A novel, environmentally friendly dual-signal water toxicity biosensor developed through the continuous release of Fe3.

In this work, a novel, environmentally friendly and simple electrochemical/colorimetric water toxicity biosensor was rationally developed by the continuous release of Fe3+ in a medium. The bioluminescent bacterium Vibrio Fischeri (V. fischeri) was used for the first time as a model bacterium to assess water toxicity for a mediated electrochemical biosensor. The green substance composited by Prussian blue (PB) and yellow K3[Fe(CN)6] was used as the indicator of the colorimetric biosensor. To obtain an ideal electrochemical/colorimetric performance, analytical conditions of the bioassay including NaCl concentration, temperature, concentrations of cells and K3[Fe(CN)6], and incubation time were optimized to 0.5%, 22 oC, 4 (OD600), 10 mM, and 15 min, respectively. The IC50 values of Zn2+, Hg2+, Cd2+ and 3,5-dichlorophenol (3,5-DCP) obtained by electrochemical method were 4.7, 5.0, 17.6 and 10.6 mg/L, respectively. The limits of detection (LODs) of Zn2+, Hg2+, Cd2+ and 3,5-DCP obtained by the naked eye were 6.3, 1.6, 12.5 and 12.5 mg/L, respectively. Two real water samples taken from tap water pipe and the Yitong river were also detected sensitively, and the inhibition ratios obtained were 3.8% and 14.0%, respectively. These results indicate that the V. fischeri-based bioassay is simple, sensitive and inexpensive, which is promising alternative for acute biotoxicity assessment.

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.

Kinetically restrained oxygen reduction to hydrogen peroxide with nearly 100% selectivity.

Hydrogen peroxide has been synthesized mainly through the electrocatalytic and photocatalytic oxygen reduction reaction in recent years. Herein, we synthesize a single-atom rhodium catalyst (Rh1/NC) to mimic the properties of flavoenzymes for the synthesis of hydrogen peroxide under mild conditions. Rh1/NC dehydrogenates various substrates and catalyzes the reduction of oxygen to hydrogen peroxide. The maximum hydrogen peroxide production rate is 0.48 mol gcatalyst-1 h-1 in the phosphorous acid aerobic oxidation reaction. We find that the selectivity of oxygen reduction to hydrogen peroxide can reach 100%. This is because a single catalytic site of Rh1/NC can only catalyze the removal of two electrons per substrate molecule; thus, the subsequent oxygen can only obtain two electrons to reduce to hydrogen peroxide through the typical two-electron pathway. Similarly, due to the restriction of substrate dehydrogenation, the hydrogen peroxide selectivity in commercial Pt/C-catalyzed enzymatic reactions can be found to reach 75%, which is 30 times higher than that in electrocatalytic oxygen reduction reactions.

Interfacial Electron Regulation of Rh Atomic Layer-Decorated SnO2 Heterostructures for Enhancing Electrocatalytic Nitrogen Reduction.

Ammonia (NH3), which serves as a fertilizer supply, is struggling to satisfy the ever-growing population requirements over the world. The electrocatalytic nitrogen reduction to NH3 production is highly desired but shows the extremely poor activity and selectivity of reported electrocatalysts. In this work, we rationally design a novel Rh atomic layer-decorated SnO2 heterostructure catalyst through the interfacial engineering strategy, simultaneously achieving the highest NH3 yield rate (149 µg h-1 mgcat-1) and Faradaic efficiency (11.69%) at -0.35 V vs the reversible hydrogen electrode. This result is superior to the optimum response of previously reported SnO2- or Rh-based catalysts for electrochemical nitrogen reduction. Both X-ray absorption spectra characterization and density functional theory calculations reveal the strong electron interaction between the Rh atomic layer and the SnO2 heterostructure, which effectively regulated the interfacial electron transfer and d-band center. The downshift of the d-band center results in the greatly reduced H adsorption energy and the highly accelerated reaction kinetics for nitrogen reduction. This work endows a new insight into the interfacial electron regulation for weakening H adsorption and further enhancing the electrocatalytic N2 reduction.

Study on simplified strategies for procedure of rapid detection of water toxicity.

