p-d Orbital Hybridization-Engineered PdSn Nanozymes for a Sensitive Immunoassay.

Nanozymes with peroxidase-like activity have been extensively studied for colorimetric biosensing. However, their catalytic activity and specificity still lag far behind those of natural enzymes, which significantly affects the accuracy and sensitivity of colorimetric biosensing. To address this issue, we design PdSn nanozymes with selectively enhanced peroxidase-like activity, which improves the sensitivity and accuracy of a colorimetric immunoassay. The peroxidase-like activity of PdSn nanozymes is significantly higher than that of Pd nanozymes. Theoretical calculations reveal that the p-d orbital hybridization of Pd and Sn not only results in an upward shift of the d-band center to enhance hydrogen peroxide (H2O2) adsorption but also regulates the O-O bonding strength of H2O2 to achieve selective H2O2 activation. Ultimately, the nanozyme-linked immunosorbent assay has been successfully developed to sensitively and accurately detect the prostate-specific antigen (PSA), achieving a low detection limit of 1.696 pg mL-1. This work demonstrates a promising approach for detecting PSA in a clinical diagnosis.

Bioinspired FeN5 Sites with Enhanced Peroxidase-like Activity Enable Colorimetric Sensing of Uranyl Ions in Seawater.

Nanozymes with peroxidase (POD)-like activity have garnered significant attention due to their exceptional performance in colorimetric assays. However, nanozymes often possess oxidase (OD) and POD-like activity simultaneously, which affects the accuracy and sensitivity of the detection results. To address this issue, inspired by the catalytic pocket of natural POD, a single-atom nanozyme with FeN5 configuration is designed, exhibiting enhanced POD-like activity in comparison with a single-atom nanozyme with FeN4 configuration. The axial N atom in FeN5 highly mimics the amino acid residues in natural POD to optimize the electronic structure of the metal active center Fe, realizing the efficient activation of H2O2. In addition, in the presence of both H2O2 and O2, FeN5 enhances the activation of H2O2, effectively avoiding the interference of dissolved oxygen in colorimetric sensing. As a proof-of-concept application, a colorimetric detection platform for uranyl ions (UO22+) in seawater is successfully constructed, demonstrating satisfactory sensitivity and specificity.

Catalase-like Fe Nanoparticles and Single Atoms Catalysts with Boosted Activity and Stability of Oxygen Reduction for Pesticide Detection.

Although oxygen reduction reaction (ORR) as an effective signal amplification strategy has been extensively investigated for the improvement of sensitivity of electrochemical sensors, their activity and stability are still a great challenge. Herein, single-atom Fe (FeSA) and Fe nanoparticles (FeNP) on nitrogen-doped carbon (FeSA/FeNP) catalysts demonstrate a highly active and stable ORR performance, thus achieving the sensitive and stable electrochemical sensing of organophosphorus pesticides (OPs). Experimental investigations indicate that FeNP in FeSA/FeNP can improve the ORR activity by adjusting the electronic structure of FeSA active sites. Besides, owing to the excellent catalase-like activity, FeSA/FeNP can rapidly consume in situ generated H2O2 in the ORR process and avoid the leakage of active sites, thereby improving the stability of ORR. Utilizing the excellent ORR performance of FeSA/FeNP, an electrochemical sensor for OPs is established based on the thiocholine-induced poison of the active sites, demonstrating satisfactory sensitivity and stability. This work provides new insight into the design of high performance ORR catalysts for sensitive and stable electrochemical sensing.

Crystalline-Amorphous Interfaces Engineering of CoO-InOx for Highly Efficient CO2 Electroreduction to CO.

As a fundamental product of CO2 conversion through two-electron transfer, CO is used to produce numerous chemicals and fuels with high efficiency, which has broad application prospects. In this work, it has successfully optimized catalytic activity by fabricating an electrocatalyst featuring crystalline-amorphous CoO-InOx interfaces, thereby significantly expediting CO production. The 1.21%CoO-InOx consists of randomly dispersed CoO crystalline particles among amorphous InOx nanoribbons. In contrast to the same-phase structure, the unique CoO-InOx heterostructure provides plentiful reactive crystalline-amorphous interfacial sites. The Faradaic efficiency of CO (FECO ) can reach up to 95.67% with a current density of 61.72 mA cm-2 in a typical H-cell using MeCN containing 0.5 M 1-Butyl-3-methylimidazolium hexafluorophosphate ([Bmim]PF6 ) as the electrolyte. Comprehensive experiments indicate that CoO-InOx interfaces with optimization of charge transfer enhance the double-layer capacitance and CO2 adsorption capacity. Theoretical calculations further reveal that the regulating of the electronic structure at interfacial sites not only optimizes the Gibbs free energy of *COOH intermediate formation but also inhibits HER, resulting in high selectivity toward CO.

