Photoexcited Ru single-atomic sites for efficient biomimetic redox catalysis.

The unsatisfactory catalytic activity of nanozymes owing to their inefficient electron transfer (ET) is the major challenge in biomimetic catalysis-related biomedical applications. Inspired by the photoelectron transfers in natural photoenzymes, we herein report a photonanozyme of single-atom Ru anchored on metal-organic frameworks (UiO-67-Ru) for achieving photoenhanced peroxidase (POD)-like activity. We demonstrate that the atomically dispersed Ru sites can realize high photoelectric conversion efficiency, superior POD-like activity (7.0-fold photoactivity enhancement relative to that of UiO-67), and good catalytic specificity. Both in situ experiments and theoretical calculations reveal that photoelectrons follow the cofactor-mediated ET process of enzymes to promote the production of active intermediates and the release of products, demonstrating more favorable thermodynamics and kinetics in H2O2 reduction. Taking advantage of the unique interaction of the Zr-O-P bond, we establish a UiO-67-Ru-based immunoassay platform for the photoenhanced detection of organophosphorus pesticides.

Nanozyme Metabolism Controls Air Pollution over an Atomic Potassium Cyano Site.

Increasing threats of air pollution prompt the design of air purification systems. As a promising initiative defense strategy, nanocatalysts are integrated to catalyze the detoxification of specific pollutants. However, it remains a grand challenge to tailor versatile nanocatalysts to cope with diverse pollutants in practice. Here, we report a nanozyme metabolism system to realize broad-spectrum protection from air pollution. Atomic K-modified carbon nitride featuring flavin oxidase-like and peroxidase-like activities was synthesized to initiate nanozyme metabolism. In situ experiments and theoretical investigations collectively show that K sites optimize the geometric and electronic structure of cyano sites for both enzyme-like activities. As a proof of concept, the nanozyme metabolism was applied to the mask against volatile organic compounds, persistent organic pollutants, reactive oxygen species, bacteria, and so on. Our finding provides a thought to tackle global air pollution and deepens the understanding of nanozyme metabolism.

Regulating Reactive Oxygen Species over M-N-C Single-Atom Catalysts for Potential-Resolved Electrochemiluminescence.

The development of potential-resolved electrochemiluminescence (ECL) systems with dual emitting signals holds great promise for accurate and reliable determination in complex samples. However, the practical application of such systems is hindered by the inevitable mutual interaction and mismatch between different luminophores or coreactants. In this work, for the first time, by precisely tuning the oxygen reduction performance of M-N-C single-atom catalysts (SACs), we present a dual potential-resolved luminol ECL system employing endogenous dissolved O2 as a coreactant. Using advanced in situ monitoring and theoretical calculations, we elucidate the intricate mechanism involving the selective and efficient activation of dissolved O2 through central metal species modulation. This modulation leads to the controlled generation of hydroxyl radical (·OH) and superoxide radical (O2·-), which subsequently trigger cathodic and anodic luminol ECL emission, respectively. The well-designed Cu-N-C SACs, with their moderate oxophilicity, enable the simultaneous generation of ·OH and O2·-, thereby facilitating dual potential-resolved ECL. As a proof of concept, we employed the principal component analysis statistical method to differentiate antibiotics based on the output of the dual-potential ECL signals. This work establishes a new avenue for constructing a potential-resolved ECL platform based on a single luminophore and coreactant through precise regulation of active intermediates.

Potential-Resolved Ratiometric Aptasensor for Sensitive Acetamiprid Analysis Based on Coreactant-free Electrochemiluminescence Luminophores of Gd-MOF and "Light Switch" Molecule of [Ru(bpy)2dppz]2.

