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Electrochemiluminescence (ECL) is a powerful transduction technique with a leading role in the biosensing field due to its high sensitivity and low background signal. Although the intrinsic analytical strength of ECL depends critically on the overall efficiency of the mechanisms of its generation, studies aimed at enhancing the ECL signal have mostly focused on the investigation of materials, either luminophores or coreactants, while fundamental mechanistic studies are relatively scarce. Here, we discover an unexpected but highly efficient mechanistic path for ECL generation close to the electrode surface (signal enhancement, 128%) using an innovative combination of ECL imaging techniques and electrochemical mapping of radical generation. Our findings, which are also supported by quantum chemical calculations and spin trapping methods, led to the identification of a family of alternative branched amine coreactants, which raises the analytical strength of ECL well beyond that of present state-of-the-art immunoassays, thus creating potential ECL applications in ultrasensitive bioanalysis. Electrochemiluminescence (ECL) is a leading technique in biosensing. Here the authors identify an ECL generation mechanism near the electrode surface, which they exploit in combination with the use of branched amine coreactants to improve the ECL signal beyond the state-of-the-art immunoassays.

Pyridines and related N -heteroarenes are commonly found in pharmaceuticals, agrochemicals and other biologically active compounds 1 , 2 . Site-selective C–H functionalization would provide a direct way of making these medicinally active products 3 – 5 . For example, nicotinic acid derivatives could be made by C–H carboxylation, but this remains an elusive transformation 6 – 8 . Here we describe the development of an electrochemical strategy for the direct carboxylation of pyridines using CO 2 . The choice of the electrolysis setup gives rise to divergent site selectivity: a divided electrochemical cell leads to C5 carboxylation, whereas an undivided cell promotes C4 carboxylation. The undivided-cell reaction is proposed to operate through a paired-electrolysis mechanism 9 , 10 , in which both cathodic and anodic events play critical roles in altering the site selectivity. Specifically, anodically generated iodine preferentially reacts with a key radical anion intermediate in the C4-carboxylation pathway through hydrogen-atom transfer, thus diverting the reaction selectivity by means of the Curtin–Hammett principle 11 . The scope of the transformation was expanded to a wide range of N -heteroarenes, including bipyridines and terpyridines, pyrimidines, pyrazines and quinolines. An electrochemical strategy is described in which the direct carboxylation of pyridines and related N -heteroarenes with CO 2 shows divergent site selectivity depending on the type of reactor used.

Since their conception, ionic liquids (ILs) have been investigated for an extensive range of applications including in solvent chemistry, catalysis, and electrochemistry. This is due to their designation as designer solvents, whereby the physiochemical properties of an IL can be tuned for specific applications. This has led to significant research activity both by academia and industry from the 1990s, accelerating research in many fields and leading to the filing of numerous patents. However, while ILs have received great interest in the patent literature, only a limited number of processes are known to have been commercialised. This review aims to provide a perspective on the successful commercialisation of IL-based processes, to date, and the advantages and disadvantages associated with the use of ILs in industry.

Soil contamination by heavy metals constitutes an important environmental problem, whereas field applicability of existing remediation technologies has encountered numerous obstacles, such as long operation time, high chemical cost, large energy consumption, secondary pollution, and soil degradation. Here we report the design and demonstration of a remediation method based on a concept of asymmetrical alternating current electrochemistry that achieves high degrees of contaminant removal for different heavy metals (copper, lead, cadmium) at different initial concentrations (from 100 to 10,000 ppm), all reaching corresponding regulation levels for residential scenario after rational treatment time (from 30 min to 6 h). No excessive nutrient loss in treated soil is observed and no secondary toxic product is produced. Long-term experiment and plant assay show the high sustainability of the method and its feasibility for agricultural use. Soil pollution by heavy metals is a problem of global concern, requiring the development of remediation technologies. Here the authors report a method based on asymmetrical alternating current electrochemistry, which enables recycling of soil washing chemicals and eliminates secondary pollution.

Pseudocapacitance is commonly associated with surface or near-surface reversible redox reactions. The kinetics of charge storage in T -Nb 2 O 5 electrodes is now quantified and the mechanism of lithium intercalation pseudocapacitance should prove to be important in obtaining high-rate charge-storage devices. Pseudocapacitance is commonly associated with surface or near-surface reversible redox reactions, as observed with RuO 2 · x H 2 O in an acidic electrolyte. However, we recently demonstrated that a pseudocapacitive mechanism occurs when lithium ions are inserted into mesoporous and nanocrystal films of orthorhombic Nb 2 O 5 ( T -Nb 2 O 5 ; refs  1 , 2 ). Here, we quantify the kinetics of charge storage in T -Nb 2 O 5 : currents that vary inversely with time, charge-storage capacity that is mostly independent of rate, and redox peaks that exhibit small voltage offsets even at high rates. We also define the structural characteristics necessary for this process, termed intercalation pseudocapacitance, which are a crystalline network that offers two-dimensional transport pathways and little structural change on intercalation. The principal benefit realized from intercalation pseudocapacitance is that high levels of charge storage are achieved within short periods of time because there are no limitations from solid-state diffusion. Thick electrodes (up to 40 μm thick) prepared with T -Nb 2 O 5 offer the promise of exploiting intercalation pseudocapacitance to obtain high-rate charge-storage devices.

