Anisotropic growth of gold anchors on CdSe semiconductor quantum platelets for self-assembled architectures with well-connected electronic circuits for the electrochemical detection of enrofloxacin.

Anisotropic growth of nanomaterials enables advances in building diverse and complex architectures, which exhibit unique properties and enrich the choice of nano-building modules for electrochemical sensor devices. Herein, an anisotropic growth method was proposed to anchor gold nanoparticles (AuNPs) onto both ends of quasi-two-dimensional CdSe semiconductor quantum nanoplatelets (NPLs), appearing with a monodisperse and uniform nano-dumbbell shape. Then, these AuNPs were exploited as natural anchor points and further initiated self-assembly to create complex architectures via dithiol bridges. Detailed studies illustrated that the covalent Se-Au bonds facilitate effective charge transfer in the internal metal-semiconductor (M-S) electric field. The narrowed energy gap and up-shifted highest occupied molecular orbital were favored for electron removal during the electro-oxidation process. The ultrathin CdSe NPLs supplied a large specific surface area, carrying remaining holes and abundant active sites for target electro-catalysis. As a result, using the assembled complex as the electrode matrix with well-connected electronic circuits, a reliable electrochemical sensor was achieved for enrofloxacin detection. Under the optimal conditions, the current response exhibits two linear dynamic ranges, 0.01-10.0 µM and 10.0-250 µM, and the detection limit was calculated as 0.0026 µM. This work not only opens up broad application prospects for heterogeneous M-S combinations as effective electrochemical matrixes but also develops reliable antibiotic assays for food and environmental safety.

Two-Dimensional Fe-N-C Single-Atomic-Site Catalysts with Boosted Peroxidase-Like Activity for a Sensitive Immunoassay.

Single-atomic-site catalysts (SASCs) with peroxidase (POD)-like activities have been widely used in various sensing platforms, like the enzyme-linked immunosorbent assay (ELISA). Herein, a two-dimensional Fe-N-C-based SASC (2D Fe-SASC) is successfully synthesized with excellent POD-like activity (specific activity = 90.11 U/mg) and is used to design the ELISA for herbicide detection. The 2D structure of Fe-SASC enables the exposure of numerous single atomic active sites on the surface as well as boosts the POD-like activity, thereby enhancing the sensing performance. 2D Fe-SASC is assembled into competitive ELISA kit, which achieves an excellent detection performance for 2,4-dichlorophenoxyacetic acid (2,4-D). Fe-SASC has great potential in replacing high-cost natural enzymes and working on various advanced sensing platforms with high sensitivity for the detection of various target biomarkers.

An Iron(III)-Based Metal-Organic Gel-Catalyzed Dual Electrochemiluminescence System for Cytosensing and In Situ Evaluation of the VEGF165 Subtype.

The recent surge of interest in metal-organic gels (MOGs) has emerged for their soft porous structure, large surface area, and abundant active metal sites, making them a promising candidate for building catalyst matrices. In this work, facilely synthesized Fe(III)-organic gel was directly used as a robust electrode matrix. Detailed studies illustrated that their Fe(III) centers can speed up the electro-oxidation/reduction of the H2O2 coreactant to produce reactive oxygen species for enhancing a potential-resolved dual electrochemiluminescence (ECL) emission. Among them, the anodic signal of luminol varied with the cell concentration based on the impedance ECL mechanism, while the cathodic signal of CdS quantum dots traced the VEGF165 subtype at cell surface by specific aptamer recognition. Based on this, a ratiometric strategy was proposed for accurate cytosensing by eliminating environmental interference. Moreover, by cooperating these two signals, a novel strategy was developed for direct evaluation of the VEGF165 subtype, further realizing rapid drug screening and subtype assessment on different cell lines. This work not only opens up the promising application of MOGs as an effective catalyst matrix but also develops reliable cell assays and protein subtype identification for clinical diagnosis and research.

Single-Atomic Iron Doped Carbon Dots with Both Photoluminescence and Oxidase-Like Activity.

