Rigidifying AIEgens in covalent organic framework nanosheets for electrochemiluminescence enhancement: TABE-PZ-CON as a novel emitter for microRNA-21 detection.

Enhancing electrochemiluminescence (ECL) properties of luminophores is a hot direction in the current ECL field. Herein, we found that covalent rigidification of the aggregation-induced emission luminogens (AIEgens) TABE (TABE = tetra-(4-aldehyde-(1,1-biphenyl))ethylene) into covalent organic framework nanosheets (TABE-PZ-CON, PZ = piperazine) could result in stronger ECL emission than those of TABE aggregates and TABE monomers. We termed the interesting phenomenon "covalent rigidification-triggered electrochemiluminescence (CRT-ECL) enhancement". The superior ECL performance of TABE-PZ-CON not only because massive TABE luminogens were covalently assembled into the rigid TABE-PZ-CON network, which limited the intramolecular motions of TABE and hampered the radiationless transition, but also because the ultrathin porous TABE-PZ-CON significantly reduced the transportation distance of ions, electrons, and coreactants, which enabled the electrochemical excitation of more TABE luminogens and thus enhanced the ECL efficiency. Bearing in mind the exceptional ECL performance of TABE-PZ-CON, it was utilized as a high-efficient ECL indicator in combination with the DNA walker and duplex-specific nuclease-assisted target recycling amplification strategies to design an "off-on" ECL biosensor for the ultrasensitive assay of microRNA-21, exhibiting a favorable response range (100 aM-1 nM) with an ultralow detection limit of 17.9 aM. Overall, this work offers a valid way to inhibit the intramolecular motions of AIEgens for ECL enhancement, which gives a new vision for building high-performance AIEgen-based ECL materials, thus offering more chances for assembling hypersensitive ECL biosensors.

Highly stable Ru-complex-based metal-covalent organic frameworks as novel type of electrochemiluminescence emitters for ultrasensitive biosensing.

Developing novel types of high-performance electrochemiluminescence (ECL) emitters is of great significance for constructing ultrasensitive ECL sensors. Herein, a highly stable metal-covalent organic framework (MCOF), termed Ru-MCOF, has been devised and synthesized by employing a classic ECL luminophore, tris(4,4'-dicarboxylicacid-2,2'-bipyridyl)ruthenium(II) (Ru(dcbpy)32+), as building unit and applied as a novel ECL probe to construct an ultrasensitive ECL sensor for the first time. Impressively, the topologically ordered and porous architectures of the Ru-MCOF not only allow Ru(bpy)32+ units to precisely locate and homogeneously distribute in the skeleton via strong covalent bonds but also facilitate the transport of co-reactants and electrons/ions in channels to promote the electrochemical activation of both external and internal Ru(bpy)32+ units. All these features endow the Ru-MCOF with excellent ECL emission, high ECL efficiency, and outstanding chemical stability. As expected, the constructed ECL biosensor based on the Ru-MCOF as a high-efficiency ECL probe accomplishes the ultrasensitive detection of microRNA-155. Overall, the synthesized Ru-MCOF not only enriches the MCOF family but also displays excellent ECL performance and thus expands the application of MCOFs in bioassays. Considering the structural diversity and tailorability of MCOFs, this work opens a new horizon to design and synthesize high-performance ECL emitters, therefore paving a new way to develop highly stable and ultrasensitive ECL sensors and motivating further research on MCOFs.

Ruthenium(II) complex-grafted conductive metal-organic frameworks with conductivity- and confinement-enhanced electrochemiluminescence for ultrasensitive biosensing application.

