Electrochemical Reduction of Carbon Dioxide at TiO2/Au Nanocomposites.

Herein, we report on the facile synthesis of nanocomposite consisting of TiO2 and Au nanoparticles (NPs) via a tailored galvanic replacement reaction (GRR). The electrocatalytic activity of the synthesized TiO2/Au nanocomposites for CO2 reduction was investigated in an aqueous solution using various electrochemical methods. Our results demonstrated that the TiO2/Au nanocomposites formed through the GRR process exhibited improved catalytic activities for CO2 reduction, while generating more hydrocarbon molecules than the typical formation of CO in contrast to polycrystalline Au. GC analysis and NMR spectroscopy revealed that CO and CH4 were the gas products, whereas HCOO-, CH3COO-, CH3OH, and CH3CH2OH were the liquid products from the CO2 reduction at different cathodic potentials. This remarkable change was further studied using the density functional theory (DFT) calculations, showing that the TiO2/Au nanocomposites may increase the binding energy of the formed ·CO intermediate and reduce the free energy compared to Au, thus favoring the downstream generation of multicarbon products. The TiO2/Au nanocomposites have high catalytic activity and excellent stability and are easy to fabricate, indicating that the developed catalyst has potential application in the electrochemical reduction of CO2 to value-added products.

Metal-dependent electrochemical discrimination of DNA quadruplex sequences.

Films of four different DNA quadruplex-forming (G4) sequences (c-KIT, c-MYC, HTelo, and BCL2) on gold surfaces were investigated by electrochemical impedance spectroscopy (EIS) to evaluate whether they evoke unique electrochemical responses that can be used for their identification. This could render EIS an alternative means for the determination of G4 sequences of unknown structure. Towards, this end, cation-dependent topology changes in the presence of either K+, K+ in combination with Li+, or Pb2+ in the presence of Li+ were first evaluated by circular dichroism (CD) spectroscopy, and electrochemical studies were performed subsequently. As a result, G4-sequence specific charge transfer resistance (RCT) patterns were in fact observed for each G4 sequence, allowing their discrimination by EIS.

Nanoporous Gold for the Miniaturization of In Vivo Electrochemical Aptamer-Based Sensors.

Electrochemical aptamer-based sensors enable real-time molecular measurements in the living body. The spatial resolution of these measurements and ability to perform measurements in targeted locations, however, is limited by the length and width of the device's working electrode. Historically, achieving good signal to noise in the complex, noisy in vivo environment has required working electrode lengths of 3-6 mm. To enable sensor miniaturization, here we have enhanced the signaling current obtained for a sensor of given macroscopic dimensions by increasing its surface area. Specifically, we produced nanoporous gold via an electrochemical alloying/dealloying technique to increase the microscopic surface area of our working electrodes by up to 100-fold. Using this approach, we have miniaturized in vivo electrochemical aptamer-based (EAB) sensors (here using sensors against the antibiotic, vancomycin) by a factor of 6 while retaining sensor signal and response times. Conveniently, the fabrication of nanoporous gold is simple, parallelizable, and compatible with both two- and three-dimensional electrode architectures, suggesting that it may be of value to a range of electrochemical biosensor applications.

Development of a novel label-free impedimetric electrochemical sensor based on hydrogel/chitosan for the detection of ochratoxin A.

Ochratoxin A (OTA) is one of the most abundant mycotoxins that contaminate various food products. Herein, we propose a novel label-free impedimetric electrochemical sensor consisting of chitosan/dipeptide nanofibrous hydrogel and immobilized DNA probes with OTA aptamer for the detection of OTA. The thin film of chitosan/dipeptide nanofibrous hydrogel was used as sensing interface and carrier for hybridization chain reaction (HCR) of OTA aptamer and DNA2 strand to form DNA concatemer. The concatemer was dissociated to single-stranded DNA (ssDNA) in the presence of target OTA, and the signal amplification was further implemented by introducing RecJf exonuclease, which could digest the single-stranded DNA resulting in OTA recycle. Electrochemical impedance spectroscopy (EIS) has been employed to characterize the properties of the fabricated sensor. A linear detection range of 0.1-100 ng mL-1 was obtained for OTA with a low detection limit of 0.03 ng mL-1. Furthermore, the developed sensor was demonstrated in white wine to detect OTA, indicating that the proposed impedimetric sensor has a promising potential application in the food industry.

Consecutive Silver(I) Ion Incorporation into Oligonucleotides containing Cytosine-Cytosine Mispairs.

Invited for this month's cover is the group of Prof. Heinz-Bernhard Kraatz from the University of Toronto, Canada. The cover picture shows the consecutive incorporation of AgI ions into a DNA duplex containing adjacent C-C mispairs. Read the full text of the article at 10.1002/cplu.202000607.

Copper decorated with nanoporous gold by galvanic displacement acts as an efficient electrocatalyst for the electrochemical reduction of CO2.

The reduction of carbon dioxide (CO2) is recognized as a key component in the synthesis of renewable carbon-containing fuels. Herein, we report on nanoporous gold (NPAu) decorated with copper atoms for the efficient electrochemical reduction of CO2. A facile and green galvanic displacement technique was developed to incorporate Cu onto the surface of the nanoporous gold-zinc (NPAuZn) electrode. The effect of zinc on the morphology and electrochemical performance of the formed NPAuCu electrodes for CO2 reduction was systematically investigated. The NPAuCu electrode exhibited 16.9 and 2.86 times higher current density than those of polycrystalline gold and NPAuZn at -0.60 V (vs. RHE) in a 0.1 M CO2-saturated NaHCO3 solution, respectively. A far higher faradaic efficiency was achieved at the NPAuCu electrode for the electrochemical reduction of CO2 to CO, CH4 and HCOOH. The facile synthesis of the NPAuCu electrode demonstrated in the present study can be employed as a promising strategy in the development of high-performance electrocatalysts for energy and environmental applications.

