Label-Free Colorimetric Detection of Aqueous Mercury Ion (Hg2+) Using Hg2+-Modulated G-Quadruplex-Based DNAzymes

Mercury ion (Hg2+) is able to specifically bind to the thymine-thymine (T-T) base pair in a DNA duplex, thus providing a rationale for DNA-based selective detection of Hg2+ with various means. In this work, we for the first time utilize the Hg2+-mediated T-T base pair to modulate the proper folding of G-quadruplex DNAs and inhibit the DNAzyme activity, thereby pioneering a facile approach to sense Hg2+ with colorimetry. Two bimolecular DNA G-quadruplexes containing many T residues are adopted here, which function well in low- and high-salt conditions, respectively. These G-quadruplex DNAs are able to bind hemin to form the peroxidase-like DNAzymes in the folded state. Upon addition of Hg2+, the proper folding of G-quadruplex DNAs is inhibited due to the formation of T-Hg2+-T complex. Ibis is reflected by the notable change of the Soret band of hemin when investigated by using UV-vis absorption spectroscopy. As a result of Hg2+ inhibition, a sharp decrease in the catalytic activity toward the H2O2-mediated oxidation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)diammonium salt (ABTS) is observed, accompanied by a change in solution color. Through this approach, aqueous Hg2+ can be detected at 50 nM (10 ppb) with colorimetry in a facile way, with high selectivity against other metal ions.

Sensitive, selective and label-free protein detection using a smart polymeric transducer and aptamer/ligand system

We have demonstrated a smart polymeric transducer and aptamer/intercalating dye system that allows the label-free detection of protein with high sensitivity and selectivity.

Enhanced catalytic DNAzyme for label-free colorimetric detection of DNA

A DNAzyme-based label-free method for the colorimetric detection of DNA is introduced, with a supramolecular hemin G-quartet complex as the sensing element and a 36-mer single-strand DNA as the analyte that is detected at 10 nM.

Label free electrochemiluminescence protocol for sensitive DNA detection with a tris(2,2'-bipyridyl)ruthenium(II) modified electrode based on nucleic acid oxidation

Label free electrochemiluminescence (ECL) DNA detection based on catalytic guanine and adenine bases oxidation using tris(2,2'-bipyridyl)ruthenium(II) [Ru(bpy)(3)(2+)] modified glassy carbon (GC) electrode was demonstrated in this work. The modified GC electrode was prepared by casting carbon nanotubes (CNT)/Nafion/Ru(bpy)(3)(2+) composite film on the electrode surface. ECL signals of doublestranded DNA and their thermally denatured counterparts can be distinctly discriminated using cyclic voltammetry (CV) with a low concentration (3.04 x 10(-8) mol/L for Salmon Testes-DNA). Most importantly, sensitive single-base mismatch detection of p53 gene sequence segment was realized with 3.93 x 10(-10) mol/L employing CV stimulation (ECL signal of C/A mismatched DNA oligonucleotides was 1.5-fold higher than that of fully base-paired DNA oligonucleotides). Label free, high sensitivity and simplicity for single-base mismatch discrimination were the main advantages of the present ECL technique for DNA detection over the traditional DNA sensors.

Analysis of chemical calorific effect during reactive extrusion processes for free radical polymerization

In the reactive extrusion process for polymerization, the chemical calorific effect has a great influence on the temperature. In order to quantitatively analyze the polymerization trend and optimize the processing conditions, the phenomena of the chemical calorific effect during reactive extrusion processes for free radical polymerization were analyzed. Numerical computation expressions of the heat of chemical reaction and the reactive calorific intensity were deduced, and then a numerical simulation of the reactive extrusion process for the polymerization of n-butyl methacrylate was carried out. The evolutions of the heat of chemical reaction and the reactive calorific intensity along the! axial direction of the extruder are presented, on the basis of which reactive processing conditions can be optimized.

Adaptive recognition of small molecules by nucleic acid aptamers through a label-free approach

We report a novel label-free method for the investigation of the adaptive recognition of small molecules by nucleic acid aptamers using capillary electrophoresis analysis. Cocaine and argininamide were chosen as model molecules, and the two corresponding DNA aptamers were used. These single-strand DNAs folded into their specific secondary structures, which were mainly responsible for the binding of the target molecules with high affinity and specificity. For molecular recognition, the nucleic acid structures then underwent additional conformational changes, while keeping the target molecules stabilized by intermolecular hydrogen bonds. The intrinsic chemical and physical properties of the target molecules enabled them to act as indicators for adaptive binding. Thus any labeling or modification of the aptamers or target molecules were made obsolete. This label-free method for aptamer-based molecular recognition was also successfully applied to biological fluids and therefore indicates that this approach is a promising tool for bioanalysis.