Improving the electrochemiluminescence (ECL) performance of luminophores is an ongoing research hotspot in the ECL realm. Herein, a high-performance metal-organic framework (MOF)-based ECL material (Ru@Ni3(HITP)2, HITP = 2,3,6,7,10,11-hexaiminotriphenylene) with conductivity- and confinement-enhanced ECL was successfully constructed by using conductive MOF Ni3(HITP)2 as the carrier to graft Ru(bpydc)34- (H2bpydc = 2,2'-bipyridine-4,4'-dicarboxylic acid) into the channels of Ni3(HITP)2. Compared to Ru@Cu3(HITP)2 and Ru@Co3(HITP)2 with relatively low conductivity, the ECL intensity of Ru@Ni3(HITP)2 was prominently increased about 6.76 times and 18.8 times, respectively, which demonstrated that the increase in conductivity induced the ECL enhancement of the MOF-based ECL materials. What's more, the hydrophobic and porous Ni3(HITP)2 can not only effectively enrich the lipophilic tripropylamine (TPrA) coreactants in its channels to enhance the electrochemical oxidation efficiency of TPrA, but also provide a conductive reaction micro-environment to boost the ECL reaction between Ru(bpydc)33- intermediates and TPrA• in confined spaces, thus realizing a remarkable confinement-enhanced ECL. Considering the excellent ECL performance of Ru@Ni3(HITP)2, an ultrasensitive ECL biosensor was prepared based on the Ru@Ni3(HITP)2 ECL indicator combining an exonuclease I-aided target cycling amplification strategy for thrombin determination. The constructed ECL biosensor showcased a wide linear range from 1 fM to 1 nM with a low detection limit of 0.62 fM. Overall, the conductivity- and confinement-enhanced ECL based on Ru@Ni3(HITP)2 provided effective and feasible strategies to enhance ECL performance, which paved a promising avenue for exploring high-efficient MOF-based ECL materials and thus broadened the application scope of conductive MOFs.

In situ growth of metal-organic layer on ultrathin Ti3C2Tx MXene nanosheet boosting fast electron/ion transport for electrochemiluminescence enhancement.

Ultrathin metal-organic layers (MOLs) have attracted substantial attention in fabricating highly efficient electrochemiluminescence (ECL) materials due to their porous structure, small diffusion blockage, and short electron/ion-diffusion pathway, yet MOLs suffer from the inherent poor electrical conductivity that astricted the electrochemical activation, resulting in the unsatisfactory utilization ratio of ECL emitters. Herein, to address this limitation, we in situ hybridized Zr-based ultrathin MOL (Zr-TCBPE-MOL, H4TCBPE = 1,1,2,2-tetra(4-carboxylbiphenyl)ethylene) with the highly conductive Ti3C2Tx MXene nanosheet to obtain a unique 2D-2D hybrid nanocomposite (Zr-TCBPE-MOL/MXene). Benefiting from the above-mentioned attractive virtues of ultrathin MOLs and the superior conductivity of Ti3C2Tx MXene nanosheet, the resulting Zr-TCBPE-MOL/MXene nanocomposite permitted fast electron/ion transport across the whole framework of Zr-TCBPE-MOL/MXene, which efficiently boosted the electrochemical activation of TCBPE luminophores and thus improved the utilization ratio of luminophores to realize a remarkable ECL emission. Gratifyingly, we found that the ECL signal of Zr-TCBPE-MOL/MXene nanocomposite was greatly enhanced by around 4.1 times in contrast to that of pure Zr-TCBPE-MOL. On basis of the prominent ECL performance of Zr-TCBPE-MOL/MXene nanocomposite, a novel "off-on" ECL biosensor was proposed to sensitively analyze microRNA-141, which possessed a wide response range (100 aM-1 nM) and a low detection limit of 16.2 aM. Overall, this work puts forward a rational strategy to construct high-performance ECL materials and sheds new light on developing sensitive ECL sensing platforms.

Curved π-Conjugated Helical Carbon Frameworks: Syntheses, Structural Analyses, and Properties.

Two enantiomers with helical carbon frameworks (M-HCFa and P-HCFa) and their conformational isomers (M-HCFb and P-HCFb) have been synthesized and characterized. The single-crystal analysis revealed the novel structures in which three propeller blades spiro-fused on two central benzene rings. The optical properties were further investigated, and stable bipolar electrochemiluminescence emissions were discovered for the first time existing in helical carbon frameworks, which provide new insights into the future development of high-performance molecular luminescent devices.

Pyrene-Based Hydrogen-Bonded Organic Frameworks as New Emitters with Porosity- and Aggregation-Induced Enhanced Electrochemiluminescence for Ultrasensitive MicroRNA Assay.