For conventional potential-resolved ratiometric electrochemiluminescence (ECL) systems, the introduction of multiplex coreactants is imperative. However, the undesirable interactions between different coreactants inevitably affect analytical accuracy and sensitivity. Herein, through the coordination of aggregation-induced emission ligands with gadolinium cations, the self-luminescent metal-organic framework (Gd-MOF) is prepared and serves as a novel coreactant-free anodic ECL emitter. By the intercalation of [Ru(bpy)2dppz]2+ with light switch effect into DNA duplex, one high-efficiency cathodic ECL probe is obtained using K2S2O8 as a coreactant. In the presence of acetamiprid, the strong affinity between the target and its aptamer induces the release of [Ru(bpy)2dppz]2+, resulting in a decreasing cathode signal and an increasing anode signal owing to the ECL resonance energy transfer from Gd-MOF to [Ru(bpy)2dppz]2+. In this way, an efficient dual-signal ECL aptasensor is constructed for the ratiometric analysis of acetamiprid, exhibiting a remarkably low detection limit of 0.033 pM. Strikingly, by using only one exogenous coreactant, the cross interference from multiple coreactants can be eliminated, thus improving the detection accuracy. The developed high-performance ECL sensing platform is successfully applied to monitor the residual level of acetamiprid in real samples, demonstrating its potential application in the field of food security.

A Controlled Release Aptasensor Utilizing AIE-Active MOFs as High-Efficiency ECL Nanoprobe for the Sensitive Detection of Adenosine Triphosphate.

Improving the sensitivity in electrochemiluminescence (ECL) detection systems necessitates the integration of robust ECL luminophores and efficient signal transduction. In this study, we report a novel ECL nanoprobe (Zr-MOF) that exhibits strong and stable emission by incorporating aggregation-induced emission ligands into Zr-based metal-organic frameworks (MOFs). Meanwhile, we designed a high-performance signal modulator through the implementation of a well-designed controlled release system with a self-on/off function. ZnS quantum dots (QDs) encapsulated within the cavities of aminated mesoporous silica nanoparticles (NH2-SiO2) serve as the ECL quenchers, while adenosine triphosphate (ATP) aptamers adsorbed on the surface of NH2-SiO2 through electrostatic interaction act as "gatekeepers." Based on the target-triggered ECL resonance energy transfer between Zr-MOF and ZnS QDs, we establish a coreactant-free ECL aptasensor for the sensitive detection of ATP, achieving an impressive low detection limit of 0.033 nM. This study not only demonstrates the successful combination of ECL with controlled release strategies but also opens new avenues for developing highly efficient MOFs-based ECL systems.

Improving Interface Matching in MOF-on-MOF S-Scheme Heterojunction through π-π Conjugation for Boosting Photoelectric Response.

Accelerating the migration of interfacial carriers in a heterojunction is of paramount importance for driving high-performance photoelectric responses. However, the inferior contact area and large resistance at the interface limit the eventual photoelectric performance. Herein, we fabricated an S-scheme heterojunction involving a 2D/2D dual-metalloporphyrin metal-organic framework with metal-center-regulated CuTCPP(Cu)/CuTCPP(Fe) through electrostatic self-assembly. The ultrathin nanosheet-like architectures reduce the carrier migration distance, while the similar porphyrin backbones promote reasonable interface matching through π-π conjugation, thereby inhibiting the recombination of photogenerated carriers. Furthermore, the metal-center-regulated S-scheme band alignments create a giant built-in electric field, which provides a huge driving force for efficient carrier separation and migration. Coupling with the biomimetic catalytic activity of CuTCPP(Fe), the resultant heterojunction was utilized to construct photoelectrochemical uric acid biosensors. This work provides a general strategy to enhance photoelectric responses by engineering the interfacial structure of heterojunctions.

Anisotropic Dual S-Scheme Heterojunctions Mimic Natural Photosynthetic System for Boosting Photoelectric Response.

