Yuanhua Shao

Electrochemical DNAzyme sensor for lead based on amplification of DNA-Au bio-bar codes.

An electrochemical DNAzyme sensor for sensitive and selective detection of lead ion (Pb(2+)) has been developed, taking advantage of catalytic reactions of a DNAzyme upon its binding to Pb(2+) and the use of DNA-Au bio-bar codes to achieve signal enhancement. A specific DNAzyme for Pb(2+) is immobilized onto an Au electrode surface via a thiol-Au interaction. The DNAzyme hybridizes to a specially designed complementary substrate strand that has an overhang, which in turn hybridizes to the DNA-Au bio-bar code (short oligonucleotides attached to 13 nm gold nanoparticles). A redox mediator, Ru(NH3)6(3+), which can bind to the anionic phosphate of DNA through electrostatic interactions, serves as the electrochemical signal transducer. Upon binding of Pb(2+) to the DNAzyme, the DNAzyme catalyzes the hydrolytic cleavage of the substrate, resulting in the removal of the substrate strand along with the DNA bio-bar code and the bound Ru(NH3)6(3+) from the Au electrode surface. The release of Ru(NH3)6(3+) results in lower electrochemical signal of Ru(NH3)6(3+) confined on the electrode surface. Differential pulse voltammetry (DPV) signals of Ru(NH3)6(3+) provides quantitative measures of the concentrations of Pb(2+), with a linear calibration ranging from 5 nM to 0.1 microM. Because each nanoparticle carries a large number of DNA strands that bind to the signal transducer molecule Ru(NH3)6(3+), the use of DNA-Au bio-bar codes enhances the detection sensitivity by five times, enabling the detection of Pb(2+) at a very low level (1 nM). The DPV signal response of the DNAzyme sensor is negligible for other divalent metal ions, indicating that the sensor is highly selective for Pb(2+). Although this DNAzyme sensor is demonstrated for the detection of Pb(2+), it has the potential to serve as a general platform for design sensors for other small molecules and heavy metal ions.

Electrochemically Fabricated Polypyrrole and MoSx Copolymer Films as a Highly Active Hydrogen Evolution Electrocatalyst

DOI: 10.1002/adma.201400265 surface area, as well as good stability. [ 14 ] Moreover, It has been demonstrated that [MoS 4 ] 2− and some other molybdenum sulfi de anions can be doped into PPy during the polymerization process, [ 15 ] which makes it an ideal carrier for MoS x . Herein, we demonstrate a simple way to fabricate polypyrrole/MoS x hybrid (PPy/MoS x ) fi lms by a one-step electrochemical copolymerization. The PPy/MoS x fi lms exhibit an outstanding HER performance that is comparable to that of commercial Pt/C catalysts. The highly active PPy/MoS x fi lms for HER were prepared in 0.1 M NaClO 4 containing 0.5 M pyrrole (Py) and 2 m M

Electrochemistry at micro- and nanoscopic liquid/liquid interfaces

In this tutorial review, we will briefly introduce the history and basic concepts of micro- and nanoscopic liquid/liquid interfaces (size from nm to μm) in electrochemical studies of charge (electron and ion) transfer reactions at soft molecular interfaces. Their advantages and problems are usually compared with those of conventional liquid/liquid interfaces (size from mm to cm); and with solid/electrolyte interfaces. Three methods of fabrication of micro-liquid/liquid interfaces and one approach to support a nano-liquid/liquid interface are surveyed. The experimental and theoretical aspects are discussed along with possible approaches to characterize these micro- and nanoscopic liquid/liquid interfaces, and the methods to modify them with new functionality. Unique examples of applications of electrochemistry at micro- and nanoscopic liquid/liquid interfaces are provided. Some novel and potential research interests in the future in this field are discussed.

Aptamer-based affinity chromatographic assays for thrombin.

Affinity chromatographic assays for thrombin were developed using two aptamers as affinity ligands. The efficient capture and step elution of thrombin with NaClO4 enabled the determination of thrombin by using either absorbance or fluorescence detection. Preconcentration of thrombin on the affinity column improved the detection limit of thrombin to 0.1 nM. Using an aptamer for the fibrinogen-binding site of thrombin and a second aptamer for the heparin-binding site, a sandwich chromatographic assay was developed, showing improved selectivity of thrombin detection and eliminating the need for labeling thrombin in the sample. The increased local concentration of aptamers immobilized on monolithic columns favored the formation of aptamer-thrombin complexes, resulting in improved retention and detection of thrombin at trace levels.

Fast Ion‐Transfer Processes at Nanoscopic Liquid/Liquid Interfaces

Keeping up: The fastest kinetic data for ion transfer at a liquid/liquid interface were evaluated by nanopipette voltammetry. The steady-state voltammograms can be explained by theoretical models. In previous electrochemical measurements the systematic underestimation of k0 is probably a result of inefficient mass transfer to the relatively large interface.

Determination of the half-wave potential of the species limiting the potential window. Measurement of gibbs transfer energies at the water/1,2-dichloroethane interface

The numerical integration of the differential equation for cyclic voltammetry has been performed for the case where the reverse potential is set prior to the forward peak potential. A working curve stemming from these integrations allows the determination of the half-wave potential of species limiting the potential window. This technique has been applied to the measurement of formal Gibbs energies of transfer of ions across the water/1,2-dichloroethane interface. The validity of the TATB (tetraphenylarsonium tetraphenylborate) assumption is also discussed.

Electrochemical sensor for melamine based on its copper complex

A reliable and highly sensitive electrochemical sensor was first developed for analysis of non-electroactive melamine (Mel) based on its conversion to an electroactive complex by coordination of copper salt to Mel. This provides a simple and easy approach to the detection of Mel in milk products.

Voltammetry at a liquid-liquid interface supported on a metallic electrode

Abstract A liquid–liquid interface supported on a metallic electrode has been used to study ion transfer (IT) and electron transfer (ET) reactions by cyclic voltammetry. The system is composed of an aqueous droplet supported on a platinum disc electrode and immersed into an organic electrolyte solution. Depending on the nature of the dissolved species present in the aqueous solution, and in the organic electrolyte solution, different electrochemical coupled reactions can be observed. This method enables a fast and convenient method to measure standard transfer potentials for example of ionised drug molecules.

Enhanced electrocatalytic activity of MoP microparticles for hydrogen evolution by grinding and electrochemical activation

Transition metal phosphides like CoP, MoP, Ni2P are suggested to be highly efficient catalysts for hydrogen evolution reaction (HER). However, HER-inert oxides would usually form on the surfaces of these phosphides during preparation and long-term storage. In this study, a simple combination method of grinding and electrochemical activation is used to tune the surface states of long-term stored commercial MoP microparticles, which show low activity for HER due to the molybdenum and phosphorus oxides on the surface, resulting in more exposed active sites of MoP and an enhanced catalytic activity for HER with an onset potential of 0.08 V vs. RHE and a Tafel slope of 50 mV dec−1.

Ion current rectification and rectification inversion in conical nanopores: a perm-selective view

Ionic transport in charged conical nanopores is known to give rise to ion current rectification. The present study shows that the rectification direction can be inverted when using electrolyte solutions at very low ionic strengths. To elucidate these phenomena, electroneutral conical nanopores containing a perm-selective region at the tip have been investigated and shown to behave like classical charged nanopores. An analytical model is proposed to account for these rectification processes.