Single-Atom Indium Boosts Electrochemical Dopamine Sensing.

A rational design of high-efficiency electrocatalysts and thus achieving sensitive electrochemical sensing remains a great challenge. In this work, single-atom indium anchored on nitrogen-doped carbon (In1-N-C) with an In-N4 configuration is prepared successfully through a high-temperature annealing strategy; the product can serve as an advanced electrocatalyst for sensitive electrochemical sensing of dopamine (DA). Compared with In nanoparticle catalysts, In1-N-C exhibits high catalytic performance for DA oxidation. The theoretical calculation reveals that In1-N-C has high adsorption energy for hydroxy groups and a low energy barrier in the process of DA oxidation compared to In nanoparticles, indicating that In1-N-C with atomically dispersed In-N4 sites possesses enhanced intrinsic activity. An electrochemical sensor for DA detection is established as a concept application with high sensitivity and selectivity. Furthermore, we also verify the feasibility of In1-N-C catalysts for the simultaneous detection of uric acid, ascorbic acid, and DA. This work extends the application prospect of p-block metal single-atom catalysts in electrochemical sensing.

Single-Site SnOCu Pairs with Interfacial Electron Transfer Effect for Enhanced Electrochemical Catalysis and Sensing.

As advanced electrochemical catalysts, single-atom catalysts have made great progress in the field of catalysis and sensing due to their high atomic utilization efficiency and excellent catalytic performance. Herein, stannum-doped copper oxide (CuOSn1 ) nanosheets with single-site SnOCu pairs as active sites are synthesized as electrocatalysts for biological molecule detection. Compared with CuO-based electrochemical sensors, the CuOSn1 -based electrochemical sensors have improved detection sensitivity with a rapid electrochemical response. Theoretical calculation reveals that the single-site SnOCu pairs induced interfacial electronic transfer effect can strengthen hydroxy adsorption and thus reduce the energy barrier of the biological molecule oxidation process. As a concept application, electrochemical detection of dopamine and uric acid molecules is achieved, exhibiting satisfactory sensitivity and selectivity. This work demonstrates the advantages of single-site SnOCu pairs in electrochemical catalysis and sensing, which provides theoretical guidance for understanding the structure-activity relationship for sensitive electrochemical sensing.

Progress in Hybridization of Covalent Organic Frameworks and Metal-Organic Frameworks.

Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) hybrid materials are a class of porous crystalline materials that integrate MOFs and COFs with hierarchical pore structures. As an emerging porous frame material platform, MOF/COF hybrid materials have attracted tremendous attention, and the field is advancing rapidly and extending into more diverse fields. Extensive studies have shown that a broad variety of MOF/COF hybrid materials with different structures and specific properties can be synthesized from diverse building blocks via different chemical reactions, driving the rapid growth of the field. The allowed complementary utilization of π-conjugated skeletons and nanopores for functional exploration has endowed these hybrid materials with great potential in challenging energy and environmental issues. It is necessary to prepare a "family tree" to accurately trace the developments in the study of MOF/COF hybrid materials. This review comprehensively summarizes the latest achievements and advancements in the design and synthesis of MOF/COF hybrid materials, including COFs covalently bonded to the surface functional groups of MOFs (MOF@COF), MOFs grown on the surface of COFs (COF@MOF), bridge reaction between COF and MOF (MOF+COF), and their various applications in catalysis, energy storage, pollutant adsorption, gas separation, chemical sensing, and biomedicine. It concludes with remarks concerning the trend from the structural design to functional exploration and potential applications of MOF/COF hybrid materials.

Simple and sensitive fluorescent and electrochemical trinitrotoluene sensors based on aqueous carbon dots.

Aqueous N-rich carbon dots (CDs), prepared by the microwave-assisted pyrolysis method, are applied as a dual sensing platform for both the fluorescent and electrochemical detection of 2,4,6-trinitrotoluene (TNT). The fluorescent sensing platform is established on the strong TNT-amino interaction which can quench the photoluminescence of amino functionalized CDs through charge transfer. The resultant linear detection ranges from 10 nM to 1.5 µM with a fast response time of 30 s. Glassy carbon electrode modified with CDs exhibits a fine capability for TNT reduction with the linear range from 5 nM to 30 µM, better than that obtained by the fluorescent method. Moreover, the minimum distinguishable response concentration with respect to these two methods is down to the nanomolar level with a high specificity and sensitivity.