Multifunctional nanozymes can benefit biochemical analysis via expanding sensing modes and enhancing analytical performance, but designing multifunctional nanozymes to realize the desired sensing of targets is challenging. In this work, single-atomic iron doped carbon dots (SA Fe-CDs) are designed and synthesized via a facile in situ pyrolysis process. The small-sized CDs not only maintain their tunable fluorescence, but also serve as a support for loading dispersed active sites. Monoatomic Fe offers SA Fe-CDs exceptional oxidase-mimetic activity to catalyze 3,3',5,5'-tetramethylbenzidine (TMB) oxidation with fast response (Vmax  = 10.4 nM s-1 ) and strong affinity (Km  = 168 µM). Meanwhile, their photoluminescence is quenched by the oxidation product of TMB due to inner filter effect. Phosphate ions (Pi) can suppress the oxidase-mimicking activity and restore the photoluminescence of SA Fe-CDs by interacting with Fe active sites. Based on this principle, a dual-mode colorimetric and fluorescence assay of Pi with high sensitivity, selectivity, and rapid response is established. This work paves a path to develop multifunctional enzyme-like catalysts, and offers a simple but efficient dual-mode method for phosphate monitoring, which will inspire the exploration of multi-mode sensing strategies based on nanozyme catalysis.

2D Catalysts for CO2 Photoreduction: Discussing Structure Efficiency Strategies and Prospects for Scaled Production Based on Current Progress.

Currently, the excessive consumption of fossil fuels is accompanied by massive emissions of CO2 , leading to severe energy shortages and intensified global warming. It is of great significance to develop and use renewable clean energy while reducing the concentration of CO2 in the atmosphere. Photocatalytic technology is a promising strategy for carbon dioxide conversion. Clearly, the achievement of the above goals largely depends on the design and construction of catalysts. This review is mainly focused on the application of 2D materials for photocatalytic CO2 reduction. The contribution of synthetic strategies to their structure and performance is emphasized. Finally, the current challenges, and prospects of 2D materials for photoreduction of CO2 with high efficiency, even for practical applications are discussed. It is hoped that this review can provide some guidance for the rational design, controllable synthesis of 2D materials, and their application for efficient photocatalytic CO2 reduction.

Single-Atomic Site Catalyst with Heme Enzymes-Like Active Sites for Electrochemical Sensing of Hydrogen Peroxide.

Heme enzymes, with the pentacoordinate heme iron active sites, possess high catalytic activity and selectivity in biosensing applications. However, they are still subject to limited catalytic stability in the complex environment and high cost for broad applications in electrochemical sensing. It is meaningful to develop a novel substitute that has a similar structure to some heme enzymes and mimics their enzyme activities. One emerging strategy is to design the Fe-N-C based single-atomic site catalysts (SASCs). The obtained atomically dispersed Fe-Nx active sites can mimic the active sites of heme enzymes effectively. In this work, a SASC (Fe-SASC/NW) is synthesized by doping single iron atoms in polypyrrole (PPy) derived carbon nanowire via a zinc-atom-assisted method. The proposed Fe-SASC/NW shows high heme enzyme-like catalytic performance for hydrogen peroxide (H2 O2 ) with a specific activity of 42.8 U mg-1 . An electrochemical sensor based on Fe-SASC/NW is developed for the detection of H2 O2 . This sensor exhibits a wide detection concentration range from 5.0 × 10-10 m to 0.5 m and an excellent limit of detection (LOD) of 46.35 × 10-9 m. Such excellent catalytic activity and electrochemical sensing sensitivity are attributed to the isolated Fe-Nx active sites and their structural similarity with natural metalloproteases.

Controlled Synthesis of EDTA-Modified Porous Hollow Copper Microspheres for High-Efficiency Conversion of CO2 to Multicarbon Products.

Electrochemical reduction of CO2 into value-added products is an effective approach to relieve environmental and energetic issues. Herein, EDTA anion-modified porous hollow copper microspheres (H-Cu MPs) were constructed by EDTA-2Na-assisted electrodeposition. The faradic efficiency (FE) of ethylene doubled from 23.3% to 50.1% at -0.82 V vs RHE in nearly neutral 0.1 M KHCO3 solution, one of the highest values among copper-based electrodeposited catalysts. Apart from the favorable influence from morphology regulated by EDTA-2Na, theoretical calculations revealed that the adsorbed EDTA anions were able to create a local charged copper surface to stabilize the transition state and dimer and to assist in the stabilization by interacting with OCCO adsorbate synergistically, which contributed to the outstanding catalytic performance together.

Hydrogen Evolution Reaction Monitored by Electrochemiluminescence Blinking at Single-Nanoparticle Level.