Exploring new electrochemiluminescence (ECL) luminophores with strong ECL emission is highly desirable for developing ultrasensitive ECL sensors. Herein, a pyrene-based hydrogen-bonded organic framework (Py-HOF) featuring prominent ECL performance was prepared by utilizing 1,3,6,8-tetrakis(p-benzoic acid) pyrene (H4TBAPy) with an aggregation-induced enhanced emission (AIEE) property as a building block, exhibiting a stronger ECL emission than those of H4TBAPy monomers, H4TBAPy aggregates, the low-porosity Py-HOF-210 °C and Py-HOF-180 °C. We have coined the term "the porosity- and aggregation-induced enhanced ECL (PAIE-ECL)" for this intriguing phenomenon. The Py-HOF displayed superb and stable ECL intensity, not only because the luminophore H4TBAPy was assembled into the Py-HOF via four pairs of O-H···O hydrogen bonds, which constrained the intramolecular movements to reduce nonradiative transition, but also because the H4TBAPy in Py-HOF was stacked in a slipped face-to-face mode to form J-aggregates that benefited the ECL enhancement. Furthermore, the high porosity of Py-HOF allowed the enrichment of coreactants and facilitated the migration of ions, electrons, and coreactants, which made it possible for the inner and outer H4TBAPy to be electrochemically excited. Considering the remarkable ECL performance, Py-HOF was first employed as an ECL probe combined with a 3D DNA nanomachine amplification strategy to assemble a hypersensitive "on-off" ECL sensor for the microRNA-141 assay, presenting a satisfactory linear range (100 aM to 1 nM) with a detection limit of 14.4 aM. The PAIE-ECL manifested by Py-HOF provided a bright avenue for the design and synthesis of outstanding HOF-based ECL materials and offered new opportunities for the development of ECL biosensors with excellent sensitivity.

Electrochemiluminescence enhanced by isolating ACQphores in pyrene-based porous organic polymer: A novel ECL emitter for the construction of biosensing platform.

In this work, a pyrene-based porous organic polymer (Py-POP) with strong electrochemiluminescence (ECL) emission was synthesized and used to fabricate an ECL sensor for the extra-sensitive detection of microRNA-155. The ECL intensity of the Py-POP prepared by tetra(p-aminophenyl)methane (TAPM) and 1,3,6,8-tetrakis(4-formylphenyl)pyrene (TFPPy) was about 3.1 times that of TFPPy aggregates, which was primarily ascribed to the elimination of the effect of aggregation-caused quenching (ACQ) by increasing the distance between ACQ luminophores (pyrene cores) in Py-POP. Meanwhile, the strong covalent connections between 1,3,6,8-tetraphenylpyrene (TPPy) and tetraphenylmethane (TPM) units in the rigid framework of Py-POP could partly block the intramolecular motion of TPPy and TPM, which reduced the non-radiative decay and thus further improved the ECL emission. Furthermore, the hydrophobic porous structure of Py-POP was beneficial to the enrichment of lipophilic tripropylamine (TPrA) coreactants in pores of Py-POP, which greatly shortened the electron migration distance between TPrA coreactants and pyrene luminophores on the pore walls of Py-POP, thereby also enhancing the ECL intensity. By using the Py-POP as a new ECL tag and with the help of the strand displacement processes and target recycling, the fabricated ECL biosensor had a sensitive response for microRNA-155 from 1 fM to 1 nM and a detection limit of 0.326 fM. Overall, this work provided a new and feasible strategy to surmount the ACQ effect for enhancing ECL emission, which not only paved a new way to exploit high-performance ECL materials for fabricating extra-sensitive sensors but also broadened the application of POPs in bioanalysis and ECL fields.

Conductive Covalent Organic Frameworks with Conductivity- and Pre-Reduction-Enhanced Electrochemiluminescence for Ultrasensitive Biosensor Construction.

