Crystalline Energy Funneling in Mixed-Ligand Zr-MOFs Drives Radical-Triggered ECL Amplification for Ultrasensitive Thrombin Sensing.

Luminescence resonance energy transfer (LRET) is a powerful technique for probing changes in the distance between energy donors and acceptors, which has often been used in bioassays.1 Electrochemiluminescence (ECL) technique has been widely used in sensing applications, however, it has been seldom reported in LRET due to the difficulty in finding suitable energy donor/acceptor pair. In order to expand its application, it is very important to establish more suitable ECL resonance energy transfer (ECL-RET) pairs. Recently, we found that some traditional ECL reagents, such as luminol, Ru(bpy)3 2+, and lucigenin, can transfer their ECL energy to nanomaterials including semiconductor quantum dots and graphene. The obtained ECL-RET signals are usually stronger than the original ECL signals, which makes the ECL-RET more suitable for biosensing application. Electrochemluminescence resonance energy transfer (ECL-RET) between luminol as a donor and CdSe@ZnS quantum dots (QDs) as an acceptor can be obtained in neutral condition. CdSe@ZnS quantum dots modified on a glassy carbon electrode can catalyze the luminol oxidation to promote the anodic luminol ECL without coreactant. The intensity of anodic luminol ECL (0.60 V) at the CdSe@ZnS/GCE was enhanced more than one magnitude compared with that at the bare GCE. Another strong anodic ECL peak observed at more positive potential (1.10 V) could be assigned to the ECL-RET between the excited state of luminol and the QDs. A label-free ECL aptasensor for the detection of thrombin was fabricated based on the synergic effect of the electrocatalysis and the ECL-RET. The approach showed high sensitivity, good selectivity, and wide linearity for the detection of thrombin in the range of 10 fM-100 pM with a detection limit of 1.4 fM (S/N=3). The energy transfer between lucigenin and CdSe QDs was investigated. Strong anodic ECL can be obtained in neutral lucigenin solution at a CdSe quantum dots modified glassy carbon electrode in the presence of bromide. Electrochemical results suggested that CdSe quantum dots can catalyze the oxidation of lucigenin and bromide, which can generate the anodic ECL. The fluorescence and the ECL spectra revealed that the ECL-RET can occur between lucigenin and CdSe quantum dots. The oxidation product of bromide can promote the ECL-RET and increase the anodic ECL signal significantly. Cytochrome c exhibited apparent inhibiting effect on the anodic ECL emission, based on which a sensitive ECL sensor for the detection of cytochrome c was established.3 The ECL-RET can also occur between Ru(bpy)3 2+ ECL and gold nanoparticles/graphene oxide nanocomposite. Strong anodic Ru(bpy)3 2+ ECL was observed at a graphene oxide modified glassy carbon electrode (GO/GCE) in the absence of coreactants. The catalytical effect of GO on the oxidation of Ru(bpy)3 2+ suggested that GO itself can act as the coreactant of Ru(bpy)3 2+ ECL. Thiol group terminated adenosine triphosphate (ATP) aptamer was immobilized on the GO film via DNA hybridization. When gold nanoparticles/graphene oxide (AuNPs/GO) nanocomposites were modified on the aptamer through S-Au bond to form sandwich-like structure, the ECL-RET could occur between Ru(bpy)3 2+and AuNPs/GO nanocomposites, resulting in apparent decrease of ECL signal. After the ECL sensor was incubated in ATP solution, the AuNPs/GO nanocomposites were released from the electrode due to the specific interaction between aptamer and ATP, leading to the increased ECL signal. Based on these results, an ECL aptasensor was fabricated and could be used in the sensitive and selective detection of ATP in the range of 0.02-200 pM with a detection limit of 6.7 fM (S/N=3). The above results suggested that the ECL-RET between the traditional luminescent reagents and nanomaterials can be used to fabricate different kinds of biosensors for the detection of protein and DNA, which will sufficiently expand the application of ECL technique in biosensing field.

