Fe3O4 magnetic nanoparticles as peroxidase mimetics and their applications in H2O2 and glucose detection

Artificial enzyme mimetics are a current research interest because natural enzymes bear some serious disadvantages, such as their catalytic activity can be easily inhibited and they can be digested by proteases. A very recently study reported by Yan et al. has proven that Fe3O4 magnetic nanoparticles (MNPs) exhibit an intrinsic enzyme mimetic activity similar to that found in natural peroxidases, though MNPs are usually thought to be biological and chemical inert (Gao, L. Z.; Zhuang, J.; Nie, L.; Zhang, J. B.; Zhang, Y.; Gu, N.; Wang, T. H.; Feng, J.; Yang, D. L.; Perrett, S.; Yan, X. Y. Nat. Nanotechnol. 2007, 2, 577-583).

Multifunctional label-free electrochemical biosensor based on an integrated aptamer

Aptamers, which are in vitro selected functional oligonucleotides, have been employed to design novel biosensors (i.e., aptasensors) due to their inherent selectivity, affinity, and their multifarious advantages over traditional recognition elements. In this work, we reported a multifunctional reusable label-free electrochemical biosensor based on an integrated aptamer for parallel detection of adenosine triphosphate (ATP) and alpha-thrombin, by using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). A An electrode as the sensing surface was modified with a part DNA duplex which contained a 5'-thiolated partly complementary strand (PCS) and a mixed aptamer (MBA).

Coating Didodecyldimethylammonium Bromide onto Au Nanoparticles Increases the Stability of Its Complex with DNA

The stability of the complex of cationic lipid with nucleic acid, especially when facing serum, is crucial for the efficiency of gene delivery. Here, we demonstrated that the stability of the complex of didodecyldimethylammonium bromide (DDAB, a cationic lipid) with DNA in the presence of serum dramatically increased after coating DDAB onto the surface of the gold nanoparticles. The stability of the complex was demonstrated with dye intercalation assay, and agarose gel electrophoresis.

[Ru(bpy)2dppz]2+ electrochemiluminescence switch and its applications for DNA interaction study and label-free ATP aptasensor

[Ru(bpy)2dppz]2+ electrochemiluminescence (ECL) was studied, and it was used to investigate DNA interaction and develop a label-free ATP aptasensor for the first time. ECL of [Ru(bpy)2dppz]2+ is negligible in aqueous solution, and increases approximately 1000 times when [Ru(bpy)2dppz]2+ intercalates into the nucleic acid structure. The ECL switch behavior of [Ru(bpy)2dppz]2+ is ascribed to the intercalation that shields the phenazine nitrogens from the solvent and results in a luminescent excited state. The ECL switch by DNA was applied to investigate the interaction of [Ru(bpy)2dppz]2+ with herring sperm DNA. The calculated equilibrium constant (K) is 1.35 x 10(6) M(-1), and the calculated binding-site size (s) is 0.88 base pair, which is consistent with the reported values.

Flourescent Switch Constructed Based on Hemin-Sensitive Anionic Conjugated Polymer and Its Applications in DNA-Related Sensors

Here, a fluorescent switch is constructed combining hemin, hemin aptamer, and a newly synthesized anionic conjugated polymer (ACP), poly(9,9-bis(6'-phosphate-hexyl) fluorenealt-1,4-phenylene) sodium salt (PFHPNa/PFP). In the "off-state", the fluorescence of PFP is sensitively quenched by hemin, with a high K-sv value of similar to 10(7). While in the "on-state", the formation of the aptamer/hemin complex recovers the fluorescence intensity. The fluorescent switch is sensitive and selective to hemin. To testify the universality and practicality of the fluorescent switch, a series of label-free DNA-related sensing platforms are developed, containing three DNA sensing strategies and one ATP recognition strategy. The fluorescent switch developed is simple, sensitive, and universal, which extends applications of the anionic conjugated polymers.