Covalent organic frameworks (COFs) have attracted widespread attention in the electrochemiluminescence (ECL) field owing to their high load capacity of ECL luminophores and porous structures, but their ECL performance is still limited by the intrinsic poor conductivity (generally <10-8 S m-1). To address this shortcoming, we used 2,3,6,7,10,11-hexaaminotriphenylene (HATP) and 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) to synthesize a conductive COF (HHTP-HATP-COF, conductivity = 3.11 × 10-4 S m-1). Compared with HATP, HHTP, and low-conductive HHTP-DABZ-COF, HHTP-HATP-COF exhibited superior ECL performance, not only because HHTP-HATP-COF possessed massive ECL luminophores but also because its conductive porous framework accelerated charge transport in the whole framework and improved the utilization ratio of ECL luminophores. More interestingly, the ECL intensity of the HHTP-HATP-COF/S2O82- system was further improved after pre-reduction electrolysis due to the accumulation of HHTP-HATP-COF cation radicals. The experimental results showed that the ECL intensity of the HHTP-HATP-COF/S2O82- system after pre-reduction was about 1.64-, 3.96-, 6.88-, and 8.09-fold higher than those of HHTP-HATP-COF/S2O82-, HHTP-DABZ-COF/S2O82-, HHTP/S2O82-, and HATP/S2O82- systems, respectively. Considering the superior ECL property of the HHTP-HATP-COF/S2O82- system after pre-reduction, it was used as a high-efficient ECL beacon together with an aptamer/protein proximity binding-induced three-dimensional bipedal DNA walker to construct an ultrasensitive biosensor for thrombin detection, which displayed broad linearity (100 aM to 1 nM) with a detection limit of 62.1 aM. Overall, the work offered effective ways to increase ECL performance by the enhancement of conductivity and by the pre-reduction, proposing new ideas to design high-efficiency COF-based ECL materials and endowing conductive COFs with ECL biosensor application for the first time.

Overcoming Aggregation-Induced Quenching by Metal-Organic Framework for Electrochemiluminescence (ECL) Enhancement: Zn-PTC as a New ECL Emitter for Ultrasensitive MicroRNAs Detection.

Polycyclic aromatic hydrocarbons (PAHs) as traditional electrochemiluminescence (ECL) luminophores have been widely applied in the analysis field. However, their ECL intensity and efficiency are still limited due to the aggregation-induced quenching (ACQ) effect of PAHs. Hence, to overcome this limitation, we put forward a new strategy to increase the ECL intensity and efficiency by eliminating the ACQ effect of PAHs through the coordinative immobilization of PAHs within metal-organic frameworks (MOFs). As anticipated, the proof-of-concept experiment indicated that the coordinative immobilization of perylene-3,4,9,10-tetracarboxylate (PTC) into a Zn-PTC MOF could distinctly increase the ECL intensity and efficiency compared with H4PTC aggregates and H4PTC monomers. The reason for the ECL enhancement of Zn-PTC was that the immobilization of PTC within the MOF effectively amplified the distance between perylene rings of PTC ligands and thus eliminated the ACQ effect. Furthermore, the PTC into Zn-PTC was stacked in an edge-to-edge mode to form J-aggregation, which was also conducive to ECL enhancement. On the basis of the excellent ECL performance, we utilized Zn-PTC as a new ECL emitter combined with exonuclease III-stimulated target cycling and DNAzyme-assisted cycling dual amplification strategies to construct an ECL sensor for microRNA-21 detection, which had a wide signal response (100 aM to 100 pM) with a detection limit of 29.5 aM. Overall, this work represents a new and convenient method to overcome the ACQ effect of PAHs and boost the ECL performance, which opens a new horizon for developing high-performance ECL materials, thus offering more opportunities for building highly sensitive ECL biosensors.

Crystallization-Induced Enhanced Electrochemiluminescence from Tetraphenyl Alkene Nanocrystals for Ultrasensitive Sensing.

Organic materials with diverse structures and brilliant glowing colors have been attracting extensive attention in optical electronic devices and electrochemiluminescence (ECL) fields and are currently faced with the issue of low ECL efficiency. Herein, a series of tetraphenyl alkene nanocrystals (TPA NCs) with an ordered molecular structure were synthesized to explore regularities in the crystallization-induced enhanced (CIE) ECL emission effects by altering the number and position of vinyl on the backbone of TPA molecules. Among those TPA NCs, tetraphenyl-1,3-butadiene (TPB) NCs exhibit the brightest ECL emission via a coreactant pathway, with the relative ECL efficiency of up to 31.53% versus the standard [Ru(bpy)3]2+/TEA system, which is thousands of times higher than that of free TPB molecules. The high ECL efficiency of TPB NCs originates from the effective electron transfer of unique J-aggregates on the a axis of the nanocrystals to notably promote radiative transition and the restriction on the free rotation of TPB molecules to further suppress the nonradiative transition, which has exhibited great potential in ultrasensitive biosensing, efficient light-emitting devices, and clear ECL imaging fields. As a proof of concept, since dopamine (DA) can form benzoquinone species by electrochemical oxidation to realize intermediate radical quenching and excited-state quenching on the TPB NCs/TEA system, the TPB NCs with the CIE ECL effect are used to construct an ultrasensitive ECL-sensing platform for the determination of DA with a lower detection limit of 3.1 nM.

