticles. The prepared MoS2QDs@g-C3N4 exhibited good spectral overlap with the UV-vis absorption spectrum of NH2-SiO2@PTCA. Based on this, we designed an "off-on" ECL sensing strategy for sensitive and selective detection of glutathione (GSH). Under the best conditions, the linear range of the sensor for GSH detection was from 0.001 to 100 μM with a detection limit of 0.63 nM (S/N = 3). More importantly, GSH in commercial samples can be detected using the proposed sensor, which indicated its superior detection capabilities and potential application value in commercial medicines.

A robust and efficient aqueous electrochemiluminescence emitter constructed by sulfonate porphyrin-based metal-organic frameworks and its application in ascorbic acid detection

The robust and strong electrochemiluminescence (ECL) emission of organic emitters in an aqueous solution is crucial for expanding their applications in early diagnosis. Herein, a Zn porphyrin-based metal-organic framework ((Zn)porphMOF) was facilely obtained by chelating Zn(ii)meso-tetra (4-sulfonatophenyl) porphine (Zn-TSPP) with Zn ions, showing substantially enhanced ECL radiation with K₂S₂O₈ as the coreactant via the "reduction-oxidation" route in aqueous media. In contrast with Zn-TSPP, (Zn)porphMOF displayed 22-fold increase in the ECL intensity because of the agglomeration effect. By virtue of the dramatic confinement towards the energy and electron transfer of ascorbic acid (AA) during the ECL process, an ultrasensitive biosensor was developed with a wide linear range (3.77 to 26.4 μM) and ultra-low detection limit of 0.29 μM at 3 times of the signal-to-noise ratio (3S/N). This work offers a feasible avenue to harvest the steady and boosted ECL responses of organic molecules in aqueous media, also greatly expanding the MOF applications in bioanalysis.

Triple Amplification of 3,4,9,10-Perylenetetracarboxylic Acid by Co2+-Based Metal-Organic Frameworks and Silver-Cysteine and Its Potential Application for Ultrasensitive Assay of Procalcitonin

In this work, a triple-amplified biosensor with a bioactivity-maintained peculiarity was constructed for quantitative procalcitonin (PCT) detection. As everyone knows, a strong electrochemiluminescence (ECL) signal is the premise to ensure high sensitivity for trace target detection. Hence, a valid tactic was developed to achieve signal amplification of luminophor by using Co²⁺-based metal-organic frameworks (ZIF-67) and silver-cysteine (AgCys). The ZIF-67 particles, which have more atomically dispersed Co²⁺, could play the role of a co-reaction accelerator to catalyze S₂O₈^2- to generate abundant Co³⁺ and sulfate radical anions (SO₄^•-). Afterward, a mass of Co³⁺ was reduced to more hydroxyl radicals (OH^•) by H₂O, thus ulteriorly reducing S₂O₈^2- to generate more SO₄^•-. Remarkably, S₂O₈^2- was reduced to SO₄^•- continuously with the recycling of Co²⁺ and Co³⁺, which realized an effective signal amplification. Meanwhile, the AgCys complex with superior catalysis and biocompatibility was prepared to further improve the ECL signal and maintain the bioactivity of the biomolecule. Furthermore, HWRGWVC, a heptapeptide that was used for combining the Fc fragments of an antibody by Au-S bonding to achieve the fixed point fixation, could not only maintain bioactivity of an antibody but also improved its incubation efficiency, thus further enhancing biosensor sensitivity. Under optimum conditions, the proposed biosensor realized highly sensitive assay for PCT with a wide dynamic range from 10 fg/mL to 100 ng/mL and a detection limit as low as 3.67 fg/mL. With superior stability, selectivity, and repeatability, the prepared biosensor revealed immense potential application of ultrasensitive assay for PCT in human serum.

