Unlock CO2 Reduction Reaction Pathways in Aprotic Li-CO2 Batteries with In Situ Isotope-Labeled Spectroscopy and Theoretical Calculations.

The CO2 reduction reaction (CO2RR) pathway significantly dictates the reversibility and overpotential of aprotic Li-CO2 batteries; however, it has remained incompletely understood due to the lack of direct in situ spectroscopic evidence. Herein, the Li-CO2RR pathways at the model Au | dimethyl sulfoxide (DMSO) interface are interrogated using a combination of in situ isotope-labeled spectroscopy techniques and theoretical calculations. This obtained direct spectroscopic evidence presents that the primary CO2RR proceeds through the CO2-to-CO pathway (i.e., 2Li+ + 2CO2 + 2e- → CO + Li2CO3) initiated at a low overpotential (ca. 2.1 V vs Li/Li+), and the CO2-to-Li2C2O4 pathway (i.e., 2Li+ + 2CO2 + 2e- → Li2C2O4) initiated at a high overpotential (ca. 1.7 V vs Li/Li+), where the potential-dependent pathways critically depend on the coverage of LiCO2 intermediates. Simultaneously, the entire Li-CO2RR process is also accompanied by parasitic reactions to form gaseous C2H4 with COOH* as the crucial intermediate, which is induced by the H+-abstraction reaction between the reactive LiCO2 intermediate and the DMSO solvent. These fundamental insights enable us to establish a molecular picture for Li-CO2RR pathways in aprotic media and will serve as a crucial guideline for reversible Li-CO2 electrochemistry.

Toward Minute-Level DNA Computing: An Ultrafast, Cost-Effective, and Universal System for Lighting Up Various Concurrent DNA Logic Nanodevices (CDLNs) and Concatenated Circuits.

DNA logic nanodevices are powerful tools for both molecular computing tasks and smart bioanalytical applications. Nevertheless, the hour-level operation time and high cost caused by the frequent redesign/reconstruction of gates, tedious strand-displacement reaction, and expensive labeled probes (or tool enzymes) in previous works are ineluctable drawbacks. Herein, we report an ultrafast and cost-effective system for engineering concurrent DNA logic nanodevices (CDLNs) by combining polythymine CuNCs with SYBR Green I (SG I) as universal dual-output producers. Particularly, benefiting from the concomitant minute-level quick response of both unlabeled illuminators and the exquisite strand-displacement-free design, all CDLNs including contrary logic pairs (YES∧NOT, OR∧NOR, and Even∧Odd number classifier), noncontrary ones (IDE∧IMP, OR∧NAND), and concatenated circuits are implemented in just 10 min via a "one-stone-two-birds" method, resulting in only 1/12 the operation time and 1/4 the cost needed in previous works, respectively. Moreover, all of them share the same threshold value, and the dual output can be easily visualized by the naked eye under a portable UV lamp, indicating the universality and practicality of this system. Furthermore, by exploiting the "positive/negative cross-verification" advantages of concurrent contrary logic, the smart in vitro analysis of the polyadenine strand and its polymerase is realized, providing novel molecular tools for the early diagnosis of cancer-related diseases.

Label-Free Single-Cell SERS Detection and Fluorescence Imaging of Molecular Responses to Endoplasmic Reticulum Stress under Electrical Stimulation.

The endoplasmic reticulum (ER) is one of the most important organelles in eukaryotic cells, in which most proteins and lipids are synthesized to regulate complex cellular processes. Generally, the excessive accumulation of unfolded or misfolded proteins can disturb ER homeostasis and induce endoplasmic reticulum stress (ERS). Howbeit, the molecular stress responses within ERS and metastatic behaviors of tumor cells during electrical stimulation (ES) are still poorly investigated and remain a challenge. In this study, by the combined use of fluorescence imaging, ER-targeting plasmonic nanoprobes were developed to trace molecular stress response profiling within the ER during a constant-voltage ES process at ∼1 V based on label-free surface-enhanced Raman spectroscopy (SERS). The excess accumulation of ß-misfolded proteins was found after the ES, leading to breaking of the ER homeostasis and further inducing mitochondrial dysfunction. Notably, the excessive stress of ER under ES can destroy the calcium ion balance and induce significant upregulation of calreticulin expression. Importantly, the content ratio of two kinds of cadherin between E-cadherin and N-cadherin was gradually improved with the voltages boosted. Meanwhile, the epithelial adhesion factor expression was ascended with voltages amplified, leading to inhibiting tumor cell migration at low voltages or death under higher voltages (∼1 V). This study provides cellular insights into the ES approach for tumor therapy and also provides a simple and effective method for detecting molecular stress responses in endoplasmic reticulum stress.