Highly efficient electrochemiluminescence resonance energy transfer material constructed from an AIEgen-based 2D ultrathin metal-organic layer for thrombin detection.

A facile strategy to design a highly efficient electrochemiluminescence resonance energy transfer (ECL-RET) system was proposed by using an AIEgen-based 2D ultrathin metal-organic layer (MOL) to coordinatively immobilize energy donors and acceptors simultaneously, in which the distance between adjacent donor-acceptor pairs was precise and short for obtaining high ECL-RET efficiency.

Ruthenium(II) Complex-Grafted Hollow Hierarchical Metal-Organic Frameworks with Superior Electrochemiluminescence Performance for Sensitive Assay of Thrombin.

Metal-organic frameworks (MOFs) with porous structures exhibit favorable promise in synthesizing high-performance electrochemiluminescence (ECL) materials, yet their micropores and narrow channels not only restrict the loading capacity of ECL luminophores but also constrain the diffusion of coreactants, ions, and electrons. Hence, we developed a new and simple hydrothermal etching strategy for the fabrication of a hollow hierarchical MOF (HH-UiO-66-NH2) with a hierarchical-pore shell, which was employed as a carrier to graft Ru(bpy)2(mcpbpy)2+ (bpy = 2,2'-bipyridine, mcpbpy = 4-(4'-methyl-[2,2'-bipyridin]-4-yl) butanoic acid) onto the coordinatively unsaturated Zr6 nodes of HH-UiO-66-NH2, creating the Ru-complex-grafted HH-UiO-66-NH2 (abbreviated as HH-Ru-UiO-66-NH2). Impressively, the HH-Ru-UiO-66-NH2 presented brilliant ECL emission. On the one hand, the HH-UiO-66-NH2 with a hierarchical-pore shell and hollow cavity was conducive to immobilize the Ru(bpy)2(mcpbpy)2+ of large steric hindrance into the interior of the MOF, markedly improving the load number of luminophores. On the other hand, the hierarchical-pore shell of HH-UiO-66-NH2 permitted fast diffusion of coreactants, ions, and electrons that facilitated the excitation of more grafted luminophores and greatly enhanced the utilization ratio of ECL luminophores. Inspired by the superior ECL performance of HH-Ru-UiO-66-NH2, an ECL sensing platform was constructed on the basis of HH-Ru-UiO-66-NH2 as an ECL beacon combining catalytic hairpin assembly as a signal amplification strategy, showing excellent selectivity and high sensitivity for thrombin determination. This proof-of-concept work proposed a simple and feasible hydrothermal etching strategy to construct hollow hierarchical MOFs that served as carrier materials to immobilize ECL luminophores, providing significant inspiration to develop highly efficient ECL materials and endowing hollow hierarchical MOFs with ECL sensing applications for the first time.

Highly Stable Covalent Organic Framework Nanosheets as a New Generation of Electrochemiluminescence Emitters for Ultrasensitive MicroRNA Detection.

A pyrene-based sp2 carbon-conjugated covalent organic framework (COF) nanosheet (Py-sp2c-CON) with strong and stable electrochemiluminescence (ECL) emission was constructed by C═C polycondensation of tetrakis(4-formylphenyl)pyrene (TFPPy) and 2,2'-(1,4-phenylene)diacetonitrile, which was employed as a highly efficient ECL emitter to fabricate an ECL biosensor for the first time. The Py-sp2c-CON exhibited higher ECL intensity and efficiency than those of TFPPy, bulk Py-sp2c-COF, and imine-linked pyrene COF, not only because the pyrene luminophores and aggregation-induced emissive luminogens (cyano-substituted phenylenevinylene) were topologically linked into Py-sp2c-CON, which greatly increased the immobilization amount of luminophores and decreased the aggregation-caused quenching effect and nonradiative transition but also because the porous ultrathin structure of Py-sp2c-CON effectively shortened transport distances of an electron, ion, and co-reactant (S2O82-), which made more ECL luminophores be activated and thus efficiently increased the utilization ratio of luminophores. More interestingly, when Bu4NPF6 was introduced into the Py-sp2c-CON/S2O82- system as a co-reaction accelerator, the ECL signal of Py-sp2c-CON was further amplified. As expected, the average ECL intensity of the Py-sp2c-CON/S2O82-/Bu4NPF6 system was about 2.03, 5.76, 24.31, and 190.33-fold higher than those of Py-sp2c-CON/S2O82-, Py-sp2c-COF/S2O82-, TFPPy/S2O82,- and imine-linked pyrene COF/S2O82- systems. Considering these advantages, the Py-sp2c-CON/S2O82-/Bu4NPF6 system was employed to prepare an ECL biosensor for microRNA-21 detection, which exhibited a broad linear response (100 aM to 1 nM) and a low detection limit (46 aM). Overall, this work demonstrated that sp2 carbon CONs can be directly used as a high-performance ECL emitter, thus expanding the application scope of COFs and opening a new horizon to develop new types of ECL emitters.