CuS@PDA-FA nanocomposites: a dual stimuli-responsive DOX delivery vehicle with ultrahigh loading level for synergistic photothermal-chemotherapies on breast cancer

In this study, CuS@PDA nanoparticles were synthesized and used to create a novel tumor-targeting nanocomposite platform composed of copper sulfide@polydopamine-folic acid/doxorubicin (CuS@PDA-FA/DOX) for performing both photothermal and chemotherapeutic cancer treatment. The nanocomposite platform has ultrahigh loading levels (4.2 ± 0.2 mg mg-1) and a greater photothermal conversion efficiency (η = 42.7%) than CuS/PDA alone. The uptake of CuS@PDA-FA/DOX nanocomposites is much higher in MCF-7 cells than in A549 cells because MCF-7 cells have much higher folic acid receptors than A549. Under near infrared (NIR) irradiation, the CuS@PDA-FA/DOX system using a synergistic combination of photothermal therapy and chemotherapy yields a better therapeutic effect than either photothermal therapy or chemotherapy alone. The treatment is very effective with the cell viability is only 5.6 ± 1.4%.

Electrochemiluminescence immunoassay for the N-terminal pro-B-type natriuretic peptide based on resonance energy transfer between a self-enhanced luminophore composed of silver nanocubes on gold nanoparticles and a metal-organic framework of type MIL-125

The N-terminal pro-B-type natriuretic peptide (NT-proBNP) is a marker of heart failure. A novel sandwich type electrochemiluminescence (ECL) immunoassay is described for the NT-proBNP. The method is based on ECL resonance energy transfer (RET) between silver nanocubes that were covered with semicarbazide-modified gold nanoparticles (AgNC-sem@AuNPs) as the donor, and a Ti(IV)-based metal-organic framework of type MIL-125 as the acceptor. The ECL signal was strongly amplified by increasing the luminous efficiency. ECL-RET occurs due to the partial overlap between the ECL emission of the AgNC-sem@AuNPs (emission wavelength at 470 nm to 900 nm) and the visible absorption spectrum of MIL-125 (absorption wavelength at 406 nm to 900 nm). This results in the quenching of ECL. The AgNC-sem@AuNPs were placed on the electrode. The antibody was immobilized on AgNC-sem@AuNPs via Au-NH₂ bond, and MIL-125 was utilized as a label for the secondary antibody. The assay works in the 0.25 pg mL^-1 to 100 ng mL^-1 concentration range and has a 0.11 pg mL^-1 lower detection limit (at S/N = 3). Graphical abstract Schematic representation of self-enhanced luminescence mechanism (semicarbazide (Sem) as co-reaction accelerator) and Electrochemiluminescence resonance energy transfer (ECL-RET): silver nanocubes (AgNCs) as the energy donor and MIL-125 as the energy acceptor.

An electrochemical peptide-based biosensor for the Alzheimer biomarker amyloid-β(1-42) using a microporous gold nanostructure

Alzheimer's disease (AD) is connected to aggregation of amyloid-β (Aβ) peptide and formation of insoluble plaques in the brain. Aβ level can be monitored as an AD early diagnosis route. In this study, an irregular shaped microporous gold nanostructure with a typical size of 150 × 250 nm was electrodeposited on a polycrystalline gold surface at 0 mV (vs. AgCl) using sodium alendronate. The nanostructure was then characterized by field-emission scanning electron microscopy. An electrochemical peptide-based biosensor was fabricated by immobilizing an Aβ_(1-42)-binding peptide on the gold nanostructure. Binding of Aβ_(1-42) by the peptide was followed electrochemically using ferro/ferricyanide as a redox probe. Differential pulse voltammograms in a potential range of 0-500 mV (vs. AgCl) with typical peak potentials at 224 mV are linear in the 3-7000 pg mL^-1 Aβ_(1-42) concentration range, with a 0.2 pg mL^-1 detection limit. The biosensor is free of interferences and was applied to the quantitation of Aβ_(1-42) in artificial cerebrospinal fluid and spiked serum samples. Graphical abstractSchematic presentation of an immobilized amyloid-β_(1-42)-specific peptide on the surface of a microporous gold nanostructure to fabricate an electrochemical biosensor for early diagnosis of Alzheimer's disease. Aβ_(1-42) capturing by the peptide led to repulsion of ferrocyanide/ferricyanide redox couple.