A New Fluorescent Probe Tool: ERNathG.

ß-d-Glucuronidase (GUS) plays a pivotal role in both clinical treatment assessment and environmental monitoring. Existing tools for GUS detection suffer from (1) poor continuity due to a gap between the optimal pH of the probes and the enzyme and (2) diffusion from the detection site due to lack of an anchoring structure. Here we report a novel GUS pH-matching and endoplasmic reticulum-anchoring strategy for GUS recognition. The new fluorescent probe tool was termed ERNathG, which was designed and synthesized with ß-d-glucuronic acid as the GUS-specific recognition site and 4-hydroxy-1,8-naphthalimide as a fluorescence reporting group, with a p-toluene sulfonyl as an anchoring group. This probe enabled the continuous and anchored detection of GUS without pH-adjustment for the related assessment of common cancer cell lines and gut bacteria. The probe's properties are far superior to those of commonly used commercial molecules.

Hyphenated DEMS and ATR-SEIRAS techniques for in situ multidimensional analysis of lithium-ion batteries and beyond.

A wide spectrum of state-of-the-art characterization techniques have been devised to monitor the electrode-electrolyte interface that dictates the performance of electrochemical devices. However, coupling multiple characterization techniques to realize in situ multidimensional analysis of electrochemical interfaces remains a challenge. Herein, we presented a hyphenated differential electrochemical mass spectrometry and attenuated total reflection surface enhanced infrared absorption spectroscopy analytical method via a specially designed electrochemical cell that enables a simultaneous detection of deposited and volatile interface species under electrochemical reaction conditions, especially suitable for non-aqueous, electrolyte-based energy devices. As a proof of concept, we demonstrated the capability of the homemade setup and obtained the valuable reaction mechanisms, by taking the tantalizing reactions in non-aqueous lithium-ion batteries (i.e., oxidation and reduction processes of carbonate-based electrolytes on Li1+xNi0.8Mn0.1Co0.1O2 and graphite surfaces) and lithium-oxygen batteries (i.e., reversibility of the oxygen reaction) as model reactions. Overall, we believe that the coupled and complementary techniques reported here will provide important insights into the interfacial electrochemistry of energy storage materials (i.e., in situ, multi-dimensional information in one single experiment) and generate much interest in the electrochemistry community and beyond.

Beyond Photosynthesis: H2O/H2O2/O2 Self-Circulation-Based Biohybrid Photoelectrochemical Cells for Direct and Sustainable Solar-to-Fuel-to-Electric Power Conversion.

Solar-to-fuel conversion followed by secondary utilization in fuel cells provides an appealing approach to alleviating global energy shortages but is largely restricted by the complex design of power systems and the development of functional catalysts. Herein, we presented a biohybrid photoelectrochemical cell (BPEC) to implement sustainable solar-to-fuel-to-electric power conversion in a single compartment, by ingeniously combining reliable photoelectrochemical H2O2 generation with efficient bioelectrochemical H2O2 consumption. Specifically, the BPEC is composed of a Mo-modified BiVO4 (Mo:BiVO4) photoanode and a horseradish peroxidase (HRP)/pyrene-modified 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (bis-Pyr-ABTS)/carbon nanotubes with an encapsulated Co nanoparticle (Co/CNTs) biocathode. Upon photoexcitation, two-electron H2O oxidation can be carried out at the Mo-BiVO4 photoanode to produce H2O2, followed by electroenzymatic reduction of H2O2 to H2O by HRP with the help of a bis-Pyr-ABTS redox mediator at the biocathode. Besides, in response to the insufficient Faradaic efficiency of H2O2 generation at the photoanode, the functional Co/CNTs catalysts, possessing prominent electrocatalytic selectivity toward two-electron O2 reduction (electron transfer number = 2.6), are modified on the biocathode, thus clearly defining effective H2O/H2O2/O2 self-circulation in this device. This developed BPEC obtains an open-circuit potential of 1.03 ± 0.02 V and a maximum power density of 0.18 ± 0.02 mW cm-2. Moreover, inspired by the particular advantage of enzymatic biofuel cells for easy miniaturization, an enclosed "sandwich-like" BPEC of approximately 1 cm3 size is fabricated and delivers a power output of 0.13 ± 0.03 mW cm-2. Our work represents a controllable approach for meaningful solar energy utilization, beyond traditional artificial photosynthesis, and can further provide a significant paradigm shift in building an energy-sustainable society.

