In Situ Carbon Corrosion and Cu Leaching as a Strategy for Boosting Oxygen Evolution Reaction in Multimetal Electrocatalysts.

The number of active sites and their intrinsic activity are key factors in designing high-performance catalysts for the oxygen evolution reaction (OER). The synthesis, properties, and in-depth characterization of a homogeneous CoNiFeCu catalyst are reported, demonstrating that multimetal synergistic effects improve the OER kinetics and the intrinsic activity. In situ carbon corrosion and Cu leaching during the OER lead to an enhanced electrochemically active surface area, providing favorable conditions for improved electronic interaction between the constituent metals. After activation, the catalyst exhibits excellent activity with a low overpotential of 291.5 ± 0.5 mV at 10 mA cm-2 and a Tafel slope of 43.9 mV dec-1 . It shows superior stability compared to RuO2 in 1 m KOH, which is even preserved for 120 h at 500 mA cm-2 in 7 m KOH at 50 °C. Single particles of this CoNiFeCu after their placement on nanoelectrodes combined with identical location transmission electron microscopy before and after applying cyclic voltammetry are investigated. The improved catalytic performance is due to surface carbon corrosion and Cu leaching. The proposed catalyst design strategy combined with the unique single-nanoparticle technique contributes to the development and characterization of high-performance catalysts for electrochemical energy conversion.

Amperometric Detection of dsDNA Using an Acridine-Orange-Modified Glucose Oxidase.

In the present "genomic era" and in the developing world of DNA chips, DNA detection based on intercalation of specific molecules is of particular interest because the detection process is largely independent of the sequence of the target DNA. In this work, an acridine-orange-based intercalation compound, which was tethered to deglycosylated glucose oxidase was synthesized ad hoc and investigated for its ability to interact with dsDNA. Amperometric detection of DNA hybridization was achieved by signal amplification based on the catalytic oxidation of glucose by DNA-bound glucose oxidase. A clear distinction between dsDNA and ssDNA was achieved by careful design of a DNA-modified electrode surface and prevention of nonspecific adsorption of the acridine-orange-modified enzyme by implementing a potential-assisted immobilization method.

Amperometric Detection of dsDNA using an Acridine-Orange-Modified Glucose Oxidase.

Invited for this month's cover is the group of Prof. Dr. Wolfgang Schuhmann, Dr. Daliborka Jambrec and Dr. Adrian Ruff at Ruhr-Universität in Bochum, Germany. The cover picture shows a novel procedure for the preferential post-hybridization labeling of double-stranded DNA based on the intercalating compound acridine orange, which was covalently bound to glucose oxidase. Labeling with a highly active biocatalyst allows for a simple and sequence-independent amplification of the signal proportional to the amount of hybridized DNA that may be coupled with other amplification strategies. Read the full text of the article at 10.1002/cplu.201700279.

DNA Intercalators for Detection of DNA Hybridisation: SCS(MI)-MP2 Calculations and Electrochemical Impedance Spectroscopy.

Quantum mechanical SCS(MI)-MP2/cc-pVTZ calculations predict the strength of proflavine, ellipticine and 1-pyrenemethylamine intercalation into single-stranded (ss) and double-stranded (ds) DNA. The results were compared with experimental results obtained from electrochemical impedance spectroscopy (EIS). Similar interaction energies of ellipticine with the guanine-cytosine base pair compared to the individual nucleobases guanine and cytosine suggested non-specific binding also to ssDNA. Accordingly, EIS identified ellipticine as being non-selective and therefore unsuitable for the detection of DNA hybridisation. The interaction energy of proflavine is significantly higher than the minimum required energy for a single intercalation site, and substantially lower with respect to the minimum energy needed for binding with ssDNA. In EIS studies, proflavine did not show any change in the charge-transfer resistance with respect to ssDNA and a decrease with respect to dsDNA. Calculations showed that 1-pyrenemethylamine has sufficiently high interaction energy to intercalate into dsDNA, however, the interaction energy towards ssDNA is close to the minimum required value, suggesting a weak interaction with ssDNA. EIS measurements support the calculations. A method for the calculation of interaction energies is provided, which can be used to characterise the interaction strength between new intercalators and DNA before being synthesised.

Potential-Assisted DNA Immobilization as a Prerequisite for Fast and Controlled Formation of DNA Monolayers.

Highly reproducible and fast potential-assisted immobilization of single-stranded (ss)DNA on gold surfaces is achieved by applying a pulse-type potential modulation. The desired DNA coverage can be obtained in a highly reproducible way within minutes. Understanding the underlying processes occurring during potential-assisted ssDNA immobilization is crucial. We propose a model that considers the role of ions surrounding the DNA strands, the distance dependence of the applied potentials within the electrolyte solution, and most importantly the shift of the potential of zero charge during the immobilization due to the surface modification with DNA. The control of the surface coverage of ssDNA as well as the achieved speed and high reproducibility are seen as prerequisites for improved DNA-based bioassays.

Doping Level of Boron-Doped Diamond Electrodes Controls the Grafting Density of Functional Groups for DNA Assays.

The impact of different doping levels of boron-doped diamond on the surface functionalization was investigated by means of electrochemical reduction of aryldiazonium salts. The grafting efficiency of 4-nitrophenyl groups increased with the boron levels (B/C ratio from 0 to 20,000 ppm). Controlled grafting of nitrophenyldiazonium was used to adjust the amount of immobilized single-stranded DNA strands at the surface and further on the hybridization yield in dependence on the boron doping level. The grafted nitro functions were electrochemically reduced to the amine moieties. Subsequent functionalization with a succinic acid introduced carboxyl groups for subsequent binding of an amino-terminated DNA probe. DNA hybridization significantly depends on the probe density which is in turn dependent on the boron doping level. The proposed approach opens new insights for the design and control of doped diamond surface functionalization for the construction of DNA hybridization assays.