In this work, a simplified procedure of detection of water toxicity based on Pt ultramicroelectrode (UME) and mixed microorganism cultured without sterilization was the first proposed. A stable Pt UME was successfully prepared with a special glass tube as insulation and support material, which was used as working electrode in the biosensor. The Pt UME exhibits the typical cyclic voltammogram (CV) of Pt UME with sigmoid shape and possesses good stability, enlarged current response and tunable dimension. In addition, it was an effective and simple method for toxicity biosensor using mixed microorganisms cultured in unsterilized lysogeny broth (LB) as the bioreceptor. K3[Fe(CN)6] was used as an electron mediator. Under the optimal conditions of 30 mM K3[Fe(CN)6], OD600 = 1 cell concentration, and 50 mM phosphate-buffered solution (PBS), the half-maximal inhibitory concentration (IC50) values measured for Cd2+, Cu2+ and Ni2+ were 3.99 mg/L, 1.16 mg/L and 2.37 mg/L, respectively. The results indicated that the biosensor with large diameter Pt UME and mixed microorganisms cultured in unsterilized LB realized rapid and simple detection of water toxicity.

Glucose-oxidase like catalytic mechanism of noble metal nanozymes.

Au nanoparticles (NPs) have been found to be excellent glucose oxidase mimics, while the catalytic processes have rarely been studied. Here, we reveal that the process of glucose oxidation catalyzed by Au NPs is as the same as that of natural glucose oxidase, namely, a two-step reaction including the dehydrogenation of glucose and the subsequent reduction of O2 to H2O2 by two electrons. Pt, Pd, Ru, Rh, and Ir NPs can also catalyze the dehydrogenation of glucose, except that O2 is preferably reduced to H2O. By the electron transfer feature of noble metal NPs, we overcame the limitation that H2O2 must be produced in the traditional two-step glucose assay and realize the rapid colorimetric detections of glucose. Inspired by the electron transport pathway in the catalytic process of natural enzymes, noble metal NPs have also been found to mimic various enzymatic electron transfer reactions including cytochrome c, coenzymes as well as nitrobenzene reductions.

Fabrication of a Novel, Cost-Effective Double-Sided Indium Tin Oxide-Based Nanoribbon Electrode and Its Application of Acute Toxicity Detection in Water.

Microelectrode plays a crucial role in developing a rapid biosensor for detecting toxicity in water. In this study, a nanoribbon electrode (NRE) with amplified microelectrode signal was successfully prepared by electrodepositing 2-allylphenol on a double-sided indium tin oxide glass. The NRE provided a simple mean for obtaining large steady-state current response. Its advantages were discussed by contrasting the toxicity detection of 3,5-dichlorophenol (DCP) with single microelectrode, microelectrode array, and millimeter electrode as working electrodes in which potassium ferricyanide (K3[Fe(CN)6]) was adopted as a mediator, and Escherichia coli was selected as bioreceptor. At a constant potential of 450 mV, the current reached a steady state within 10 s. The biosensor was constructed using the NRE as working electrode, and its feasibility was verified by determining the toxicity of DCP. A 50% inhibitory concentration (IC50) of 3.01 mg/L was obtained by analyzing the current responses of different concentrations of DCP within 1 h. These results exhibited that the proposed method based on the as-prepared NRE was a rapid, sensitive, and cost-effective way for toxicity detection in water.

Coenzyme-dependent nanozymes playing dual roles in oxidase and reductase mimics with enhanced electron transport.

Although nanozymes overcome a series of shortcomings of natural enzymes, their wide applications are hampered due to their limited varieties. In this work, we propose a coenzyme-dependent nanozyme, a synergistic composite comprising zeolitic imidazolate frameworks encapsulated with polyethylenimine (PEI) and functionalized with a flavin mononucleotide (PEI/ZIF-FMN). The flavin mononucleotide (FMN) plays the role of a prosthetic group, and the positively charged NH2 groups in PEI readily provide the binding affinity to nicotinamide adenine dinucleotide (NADH), which facilitates the electron transfer from NADH to FMN and terminal electron acceptors (such as O2) with a greatly enhanced (80 times) catalytic performance. The integrated nanoparticle-coenzyme composite works as an NADH oxidase mimic and couples with dehydrogenases for the tandem enzymatic reaction. PEI/ZIF-FMN also mediated the electron transfer from NADH to cytochrome c (Cyt c), thereby exhibiting Cyt c reductase-like activity.