Two Birds with One Stone: Surface Functionalization and Delamination of Multilayered Ti3C2Tx MXene by Grafting a Ruthenium(II) Complex to Achieve Conductivity-Enhanced Electrochemiluminescence.

Two-dimensional (2D) nanosheets have captured significant attention in constructing highly efficient electrochemiluminescent (ECL) materials because their high surface area and fully exposed postmodification sites could greatly increase the loading amount of luminophores. However, traditional 2D nanosheets as carriers exhibited natively poor electrical conductivity that restricted the electrochemical activation and the utilization ratio of ECL luminophores. Herein, to overcome this drawback, we utilized conductive 2D Ti3C2Tx MXene nanosheets as carriers to graft Ru(bpy)2(mcpbpy)2+ (bpy = 2,2'-bipyridine, mcpbpy = 4-(4'-methyl-[2,2'-bipyridin]-4-yl) butanoic acid) via a dehydrative condensation reaction and electrostatic interaction. Interestingly, Ru(bpy)2(mcpbpy)2+ played the role of "two birds with one stone", where Ru(bpy)2(mcpbpy)2+ acted as both an ECL luminophore and an intercalation molecule to achieve surface functionalization and delamination of multilayered Ti3C2Tx successfully, obtaining 2D ultrathin Ru-complex-grafted MXene nanosheets (Ru@MXene). Owing to the high load capacity and superior electrical conductivity of an ultrathin 2D MXene nanosheet, the obtained Ru@MXene exhibited a superb ECL emission. As expected, compared with the nonconductive 2D ultrathin metal-organic layers (MOLs) as carriers to graft Ru(bpy)2(mcpbpy)2+, the ECL intensity and ECL efficiency of Ru@MXene presented about 5-fold and 1.7-fold enhancement, respectively. Considering these advantages, Ru@MXene was applied to construct an ECL sensor for ultrasensitive determination of mucin 1 (MUC1), which displayed superb sensitivity (100 ag/mL to 10 ng/mL) with a low detection limit of 26.9 ag/mL. Overall, the conductivity-enhanced ECL based on Ru@MXene opened a fire-new chapter to develop splendent performance ECL emitters and shed new light on the application potential of conductive materials in the bioanalysis field.

One-Pot Synthesis of 2,4-Diacyl Thiophenes from α-Oxo Ketene Dithioacetals and Propargylic Alcohols.

Although thiophenes having various functionalities are the basic structural units in numerous bioactive compounds and optoelectronic materials, synthetic routes to acylated thiophenes from aliphatic sulfur-containing starting materials are still rare. In particular, there have been no reports concerning the straightforward synthesis of 2,4-diacylthiophenes from alkynes. Herein, we describe a highly efficient and metal-free three-step one-pot synthetic approach to tetrasubstituted 2,4-diacylthiophenes from propargylic alcohols and α-oxo ketene dithioacetals. This research features a relay catalysis system that integrates Brønsted acid-catalyzed propargylation, molecular iodine-mediated electrophilic cyclization, and visible light-induced deiodinative oxygenation. The 2,4-diacylthiophenes serving as the key starting materials are readily synthesized, enabling facile construction of analogues of related biologically active compounds and the modular assembly of tetrasubstituted thienothiophenes.

Restriction of intramolecular motions (RIM) by metal-organic frameworks for electrochemiluminescence enhancement:2D Zr12-adb nanoplate as a novel ECL tag for the construction of biosensing platform.