Monitoring and characterization methods that provide performance tracking of hydrogen evolution reaction (HER) at the single-nanoparticle level can greatly advance our understanding of catalysts' structure and activity relationships. Electrochemiluminescence (ECL) microscopy is implemented for the first time to identify HER activities of single nanocatalysts and to provide a direction for further optimization. Here, we develop a novel ECL blinking technique at the single-nanoparticle level to directly monitor H2 nanobubbles generated from hollow carbon nitride nanospheres (HCNSs). The ECL ON and OFF mechanisms are identified being closely related to the generation, growth, and collapse of H2 nanobubbles. The power-law distributed durations of ON and OFF states demonstrate multiple catalytic sites with stochastic activities on a single HCNS. The power-law coefficients of ECL blinking increase with improved HER activities from modified HCNSs with other active HER catalysts. Besides, ECL blinking phenomenon provides an explanation for the low cathodic ECL efficiency of semiconductor nanomaterials.

Producing non-traditional flour from watermelon rind pomace: Artificial neural network (ANN) modeling of the drying process.

An artificial neural network (ANN) model was developed to simulate the convective drying process of watermelon rind pomace used in the fabrication of non-traditional flour. Also, the drying curves obtained experimentally were fitted with eleven different empirical models to compare both modeling approaches. Lastly, to reduce the required fossil fuel in the convective drying process, two types of solar air heaters (SAH) were presented and experimentally evaluated. The optimization of the ANN by a genetic algorithm (GA) resulted in an optimal number of neurons of nine (9) for the first hidden layer and ten (10) for the second hidden layer. Also, the ANN performed better than the best fitted empirical model. Simulations with the trained ANN showed very promising generalization capabilities. The type II SAH showed the best performance and the highest air temperature it reached was 45 °C. The specific energy consumption (SEC) needed to dry the watermelon rind at this temperature and the CO2 emissions were 609 kWh.kg-1 and 318 kg CO2.kWh-1, respectively. Using the type II SAH, this energy amount would be saved without CO2 emissions. To reach higher drying temperatures the combination of the SAH and the electrical convective dryer is possible.

Bio-Coreactant-Enhanced Electrochemiluminescence Microscopy of Intracellular Structure and Transport.

A bio-coreactant-enhanced electrochemiluminescence (ECL) microscopy realizes the ECL imaging of intracellular structure and dynamic transport. This microscopy uses Ru(bpy)32+ as the electrochemical molecular antenna connecting extracellular and intracellular environments, and uses intracellular biomolecules as the coreactants of ECL reactions via a "catalytic route". Accordingly, intracellular structures are identified without using multiple labels, and autophagy involving DNA oxidative damage is detected using nuclear ECL signals. A time-resolved image sequence discloses the universal edge effect of cellular electroporation due to the influence of the geometric properties of cell membranes on the induced transmembrane voltage. The dynamic transport of Ru(bpy)33+ in the different cellular compartments unveils the heterogeneous intracellular diffusivity correlating with the actin cytoskeleton. In addition to single-cell studies, the bio-coreactant-enhanced ECL microscopy is used to image a slice of a mouse liver and a colony of Shewanella oneidensis MR-1.

Stable and Monochromatic All-Inorganic Halide Perovskite Assisted by Hollow Carbon Nitride Nanosphere for Ratiometric Electrochemiluminescence Bioanalysis.

Lead halide perovskites have been promising electrochemiluminescence (ECL) candidates because of their excellent photophysical attributes, but their poor stability has severely restricted ECL applications. Herein, the in situ assembly of all-inorganic perovskite CsPbBr3 nanocrystals (CPB) into hollow graphitic carbon nitride nanospheres (HCNS) were described as a novel ECL emitter. The architecture guaranteed not only improved stability because of the peripheral HCNS protecting shell but also high-performance ECL of CPB because of a matching band-edge arrangement. Dual-ECL readouts were obtained from the nanocomposite including an anodic ECL from CPB and a cathodic ECL from HCNS. The former displayed prominent color purity to construct an efficient ECL resonance energy transfer system, and the latter served as an internal standard for a ratiometric analysis. A well-designed DNA probe was further utilized for the targeting of CD44 receptors on the MCF-7 cell surface and the double signal amplification. The sensing strategy exhibited good analytical performance for MCF-7 cells, ranging from 1.0 × 103 to 3.2 × 105 cells mL-1 with a detection limit of 320 cells mL-1. Sensitive and accurate evaluation of CD44 expression was finally achieved at 0.22 pM. This work is the first attempt to use halide perovskite for reliable ECL bioanalysis and provides a perspective to design a perovskite-based nanocomposite as a high-performance ECL emitter for its exclusive ECL system.