Synthesis of low dimensional hierarchical transition metal oxides via a direct deep eutectic solvent calcining method for enhanced oxygen evolution catalysis.

Transition metal oxides (TMOs) are regarded as important materials due to their wide applications in catalysis, sensors, energy storage and conversion devices owing to their advantages of facile synthesis, low cost, and high activity. Here we develop a direct deep eutectic solvent (DES) calcining method to prepare low-dimensional and highly active TMOs for the electrochemical oxygen evolution reaction (OER). Glucose monohydrate and urea can form a glucose-urea DES, which was calcined under a N2 atmosphere to produce 2D N,O-doped graphene. When metal precursors were introduced into the glucose-urea DES and calcined together, the TMOs were templated by graphene flakes and exhibited low-dimensional morphologies. With this method, 2D nanonet-shaped La0.5Sr0.5Co0.8Fe0.2O3 (LSCF), Co3O4, NiCo2O4, and RuO2 and 1D nanowire-shaped Ba0.5Sr0.5Co0.8Fe0.2O3 (BSCF) were readily synthesized, and their thickness and porosity can be conveniently tuned by adjusting the concentrations of metal salts. Our nanostructured TMOs were further applied for the OER, and they showed quite competitive activities over their counterparts obtained from other methods. The 2D porous LSCF20-DES exhibited the largest specific surface area (28.9 m2 g-1) and the highest OER electrocatalytic activities (0.304 V overpotential at a current density of 10 mA cm-2). These results demonstrate that the DES calcining method is a comprehensive approach to synthesize hierarchical TMOs as highly active OER catalysts.

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.

Coupling Cu with Au for enhanced electrocatalytic activity of nitrogen reduction reaction.

The electrochemical nitrogen reduction reaction (NRR) under ambient conditions is currently attracting intense attention, but it still remains a great challenge to develop highly selective and active NRR electrocatalysts. Inspired by the intrinsic NRR activity of Au, we systematically studied the synergistic enhanced effect of incorporating other transition metals into Au on its NRR activity. A general strategy was used to synthesize a series of Au-based bimetallic nanocatalysts (AuCu, AuAg, AuPd and AuRu), and the NRR catalytic performance of the as-obtained electrocatalysts was investigated in detail. The experimental results indicate that the positive effect of Cu on NRR was the most remarkable in comparison with that of Ag, Ru and Pd, which can be ascribed to the synergy of the Au and Cu components via modulating the electronic structure and further changing the binding affinity of adsorbed N atoms on the catalyst. Finally, the optimized nanocatalyst with the atom ratio of Au1Cu1 achieved the highest faradaic efficiency (54.96%) and ammonia yield rate (154.91 µg h-1 mgcat-1) at -0.2 V vs. RHE, exceeding those of the previously reported Au nanocatalysts.

A respiration substrate-less isolation method for acute toxicity assessment.

Respiration substrate (RS)-less isolation method was developed for enhancing the sensitivity of acute toxicity assessment of heavy metal ions. RS was removed from the first step of previous isolation method, which was an effective strategy for improving acute toxicity assessment. 50% inhibiting concentration (IC50) values of Cu2+, Cd2+, Zn2+, Hg2+ and Ni2+ were 0.39 mg L-1, 5.99 mg L-1, 3.99 mg L-1, 0.23 mg L-1 and 5.74 mg L-1, respectively. Beyond that, the complicacy of organic toxicants assessments was investigated by choosing 3,5-dichlorophenol (DCP) as model toxicant. Biofilm sensor, morphology method and suspended microbes-based methods including one-pot method, RS-isolation method, RS-less isolation method, RS-less isolation method with added potassium ferricyanide (+F), were compared. The sensitivity to DCP can be ranked as morphology method > suspended microbes-based methods > biofilm method. The difference of the present results implicated that the methodological interference, leading in different detection mechanisms of these methods. The relative investigations can provide theoretical guidance for developing comprehensive detection methods of pollutants.

Bio-inspired nanozyme: a hydratase mimic in a zeolitic imidazolate framework.

