Signal amplified colorimetric nucleic acid detection based on autocatalytic hairpin assembly.

Herein, a nucleic acid assay based on autocatalytic hairpin assembly (ACHA) was proposed. In this system, two split G-quadruplex sequences were integrated into H1 and H2, respectively. And a DNA strand with the same sequence to target DNA was integrated into the assistant hairpin H3.

Signal Extraction, Transformation, and Magnification for Ultrasensitive and Specific Detection of Nucleic Acids.

Nucleic acid noises caused by the background and nonspecificity amplifications can jeopardize accurate polymerization and detection of nucleic acids, especially when they are analyzed in low copies. We hypothesize to reduce the noises by designing a system for specific signal extraction, transformation, and magnification to improve the specificity and sensitivity. Herein, by developing an extractor-trigger complex (ET-Combo) for the system, we have established isothermal and hybridizing combined amplifications: a one-pot detection system with two-step amplification coupled by ET-Combo.

A label-free fluorescent biosensor based on a catalyzed hairpin assembly for HIV DNA and lead detection.

Herein, a label-free fluorescent signal amplification system based on a catalyzed hairpin assembly (CHA) is reported. In this system, two hairpin probes, H1 and H2, were well-designed in which G-quadruplex sequences were integrated into H2. The CHA reaction was triggered by target/trigger DNA and G-quadruplex sequences were released, which can bind the fluorescent amyloid dye thioflavin T (ThT) to provide fluorescence signals.

Rapid and colorimetric detection of nucleic acids based on entropy-driven circuit and DNAzyme-mediated autocatalytic reactions.

In this work, a novel, rapid and enzyme-free colorimetric biosensor for the detection of nucleic acids has been developed based on entropy-driven (EDC) circuit and DNAzyme-mediated autocatalytic reactions. On sensing the target DNA, the EDC reaction could be initiated and the intact Mg2+-dependent DNAzyme was formed in the reaction product; then, a "mimic target" DNA was generated during the cleavage process of DNAzyme, which in turn catalyzed the EDC reaction corresponding to an autocatalytic process. Meanwhile, numerous G-quadruplex structures were released and further interacted with hemin to form peroxidase-mimicking DNAzyme, inducing a remarkably amplified colorimetric signal.

Self-Replication-Assisted Rapid Preparation of DNA Nanowires at Room Temperature and Its Biosensing Application.

A rapid room-temperature DNA nanowires preparation strategy on the basis of self-replicating catalyzed hairpin assembly (SRCHA) was reported. In this system, three hairpin probes (P1, P2, and P3) were well-designed and partially hybridize to each other, and two split trigger DNA sequences were integrated into P1 and P3, respectively. When the SRCHA was initiated by the trigger DNA, a series of DNA assembly steps based on the toehold-mediated DNA strand displacement were activated, and the Y shaped DNA (P1-P2-P3) was formed.

Rapid DNA detection based on self-replicating catalyzed hairpin assembly using nucleotide base analog pyrrolo-deoxycytidine as fluorophore.

A rapid signal amplified DNA detection method based on self-replicating catalyzed hairpin assembly (SRCHA) has been proposed. In this SRCHA system, two split target DNA sequences were respectively integrated into hairpin auxiliary probes H1 and H2. H2 was used as fluorescent probe which containing a fluorescent nucleotide base analog pyrrolo-deoxycytidine (P-dC) at the end of the stem.

Self-assembly of DNA nanoparticles through multiple catalyzed hairpin assembly for enzyme-free nucleic acid amplified detection.

It is known that DNA molecules can be used to build a various of complicated geometrical DNA nanostructures with programmable sequence design, and these DNA nanomaterials show a promising application in biotechnology and biomedicine. However, the construction of large-sized three dimensional DNA-based nanomaterials still remains a challenge. In this work, we propose a new strategy that only employs one target DNA to trigger multiple catalyzed hairpin assembly (CHA) reactions and sticky ends self-assembly to prepare hundreds of nanometer-sized DNA nanoparticles.

Functional reduced graphene oxide-based membranes with selective ion transport channels for zwitterionic ions separation based on the pH gradient.

In this work, we report a method for the fabrication of a functional free-standing graphene membrane (FFGM) with high mechanical strength, enlarged interlayer spacing and ion channels for zwitterionic ions separation. To obtain the FFGM, the anionic dye Eosin Y (EY) was introduced into a graphene oxide (GO) and hydroquinone (HQ) mixture to prepare functional graphene-based membranes on Cu foil using simply a drop-casting method. In comparison with a GO membrane, the molar flux and the mechanical strength of the FFGM were dramatically increased.

Self-Replicating Catalyzed Hairpin Assembly for Rapid Signal Amplification.