Bipyridine-Assisted Assembly of Au Nanoparticles on Cu Nanowires To Enhance the Electrochemical Reduction of CO2.

We report a new strategy to prepare a composite catalyst for highly efficient electrochemical CO2 reduction reaction (CO2 RR). The composite catalyst is made by anchoring Au nanoparticles on Cu nanowires via 4,4'-bipyridine (bipy). The Au-bipy-Cu composite catalyzes the CO2 RR in 0.1 m KHCO3 with a total Faradaic efficiency (FE) reaching 90.6 % at -0.9 V to provide C-products, among which CH3 CHO (25 % FE) dominates the liquid product (HCOO- , CH3 CHO, and CH3 COO- ) distribution (75 %). The enhanced CO2 RR catalysis demonstrated by Au-bipy-Cu originates from its synergistic Au (CO2 to CO) and Cu (CO to C-products) catalysis which is further promoted by bipy. The Au-bipy-Cu composite represents a new catalyst system for effective CO2 RR conversion to C-products.

Tuning Sn-Catalysis for Electrochemical Reduction of CO2 to CO via the Core/Shell Cu/SnO2 Structure.

Tin (Sn) is known to be a good catalyst for electrochemical reduction of CO2 to formate in 0.5 M KHCO3. But when a thin layer of SnO2 is coated over Cu nanoparticles, the reduction becomes Sn-thickness dependent: the thicker (1.8 nm) shell shows Sn-like activity to generate formate whereas the thinner (0.8 nm) shell is selective to the formation of CO with the conversion Faradaic efficiency (FE) reaching 93% at -0.7 V (vs reversible hydrogen electrode (RHE)). Theoretical calculations suggest that the 0.8 nm SnO2 shell likely alloys with trace of Cu, causing the SnO2 lattice to be uniaxially compressed and favors the production of CO over formate. The report demonstrates a new strategy to tune NP catalyst selectivity for the electrochemical reduction of CO2 via the tunable core/shell structure.

Acceptance and Continuation of Contraceptive Methods Immediate Postabortion.

BACKGROUND/AIMS: Providing preabortion contraceptive counseling for the method of contraception may reduce the incidence of repeat abortions. This study aimed to compare the acceptance and continuation rates of intrauterine devices (IUDs), combined oral contraceptives (COCs), and condom use after abortion in women who received preabortion contraceptive counseling. METHODS: Women seeking a first-trimester abortion prospectively received preabortion contraceptive counseling and the choice of method of contraception was based on the counseling and not related to prior methods of birth control. Outcomes included continuation of postabortion contraceptive use and repeat abortions over a 6-month follow-up period. RESULTS: Four hundred and fifty-five women (IUD group: n = 161; COC group: n = 149; condom group: n = 135) completed 6-month follow-up after the abortions. At the sixth month follow-up, patients continued using the IUD, COC, and condoms for contraception were 64.2, 10, and 51.5%, respectively. Higher age, being married, parity ≥1, and previous abortion were factors that were associated with more frequent selection of an IUD, while a higher education level was associated with a more frequent selection of COC and condoms. CONCLUSION: The continued use of COCs after abortion is low even with preabortion contraceptive counseling. The IUD offers reliable birth control with a lower discontinuation rate than COCs or condoms.

New approach to fully ordered fct-FePt nanoparticles for much enhanced electrocatalysis in acid.

Fully ordered face-centered tetragonal (fct) FePt nanoparticles (NPs) are synthesized by thermal annealing of the MgO-coated dumbbell-like FePt-Fe3O4 NPs followed by acid washing to remove MgO. These fct-FePt NPs show strong ferromagnetism with room temperature coercivity reaching 33 kOe. They serve as a robust electrocatalyst for the oxygen reduction reaction (ORR) in 0.1 M HClO4 and hydrogen evolution reaction (HER) in 0.5 M H2SO4 with much enhanced activity (the most active fct-structured alloy NP catalyst ever reported) and stability (no obvious Fe loss and NP degradation after 20 000 cycles between 0.6 and 1.0 V (vs RHE)). Our work demonstrates a reliable approach to FePt NPs with much improved fct-ordering and catalytic efficiency for ORR and HER.