Highly selective electroreduction of CO2 to CO with ZnO QDs/N-doped porous carbon catalysts.

ZnO quantum dots (QDs) supported on porous nitrogen-doped carbon (ZnOQDs/P-NC) exhibited excellent electrochemical performance for the electroreduction of CO2 to CO with a faradaic efficiency of 95.3% and a current density of 21.6 mA cm-2 at -2.2 V vs. Ag/Ag+.

Inhibition effect of p-d orbital hybridized PtSn nanozymes for colorimetric sensor array of antioxidants.

Rational design of peroxidase (POD)-like nanozymes with high activity and specificity still faces a great challenge. Besides, the investigations of nanozymes inhibitors commonly focus on inhibition efficiency, the interaction between nanozymes-involved catalytic reactions and inhibitors is rarely reported. In this work, we design a p-block metal Sn-doped Pt (p-d/PtSn) nanozymes with the selective enhancement of POD-like activity. The p-d orbital hybridization interaction between Pt and Sn can effectively optimize the electronic structure of PtSn nanozymes and thus selectively enhance POD-like activity. In addition, the antioxidants as nanozymes inhibitors can effectively inhibit the POD-like activity of p-d/PtSn nanozymes, which results in the fact that antioxidants absorbed on the p-d/PtSn surface can hinder the adsorption of hydrogen peroxide. The inhibition type (glutathione as a model molecule) is reversible mixed-inhibition with inhibition constants (Ki' and Ki) of 0.21 mM and 0.03 mM. Finally, based on the varying inhibition levels of antioxidant molecules, a colorimetric sensor array is constructed to distinguish and simultaneously detect five antioxidants. This work is expected to design highly active and specific nanozymes through p-d orbital hybrid engineering, and also provides insights into the interaction between nanozymes and inhibitors.

Recent Advances in Electrospun Nanofiber-Based Strategies for Diabetic Wound Healing Application.

Diabetic ulcers are the second largest complication caused by diabetes mellitus. A great number of factors, including hyperchromic inflammation, susceptible microbial infection, inferior vascularization, the large accumulation of free radicals, and other poor healing-promoting microenvironments hold back the healing process of chronic diabetic ulcer in clinics. With the increasing clinical cases of diabetic ulcers worldwide, the design and development of advanced wound dressings are urgently required to accelerate the treatment of skin wounds caused by diabetic complications. Electrospinning technology has been recognized as a simple, versatile, and cost-reasonable strategy to fabricate dressing materials composed of nanofibers, which possess excellent extracellular matrix (ECM)-mimicking morphology, structure, and biological functions. The electrospinning-based nanofibrous dressings have been widely demonstrated to promote the adhesion, migration, and proliferation of dermal fibroblasts, and further accelerate the wound healing process compared with some other dressing types like traditional cotton gauze and medical sponges, etc. Moreover, the electrospun nanofibers are commonly harvested in the structure of nonwoven-like mats, which possess small pore sizes but high porosity, resulting in great microbial barrier performance as well as excellent moisture and air permeable properties. They also serve as good carriers to load various bioactive agents and/or even living cells, which further impart the electrospinning-based dressings with predetermined biological functions and even multiple functions to significantly improve the healing outcomes of different chronic skin wounds while dramatically shortening the treatment procedure. All these outstanding characteristics have made electrospun nanofibrous dressings one of the most promising dressing candidates for the treatment of chronic diabetic ulcers. This review starts with a brief introduction to diabetic ulcer and the electrospinning process, and then provides a detailed introduction to recent advances in electrospinning-based strategies for the treatment of diabetic wounds. Importantly, the synergetic application of combining electrospinning with bioactive ingredients and/or cell therapy was highlighted. The review also discussed the advantages of hydrogel dressings by using electrospun nanofibers. At the end of the review, the challenge and prospects of electrospinning-based strategies for the treatment of diabetic wounds are discussed in depth.

Immobilizing glucose oxidase on AuCu hydrogels for enhanced electrochromic biosensing.