The design of heterojunctions that mimic natural photosynthetic systems holds great promise for enhancing photoelectric response. However, the limited interfacial space charge layer (SCL) often fails to provide sufficient driving force for the directional migration of inner charge carriers. Drawing inspiration from the electron transport chain (ETC) in natural photosynthesis system, we developed a novel anisotropic dual S-scheme heterojunction artificial photosynthetic system composed of Bi2O3-BiOBr-AgI for the first time, with Bi2O3 and AgI selectively distributed along the bicrystal facets of BiOBr. Compared to traditional semiconductors, the anisotropic carrier migration in BiOBr overcomes the recombination resulting from thermodynamic diffusion, thereby establishing a potential ETC for the directional migration of inner charge carriers. Importantly, this pioneering bioinspired design overcomes the limitations imposed by the limited distribution of SCL in heterojunctions, resulting in a remarkable 55-fold enhancement in photoelectric performance. Leveraging the etching of thiols on Ag-based materials, this dual S-scheme heterojunction is further employed in the construction of photoelectrochemical sensors for the detection of acetylcholinesterase and organophosphorus pesticides.

Harmonizing Enzyme-like Cofactors to Boost Nanozyme Catalysis.

Engineering isolated metal sites resembling the primary coordination sphere of metallocofactors enables atomically dispersed materials as promising nanozymes. However, most existing nanozymes primarily focus on replicating specific metallocofactors while neglecting other supporting cofactors within active pockets, leading to reduced electron transfer (ET) efficiency and thus inferior catalytic performances. Herein, we report a metal-organic framework UiO-67 nanozyme with atomically dispersed iron sites, which involves multiple tailored enzyme-like nanocofactors that synergistically drive the ET process for enhanced peroxidase-like catalysis. Among them, the linker-coupled atomic iron site plays a critical role in substrate activation, while bare linkers and zirconia nodes facilitate the ET efficiency of intermediates. The synergy of three nanocofactors results in a 4.29-fold enhancement compared with the single effort of isolated metal site-based nanocofactor, holding promise in immunoassay for sensitive detection of chlorpyrifos. This finding opens a new way for designing high-performance nanozymes by harmonizing various nanocofactors at the atomic and molecular scale.

Horseradish Peroxidase Immobilized in Metal Aerogels Boosts Electron Transfer and an Interfacial Reaction for Photoelectrochemical Immunoassay.

Photoelectrochemical (PEC) enzymatic biosensors have attracted widespread attention for their specificity and sensitivity, but the charge migration between an enzyme and a semiconductor remains uncertain. In this work, horseradish peroxidase (HRP) was successfully immobilized on ionic liquid-functioned Cu@Cu2O (IL-Cu@Cu2O) aerogels to boost charge transfer and an interfacial redox reaction. The photogenerated electrons flow from the conduction band of Cu2O to HRP under the assistance of Cu and are subsequently captured by [Fe(CN)6]3- in the electrolyte, which boosts the PEC response. The improved interfacial catalytic ability after the immobilization of HRP is proved by the enhanced redox ability under light irradiation. Benefiting from the excellent PEC activity and catalysis reaction of IL-Cu@Cu2O@HRP, an immunoassay platform was constructed for sensing prostate-specific antigens, which presents a wide detection range and a low limit of detection. An in-depth understanding of the direct electronic communication between a photoactive material and an enzyme for boosted charge transfer and interfacial catalysis provides a new view for the design of advanced PEC sensing platforms.

Iron Single-Atom Catalyst-Enabled Peroxydisulfate Activation Enhances Cathodic Electrochemiluminescence of Tris(bipyridine)ruthenium(II).