Luminol, as a classical luminophore, plays a crucial role in electrochemiluminescence (ECL). However, the traditional luminol-H2O2 ECL system suffers from the self-decomposition of H2O2 at ambient temperature, which hinders its further application in quantitative analysis. In this work, for the first time, we developed atomically gold-supported two-dimensional VO2 nanobelts (Au/VO2) as an advanced co-reaction promoter to speed up the reduction of dissolved oxygen to superoxide radicals (O2•-), which react with the luminol anion radical and greatly promote the ECL emission. The ECL resonance energy transfer (ECL-RET) between the hollow manganese dioxide nanospheres and luminol results in a conspicuously decreased ECL signal response, and in the presence of glutathione (GSH), effective redox reaction between manganese dioxide and GSH restores the ECL signal. As a consequence, the designed sensor based on ECL-RET-assisted Au/VO2 signal amplification showed outstanding performance for "signal-on" detection of GSH in the concentration range of 10-3 to 10-10 M, and the detection limit was as low as 0.03 nM. The ECL sensor displayed excellent specificity and was successfully utilized to target GSH in real human serum samples. Importantly, this work not only highlights a powerful avenue for constructing an ultrasensitive ECL sensor for GSH but also provides some inspiration for the further design of high-performance co-reaction accelerators using the ECL technique.

Ionic liquid modified SiO2 nanoparticles as coreactant of Ru(bpy)32+ ECL and its application in the detection of glutathione

The dual-signal output self-calibration mode reduces the false positive and negative signals of electrochemiluminescence (ECL) aptamer sensors. A competitive dual-signal ECL platform was designed for the ultrasensitive detection of kanamycin (KAN) using a zirconium metal-organic framework (Zr MOF) and Luminol as ECL emitters. To enhance the ECL efficiency, a co-reactant (polyethyleneimine, PEI) was covalently bound to the Zr MOF to achieve self-enhanced ECL. Based on the selective interaction between KAN and its aptamer, the Luminol/KAN/Zr MOF-PEI "sandwich" structure was immobilized on the electrode surface. The competition for PEI between emitters increased the Luminol ECL signal and decreased the Zr MOF's ECL signal. The ratio in ECL signals between the two competitive emitters enabled the quantitative analysis of KAN, achieving a detection limit as low as 7.86 × 10-4 ng/mL. This study elucidated the synergistic mechanism between self-enhanced ECL and ECL competition, offering a novel approach for constructing dual-signal ECL sensors using a single co-reactant.

Myocardial miRNAs in peripheral blood are closely related to the pathogenic process of myocardial infarction. Rapid identification and accurate quantification of myocardial miRNAs are of great significance to clinical interventions for treating cardiovascular lesions. Therefore, a ratiometric electrochemiluminescence (ECL) biosensor integrating DNAzyme with a resonance energy transfer (RET) system was designed to detect myocardial miRNA. The dual-signal system was composed of rA marked substrate strand functionalized CdTe quantum dots (QDs) as reductive-oxidative (R-O) emitters and Cy5-labeled strand-functionalized Ru(bpy)32+-filled silica nanoparticles (RuSi NPs) as oxidative-reductive (O-R) emitters. In the presence of target miRNA, DNAzyme was activated to cut substrate strands on the CdTe QDs and release triggers for opening hairpin probes. Then, the Cy5 molecule-labeled hairpin DNA on the RuSi NPs was opened to introduce Cy5 molecules and RuSi NPs into the system. The R-O ECL was quenched by ECL-RET between CdTe QDs and Cy5 molecules and the O-R ECL was introduced by the RuSi NPs. In this way, based on the simultaneous changing of the ECL signal, the dual-potential dynamic signal ratiometric ECL sensing platform was developed. By measuring the ratio of O-R ECL signal to R-O ECL signal, the concentration of miRNA-499 was accurately quantified in the range of 10 fM to 10 nM, and the detection limit was as low as 2.44 fM (S/N = 3). This DNAzyme guided dual-potential ratiometric ECL method provides a sensitive and reliable method for myocardial miRNA detection, and it has great potential in clinical diagnosis and treatment.