Specific Nanodrug for Diabetic Chronic Wounds Based on Antioxidase-Mimicking MOF-818 Nanozymes.

Chronic wound is a common complication for diabetic patients, which entails substantial inconvenience, persistent pain, and significant economic burden to patients. However, current clinical treatments for diabetic chronic wounds remain unsatisfactory. A prolonged but ineffective inflammation phase in chronic wounds is the primary difference between diabetic chronic wounds and normal wounds. Herein, we present an effective antioxidative system (MOF/Gel) for chronic wound healing of diabetic rats through integrating a metal organic framework (MOF) nanozyme with antioxidant enzyme-like activity with a hydrogel (Gel). MOF/Gel can continuously scavenge reactive oxygen species to modulate the oxidative stress microenvironment in diabetic chronic wounds, which leads to a natural transition from the inflammation phase to the proliferation phase. Impressively, the efficacy of one-time-applied MOF/Gel was comparable to that of the human epidermal growth factor Gel, a widely used clinical drug for various wound treatments. Such an effective, safe, and convenient MOF/Gel system can meet complex clinical demands.

Platinum-Gold Alloy Catalyzes the Aerobic Oxidation of Formic Acid for Hydrogen Peroxide Synthesis.

On-site hydrogen peroxide production through electrocatalytic and photocatalytic oxygen reduction reactions has recently attracted broad research interest. However, practical applications have thus far been plagued by the low activity and the requirement of complex equipment. Here, inspired by the process of biological hydrogen peroxide synthesis catalyzed by enzymes, we report a Pt-Au alloy to mimic the catalytic function of natural formate oxidase for hydrogen peroxide synthesis through aerobic oxidation of formic acid. The mass activity of the Pt-Au alloy is three times higher than that of formate oxidase. Density functional theory calculations revealed that the efficient dehydrogenation of formic acid and the high selectivity of the subsequent reduction of oxygen to hydrogen peroxide account for the high hydrogen peroxide productivity. In addition, the formic acid aqueous solution provides an acidic environment, which is conducive to the utilization of the in situ generated hydrogen peroxide for oxidation reactions, including C-H bond oxidation and sterilization.

Interfacial Electron Engineering of Palladium and Molybdenum Carbide for Highly Efficient Oxygen Reduction.

Interfacial electron engineering between noble metal and transition metal carbide is identified as a powerful strategy to improve the intrinsic activity of electrocatalytic oxygen reduction reaction (ORR). However, this short-range effect and the huge structural differences make it a significant challenge to obtain the desired electrocatalyst with atomically thin noble metal layers. Here, we demonstrated the combinatorial strategies to fabricate the heterostructure electrocatalyst of Mo2C-coupled Pd atomic layers (AL-Pd/Mo2C) by precise control of metal-organic framework confinement and covalent interaction. Both atomic characterizations and density functional theory calculations uncovered that the strong electron effect imposed on Pd atomic layers has intensively regulated the electronic structures and d-band center and then optimized the reaction kinetics. Remarkably, AL-Pd/Mo2C showed the highest ORR electrochemical activity and stability, which delivered a mass activity of 2.055 A mgPd-1 at 0.9 V, which is 22.1, 36.1, and 80.3 times higher than Pt/C, Pd/C, and Pd nanoparticles, respectively. The present work has developed a novel approach for atomically noble metal catalysts and provides new insights into interfacial electron regulation.