Herein, a new phenomenon of enhanced electrochemiluminescence (ECL) emission by restricting intramolecular motion in the 2D ultra-thin Zr12-adb (adb = 9,10-anthracene dibenzoate) metal-organic framework (MOF) nanoplate was discovered for the first time. The coordination immobilization of adb in porous ultra-thin Zr12-adb nanoplate endowed the Zr12-adb excellent ECL performance, including stronger ECL signal and higher ECL efficiency relative to those of H2adb monomers and H2adb aggregates. In the 2D Zr12-adb nanoplate, the bridging ligand adb was stretched and fixed between two Zr12 clusters, which restricted intramolecular rotations and suppressed unnecessary energy loss caused by self-rotation, thereby remarkably improved the ECL intensity and efficiency. More importantly, the porous ultra-thin structure of Zr12-adb MOF nanoplate not only allowed the coreactants to diffuse into the MOF interior, making both internal and external adb be excited, but also shortened the migration distance of electrons, ions, coreactants and coreactant intermediates, which further improved the ECL efficiency of Zr12-adb and overcame the shortcoming of H2adb aggregates in which the internal luminophores were not easily excited. Regarding the excellent ECL properties above, Zr12-adb nanoplate was selected as a new ECL emitter incorporated with the bipedal walking molecular machine together to fabricate a biosensor for sensitive detection of mucin 1. The enhanced ECL by restriction of intramolecular motions in MOFs provided a new pathway to improve ECL intensity and efficiency, which lighted up a lamp for the design and manufacture of high-performance ECL materials based on MOFs, thus offering new opportunities to develop ultrasensitive ECL biosensors.

An AIEgen-based 2D ultrathin metal-organic layer as an electrochemiluminescence platform for ultrasensitive biosensing of carcinoembryonic antigen.

In this work, a novel two-dimensional (2D) ultrathin metal-organic layer (MOL) based on the aggregation-induced emission (AIE) ligand H4ETTC (H4ETTC = 4',4''',4''''',4'''''''-(ethene-1,1,2,2-tetrayl)tetrakis(([1,1'-biphenyl]-4-carboxylic acid))) was developed and used to construct a novel electrochemiluminescence (ECL) aptasensor for ultrasensitive detection of carcinoembryonic antigen (CEA). The newly synthesized AIE luminogen (AIEgen)-based MOL (Hf-ETTC-MOL) yielded a higher ECL intensity and efficiency than did H4ETTC monomers, H4ETTC aggregates and 3D bulk Hf-ETTC-MOF. This improvement occurred not only because the ETTC ligands were coordinatively immobilized in a rigid MOL matrix, which restricted the intramolecular free rotation and vibration of these ligands and then reduced the non-radiative transition, but also because the porous ultrathin 2D MOL greatly shortened the transport distances of ions, electrons, coreactant (triethylamine, TEA) and coreactant intermediates (TEA˙ and TEA˙+), which made more ETTC luminophores able to be excited and yielded a high ECL efficiency. On the basis of using the Hf-ETTC-MOL as a novel ECL emitter and rolling circle amplification (RCA) as a signal amplification strategy, the constructed ECL aptasensor exhibited a linear range from 1 fg mL-1 to 1 ng mL-1 with a detection limit of 0.63 fg mL-1. This work has opened up new prospects for developing novel ECL materials and is expected to lead to increased interest in using AIEgen-based MOLs for ECL sensing.

Matrix Coordination-Induced Electrochemiluminescence Enhancement of Tetraphenylethylene-Based Hafnium Metal-Organic Framework: An Electrochemiluminescence Chromophore for Ultrasensitive Electrochemiluminescence Sensor Construction.

Here, we discovered that rigidifying the tetraphenylethylene (TPE)-based ligand H4TCBPE (H4TCBPE = 1,1,2,2-tetra(4-carboxylbiphenyl)ethylene) into Hf-based metal-organic framework (Hf-TCBPE) could lead to a stronger electrochemiluminescence (ECL) emission in comparison to H4TCBPE aggregates and H4TCBPE monomers. Due to the lack of close-packed TCBPE chromophores in Hf-TCBPE, which was required for aggregation-induced ECL (AI-ECL) enhancement, we defined this unprecedented phenomenon as matrix coordination-induced ECL (MCI-ECL) enhancement. The strong ECL intensity of Hf-TCBPE not only originated from the fixation of the TCBPE ligand between Hf6 clusters that restricted the intramolecular free motions of TCBPE and suppressed the nonradiative relaxation but also stemmed from the high porosity of Hf-TCBPE that rendered both internal and external TCBPE chromophores able to be excited. Considering the unique ECL characteristic of Hf-TCBPE, we combined the new ECL indicator of Hf-TCBPE as well as the phosphate-terminal ferrocene (Fc)-labeled hairpin DNA (Fc-HP3) aptamer together as a signal probe (Hf-TCBPE/Fc-HP3), which was employed to construct a novel "off-on" ECL sensor for ultrasensitive mucin 1 (MUC1) detection with the assistance of the exonuclease III (Exo III)-assisted recycling amplification strategy. As expected, the ECL sensor displayed a desirable linear response range from 1 fg/mL to 1 ng/mL and the detection limit down to 0.49 fg/mL. The MCI-ECL enhancement demonstrated by the Hf-TCBPE developed a new and promising strategy to design and synthesize high-performance metal-organic framework (MOF)-based ECL materials for constructing ultrasensitive ECL sensors.