Development of highly sensitive and accurate biosensors still faces a great challenge. Herein, glucose oxidase (GOx) is efficiently immobilized on the AuCu hydrogels owing to their porous structure and interfacial interaction, demonstrating enhanced catalytic activity, satisfactory stability and recyclability. Besides, by integration of AuCu@GOx and electrochromic material of Prussian blue, a sensitive and stable biosensing platform based on the excellent electrochromic property of Prussian blue and the enhanced enzyme activity of AuCu@GOx is developed, which enables the electrochemical and visual dual-mode detection of glucose. The as-constructed biosensing platform possesses a wide linear range, and good selectivity for glucose detection with a limit of detection of 0.82 µM in visual mode and 0.84 µM in electrochemical mode. This easy-to-operate biosensing platform opens a door for the practical application of the multi-mode strategy for glucose detection.

Selectivity control for CO2 electroreduction to syngas using Fe/CuOx catalysts with high current density.

A novel and tunable synthesis of Fe/CuOx bimetallic catalysts has been achieved via a simple Fe-precipitation and calcination method, which was used for highly efficient CO2 electroreduction to control the wide-ranging CO to H2 ratio by simply changing the ratio of metals. The faradaic efficiency of CO could reach 86.1% with a current density of 49.1 mA cm-2. The ratio of CO/H2 could reach 1.94 to 6.18 and it was discovered that the Fe/CuOx bimetallic catalysts could easily get different ratios of syngas, which can be applied directly in industry.

Fluorescence property of ZnO nanoparticles and the interaction with bromothymol blue.

We synthesized ZnO quantum dots (QDs) simply in alcoholic solution, and investigated the interaction between ZnO QDs and bromothymol blue. The structural, morphological, size and spectral properties of ZnO QDs were studied. It was found that ZnO QDs were spherical nanoparticles in the crystal structure, and the average diameter of ZnO QDs was about 4.8 nm. The excitation and emission peaks were located at 346 nm and 520 nm, respectively, which were obtained on a common fluorophotometer. The quantum yield of ZnO QDs was obtained by using quinine sulfate as a reference reagent. In addition, the fluorescence of ZnO QDs can be quenched by bromothymol blue, and the quenching mechanism was proposed in a dynamic quenching mode.

Self-Driven Multicolor Electrochromic Energy Storage Windows Powered by a "Perpetual" Rechargeable Battery.

Electrochromic windows (ECWs) become an appealing concept for green buildings. However, conventional ECWs need external biases to operate causing energy consumption and are usually restricted by monotonous color. Recently, electrochromic energy storage windows (EESWs) integrating the functions of electrochromism and energy storage in one device have attracted particular attention in various fields, such as self-powered addressable displays, human-readable batteries, and most importantly energy-efficient smart windows. Herein, a color-tunable (nonemissive-red-yellow-green) self-powered EESW is initially presented utilizing Prussian blue (PB) as a controller of the fluorescent component of CdSe quantum dots. The key design feature is that without any external stimuli, the EESW can be powered by a rechargeable "perpetual" battery, which is composed of two half-cell couples of Fe/PB and Prussian white (PW)/Pt. This technique allows to achieve only by switching the connection status of the two half-cells, the fast discharging and self-charging process of the EESWs with high and sustainable charge-storage capacity. Remarkably, the fabricated self-powered EESWs exhibit quick response ("off" 7 s, "on" 50 s), large transmittance spectra contrast, and high fluorescent contrast modulation (60-86%) over a wide optical range, and great reproducibility (only 3% of the modulation ratio decreased after 30 cycles), which is comparable to ECWs powered by an electrochemical potentiostat.

Hydrothermal synthesis of polydopamine-functionalized cobalt-doped lanthanum nickelate perovskite nanorods for efficient water oxidation in alkaline solution.

Perovskite oxides have attracted great attention recently for their low cost and high intrinsic activity in the electrochemical oxygen evolution reaction (OER). In this work, we synthesized highly efficient OER electrocatalysts in alkaline solution by carbonization of polydopamine (PDA)-functionalized cobalt-doped lanthanum nickelate perovskite nanorod (La5Ni3Co2) complexes. The calcination temperature and molar ratio for La, Ni, and Co were optimized. The as-prepared complex with a molar ratio of 5 : 3 : 2 (La : Ni : Co) and a calcination temperature of 500 °C displayed enhanced OER activity and excellent durability. In 1.0 M KOH, the overpotential of the as-prepared catalyst at a current density of 10 mA cm-2 was 0.360 V, which is comparable to those of noble metal-based materials or perovskite-based materials. The Tafel slope is 48.1 mV dec-1, which is smaller than those of prepared composites. The satisfactory oxygen evolution activity could be attributed to the increased Co3O4, O22-/O-, pyridine N, and quaternary N species after calcination treatment, and the improved amount of Ni3+ during the OER process, as well as the high surface area and electrochemical surface area.