A rapid signal amplification system based on the self-replicating catalyzed hairpin assembly is reported in which two hairpins, H1 and H2, were well-designed in which two split target/trigger DNA and two split G-quadruplex sequences were respectively integrated into H1 and H2. Target/trigger DNA can be cyclically used in this system to form the duplex DNA assemblies (H1-H2), which will bring the two G-quadruplex fragments into close-enough proximity to induce the formation of intact G-quadruplex as a colorimetric signal readout. Similarly, the two split target/trigger DNA sequences will reunite into a DNA sequence that is identical to the target/trigger DNA; then, the obtained replica can also be cyclically used as a new activator unit to trigger the CHA reaction, leading to the rapidly and significantly enhanced formation of target/trigger DNA replicas with the concomitant generation of a higher signal.

Nucleotide base analog pyrrolo-deoxycytidine as fluorescent probe signal for enzyme-free and signal amplified nucleic acids detection.

In the present work, an enzyme-free and signal amplified nucleic acids detection method based on the fluorescent nucleotide base analog pyrrolo-deoxycytidine (P-dC) and catalyzed hairpin assembly (CHA) has been developed. In the CHA signal amplification system, two hairpin auxiliary probes, H1 and H2, which containing a fluorescent P-dC at the end of the stem, respectively, were used as the fluorescent probes. The fluorescence of P-dC in H1 and H2 was quenched owing to the stacking interaction among the bases in the stem.

Target-catalyzed autonomous assembly of dendrimer-like DNA nanostructures for enzyme-free and signal amplified colorimetric nucleic acids detection.

Self-assembly of DNA nanostructures is of great importance in nanomedicine, nanotechnology and biosensing. Herein, a novel target-catalyzed autonomous assembly pathway for the formation of dendrimer-like DNA nanostructures that only employing target DNA and three hairpin DNA probes was proposed. We use the sticky-ended Y shape DNA (Y-DNA) as the assembly monomer and it was synthesized by the catalyzed hairpin assembly (CHA) instead of the DNA strand annealing method.

Unusual sequence length-dependent gold nanoparticles aggregation of the ssDNA sticky end and its application for enzyme-free and signal amplified colorimetric DNA detection.

It is known that the adsorption of short single-stranded DNA (ssDNA) on unmodified gold nanoparticles (AuNPs) is much faster than that for long ssDNA, and thus leads to length-dependent AuNPs aggregation after addition of salt, the color of the solutions sequentially changed from red to blue in accordance with the increase of ssDNA length. However, we found herein that the ssDNA sticky end of hairpin DNA exhibited a completely different adsorption behavior compared to ssDNA, an inverse blue-to-red color variation was observed in the colloid solution with the increase of sticky end length when the length is within a certain range. This unusual sequence length-dependent AuNPs aggregation might be ascribed to the effect of the stem of hairpin DNA.

Target-triggered autonomous assembly of DNA polymer chains and its application in colorimetric nucleic acid detection.

A novel target-triggered DNA autonomous assembly pathway for the formation of one-dimensional DNA polymer chains was proposed based on the catalyzed hairpin assembly and sticky end self-assembly, which led to an enzyme-free and signal amplified gold nanoparticle (AuNP) based colorimetric nucleic acid assay with picomolar sensitivity and specificity.

Synthesis of "amphiphilic" carbon dots and their application for the analysis of iodine species (I2, I(-) and IO3(-)) in highly saline water.

"Amphiphilic" carbon dots (A-CDs) with a strong green fluorescence emission were synthesized by a simple and green method at room temperature. The characterization demonstrated that the synthesized A-CDs have both hydrophilic and hydrophobic properties and could be dispersed well in aqueous and organic solutions. As a fluorescent probe, the fluorescence of A-CDs could be obviously quenched in the presence of iodine (I2) and the quenching rate is proportional to the concentration of I2.

Double input capacitively coupled contactless conductivity detector with phase shift.

A double input capacitively coupled contactless conductivity detector (DIC(4)D) device which gets higher sensitivity has been described in this paper. The detector consists of two input electrodes and one output electrode. When two alternating current (AC) voltages with the same amplitude and different phases are imposed on each input electrode, the equivalent resistance of the output electrode is reduced because of the interference of the two signals with different phase angles.

Hierarchically porous nickel oxide nanosheets grown on nickel foam prepared by one-step in situ anodization for high-performance supercapacitors.

Porous NiO nanosheets are successfully grown on nickel foam substrate through an in situ anodization by using molten KOH as the electrolyte. High-purity NiO is directly obtained by this one-step method without any subsequent treatment. The obtained NiO supported on nickel foam is used as a binder-free electrode for a supercapacitor and its pseudocapacitive behavior has been investigated by cyclic voltammetry and galvanostatic charge-discharge tests in a 6 M aqueous solution of KOH.

Selective detection of dopamine in the presence of uric acid using a gold nanoparticles-poly(luminol) hybrid film and multi-walled carbon nanotubes with incorporated β-cyclodextrin modified glassy carbon electrode.

Gold nanoparticles-poly(luminol) (Plu-AuNPs) hybrid film and multi-walled carbon nanotubes with incorporated β-cyclodextrin modified glassy carbon electrode (β-CD-MWCNTs/Plu-AuNPs/GCE) was successfully prepared for simultaneous determination of dopamine (DA) and uric acid (UA). The surface of the modified electrode has been characterized by X-ray photo-electron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS), field-emission scanning electron microscope (SEM) and transmission electron microscope (TEM). Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV) have been used to investigate the β-CD-MWCNTs/Plu-AuNPs composite film.