The removal of highly toxic, ultra-dilute contaminants of concern has been a primary challenge for clean water technologies. Chromium and arsenic are among the most prevalent heavy metal pollutants in urban and agricultural waters, with current separation processes having severe limitations due to lack of molecular selectivity. Here, we report redox-active metallopolymer electrodes for the selective electrochemical removal of chromium and arsenic. An uptake greater than 100 mg Cr/g adsorbent can be achieved electrochemically, with a 99% reversible working capacity, with the bound chromium ions released in the less harmful trivalent form. Furthermore, we study the metallopolymer response during electrochemical modulation by in situ transmission electron microscopy. The underlying mechanisms for molecular selectivity are investigated through electronic structure calculations, indicating a strong charge transfer to the heavy metal oxyanions. Finally, chromium and arsenic are remediated efficiently at concentrations as low as 100 ppb, in the presence of over 200-fold excess competing salts. Chromium and arsenic are prevalent water pollutants, but their removal is currently limited by low selectivity. Here, the authors use redox-active metallopolymer electrodes based on poly(vinyl)ferrocene to selectively remove the two heavy metal oxyanions at concentrations as low as 100 ppb.

A uric acid (UA) electrochemical biosensor was constructed using ferrocene (Fc) decorated cuprous oxide (Cu 2 O) enhanced electro-active characteristics and covalently immobilized with uricase (UOx) on glassy carbon electrode (GCE). The electrochemical characteristics of the fabricated electrode was analysed by cyclic voltammetry, electrochemical impedance spectroscopy and differential pulse voltammetry (DPV). DPV studies revealed rapid response of fabricated electrode UOx/Fc/Cu 2 O/GCE towards UA in a wide concentration range of 0.1–1,000 μM with a sensitivity of 1.900 μA mM −1  cm −2 and very low detection limit of 0.0596 μM. A very low magnitude Michaelis–Menten constant (Km) value was evaluated as 34.7351 μM which indicated the chemical attraction of the enzyme towards the UA was much higher. The developed biosensor was successfully applied to detect UA in human urine samples. Moreover, reproducibility and stability studies demonstrated the fabricated UOx/Fc/Cu 2 O/GCE biosensor had high reproducibility with a RSD of 2.8% and good reusability with a RSD of 3.2%. Specificity studies results showed the fabricated biosensor had strong anti-interference ability. The improved sensor performance was attributed to the synergistic electronic properties of Cu 2 O and Fc that provided enhances delectrocatalytic activity and electron transfer. The present biosensor can be extended for use in clinical settings.

Epithelial-mesenchymal transition (EMT) is critically involved in a variety of biological processes. Electrochemical sensing offers potential to develop more effective technology for EMT detection. In this study, by using the unique performance of quantum dot (QD)-nanocomposite materials, we establish an electrochemical biosensor that can specifically detect the change of E-cadherin and analyze different stages of EMT. The signal for EMT is largely magnified due to the transmission of molecular information to the electronic device. In addition, differential pulse voltammetry reveals that the response of the electrochemical signals is rapid and sensitive, due to the synergistic effect of QDs and carbon nanotube-gold nanoparticles. Our study thus suggests that electrochemical sensing is an effective technology for detecting EMT and may have broad applications in analyzing various cell type transitions. Epithelial-mesenchymal transition (EMT) plays a key role in embryonic development, wound healing and cancer. Here the authors develop an electrochemical sensor to detect EMT using E-cadherin antibody-quantum dot conjugates and a carbon nanotube-gold nanoparticle-modified electrode as a detection platform.

While high sulfur loading has been pursued as a key parameter to build realistic high-energy lithium-sulfur batteries, less attention has been paid to the cathode porosity, which is much higher in sulfur/carbon composite cathodes than in traditional lithium-ion battery electrodes. For high-energy lithium-sulfur batteries, a dense electrode with low porosity is desired to minimize electrolyte intake, parasitic weight, and cost. Here we report the profound impact on the discharge polarization, reversible capacity, and cell cycling life of lithium-sulfur batteries by decreasing cathode porosities from 70 to 40%. According to the developed mechanism-based analytical model, we demonstrate that sulfur utilization is limited by the solubility of lithium-polysulfides and further conversion from lithium-polysulfides to Li 2 S is limited by the electronically accessible surface area of the carbon matrix. Finally, we predict an optimized cathode porosity to maximize the cell level volumetric energy density without sacrificing the sulfur utilization. For high-energy lithium-sulfur batteries, a dense electrode with low porosity is desired to minimize electrolyte intake, parasitic weight, and cost. Here the authors show the impact of porosity on the performance of lithium-sulfur batteries and reveal the mechanism through analytical modeling.

Aziridines—three-membered nitrogen-containing cyclic molecules—are important synthetic targets. Their substantial ring strain and resultant proclivity towards ring-opening reactions makes them versatile precursors of diverse amine products 1 – 3 , and, in some cases, the aziridine functional group itself imbues important biological (for example, anti-tumour) activity 4 – 6 . Transformation of ubiquitous alkenes into aziridines is an attractive synthetic strategy, but is typically accomplished using electrophilic nitrogen sources rather than widely available amine nucleophiles. Here we show that unactivated alkenes can be electrochemically transformed into a metastable, dicationic intermediate that undergoes aziridination with primary amines under basic conditions. This new approach expands the scope of readily accessible N -alkyl aziridine products relative to those obtained through existing state-of-the-art methods. A key strategic advantage of this approach is that oxidative alkene activation is decoupled from the aziridination step, enabling a wide range of commercially available but oxidatively sensitive 7 amines to act as coupling partners for this strain-inducing transformation. More broadly, our work lays the foundations for a diverse array of difunctionalization reactions using this dication pool approach. The synthesis of aziridines—three-membered nitrogen-containing heterocycles—is achieved by a new method involving the electrochemical coupling of alkenes and amines, via a dicationic intermediate.