The tris(bipyridine)ruthenium(II) (Ru(bpy)32+)-tripropylamine anodic electrochemiluminescence (ECL) system has been widely applied in commercial bioanalysis. However, the presence of amine compounds in the biological environment results in unavoidable anodic interference signals, which hinder further extensive use of the system. In contrast, the cathodic Ru(bpy)32+ ECL system can overcome these limitations. The Ru(bpy)32+/peroxydisulfate (S2O82-, PDS) ECL system has been extensively employed due to its ability to produce a sulfate radical anion (SO4•-) with strong oxidation ability, which enhances the ECL signal. However, the symmetrical molecular structure of PDS makes it challenging to be activated and causes low luminescence efficiency. To address this issue, we propose an efficient Ru(bpy)32+-based ternary ECL system that uses the iron-nitrogen-carbon single-atom catalyst (Fe-N-C SAC) as an advanced accelerator. Fe-N-C SAC can efficiently activate PDS into reactive oxygen species at a lower voltage, which significantly boosts the cathodic ECL emission of Ru(bpy)32+. Benefiting from the outstanding catalytic activity of Fe-N-C SAC, we successfully established an ECL biosensor that detects alkaline phosphatase activity with high sensitivity, demonstrating the feasibility of practical application.

Photothermal-Switched Single-Atom Nanozyme Specificity for Pretreatment and Sensing.

Various applications lead to the requirement of nanozymes with either specific activity or multiple enzyme-like activities. To this end, intelligent nanozymes with freely switching specificity abilities hold great promise to adapt to complicated and changeable practical conditions. Herein, a nitrogen-doped carbon-supported copper single-atom nanozyme (named Cu SA/NC) with switchable specificity is reported. Atomically dispersed active sites endow Cu SA/NC with specific peroxidase-like activity at room temperature. Furthermore, the intrinsic photothermal conversion ability of Cu SA/NC enables the specificity switch by additional laser irradiation, where photothermal-induced temperature elevation triggers the expression of oxidase-like and catalase-like activity of Cu SA/NC. For further applications in practice, a pretreatment-and-sensing integration kit (PSIK) is constructed, where Cu SA/NC can successively achieve sample pretreatment and sensitive detection by switching from multi-activity mode to specific-activity mode. This study sets the foundation for nanozymes with switchable specificity and broadens the application scope in point-of-care testing.

Nanobiocatalysis: a materials science road to biocatalysis.

With high activity and specificity to conduct catalysis under mild conditions, enzymes show great promise in many fields. However, they are not acclimatized to environments in practice after leaving the familiar biological conditions. Aiming at this issue, nanobiocatalysis, a fresh area integrating nanotechnology and enzymatic catalysis, is expected to design biocatalysis based on materials science. Specifically, nano-integrated biocatalysis and bio-inspired nanocatalysis are considered as two effective nanobiocatalytic systems to meet different design needs. Notably, both systems are not entirely separated, and the combination of both further sparks more possibilities. This review summarizes the type, construction, and function of nanobiocatalytic systems, analyzing the pros and cons of different strategies. Moreover, the corresponding applications in bioassay, biotherapy, and environmental remediation are highlighted. We hope that the advent of nanobiocatalysis will help in grasping the inherence of biocatalysis and propel biocatalytic applications.

Water Activation for Boosting Electrochemiluminescence.

In conventional luminol electrochemiluminescence (ECL) systems, hydrogen peroxide and dissolved oxygen are employed as typical co-reactants to produce reactive oxygen species (ROS) for efficient ECL emission. However, the self-decomposition of hydrogen peroxide and limited solubility of oxygen in water inevitably restrict the detection accuracy and luminous efficiency of luminol ECL system. Inspired by ROS-mediated ECL mechanism, for the first time, we used cobalt-iron layered double hydroxide as co-reaction accelerator to efficiently activate water to generate ROS for enhancing luminol emission. Experimental investigations verify the formation of hydroxyl and superoxide radicals in the process of electrochemical water oxidation, which subsequently react with luminol anion radicals to trigger strong ECL signals. Finally, the detection of alkaline phosphatase has been successfully achieved with impressive sensitivity and reproducibility for practical sample analysis.

Dual-Site Activation Coupling with a Schottky Junction Boosts the Electrochemiluminescence of Carbon Nitride.