Sensitive detection of bisphenol A based on resonance energy transfer between zinc oxide nanoparticles enhanced luminol ECL and silver nanoparticles decorated TiVC MXene

WARNING : The light-emitting molecular structures responsible for the chemiluminescence and fluorescence phenomena are not necessarily the same!

This study developed a new zirconium metal-organic framework (MOF) luminophore named Zr-DPA@TCPP with dual-emission electrochemiluminescence (ECL) characteristics at a resolved potential. First, Zr-DPA@TCPP with a core-shell structure was effectively synthesized through the self-assembly of 9,10-di(p-carboxyphenyl)anthracene (DPA) and 5,10,15,20-tetra(4-carboxyphenyl)porphyrin (TCPP) as the respective organic ligands and the Zr cluster as the metal node. The reasonable integration of the two organic ligands DPA and TCPP with ECL properties into a single monomer, Zr-DPA@TCPP, successfully exhibited synchronous anodic and cathodic ECL signals. Besides, due to the impressively unique property of ferrocene (Fc), which can quench the anodic ECL but cannot affect the cathodic ECL signal, the ratiometric ECL biosensor was cleverly designed by using the cathode signal as an internal reference. Thus, combined with DNA recycle amplification reactions, the ECL biosensor realized sensitive ratiometric detection of HPV-16 DNA with the linear range of 1 fM-100 pM and the limit of detection (LOD) of 596 aM. The distinctive dual-emission properties of Zr-DPA@TCPP provided a new idea for the development of ECL luminophores and opened up an innovative avenue of fabricating the ratiometric ECL platform.

A highly sensitive electrochemiluminescent (ECL) biosensor was designed for the detection of concanavalin A (ConA) based on glucose oxidase (GOx) as a recognition element by carbohydrate-lectin biospecific interaction, and poly(ethylenimine) (PEI) reduced graphene and hollow gold nanoparticles (HAuNPs) as supporting matrix and signal amplifier. The modification process and detection principle of the biosensor are briefly described as follows. First, PEI reduced graphene oxide with abundant amino groups was cast onto the surface of glassy carbon electrode to adsorb HAuNPs for improving the signal intensity in luminol/H2O2 ECL system. Next, GOx was further assembled onto the electrode by the interaction between Au and -NH2. In the presence of glucose in the detection solution, GOx catalyzed glucose to generate H2O2 in situ, which served as a co-reactant of luminol to enhance ECL signal of luminol. Based on the fact that ConA could result in a decrease in ECL signal when immobilized on the electrode, an ECL biosensor was prepared for the determination of ConA. The ECL signal intensity was linear with the logarithm of ConA concentration and the linear range was from 1.0 to 20ng/mL with a low detection limit of 0.31ng/mL (signal to noise ratio =3). This strategy led to a nearly 1000-fold improvement in detection limit for ConA assays compared with previously reported method, thus exhibiting a great potential application in sensitive bioassays of ConA.

A potential-resolved ratiometric electrochemiluminescence aptasensor for Pb2+: Gold nanoclusters and amino-terminated perylene derivative as both emitters and resonance energy transfer donor-acceptor pair

Ratiometric electrochemiluminescence (ECL) assays have attracted widespread attention in biosensing owing to their precise measurements by eliminating environmental interferences. In this work, g-C3N4, gold nanoparticles, CuO and luminol were integrated onto hollow carbon spheres (HCS) in sequence to fabricate potential-resolved ECL nanoprobes. The system consists of g-C3N4 as cathode ECL emittersandluminol as anode ECL emitters. The ECL of g-C3N4 is quenched by CuO due to the resonance energy transfer (RET). However, after adding dopamine (DA), the ECL signal is restored due to the redox reaction between CuO and DA. Meanwhile, there is a quenching effect between DA and luminol because DA interferes with the radical reaction process of luminol. Therefore, DA causes the reciprocal changes in cathodic ECL and anodic ECL. This phenomenon can be leveraged to create a ratiometric ECL signal, enabling the quantitative detection of DA. The developed ECL sensor exhibited a sensitive detection toward DA, performing a wide linearity in the range 5.0 × 10-4 ~ 1.0 × 10-9M with a low detection limit of 2.3 × 10-11M (S/N = 3). Furthermore, this strategy exhibited a good practicality to detect DA in human urine, providing a promising strategy in ECL bioanalysis.