A New Core/Shell NiAu/Au Nanoparticle Catalyst with Pt-like Activity for Hydrogen Evolution Reaction.

We report a general approach to NiAu alloy nanoparticles (NPs) by co-reduction of Ni(acac)2 (acac = acetylacetonate) and HAuCl4·3H2O at 220 °C in the presence of oleylamine and oleic acid. Subject to potential cycling between 0.6 and 1.0 V (vs reversible hydrogen electrode) in 0.5 M H2SO4, the NiAu NPs are transformed into core/shell NiAu/Au NPs that show much enhanced catalysis for hydrogen evolution reaction (HER) with Pt-like activity and much robust durability. The first-principles calculations suggest that the high activity arises from the formation of Au sites with low coordination numbers around the shell. Our synthesis is not limited to NiAu but can be extended to FeAu and CoAu as well, providing a general approach to MAu/Au NPs as a class of new catalyst superior to Pt for water splitting and hydrogen generation.

Monodisperse MPt (M = Fe, Co, Ni, Cu, Zn) nanoparticles prepared from a facile oleylamine reduction of metal salts.

We report a simple, yet general, approach to monodisperse MPt (M = Fe, Co, Ni, Cu, Zn) nanoparticles (NPs) by coreduction of M(acac)2 and Pt(acac)2 (acac = acetylacetonate) with oleylamine at 300 °C. In the current reaction condition, oleylamine serves as the reducing agent, surfactant, and solvent. As an example, we describe in details the synthesis of 9.5 nm CoPt NPs with their compositions controlled from Co37Pt63 to Co69Pt31. These NPs show composition-dependent structural and magnetic properties. The unique oleylamine reduction process makes it possible to prepare MPt NPs with their physical properties and surface chemistry better rationalized for magnetic or catalytic applications.

Core/shell Au/CuPt nanoparticles and their dual electrocatalysis for both reduction and oxidation reactions.

We report a facile synthesis of monodisperse core/shell 5/1.5 nm Au/CuPt nanoparticles by coreduction of platinum acetylacetonate and copper acetylacetonate in the presence of 5 nm Au nanoparticles. The CuPt alloy effect and core/shell interactions make these Au/CuPt nanoparticles a promising catalyst for both oxygen reduction reaction and methanol oxidation reaction in 0.1 M HClO4 solution. Their specific (mass) reduction and oxidation activities reach 2.72 mA/cm(2) (1500 mA/mg Pt) at 0.9 V and 0.755 mA/cm(2) (441 mA/mg Pt) at 0.8 V (vs reversible hydrogen electrode), respectively. Our studies show that the existence of the Au nanoparticle core not only minimizes the Pt usage but also improves the stability of the Au/CuPt catalyst for fuel cell reactions. The results suggest that the core/shell design is indeed effective for optimizing nanoparticle catalysis. The same concept may be extended to other multimetallic nanoparticle systems, making it possible to tune nanoparticle catalysis for many different chemical reactions.

Active and selective conversion of CO2 to CO on ultrathin Au nanowires.

In this communication, we show that ultrathin Au nanowires (NWs) with dominant edge sites on their surface are active and selective for electrochemical reduction of CO2 to CO. We first develop a facile seed-mediated growth method to synthesize these ultrathin (2 nm wide) Au NWs in high yield (95%) by reducing HAuCl4 in the presence of 2 nm Au nanoparticles (NPs). These NWs catalyze CO2 reduction to CO in aqueous 0.5 M KHCO3 at an onset potential of -0.2 V (vs reversible hydrogen electrode). At -0.35 V, the reduction Faradaic efficiency (FE) reaches 94% (mass activity 1.84 A/g Au) and stays at this level for 6 h without any noticeable activity change. Density functional theory (DFT) calculations suggest that the excellent catalytic performance of these Au NWs is attributed both to their high mass density of reactive edge sites (≥16%) and to the weak CO binding on these sites. These ultrathin Au NWs are the most efficient nanocatalyst ever reported for electrochemical reduction of CO2 to CO.