Robust electrochemiluminescence (ECL) of carbon nitride (CN) requires efficient electron-hole recombination and the suppression of electrode passivation. In this work, Au nanoparticles and single atoms (AuSA+NP ) loaded on CN serve as dual active sites that significantly accelerate charge transfer and activate peroxydisulfate. Meanwhile, the well-established Schottky junctions between Au NPs and CN act as electron sinks, effectively trapping over-injected electrons to prevent electrode passivation. As a result, the porous CN modified with AuSA+NP exhibits an enhanced and stable ECL emission, with a minimal relative standard deviation of 0.24 %. Furthermore, the designed ECL biosensor based on AuSA+NP -CN shows a remarkable performance in detecting organophosphorus pesticides. This innovative strategy has the potential to offer new insights into strong and stable ECL emission for practical applications.

Bioinspired Single-Atom Sites Enable Efficient Oxygen Activation for Switching Anodic/Cathodic Electrochemiluminescence.

Exploring advanced co-reaction accelerators with superior oxygen reduction activity that generate rich reactive oxygen species (ROS) has attracted great attention in boosting luminol-O2 electrochemiluminescence (ECL). However, tuning accelerators for efficient and selective catalytic O2 activation to switch anodic/cathodic ECL is very challenging. Herein, we report that enzyme-inspired Fe-based single-atom catalysts with axial N/C coordination structures (FeN5 , FeN4 © SACs) can generate specific ROS for cathodic/anodic ECL conversion. Mechanistic studies reveal that FeN5 sites prefer to produce highly active hydroxyl radicals and afford direct cathodic luminescence by promoting the cleavage of O-O bonds through N-induced electron redistribution. In contrast, FeN4 © sites tend to produce superoxide radicals, resulting in inefficient anodic ECL. Benefiting from the enhanced cathodic ECL, FeN5 SAC-based immunosensor was constructed for the sensitive detection of cancer biomarkers.

Peroxymonosulfate Activation on Synergistically Enhanced Single-Atom Co/Co@C for Boosted Chemiluminescence of Tris(bipyridine) Ruthenium(II) Derivative.

Tris(bipyridine) ruthenium(II)-based luminophores have been well developed in the area of electrochemiluminescence, while their applications in chemiluminescence (CL) are rarely studied due to the poor luminous efficiency and complicated CL reaction. Herein, a novel tris(bipyridine) ruthenium(II)-based ternary CL system is proposed by introducing cobalt single atoms integrated with graphene-encapsulated cobalt nanoparticles (Co SAs/Co@C) and peroxymonosulfate (PMS) as advanced coreaction accelerator and promising coreactant, respectively. On the basis of the experimental results and density functional theory calculations, it is concluded that Co@C can synergistically modulate the adsorption behavior of PMS on Co SAs and then efficiently activate PMS to produce massive singlet oxygen for remarkable CL emission. Under the optimum conditions, the as-prepared CL biosensor exhibits a good linear range, excellent sensitivity, and selectivity, holding great potential for the practical detection of prostate-specific antigen in human serum.

Single-Atom Iron Enables Strong Low-Triggering-Potential Luminol Cathodic Electrochemiluminescence.

The conventional cathodic electrochemiluminescence (ECL) always requires a more negative potential to trigger strong emission, which inevitably damages the bioactivity of targets and decreases the sensitivity and specificity. In this work, iron single-atom catalysts (Fe-N-C SACs) were employed as an efficient co-reaction accelerator for the first time to achieve the impressively cathodic emission of a luminol-H2O2 ECL system at an ultralow potential. Benefiting from the distinct electronic structure, Fe-N-C SACs exhibit remarkable properties for the activation of H2O2 to produce massive reactive oxygen species (ROS) under a negative scanning potential from 0 to -0.2 V. The ROS can oxidize the luminol anions into luminol anion radicals, avoiding the tedious electrochemical oxidation process of luminol. Then, the in situ-formed luminol anion radicals will directly react with ROS for the strong ECL emission. As a proof of concept, sensitive detection of the carcinoembryonic antigen was realized by glucose oxidase-mediated ECL immunoassay, shedding light on the superiority of SACs to construct efficient cathodic ECL systems with low triggering potential.