Aptamer responsive DNA Functionalized hydrogels electrochemiluminescence biosensor for the detection of adenosine triphosphate

Multimode sensing and imaging platform for versatile detection of GSH based on surface modification strategy of Ru(bpy)32+ doped SiO2 nanoparticles

The potential controlling silver catalysis for Ru(bpy)(3)(2+) electrochemiluminescence (ECL) signal at a special potential -0.4∼1.25 V was newly developed as the new ECL signal amplification strategy for ultrasensitive protein detection. Firstly, the wheat-like deposited silver (DpAg) particles were modified on the bare glass carbon electrode (GCE) surface by cyclic voltammetry deposition to capture the primary antibodies and then bind the antigen analytes. Secondly, as a sandwich immunoreaction format, the secondary antibodies conjugated with the Ru(bpy)(3)(2+)-doped Pt (Pt@Ru) nanoparticles by the multi-sites biotin/streptavidin (SA) affinity can be captured onto the electrode surface to generate ECL signal. In the proposed Ru(bpy)(3)(2+) ECL system without any co-reactant, the detected ECL signal was amplified due to following multiple amplification strategies: (1) the ECL catalysis for Ru(bpy)(3)(2+) was performed by electro-inducing the DpAg particles to generate Ag(+) ion and controlled by the special potential. The catalyzer Ag(+) was produced near the electrode surface and reproduced by cyclic potential scan, which improved the catalytic efficiency. (2) The amount of the ECL signal probes linked to secondary antibodies were amplified by the adsorption of Pt nanoparticles and the multiple sites bridge linkage of biotin/SA. These new multiple signal amplification strategies made the proposed ECL immunosensor achieve ultrasensitive detection for model protein human IgG with a detection limit down to 3 pg mL(-1), which can be further extended to the detection of disease biomarkers.

A highly sensitive electrochemiluminescent (ECL) aptasensor was constructed using semicarbazide (Sem) as co-reaction accelerator to promote the ECL reaction rate of CdTe quantum dots (CdTe QDs) and the co-reactant of peroxydisulfate (S2O8(2-)) for boosting signal amplification. The co-reaction accelerator is a species that when it is introduced into the ECL system containing luminophore and co-reactant, it can interact with co-reactant rather than luminophore to promote the ECL reaction rate of luminophore and co-reactant; thus the ECL signal is significantly amplified in comparison with that in which only luminophore and co-reactant are present. In this work, the ECL signal probes were first fabricated by alternately assembling the Sem and Au nanoparticles (AuNPs) onto the surfaces of hollow Au nanocages (AuNCs) via Au-N bond to obtain the multilayered nanomaterials of (AuNPs-Sem)n-AuNCs for immobilizing amino-terminated detection aptamer of thrombin (TBA2). Notably, the Sem with two -NH2 terminal groups could not only serve as cross-linking reagent to assemble AuNPs and AuNCs but also act as co-reaction accelerator to enhance the ECL reaction rate of CdTe QDs and S2O8(2-) for signal amplification. With the sandwich-type format, TBA2 signal probes could be trapped on the CdTe QD-based sensing interface in the presence of thrombin (TB) to achieve a considerably enhanced ECL signal in S2O8(2-) solution. As a result, the Sem in the TBA2 signal probes could accelerate the reduction of S2O8(2-) to produce the more oxidant mediators of SO4(•-), which further boosted the production of excited states of CdTe QDs to emit light. With the employment of the novel co-reaction accelerator Sem, the proposed ECL biosensor exhibited ultrahigh sensitivity to quantify the concentration of TB from 1 × 10(-7) to 1 nM with a detection limit of 0.03 fM, which demonstrated that the co-reaction accelerator could provide a simple, efficient, and low-cost approach for signal amplification and hold great potential for other ECL biosensors construction.