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.

This article reviews the degradability of chemically synthesized bioelastomers, mainly designed for soft tissue repair. These bioelastomers involve biodegradable polyurethanes, polyphosphazenes, linear and crosslinked poly(ether/ester)s, poly(ε-caprolactone) copolymers, poly(1,3-trimethylene carbonate) and their copolymers, poly(polyol sebacate)s, poly(diol-citrates) and poly(ester amide)s. The in vitro and in vivo degradation mechanisms and impact factors influencing degradation behaviors are discussed. In addition, the molecular designs, synthesis methods, structure properties, mechanical properties, biocompatibility and potential applications of these bioelastomers were also presented.

Sharp practice: A water/n‐octanol interface can be formed at the tip of a very short and sharp nanopipette, and can be polarized externally (see picture). This interface has been used to investigate various ion‐transfer processes and evaluate partition coefficients for ionizable species.

The electrochemical behaviors of graphene sheets attached to a self-assembled monolayer (SAM) on a gold electrode have been investigated. A gold electrode is sequentially modified by the SAM of n-octadecyl mercaptan (C 18 H 37 SH), followed by controllable adsorption of graphene sheets to obtain a graphene/SAM modified Au electrode. The graphene/SAM modified Au electrode is characterized electrochemically by using ruthenium hexaammine (Ru(NH 3 ) 6 3+) as a redox probe, and by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The experimental results indicate that the heterogeneous electron transfer (ET) blocked by the SAM can be restored by graphene sheets and that the graphene/SAM modified Au electrode has a smaller interfacial capacitance, as compared with that of a bare Au electrode. The apparent ET rate constant of Ru(NH 3 ) 6 3+, k app , on the graphene/SAM modified Au electrode has been also evaluated quantitatively by cyclic voltammetry (CV) and scanning electrochemical microscopy (SECM), and is equal to 4.2 × 10 -2 and 6.8 × 10 -2 cm s -1 , respectively. In addition, the electrochemical responses of free bases of DNA (guanine (G), adenine (A), thymine (T), and cytosine (C)) on the graphene/SAM modified Au electrode show that the graphene/SAM modified Au electrode possesses electrochemical properties similar to those of a graphene modified electrode rather than an Au electrode.

A series of starch/PVA (SP) films with the thickness of 0.05-0.1 mm were cast by solvent method. The swelling and degradation behaviors in simulated blood fluid (SBF) and simulated saliva fluid (SSF) within 30 days were investigated. In vitro biocompatibility was also evaluated. Research purpose of this work was to supply basic data for SP films' potential application in guide tissue regeneration (GTR) technology. It took 10-20 min for different samples to reach to their maximum water absorption and 30 min to lever off. The weight loss of all samples decreased rapidly in the first day in both of SBF or SSF, and then it changed slightly in SSF but decreased step by step in SBF. The mechanical properties of the wet SP films were satisfied with the requirement of GTR membrane. No matter in SBF or SSF, although the mechanical properties decreased rapidly in the first day, they changed slightly after that. Cytotoxicity and L929 fibroblasts attachment test proved that the SP film possesses excellent cell affinity. Hemolysis ratios of all samples were less than 5%. All results demonstrated that SP film is a promising candidate in GTR treatment.

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