A highly sensitive self-enhanced aptasensor based on a stable ultrathin 2D metal-organic layer with outstanding electrochemiluminescence property.

3D bulk metal-organic frameworks (MOFs) have received growing interest in electrochemiluminescence (ECL) assays because they can provide a high specific surface for loading a large quantity of ECL luminophores, but the ECL efficiency of bulk MOFs is still low since some interior luminophores are difficult to be excited. Herein, an ultrathin 2D metal-organic layer (MOL) for grafting self-enhanced ruthenium complexes (Ru-l-Lys) was first synthesized to greatly increase the utilization ratio of luminophores. Compared with 3D bulk MOFs, ultrathin 2D MOL could provide more accessible postmodification sites for grafting the Ru-l-Lys complexes; the self-enhanced Ru-l-Lys complexes on MOL were easily excited by electrons due to the shortened ion/electron-transport distance and the removal of diffusion barriers. Furthermore, the electron transfer path between the Ru(ii) luminophore and coreactant (l-Lys) was shortened and the energy loss of the luminophores decreased, which significantly improved the ECL efficiency. As expected, our work manifested that the Zr-MOL's loading amount of Ru-l-Lys was about 1.23-fold higher than that of a 3D bulk Zr-MOF, and the ECL intensity and efficiency of Ru-l-Lys-Zr-MOL were around 93.45-fold and 1.64-fold higher than those of control Ru-l-Lys-Zr-MOF, respectively. Considering all of these merits, in this work, we utilized the prepared Ru-l-Lys-Zr-MOL as a highly efficient ECL indicator for the first time to fabricate a highly sensitive self-enhanced aptasensor for mucin 1 (MUC1) determination. The proposed aptasensor showed high sensitivity with a linear range from 1 fg mL-1 to 100 pg mL-1 with a detection limit of 0.72 fg mL-1; it also exhibited excellent specificity and stability. It is noteworthy that this work not only provides a new strategy to design and synthesize high-performance ECL materials, but also opens a new way to develop ultrasensitive ECL sensors for bioanalysis.

Highly stable Ru-complex-grafted 2D metal-organic layer with superior electrochemiluminescent efficiency as a sensing platform for simple and ultrasensitive detection of mucin 1.

This work utilized ultrathin metal-organic layer (MOL) to immobilize luminophores for effectively shortening the ion/electron-transport distance and relieving the diffusional constraints of ion/electron, which greatly enhanced the ECL efficiency and intensity. Moreover, the MOL's immobilization amount of luminophores should be higher than these of bulk MOFs because MOLs possess more accessible postmodification sites for the luminophores with minimal diffusion barriers. As expected, our proof-of-concept experiment indicated that the Hf-MOL's loading number of Ru(bpy)2(mcpbpy)2+ was about 1.74 times that of a 3D mesoporous MOF (PCN-777), and the ECL efficiency and intensity of PEI@Ru-Hf-MOL were around 1.27 times and 14.5 times those of PEI@Ru-PCN-777, respectively. In view of these merits, this work utilized the prepared PEI@Ru-Hf-MOL as a highly efficient sensing platform for simple, rapid and sensitive detection of mucin 1, which exhibited a broad linearity from 1 fg/mL to 10 ng/mL and a low detection limit of 0.48 fg/mL. This work provided a practicable strategy to develop high-performance ECL materials, and therefore opened up a new avenue to design ultrasensitive ECL biosensors, which expanded the application potential of MOLs in ECL assays.