Atom-Anchoring Strategy with Metal-Organic Frameworks for Highly Efficient Solid-State Electrochemiluminescence.

A chemical fixation strategy originating from single-atom-anchoring with metal-organic frameworks as a carrying matrix was proposed for solid-state electrochemiluminescence (ECL). Herein, UiO-67(N) with the exposure of 2,2'-bipyridine (bpy) ligands could coordinate with Ru2+ to form a local structure of [Ru(bpy)3]2+ (Ru-UiO). The influence of the steric effect induced with different Ru sources was discussed. The as-obtained Ru-UiO exhibits high ECL intensity and outstanding stability in the presence of a coreactant at low concentrations. The proposed synthesis strategy may hold great potential for the synthesis of solid-state ECL materials and their further utilization in ECL analysis.

Self-adhesive and contractile silk fibroin/graphene nano-ionotronic skin for strain sensing of irregular surfaces.

Nanofiber-based artificial skin has shown promise for application in flexible wearable electronics due to its favorable breathability and comfortable wearability. However, the electrospinning method commonly used for nanofiber preparation suffers from poor spinning performance when used for ionotronic solutions. Moreover, the resulting membrane usually lacks self-adhesive and self-adapting properties when it is attached to an irregular subject, which greatly hinders its practical usage. Herein, a self-adhesive and contractile silk fibroin/graphene nano-ionotronic skin was successfully prepared using a high-yield electro-blowing technique. The electro-blowing technique was able to effectively overcome the instability of the spinning jet and raise the feed rate to at least 5 ml h-1. The high Ca2+content provided the fabricated nano-ionotronic skin with humidity-induced stretchability and robusticity. More importantly, the ionotronic skin also possessed a self-adhesive property and was able to contract to adapt to irregular surfaces. Additionally, an analytical piezoresistive model was successfully built to predict the response of the sensors to stress. Furthermore, due to its stable conductivity, sensitivity, and self-adapting property, the obtained nano-ionotronic skin can be used for body monitoring, for example, for bending of the arm and hand gestures. The design and manufacture concept proposed in this work might inspire the development of high-yield ionotronic nanofibers and the design of self-adapting artificial skin.

Oxidase-like MOF-818 Nanozyme with High Specificity for Catalysis of Catechol Oxidation.

Despite the extensive studies of the nanozymes showing their superior properties compared to natural enzymes and traditional artificial enzymes, the development of highly specific nanozymes is still a challenge. The catechol oxidase specifically catalyzing the oxidations of o-diphenol to the corresponding o-quinone is important to the biosynthesis of melanin and other polyphenolic natural products. In this study, we first propose that MOF-818, containing trinuclear copper centers mimicking the active sites of natural catechol oxidase, shows efficient catechol oxidase activity with good specificity and no peroxidase-like characteristics. MOF-818 has good specificity and high catalytic activity as a novel catechol oxidase nanozyme.

An unexpected discovery of 1,4-benzoquinone as a lipophilic mediator for toxicity detection in water.

Since most toxicological risk assessments are based on individual single-species tests, there is uncertainty in extrapolating these results to ecosystem assessments. Herein, we successfully developed a mediated microbial electrochemical biosensor with mixed microorganisms for toxicity detection by microelectrode array (MEA). In order to fully mobilize all the mixed microorganisms to participate in electron transfer to amplify the current signal, 1,4-benzoquinone (BQ) was used as the lipophilic mediator to mediate the intracellular metabolic activities. Hydrophilic K3[Fe(CN)6] was employed as an extracellular electron acceptor to transport electrons from hydroquinone (HQ) to the working electrode. Under the optimal conditions of 50 mM phosphate buffer solution (PBS), 0.4 mM BQ, 10 mM K3[Fe(CN)6] and OD600 = 0.5 bacteria concentration, the half-maximal inhibitory concentration (IC50) values measured with the composite-mediated respiration (CM-RES) of BQ-K3[Fe(CN)6] for Cu2+, Cd2+ and Zn2+ were 5.95, 7.12 and 8.86 mg L-1, respectively. IC50 values obtained with the single mediator K3[Fe(CN)6] were 2.34, 5.88 and 2.42 mg L-1 for the same samples. The results indicate that the biosensor with the single mediator K3[Fe(CN)6] had higher sensitivity to heavy metal ions than the biosensor with composite mediators. After verification, we found that the addition of BQ cannot amplify the current. The IC50 value of 0.89 mg L-1 for BQ was obtained using K3[Fe(CN)6] as the single mediator. This suggests that BQ is highly toxic, which explained why the sensitivity of the biosensor with the combined mediator BQ-K3[Fe(CN)6] was lower than that of the biosensor with the single mediator K3[Fe(CN)6]. At the same time, this also implies that toxicity itself cannot be ignored when it is used as an electronic mediator in a mediated microbial electrochemical biosensor.