Iridium Single-Atomic Site Catalysts with Superior Oxygen Reduction Reaction Activity for Sensitive Monitoring of Organophosphorus Pesticides.

Tremendous efforts have been made in developing single-atomic site catalysts (SASCs) for oxygen reduction reaction (ORR), which is regarded as a pivotal cornerstone in electrochemical energy conversion. However, SASCs for ORR have not been explored for electrochemical sensing. Herein, a template-sacrificed strategy is reported for the synthesis of atomically dispersed Ir SASCs, serving as a sensing platform to detect organophosphorus pesticides (OPs) with high sensitivity and selectivity. Owing to abundant Ir single-atom active sites, Ir SASCs show excellent ORR activity and stability in a neutral medium. It is found that the ORR activity of Ir SASCs can be inhibited by thiocholine, which is the hydrolysate of acetylthiocholine. After being integrated with acetylcholinesterase (AChE), the AChE-Ir SASC-based electrochemical sensor is established and shows a superior sensitivity, which shows a wide detection range of 0.5-500 ng mL-1 with a low detection limit of 0.17 ng mL-1 for OPs. This work exhibits a broad application prospect of ORR for sensitive detection of biomolecules.

Ultra-Low Content Bismuth-Anchored Gold Aerogels with Plasmon Property for Enhanced Nonenzymatic Electrochemical Glucose Sensing.

Effective glucose surveillance provides a strong guarantee for the high-quality development of human health. Au nanomaterials possess compelling applications in nonenzymatic electrochemical glucose biosensors owing to superior catalytic performances and intriguing biocompatibility properties. However, it has been a grand challenge to accurately control the architecture and composition of Au nanomaterials to optimize their optical, electronic, and magnetic properties for further improving the performance of electrocatalytic sensing. Herein, ultra-low content Bi-anchored Au aerogels are synthesized via a one-step reduction strategy. Benefiting from the unique structure of aerogels as well as the synergistic effect between Au and Bi, the optimized Au200Bi aerogels greatly boost the activity of glucose oxidation compared with Au aerogels. Under plasmon resonance excitation, bimetallic Au200Bi aerogels with wider photics-dependent properties further show plasmon-promoted glucose electro-oxidation activity, which is derived from the photothermal and photoelectric effects caused by the local surface plasmon resonance. Thanks to the enhanced performance, a nonenzymatic electrochemical glucose biosensor is constructed to detect glucose with high sensitivity. This plasmon-promoted electrocatalytic activity through the synergetic strategy of bimetallic aerogels has potential applications in various research fields.

Cation-Exchange Enables In Situ Preparation of PbSe Quantum Dot Ink for High Performance Solar Cells.

Lead selenide (PbSe) colloidal quantum dots (CQDs) are promising candidates for optoelectronic applications. To date, PbSe CQDs capped by halide ligands exhibit improved stability and solar cells using these CQDs as active layers have reported a remarkable power conversion efficiency (PCE) up to 10%. However, PbSe CQDs are more prone to oxidation, requiring delicate control over their processability and compromising their applications. Herein, an efficient strategy that addresses this issue by an in situ cation-exchange process is reported. This is achieved by a two-phase ligand exchange process where PbI2 serves as both a passivating ligand and cation-source inducing transformation of CdSe to PbSe. The defect density and carrier lifetime of PbSe CQD films are improved to 1.05 × 1016  cm-3 and 12.2 ns, whereas the traditional PbSe CQD films possess 1.9 × 1016  cm-3 defect density and 10.2 ns carrier lifetime. These improvements are translated into an enhancement of photovoltaic performance of PbSe solar cells, with a PCE of up to 11.6%, ≈10% higher than the previous record. Notably, the approach enables greatly improved stability and a two-month stability is successfully demonstrated. This strategy is expected to promote the fast development of PbSe CQD applications in low-cost and high-performance optoelectronic devices.