Colorimetric recognition of the coralyne-poly(dA) interaction using unmodified gold nanoparticle probes, and further detection of coralyne based upon this recognition system

Among the functional nucleic acids studied, adenine-rich nucleic acids have attracted attention due to their critical roles in many biological processes and self-assembly-based nanomaterials, especially deoxyribonucleic acids (abbreviated as poly(dA)). Therefore the ligands binding to poly(dA) might serve as potential therapeutic agents. Coralyne, a kind of planar alkaloid, has been firstly found that it could bind strongly to poly(dA). This work herein reports an approach for visual sensing of the coralyne-poly(dA) interaction. This method was based on the coralyne inducing poly(dA) into the homo-adenine DNA duplex and the difference in electrostatic affinity between single-stranded DNA and double-stranded DNA with gold nanoparticles (GNPs). Furthermore, we applied the recognition process of the interaction between coralyne and poly(dA) into specific coralyne detection with the assistance of certain software (such as Photoshop). A linear response from 0 to 728 nM was obtained for coralyne, and a detection limit of 91 nM was achieved.

Ionic liquids used in and analyzed by capillary and microchip electrophoresis

This review, covering reports published from 2001 to December 2008, shows how ionic liquids (ILs) have made significant contributions in the improvement of capillary and microchip electrophoresis (CE and mu CE) for the separation and detection of analytes such as phenols and aromatic acids, metal ions, medicines, enantiomers. biological materials, etc. Furthermore, CE methods applied in the sensitive and accurate determination of physico-chemical properties of ILs have been summarized. Accordingly, research vacancies and future development trends in these areas are discussed.

Real-time PCR microfluidic devices with concurrent electrochemical detection

Electrochemistry-based detection methods hold great potential towards development of hand-held nucleic-acid analyses instruments. In this work, we demonstrate the implementation of in situ electrochemical (EC) detection method in a microfluidic flow-through EC-qPCR (FTEC-qPCR) device, where both the amplification of the target nucleic-acid sequence and subsequent EC detection of the PCR amplicon are realized simultaneously at selected PCR cycles in the same device. The FTEC-qPCR device utilizes methylene blue (MB), an electroactive DNA intercalator, for electrochemical signal measurements in the presence of PCR reagent components. Our EC detection method is advantageous, when compared to other existing EC methods for PCR amplicon analysis, since FTEC-qPCR does not require probe-modified electrodes, or asymmetric PCR, or solid-phase PCR. Key technical issues related to surface passivation, electrochemical measurement, PCR inhibition by metal electrode, bubble-free PCR, were investigated. By controlling the concentration of MB and the exposure of PCR mixture to the bare metal electrode, we successfully demonstrated electrochemical measurement of MB in solution-phase, symmetric PCR by amplifying a fragment of lambda phage DNA.

Electrochemical impedance detection of DNA hybridization based on dendrimer modified electrode

Bioactive ultrathin films with the incorporation of amino-terminated G4 PAMAM dendrimers have been prepared via layer-by-layer self-assembly methods on a gold electrode and used for the DNA hybridization analysis. Surface plasmon resonance (SPR), X-ray photoelectron spectroscopy (XPS), and electrochemical impedance spectroscopy (EIS) are used to characterize the successful construction of the multicomponent film on the gold substrate. The dendrimer-modified surfaces improve the immobilization capacity of the probe DNA greatly, compared to the AET (2aminoethanethiol) SAM sensor surfaces without dendrimer molecules. DNA hybridization analysis is monitored by EIS. The dendrimer-based electrochemical impedance DNA biosensor shows high sensitivity and selectivity for DNA hybridization assay. The multicomponent films also display a high stability during repeated regeneration and hybridization cycles.

Comparison for DNA primary sequence

In this article, two schemes are suggested based on three exons of beta-globin gene belonging to 10 species for comparison of DNA primary sequences. At first, the positions of four nucleic acid bases were extracted, and then based on the information, as the numerical characterization of DNA sequences, the sequence invariants were derived. Sequences comparisons of 10 species selected in this work by using these invariants were performed. The results, especially with scheme 2, are quite satisfactory.

Energetic basis of molecular recognition in a DNA aptamer

The thermal stability and ligand binding properties of the L-argininamide-binding DNA aptamer (5'-GATCGAAACGTAGCGCCTTCGATC3') were studied by spectroscopic and calorimetric methods. Differential calorimetric studies showed that the uncomplexed aptamer melted in a two-state reaction with a melting temperature T-m = 50.2 +/- 0.2 degrees C and a folding enthalpy Delta H degrees(fold) = -49.0 +/- 2.1 kcal mol(-1). These values agree with values of T-m = 49.6 degrees C and Delta H degrees(fold) = -51.2 kcal mol(-1) predicted for a simple hairpin structure. Melting of the uncomplexed aptamer was dependent upon salt concentration, but independent of strand concentration. The T of aptamer melting was found to increase as L-argininamide concentrations increased. Analysis of circular dichroism titration data using a single-site binding model resulted in the determination of a binding free energy Delta G degrees(bind) = -5.1 kcal mol(-1). Isothermal titration calorimetry studies revealed an exothermic binding reaction with Delta H degrees(bind) = -8.7 kcal mol(-1). Combination of enthalpy and free energy produce ail unfavorable entropy of -T Delta S degrees = +3.6 kcal mol(-1). A molar heat capacity change of -116 cal mol(-1) K-1 was determined from calorimetric measurements at four temperatures over the range of 15-40 degrees C. Molecular dynamics simulations were used to explore the structures of the unligated and ligated aptamer structures.