Fe/N-doped hollow porous carbon spheres for oxygen reduction reaction.

Herein, we design a dual-template-assisted pyrolysis method to prepare ultra-small Fe3O4 nanoparticles anchored on Fe/N-doped hollow porous carbon spheres (0.010-Fe/NHPCS-800) for oxygen reduction reaction (ORR). The synthesized SiO2 nanospheres, which are selected as the hard template, contribute to forming macroporous structure. Pluronic ® F127 is employed to fabricate mesopores through high-temperature pyrolysis as a soft template. In this way, the 0.010-Fe/NHPCS-800 architecture represents an ordered hierarchically porous property with a large BET surface area (1812 m2 g-1), which can facilitate the mass transport of reactants and increase the electrochemically active area. The Fe3O4 nanoparticles wrapped by graphitic carbon layers provide more active sites, and the synergistic interaction between Fe3O4 nanoparticles and doping N has a positive effect on ORR performance. The 0.010-Fe/NHPCS-800 catalyst outperforms the most effective ORR activities among a series of Fe/NHPCS samples with onset potential of 0.95 V (versus reversible hydrogen potential) and half-wave potential of 0.81 V, which is almost the same as the commercial Pt/C (0.96 and 0.81 V, correspondingly) in 0.10 M KOH. However, both the stability and durability of 0.010-Fe/NHPCS-800 surpass those of commercial Pt/C. Given all these advantages, 0.010-Fe/NHPCS-800 is a promising candidate to take the place of Pt-based electrocatalysts for ORR in the future.

Water/Oxygen Circulation-Based Biophotoelectrochemical System for Solar Energy Storage and Release.

Fabricating an artificial photoelectrochemical device to provide electric power on demand is highly desirable but remains a challenge. In response to the intermittent nature of sunlight, we develop a water/oxygen circulation-based biophotoelectrochemical system (BPECS) by integrating a polypyrrole (PPy) capacitor electrode into a photobiofuel cell (PBFC). Unlike traditional PEC devices, the modular and integrated system design of BPECS can not only improve compatibility among PEC cells, BFCs, and capacitor devices, but also offers a feasible way for tackling the intermittent nature of sunlight. In this system, the molecules of water and oxygen can form a self-circulation, thus making this device intrinsically safe and cost-effective. Through the alternate two-step energy conversion (i.e., solar-to-chemical/electric and chemical-to-electric), this conceptual model obtains maximum power output densities of 0.34 ± 0.01 and 0.19 ± 0.02 mW cm-2 in light and dark conditions, respectively, and presents stable long-term cycling performance for solar energy storage and release. Our results demonstrate that such a BPECS achieves high-effective solar energy utilization, which carries great significance to the development of artificial BPECS and provides research opportunities to explore a deployable route for grid-scale photovoltaic energy storage.

Self-Indicative Gold Nanozyme for H2 O2 and Glucose Sensing.

In addition to superior enzyme-mimicking abilities, nanozymes also have intrinsic physicochemical properties. Integrating the enzyme-like activities and tunable physicochemical properties into a single nanoparticle is a promising strategy for versatile nanozyme design and application. Herein, a composite nanozyme in which Au nanoparticles are encapsulated by Au nanoclusters (AuNP@AuNCs) is presented. By integrating the peroxidase-mimicking ability of fluorescent Au NCs with the glucose oxidase-like activity of Au NPs, the composite nanozyme realized cascade assay of glucose without the aid of external indicators. Compared to traditional multistep colorimetric methods, the analytical process was highly simplified by using the self-responsive nanozyme. This synthetic strategy provided valuable insights into exploring talented nanozymes for sensing diverse targets.