Sensitive detection of protein by an aptamer-based label-free fluorescing molecular switch

We report an aptamer-based method for the sensitive detection of proteins by a label-free fluorescing molecular switch (ethidium bromide), which shows promising potential in making protein assay simple and economical.

Investigation of the gel effect in reactive extrusion processes for free radical polymerization

The gel effect in the reactive extrusion process for free radical polymerization in a closely intermeshing co-rotating twin screw extruder was investigated. First the reaction kinetic model was constructed mainly on the basis of entanglement theory. Next, numerical calculation expressions for the initiator and monomer concentrations, monomer conversion, average molecular weight and apparent viscosity were deduced. Finally, the evolution of the above variables were shown and discussed for the example of butyl methacrylate. The simulated results of the monomer conversion are in good agreement with experimental results.

Reusable, label-free electrochemical aptasensor for sensitive detection of small molecules

We report a sensitive electrochemical aptasensor for adenosine based on electrochemical impedance spectroscopy measurement, which gives not only a label-free but also a reusable platform to make the detection of small molecules simple and convenient.

Control led/living free-radical copolymerization of 4-(azidocarbonyl) phenyl methacrylate with methyl acrylate under Co-60 gamma-ray irradiation

A new vinyl acyl azide monomer, 4-(azidocarbonyl) phenyl methacrylate, has been synthesized and characterized by NMR and FTIR spectroscopy. The thermal stability of the new monomer has been investigated with FTIR and thermal gravimetry/differential thermal analysis (TG/DTA), and the monomer has been demonstrated to be stable below 50 degrees C in the solid state. The copolymerizations of the new monomer with methyl acrylate have been carried out at room temperature under Co-60 gamma-ray irradiation in the presence of benzyl 1-H-imidazole-1-carbodithioate. The results show that the polymerizations bear all the characteristics of controlled/living free-radical polymerizations, such as the molecular weight increasing linearly with the monomer conversion, the molecular weight distribution being narrow (< 1.20), and a linear relationship existing between In([M](0)/[M]) and the polymerization time. The data from H-1 NMR and FTIR confirm that no change in the acyl azide groups has occurred in the polymerization process and that acyl azide copolymers have been obtained. The thermal stability of the polymers has also been investigated with TG/DTA and FTIR.

CE with electrochemical detection for investigation of label-free recognition of amino acid amides by guanine-rich DNA aptamers

In this work, we report a simple and effective investigation into adaptive interactions between guanine-rich DNA aptamers and amino acid amides by CE with electrochemical (EC) detection. Argininamide (Arm) and tyrosinamide (Tym) were chosen as model molecules. On a copper electrode, Arm generated a good EC signal in 60 mM NaOH at 0.7 V (vs Ag/ AgCl), while Tym. was detected well on a platinum electrode at 1. 3 V in 20 mM phosphate of pH 7.0. Based on their EC properties, the ligands themselves were used as indicators for the adaptive interactions investigated by CE-EC, making any step of labeling and/or modification of aptamers with indicators exempted. Hydrophilic ionic liquid was used as an additive in running buffer of CE to improve the sensitivity of Arm detection, whereas the additive was not used for Tym. detection due to its negative effect. Two guanine-rich DNA aptamers were used for molecular recognition of Arm and Tym. When the aptamers were incubated with ligands, they bound the model molecules with high affinity and specificity, reflected by obvious decreases in the signals of ligands but no changes in those of the control molecules. However, the ligands were hardly affected by the control ssDNAs after incubation. The results revealed the specific recognition of Arm and Tym. by the aptamers.

Computer simulation of reactive extrusion processes for free radical polymerization

The reactive extrusion for polymerization is an integrated polymer processing technology. A new semi-implicit iterative algorithm was proposed to deal with the complicated relationships among the chemical reaction, the macromolecular structure and the chemorheological property. Then the numerical computation expressions of the average molecular weight, the monomer conversion, and the initiator concentration were deduced, and the computer simulation of the reactive extrusion process for free radical polymerization was carried out, on basis of which reactive processing conditions can be optimized.

Free radical grafting of polyethylene with vinyl monomers by reactive extrusion

The free radical grafting of polyethylene with vinyl monomers by reactive extrusion was studied numerically. Numerical computation expressions of key variables, such as the concentrations of the initiator and polymer, grafting degree, average molecular weight and apparent viscosity, were deduced. The evolutions of the above variables were predicted by means of an uncoupled semi-implicit iterative algorithm. The monomer conversion monotonically increases with decreasing throughput or increasing initial initiator concentration; with increasing barrel temperature, the monomer conversion first increases then decreases. The simulated results are nearly in good agreement with the experimental results.