Nanozymes provide comparative advantages over natural enzymes and conventional artificial enzymes for catalytic reactions. However, nanozymes are only suitable for limited types of reactions, whose catalytic principles are not yet fully revealed. Herein, a new nanozyme based on a bionic zeolitic imidazolate framework is proposed. Zeolitic imidazolate framework-8 (ZIF-8) possesses a similar geometric structure to that of the active center of human carbonic anhydrase II (hCAII) and exhibits catalytic performance analogous to that of the hCAII. The less imidazolate coordinated zinc cations on the external surface of ZIF-8 can act as Lewis acid sites, lowering the pKa of Zn-bound H2O molecules from 14 to 8.4, which facilitates the deprotonation of H2O molecules and generation of zinc-bound hydroxide nucleophiles. The esterase-like ZIF-8 nanozyme shows a similar affinity to p-nitrophenyl acetate compared with hCAII. The ZIF-8 nanozyme also promotes CO2 hydration and acetylthiocholine hydrolysis reaction, and a series of ZIFs are also found with intrinsic enzyme-like activities due to similar compositions and spatial structures. These results imply that the bionic nanoparticles can be developed to fabricate a new generation of nanozymes by mimicking the active sites of natural enzymes.

In situ reversible color variation of a ready-made upconversion material using the designed component of a three-state fluorescence switching system.

In recent years, upconversion materials have attracted considerable attention because of their unique physicochemical features. Numerous studies have focused on the synthesis of upconversion materials with different colors. However, an easier way to vary the upconversion colors without changing the materials' components has not been extensively studied. In this study, we realized the in situ color variation of the designed upconversion material with the help of a three-state fluorescence switching hybrid device. The device was composed of Prussian blue and upconversion materials; the former element functioned as a fluorescence resonance energy transfer acceptor and the latter acted as a donor. Smartly applying the RGB color model guaranteed multicolor of the device. Moreover, the highest fluorescence contrast of the three-state fluorescence switching system was 86% (larger than the result of a previous study), and the three-state reversibility was remarkable; this was probably owing to the unique layer-by-layer dripping/electrodepositing assembly method. To the best of our knowledge, the in situ reversible color variation of the ready-made upconversion material has been demonstrated for the first time.

Reversible regulation of CdTe quantum dots fluorescence intensity based on Prussian blue with high anti-fatigue performance.

A fluorescence switching device with excellent anti-fatigue performance based on the electrochromic material Prussian blue and fluorophore CdTe quantum dots was realized. The fluorescence switching device ultimately demonstrated a high fluorescence contrast, short response time and superior anti-fatigue property. Notably, the fluorescence contrast remains unchanged after 133 cycles.

DNA-templated silver and silver-based bimetallic clusters with remarkable and sequence-related catalytic activity toward 4-nitrophenol reduction.

Herein, we report the excellent catalytic activity of DNA-AgNCs toward 4-nitrophenol reduction and a strategy for improving their catalytic performance by forming bimetallic clusters (Ag-Pd, Ag-Au and Ag-Pt). The analogous influence of sequences on the catalytic activity of these nanoclusters is disclosed, which is quite different from their erratic fluorescence properties.

Electrochemical fabrication of nanoporous gold electrodes in a deep eutectic solvent for electrochemical detections.

Deep eutectic solvents are a class of green and sustainable solvents in chemical processes. An electrochemical method was developed to fabricate nanoporous gold electrodes by alloying and dealloying Au-Zn alloy in ZnCl2-urea deep eutectic solvent. The as-prepared active nanoporous gold electrodes facilitate the electrochemical detections of water pollutants with superior sensitivities.

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.

New applications of genetically modified Pseudomonas aeruginosa for toxicity detection in water.

A novel mediator-free method based on genetically modified bacteria was developed for detecting water toxicity, where genetically modified Pseudomonas aeruginosa (GM P. aeruginosa) was selected as the biosensor strain and pyocyanin (PYO) produced by this strain was used as the indicator. The toxicity response of GM P. aeruginosa to 3, 5-dichlorophenol (3, 5-DCP) was measured electrochemically and spectroscopically, and the half maximal inhibitory concentration (IC50) of 3, 5-DCP was determined to be 15.1 mg/L. Strikingly, the toxicity of sample solution with 3, 5-DCP could also be estimated visually by naked eyes at a concentration as low as 10 mg/L. The present study provided a convenient, sensitive and cost-effective method for water toxicity detection, and extended biosensing application of the genetically modified bacterium.