Shape-Control of Pt-Ru Nanocrystals: Tuning Surface Structure for Enhanced Electrocatalytic Methanol Oxidation.

Despite the fact that both electrochemical experiments and density functional theory calculations have testified to the superior electrocatalytic activity and CO-poisoning tolerance of platinum-ruthenium (PtRu) alloy nanoparticles toward the methanol oxidation reaction (MOR), the facet-dependent electrocatalytic properties of PtRu nanoparticles are scarcely revealed because it is extremely difficult to synthesize well-defined facets-enclosed PtRu nanocrystals. Herein, we for the first time report a general synthesis of ultrathin PtRu nanocrystals with tunable morphologies (nanowires, nanorods, and nanocubes) through a one-step solvothermal approach and a systematic investigation of the structure-directing effects of different surfactants and the formation mechanism by control experiments and time-dependent studies. In addition, we utilize these {100} and {111} facets-enclosed PtRu nanocrystals as model catalysts to evaluate the electrocatalytic characteristics of the MOR on different facets. Remarkably, {111}-terminated PtRu nanowires exhibit much higher stability and electrocatalytic mass activity toward MOR, which are 2.28 and 4.32 times higher than those of {100}-terminated PtRu nanocubes and commercial Pt/C, respectively, indicating that PtRu {111} facets possess superior methanol oxidation activity and CO-poisoning resistance relative to {100} facets. Our present work provides a series of well-defined PtRu nanocrystals with tunable facets which would be ideal model electrocatalysts for fundamental research in fuel cell electrocatalysis.

In situ fabrication of hollow ZnO@NC polyhedra from ZIF-8 for the determination of trace Cd(ii).

In this work, a novel electrochemical sensor for Cd(ii) detection with differential pulse anodic stripping voltammetry (DPASV) is fabricated based on hollow ZnO@nitrogen-doped carbon (H-ZnO@NC) polyhedra, which are prepared from ZIF-8 via in situ tannic acid etching and a subsequent calcination process. The as-obtained H-ZnO@NC exhibits a polyhedral morphology with a well-defined hollow structure and a uniform distribution of elements C, N, O, and Zn in the shell. The unique structure of H-ZnO@NC can provide an enlarged surface area and abundant active sites. Moreover, ZnO has a strong affinity for heavy metals, which can enhance the adsorption capacity of H-ZnO@NC for Cd(ii) in the accumulation step of stripping voltammetry, and thus improve the electrochemical sensing performances. As expected, the H-ZnO@NC-based sensor achieves a wide linear range of 0.3-300 µg L-1, a low detection limit of 0.1 µg L-1 (S/N = 3), and exhibits good selectivity as well as high stability and reproducibility. Moreover, the proposed electrochemical sensor can be applied for the determination of Cd(ii) in real water samples, obtaining satisfactory results.

Fuel-Free Bio-photoelectrochemical Cells Based on a Water/Oxygen Circulation System with a Ni:FeOOH/BiVO4 Photoanode.

A bio-photoelectrochemical cell (BPEC) based on a fuel-free self-circulation water-oxygen-water system was fabricated. It consists of Ni:FeOOH modified n-type bismuth vanadate (BiVO4 ) photoanode and laccase catalyzed biocathode. In this BPEC, irradiation of the photoanode generates photocurrent for photo-oxidation of water to oxygen, which is reduced to water again at the laccase biocathode. Of note, the by-products of two electrode reactions could continue to be reacted, which means the H2 O and O2 molecules are retained in an infinite loop of water-oxygen-water without any sacrificial chemical components. As a result, the assembled fuel-free BPEC exhibits good performance with an open-circuit potential of 0.97 V and a maximum power density of 205 µW cm-2 at 0.44 V. This BPEC based on a self-circulation system offers a fuel-free model to enhance multiple energy conversion and application in reality.