Electrochemical Reduction of CO2 at Coinage Metal Nanodendrites in Aqueous Ethanolamine.

Electrocatalytic reduction of CO2 into usable chemicals is a promising path to address climate change and energy challenges. Herein, we demonstrate the synthesis of unique coinage metal (Cu, Ag, and Au) nanodendrites (NDs) via a facile galvanic replacement reaction (GRR), which can be effective electrocatalysts for the reduction of CO2 in an ethanolamine (EA) solution. Each metal ND surface was directly grown on glassy-carbon (GC) substrates from a mixture of Zn dust and the respective precursor solution. The electrocatalytic activities of the synthesized ND surfaces were optimized for CO2 reduction in EA solution by varying their composition. It was determined that a 0.05 mol fraction of EA exhibited the highest catalytic activity for all metal NDs. Linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) techniques showed that metal-ND electrodes possessed higher current densities, lower onset potentials and lower charge-transfer resistances for CO2 reduction than their smooth polycrystalline electrode counterparts, indicating improved CO2 reduction catalytic activity. It was determined, using FTIR and NMR spectroscopy, that formate was produced as a result of the CO2 reduction.

Consecutive Silver(I) Ion Incorporation into Oligonucleotides containing Cytosine-Cytosine Mispairs.

Herein, the consecutive incorporation of AgI ion into the dsDNA containing adjacent C-C mispairs is demonstrated. The melting temperature (Tm ) was 8 ° C higher for DNA containing three C-C mispairs upon the addition of three AgI ions as compared to the AgI -free DNA, and no Tm was obtained in the presence of excess AgI ion, indicating a stable bridging of C-AgI -C upon the incorporation of the stoichiometric amount of AgI per C-C mispair. The circular dichroism (CD) spectra of the dsDNA showed a negative peak at ∼270 nm in the presence of excess AgI , implying that significant structural changes and a potential aggregation of DNA occurred. Subsequently, the AgI -mediated DNA strands are immobilized on Au surfaces. Their electrochemical properties are monitored using CV, EIS and SECM showing increased overpotentials and charge-transfer resistances, and decreased the rate constant in the presence of an excess of AgI , respectively. These results are further supported by the XPS and sulfide-Au reductive desorption measurements.

A novel electrochemical immunosensor for hepatitis B surface antigen based on Fe3O4 nanoflowers and heterogeneous chain reaction signal amplification strategy.

Herein, a novel sandwich-type electrochemical immunosensor was fabricated based on Fe3O4 nanoflowers (Fe3O4 NFs) and heterogeneous chain reaction (HCR) signal amplification strategy for the sensitive detection of hepatitis B surface antigen (HBsAg). The aldehyde-functionalized Fe3O4 NFs are used as a supporting matrix to immobilize the hepatitis B surface antibody 1 (HBsAb1). The biotin-modified single-strand DNA (biotin-S0) was connected onto the biotin-HBsAb2 via linkage of streptavidin (SA), followed by addition of methylene blue (MB) modified single strand DNA1 (MB-S1) and DNA2 (MB-S2) for HCR signal amplification. The designed immunosensor exhibited a detection linear range of 0.5 pg mL-1-0.25 ng mL-1 and a low detection limit of 0.16 pg mL-1, with excellent stability, selectivity and reproducibility. Furthermore, HBsAg is detected in the serum samples with a stable and fast response, indicating that the proposed immunosensor has a promising potential application in clinical analysis.

Homogeneous and heterogeneous molecular catalysts for electrochemical reduction of carbon dioxide.

Carbon dioxide (CO2) is a greenhouse gas whose presence in the atmosphere significantly contributes to climate change. Developing sustainable, cost-effective pathways to convert CO2 into higher value chemicals is essential to curb its atmospheric presence. Electrochemical CO2 reduction to value-added chemicals using molecular catalysis currently attracts a lot of attention, since it provides an efficient and promising way to increase CO2 utilization. Introducing amino groups as substituents to molecular catalysts is a promising approach towards improving capture and reduction of CO2. This review explores recently developed state-of-the-art molecular catalysts with a focus on heterogeneous and homogeneous amine molecular catalysts for electroreduction of CO2. The relationship between the structural properties of the molecular catalysts and CO2 electroreduction will be highlighted in this review. We will also discuss recent advances in the heterogeneous field by examining different immobilization techniques and their relation with molecular structure and conductive effects.

Unique copper and reduced graphene oxide nanocomposite toward the efficient electrochemical reduction of carbon dioxide.

The electrochemical reduction of CO2 to useful chemicals and fuels has garnered a keen and broad interest. Herein, we report a unique nanocomposite consisting of Cu nanoparticles (NPs) and reduced graphene oxide (rGO) supported on a Cu substrate with a high catalytic activity for CO2 reduction. The nanocomposite was optimized in terms of the composition of Cu NPs and rGO as well as the overall amount. A gas chromatograph was employed to analyze the gaseous products, whereas a chemical oxygen demand (COD) method was proposed and utilized to quantify the overall liquid products. The optimized nanocomposite could effectively reduce CO2 to CO, HCOOH and CH4 with a Faradaic efficiency (FE) of 76.6% at -0.4 V (vs. RHE) in a CO2 saturated NaHCO3 solution. The remarkable catalytic activity, high FE, and excellent stability make this Cu-rGO nanocomposite promising for the electrochemical reduction of CO2 to value-added products to address the pressing environmental and energy challenges.