Synthesis and Application of CeO2/SnS2 Heterostructures as a Highly Efficient Coreaction Accelerator in the Luminol-Dissolved O2 System for Ultrasensitive Biomarkers Immunoassay

Electrocheluminescence (ECL) immunoassay amplified by coreaction accelerators has experienced major breakthroughs in ultrasensitive detection of biomarkers. Herein, CeO₂/SnS₂ heterostructures were synthesized and applied as a novel coreaction accelerator to enhance the ECL efficiency of the luminol-dissolved O₂ system for the first time. Benefiting from the well-matched lattice spacing, ultrafine CeO₂ nanoparticles (NPs) were grown in situ on layered SnS₂ nanosheets (NSs) with improved dispersion. CeO₂/SnS₂ as an electroactive substrate can remarkably accelerate the generation of abundant superoxide anion radicals (O₂^•-) to react with luminol anion radical (L^•-), achieving about 2-fold stronger ECL intensity than that of pure CeO₂ NPs. To avoid harsh chemical synthesis of conventional ECL labels and simplify the antibody conjugation process, ferritin (Ft) was served as a natural nanocarrier to immobilize luminol molecules (Lum@Ft) via a one-step linkage, whose protein nanocage can easily connect with the detection antibody. Moreover, a robust site-oriented immobilization strategy using HWRGWVC heptapeptide as specific capturer was further adopted to maintain the bioactivity of the capture antibody on the amine-functionalized CeO₂/SnS₂ surface, which promoted the incubation efficiency markedly. On account of this advanced sensing strategy, a brand new biosensor was constructed for the accurate detection of heart failure biomarkers, which performed with favorable linearity in the range of 0.0001-50 ng/mL and achieved the detection limit of 36 fg/mL.

Highly-branched Cu2O as well-ordered co-reaction accelerator for amplifying electrochemiluminescence response of gold nanoclusters and procalcitonin analysis based on protein bioactivity maintenance

The point of fabricating ultrasensitive electrochemiluminescence (ECL)-based biosensors should be focused on how to maintain high immune recognition of antigens by antibodies in whole process. That is not effortless due to the structure of the protein can be destroyed root in toxic nanocarriers, excessive cyclic potential and superoxide radicals in coreactant, all of which can lead to reduce the bioactivity of antigen and antibody. In this work, the effect of negative voltage and divers coreactant on protein bioactivity were verified. Based on that, a motivated ECL biosensor with good biocompatibility was fabricated for procalcitonin (PCT) detection using Au nanoclusters (Au NCs) as low-potential cathodic luminophor and K₂S₂O₈ as non-toxic coreactant, respectively. Besides, highly-branched Cu₂O was utilized to catalyze K₂S₂O₈ and produce more radical anion SO₄^•-, which can oxidize Au NCs^•- to generate more high-energy-state Au NCs*, thus doubling the ECL intensity to meet the requirements of trace analysis. In addition, protein A (PA) as specific antibody capturer was employed to bind the Fc region of anti-PCT in an orientated way, further maintaining the physiological activity of antibody. As expected, all strategies undoubtedly practically improved the immune recognition of the biosensor and reduced the detection limit to 2.90 fg/mL.

Bioactivity-Protected Electrochemiluminescence Biosensor Using Gold Nanoclusters as the Low-Potential Luminophor and Cu2S Snowflake as Co-reaction Accelerator for Procalcitonin Analysis

The expansion of electrochemiluminescence (ECL) technology to immunoassay at the core of care emphasizes all immune molecules will not be inactivated in the analysis process. That poses a major challenge to ECL-based biosensors due to the deoxynucleotide sequences of an antigen or antibody could be oxidized through a route of excessive cyclic potential. Herein, an ultrasensitive ECL biosensor was developed based on a novel bioactivity-protected sensing strategy utilizing Au nanoclusters (Au NCs) as low-potential luminophor for detection of procalcitonin (PCT). Bovine serum albumin (BSA)-templated Au NCs exhibited a low-potential anodic ECL signal in triethylamine (TEA) solution at 0.87 V, where it is suitable for the survival of immune molecules. Taking advantage of good conductivity and high surface area, a Cu₂S snowflake not only functions as a satisfying substrate for connecting immune molecules but also acts as co-reaction accelerator to produce more cationic radicals TEA^•+, which could improve the ECL intensity needed to meet the requirements of trace analysis. Otherwise, HWRGWVC (HC-7) heptapeptide as specific antibody immobilizer for site-oriented fixation was introduced to further maintain the bioactivity of an antibody. In view of the preceding discussion, the obtained biosensor exhibited ultrahigh immune recognition to targets so that the detection limit was as low as an unprecedented value of 2.36 fg/mL, which will be of great significance to the application and development of a biosensor in the future.