Multi-walled carbon nanotubes decrease lactate dehydrogenase activity in enzymatic reaction.

The oxidation of 1, 4-nicotinamide adenine dinucleotide (NADH) to β-nicotinamide adenine dinucleotide (NAD(+)) coupled with converting of pyruvic acid (PA) to lactate catalyzed by lactate dehydrogenase (LDH), NADH+PA+H(+)⇌LDHNAD(+)+Lactate, was widely adopted to quantify the cell's death, membrane infiltration and proliferation induced by potential toxins. The differential pulse voltammetry (DPV) cathodic signal of NAD(+) at a hanging mercury drop electrode (HMDE) showed LDH activity decreased with the elevating dosages of and the pre-contact time (t(c)) with multi-walled carbon nanotubes (MWCNTs). Comparison of kinetic rate constant of above enzymatic reaction (ER) was able to sensitively assay the adverse influence of MWCNTs.

Electrospun Ru(bpy)(3)(2+)-doped nafion nanofibers for electrochemiluminescence sensing.

Electrospun Ru(bpy)(3)(2+)-doped Nafion (ERDN) nanofibers were successfully fabricated by a one-step electrospinning technique. The diameters of the nanofibers range from 120 nm to 220 nm. The ERDN nanofibers, evenly distributed on the substrate with their random orientations, form a porous 3-D structure nanofibrous membrane.

1-Butyl-3-methylimidazolium based ionic liquid as solvent for determination of hydrophobic naphthol with the electrogenerated chemiluminescence of tris(2,2'-bipyridine) ruthenium(II).

In this paper, we described the electrogenerated chemiluminescence (ECL) processes of tris(2,2'-bipyridine) ruthenium(II) (Ru(bpy)(3)(2+)) in room-temperature ionic liquid (RTIL). The results showed that ECL signals in RTIL, 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF(4)), were stronger than those obtained in aqueous solutions, which means that the RTIL could be used as a good solvent for ECL. The effect of tri-n-propylamine (TPrA) on the ECL process in [Bmim]BF(4) was also investigated and the results showed that the ECL peak occurred at 1.

Some thoughts on the existence of ion and water channels in highly dense and well-ordered CH3-terminated alkanethiol self-assembled monolayers on gold.

Through extensive and systematic reviewing of literatures, this paper presents some thoughts on the existence of ion and water channels in highly dense and well-ordered CH(3)-terminated alkanethiol self-assembled monolayers (C(n)SH-SAMs) on gold: (1) based on the combinational effect of "the van der Waals interaction between the neighbor hydrocarbon chains", "the framework size of C(n)SH molecule" and "the surface lattice structure of C(n)SH-SAMs on gold", a simple ideal model of the close-packed C(n)SH-SAMs is proposed for the first time. The channel with an appropriate diameter of about 3A ( approximately 3A) existing in SAMs on Au is deduced, which is found large enough for ions and water molecules to permeate; (2) through summarizing the literature reports for various experiments (e.g.

A mercury(II) ion-selective electrode based on N,N-dimethylformamide-salicylacylhydrazone as a neutral carrier.

A new PVC membrane mercury(II) ion electrode based on N,N-dimethylformamide-salicylacylhydrazone (DMFAS) as an ionophore is described, which shows excellent potentiometric response characteristics and displays a linear log[Hg(2+)] versus EMF response over a wide concentration range between 6.2 x 10(-7) and 8.0 x 10(-2) M with a Nerstian slope of 29.

Electrochemical detection of hepatitis B surface antigen using colloidal gold nanoparticles modified by a sol-gel network interface.

Background: A novel potentiometric immunosensor for the detection of hepatitis B surface antigen has been developed by self-assembling gold nanoparticles to a thiol-containing sol-gel network.

Methods: A cleaned gold electrode was first immersed in a hydrolyzed (3-mercaptopropyl) trimethoxysilane sol-gel solution to assemble a three-dimensional silica gel, and then gold nanoparticles were absorbed onto the thiol groups of the sol-gel network. Finally, hepatitis B surface antibody was assembled onto the surface of the gold nanoparticles.

New amperometric and potentiometric immunosensors based on gold nanoparticles/tris(2,2'-bipyridyl)cobalt(III) multilayer films for hepatitis B surface antigen determinations.

Two generic, fast, sensitive and novel electrochemical immunosensors have been developed. Initially, a layer of plasma-polymerized Nafion film (PPF) was deposited on the platinum electrode surface, then positively charged tris(2,2'-bipyridyl)cobalt(III) (Co(bpy)(3)(3+)) and negatively charged gold nanoparticles were assembled on the PPF-modified Pt electrode by layer-by-layer technique. Finally, hepatitis B surface antibody (HBsAb) was electrostatically adsorbed on the gold nanoparticles surface.