Structural selectivity of aromatic diamidines

Competition dialysis was used to study the interactions of 13 substituted aromatic diamidine compounds with 13 nucleic acid structures and sequences. The results show a striking selectivity of these compounds for the triplex structure poly dA:(poly dT)(2), a novel aspect of their interaction with nucleic acids not previously described. The triplex selectivity of selected compounds was confirmed by thermal denaturation studies. Triplex selectivity was found to be modulated by the location of amidine substiuents on the core phenyl-furan-phenyl ring scaffold. Molecular models were constructed to rationalize the triplex selectivity of DB359, the most selective compound in the series. Its triplex selectivity was found to arise from optimal ring stacking on base triplets, along with proper positioning of its amidine substituents to occupy the minor and the major-minor grooves of the triplex. New insights into the molecular recognition of nucleic acid structures emerged from these studies, adding to the list of available design principles for selectively targeting DNA and RNA.

Diluting thiol-derivatized oligonucleotide monolayers on Au(111) by mercaptohexanol replacement reaction

Surface replacement reaction of thiol-derivatized, single-stranded oligonucleotide (HS-ssDNA) by mercaptohexanol (MCH) is investigated in order to reduce surface density of the HS-ssDNA adsorbed to Au(111) surface. Cyclic voltammograms (CVs) and scanning tunneling microscopy (STM) are employed to assess the composition and state of these mixed monolayers. It is found that each CV of mixed self-assembled monolayers (SAMs) only shows a single reductive desorption peak, which suggests that the resulted, mixed SAMs do not form discernable phase-separated domains. The peak potential gradually shifts to negative direction and the peak area increases step by step over the whole replacement process. By analyzing these peak areas, it is concluded that two MCH molecules will replace one HS-ssDNA molecule and relative coverage can also be estimated as a function of exposing time. The possible mechanism of the replacement reaction is also proposed. The DNA surface density exponentially reduces with the exposing time increasing, in other words, the replacement reaction is very fast in the first several hours and then gradually slows down. Moreover, the morphological change in the process is also followed by STM.

A temperature-dependent interaction of neutral red with calf thymus DNA

Neutral red (NR) is used as a probe to study the temperature and concentration dependent interaction of a cationic dye with nucleic acid. A temperature-dependent interaction of NR with calf thymus DNA (CT DNA) has been studied by differential pulse voltammetry (DPV), UV-Visible absorption, circular dichroism (CD) and fluorescence spectroscopy. The experimental results of increasing peak current, changes in the UV-Visible absorption and fluorescence spectra of NR and decreasing the induced circular dichroism (ICD) intensity show that (i) the binding mode of NR molecules is changed from intercalating into DNA base pairs to aggregating along the DNA double helix and (ii) the orientation of NR chromophore in DNA double helix is also changed with the temperature.

Triplex selective 2-(2-naphthyl)quinoline compounds: Origins of affinity and new design principles

A novel competition dialysis assay was used to investigate the structural selectivity of a series of substituted 2-(2-naphthyl)quinoline compounds designed to target triplex DNA. The interaction of 14 compounds with 13 different nucleic acid sequences and structures was studied. A striking selectivity for the triplex structure poly dA:[poly dT](2) was found for the majority of compounds studied. Quantitative analysis of the competition dialysis binding data using newly developed metrics revealed that these compounds are among the most selective triplex-binding agents synthesized to date. A quantitative structure-affinity relationship (QSAR) was derived using triplex binding data for all 14 compounds used in these studies. The QSAR revealed that the primary favorable determinant of triplex binding free energy is the solvent accessible surface area. Triplex binding affinity is negatively correlated with compound electron affinity and the number of hydrogen bond donors. The QSAR provides guidelines for the design of improved triplex-binding agents.