Reversible self-powered fluorescent electrochromic windows driven by perovskite solar cells.

Self-powered electrofluorochromic devices (EFCDs) have attracted particular attention for smart windows of green buildings. In this work, we report a perovskite solar cell (PSC) driven self-powered EFCD. For the first time, electrochromic material polyoxometalates (POMs) and a fluorescent component are made into wet adhesives. A special design feature is that POMs and magnesium composed a battery powering the EFCD bleaching, and the device can be quickly coloured after connecting with the PSCs by the electrical power generated through solar energy conversion. Therefore, without any additional external bias, the fabricated EFCD undergoes an electrochromic transition from white semitransparent to dark blue-tinted, and under UV it presents reversible fluorescence switching between yellow and dark.

Self-Rechargeable-Battery-Driven Device for Simultaneous Electrochromic Windows, ROS Biosensing, and Energy Storage.

A self-powered electrochromic device (ECD) powered by a self-rechargeable battery is easily fabricated to achieve electrochromic window design, quantitative reactive oxygen species (ROS) sensing, and energy storage. The special design of the battery was composed of Prussian blue (PB) and magnesium metal as the cathode and anode, respectively, which exhibits fast self-charging and high power-density output for continuous and stable energy supply. Benefitting from the fast electrochromic response of PB, it was not only used for structuring self-rechargeable batteries but also used as an electrochromic display for highly sensitive self-powered ROS sensing and visual analysis. We believe that this work provides a solution to self-powered ECDs limited to a single application and could combine the applications in smart windows, ROS sensing, and other fields together, and in the meantime provide a solution for energy supply problems.

Multiscale porous Fe-N-C networks as highly efficient catalysts for the oxygen reduction reaction.

Non-Pt catalysts with excellent performance regarding the oxygen reduction reaction (ORR) have aroused enormous interest in recent years. Herein, we propose a dual-template method to synthesize a multiscale porous Fe-N-C (FeNC) catalyst. SiO2 and Zn are used as co-templates to produce a multiscale porous structure. Chitosan and glutaraldehyde are used as building blocks to fabricate the frameworks of the hydrogel. After lyophilization and annealing treatments, FeNC aerogel with a multiscale porous structure could be obtained. The as-prepared FeNC catalyst annealed at 900 °C (FeNC-900) exhibits a larger electrochemically active surface area and an improved ORR activity compared to FeNC annealed at other temperatures. FeNC-900 shows a superior ORR performance in comparison with that of commercial Pt/C in terms of the onset potential and half-wave potential, i.e., 0.959 and 0.837 V, which are 28 mV and 10 mV higher than those of Pt/C, respectively. Multiscale porosity is responsible for the outstanding ORR performance of FeNC-900. The electron transfer number of FeNC-900 for the ORR was calculated to be 3.95, which is comparable with that of Pt/C. In addition, the FeNC-900 catalyst possesses an excellent long-term duration and anti-poisoning capacity against methanol crossover. All these results endow the FeNC catalyst with tremendous potential for use in fuel cells.

Recent advances in spectroelectrochemistry.

The integration of two quite different techniques, conventional electrochemistry and spectroscopy, into spectroelectrochemistry (SEC) provides a complete description of chemically driven electron transfer processes and redox events for different kinds of molecules and nanoparticles. SEC possesses interdisciplinary advantages and can further expand the scopes in the fields of analysis and other applications, emphasizing the hot issues of analytical chemistry, materials science, biophysics, chemical biology, and so on. Considering the past and future development of SEC, a review on the recent progress of SEC is presented and selected examples involving surface-enhanced Raman scattering (SERS), ultraviolet-visible (UV-Vis), near-infrared (NIR), Fourier transform infrared (FTIR), fluorescence, as well as other SEC are summarized to fully demonstrate these techniques. In addition, the optically transparent electrodes and SEC cell design, and the typical applications of SEC in mechanism study, electrochromic device fabrication, sensing and protein study are fully introduced. Finally, the key issues, future perspectives and trends in the development of SEC are also discussed.